INTRODUCTION

Vitamins are minor components of foodsthat play an essential role in human nutri-tion. Many vitamins are unstable under cer-tain conditions of processing and storage(Table 9-1), and their levels in processedfoods, therefore, may be considerably re-duced. Synthetic vitamins are used exten-sively to compensate for these losses and torestore vitamin levels in foods. The vitaminsare usually divided into two main groups,the water-soluble and the fat-soluble vita-mins. The occurrence of the vitamins in thevarious food groups is related to their water-or fat-solubility. The relative importance ofcertain types of foods in supplying some ofthe important vitamins is shown in Table9-2. Some vitamins function as part of acoenzyme, without which the enzyme wouldbe ineffective as a biocatalyst. Frequently,such coenzymes are phosphorylated formsof vitamins and play a role in the metabo-lism of fats, proteins, and carbohydrates.Some vitamins occur in foods as provita-minscompounds that are not vitamins butcan be changed by the body into vitamins.Vitamers are members of the same vitaminfamily.

Lack of vitamins has long been recog-nized to result in serious deficiency diseases.

It is now also recognized that overdoses ofcertain vitamins, especially some of the fat-soluble ones, may result in serious toxiceffects. For this reason, the addition of vita-mins to foods should be carefully controlled.

The sources of vitamins in significantamounts by food groups have been listed byCombs (1992) as follows:

Meats, poultry, fish, and beans providethiamin, riboflavin, niacin, pyridoxine,pantothenic acid, biotin, and vitaminB12.

Milk and milk products provide vitaminsA and D, riboflavin, pyridoxine, andvitamin B12.

Bread and cereals provide thiamin, ribo-flavin, niacin, pyridoxine, folate, pan-tothenic acid, and biotin.

Fruits and vegetables provide vitamins Aand K, ascorbic acid, riboflavin, andfolate.

Fats and oils provide vitamins A and E.

FAT-SOLUBLE VITAMINS

Vitamin A (Retinol)

The structural formula of vitamin A isshown in Figure 9-1. It is an alcohol thatoccurs in nature predominantly in the form

Vitamins

CHAPTER 9

Table 9-1 Stability of Vitamins under Different Conditions

Unstable To:

Vitamin

vitamin A

vitamin D

vitamin E

vitamin K

vitamin Cthiamine

riboflavinniacin

vitamin B6

biotinpantothenic

acidfolatevitamin B12

Vitamer

retinolretinalretinoic aciddehydroret.ret. estersp-caroteneD2D3tocopherolstocopherolesters

KMKmenadioneascorbic aciddisulfide formhydrochlorided

riboflavinnicotinic acidnicotinamidepyridoxalpyridoxol (HCI)biotinfree acid1

Ca saltyd

FH4CN-B12

UVLight

+

++

+++

+e

+

+

++

Heat*

+++

+++

+

++

O2

++

+

++++

++

+b

++

++

+

Acid++

++++

++

+a+h

Base

++

+++++++

++

Metals?++

+++

+++++++

+V

Most Stabledark, sealsealgood stabilitysealgood stabilitysealdark, cool, sealdark, cool, sealcool, neutral pHgood stability

avoid reductants0

avoid reductantsc

avoid reductants0

seal, neutral pHneutral pHc

seal, neutral pHc

dark, pH 1.5-4C

good stabilitygood stabilitycoolgood stabilityseal, neutral pHcool, neutral pHseal, pH 6-7good stability0

good stability0

ai.e., 10O0Cbin solution with Fe+++ and Cu++cunstable to reducing agentsdslightly hygroscopicEspecially in alkaline solutionVery hygroscopic9pH

of fatty acid esters. Highest levels of vitaminA are found in certain fish liver oils, such ascod and tuna. Other important sources aremammalian liver, egg yolk, and milk andmilk products. The levels of vitamin A andits provitamin carotene in some foods arelisted in Table 9-3.

The structural formula of Figure 9-1shows the unsaturated character of vitaminA. The all-trans form is the most active bio-logically. The 13-cis isomer is known as neo-vitamin A; its biological activity is onlyabout 75 percent of that of the all-trans form.The amount of neo-vitamin A in natural vita-min A preparations is about one-third of the

total. The amount is usually much less insynthetic vitamin A. The synthetic vitamin Ais made as acetate or palmitate and marketedcommercially in the form of oil solutions,stabilized powders, or aqueous emulsions.The compounds are insoluble in water butsoluble in fats, oils, and fat solvents.

Table 9-3 Vitamin A and Carotene Content ofSome Foods

Figure 9-1 Structural Formula of Vitamin A.Acetate: R = CO-CH3. Palmitate: R =CO(CH2)14CH3.

Product

Beef (grilled sirloin)Butter (May-

November)Cheddar cheeseEggs (boiled)Herring (canned)MilkTomato (canned)PeachCabbageBroccoli (boiled)Spinach (boiled)

Vitamin A(IU/100g)

372363-3452

553-1078165-488

178110-307

OOOOO

Carotene(mg/100g)

0.040.43-0.77

0.07-0.710.01-0.15

0.070.01-0.06

0.50.340.32.56.0

Table 9-2 Contributions (%) of Various Food Groups to the Vitamin Intake of Americans

Source: Reprinted with permission from G.F. Combs, The Vitamins: Fundamental Aspects in Nutrition andHealth, p. 441, 1992, Academic Press.

Foods

vegetableslegumesfruitsgrain productsmeatsmilk productseggsfats and oilsother

Vitamin A

39.4

8.0

22.513.25.88.22.7

Vitamin C

51.8

39.0

2.03.7

3.4

Thiamin

11.75.44.441.227.18.12.0

Riboflavin

6.9

2.222.122.239.14.9

Niacin

12.08.22.527.445.01.4

3.3

Vitamin B6

22.25.48.210.240.011.62.1

Vitamin B12

1.669.220.78.5

There are several provitamins A; thesebelong to the carotenoid pigments. The mostimportant one is p-carotene, and some of thepigments that can be derived from it are ofpractical importance. These are p-apo-8'-carotenal and p-apo-8'-carotenoic acidethyl ester (Figure 9-2). Other provitaminsare a- and y-carotene and cryptoxanthin.

Beta-carotene occurs widely in plant prod-ucts and has a high vitamin A activity. In the-ory, one molecule of p-carotene could yieldtwo molecules of vitamin A. The enzyme 15-15'-dioxygenase is able to cleave a P-caro-tene molecule symmetrically to produce twomolecules of vitamin A (Figure 9-3). Thisenzyme occurs in intestinal mucosa, but theactual conversion is much less efficient. Asshown in Figure 9-3, there are other reac-tions that may cause the yield of retinol to beless than 2. After cleavage of the p-carotene,the first reaction product is retinal, which isreduced to retinol (Rouseff and Nagy 1994).A general requirement for the conversion ofa carotenoid to vitamin A is an unsubstitutedp-ionone ring. Citrus fruits are a good sourceof provitamin A, which results mostly from

the presence of p-cryptoxanthin, p-carotene,and a-carotene. Gross (1987) reported a totalof 16 carotenoids with provitamin A activityin citrus fruits.

Vitamin A levels are frequently expressedin International Units (IU), although this unitis officially no longer accepted. One IUequals 0.344 |U,g of crystalline vitamin A ace-tate, or 0.300 |Lig vitamin A alcohol, or 0.600|ig p-carotene. The recommended dailyallowance (RDA) of vitamin A of the NationalResearch Council Food and Nutrition Boardis 5000 IU for an adult. Other sources quotethe human requirement at about 1 |uig/day.Conditions of rapid growth, pregnancy, orlactation increase the need for vitamin A.

Vitamin A, or retinol, is also known as vita-min A1. Another form, vitamin A2, is foundin fish liver oils and is 3-dehydroretinol.

The Food and Agriculture Organizationand the World Health Organization of theUnited Nations (FAOAVHO) and the NationalAcademy of Sciences of the United States(1974a) have recommended that vitamin Aactivity be reported as the equivalent weightof retinol. To calculate total retinol equiva-

A

B

Figure 9-2 Structural Formulas of Some Provitamins A. (A) p-carotene, and (B) apocarotenal (R =CHO) and apocarotenoic acid ester (R = COOC2H5).

lents, it is proposed that food analyses listretinol, carotene, and other provitamin A car-otenoids separately. It is also desirable to dis-tinguish between the cis- and trans- forms ofthe provitamins in cooked vegetables. Bydefinition, 1 retinol equivalent is equal to 1|Lig of retinol, or 6 |Hg of (3-carotene, or 12 [Lgof other provitamin A carotenoids. TheNational Academy of Sciences (1974a)states that 1 retinol equivalent is equal to 3.3IU of retinol or 10 IU of p-carotene.

Vitamin A occurs only in animals and notin plants. The A1 form occurs in all animals

and fish, the A2 form in freshwater fish andnot in land animals. The biological value ofthe A2 form is only about 40 percent of thatof A1. Good sources of provitamin A in veg-etable products are carrots, sweet potatoes,tomatoes, and broccoli. In milk and milkproducts, vitamin A and carotene levels aresubject to seasonal variations. Hartman andDry den (1965) report the levels of vitamin Ain fluid whole milk in winter at 1,083 IU/Land in summer at 1,786 IU/L. Butter containsan average of 2.7 |Ug of carotene and 5.0 |Ligof vitamin A per g during winter and 6.1 |Lig

B- CAROTENE

RETINAL

RETINOL

Figure 9-3 Conversion of Beta-Carotene to Vitamin A. Source: Reprinted with permission from R.R.Rouseff and S. Nagy, Health and Nutritional Benefits of Citrus Fruit Components, Food Technology,Vol. 48, No. 11, p. 125, 1994, Institute of Food Technologists.

of carotene and 7.6 |Lig of vitamin A per gduring summer.

Vitamin A is used to fortify margarine andskim milk. It is added to margarine at a levelof 3,525 IU per 100 g. Some of the car-otenoids (provitamin A) are used as food col-ors.

Vitamin A is relatively stable to heat in theabsence of oxygen (Table 9-4). Because ofthe highly unsaturated character of the mole-cule, it is quite susceptible to oxidationespecially under the influence of light,whether sunlight or artificial light. VitaminA is unstable in the presence of mineral acidsbut stable in alkali. Vitamin A and the car-otenoids have good stability during various

food processing operations. Losses may occurat high temperatures in the presence of oxy-gen. These compounds are also susceptibleto oxidation by lipid peroxides, and condi-tions favoring lipid oxidation also result invitamin A breakdown. The prooxidant cop-per is especially harmful, as is iron to a lesserextent. Pasteurization of milk does not resultin vitamin A loss, but exposure to light does.It is essential, therefore, that sterilized milkbe packaged in light-impervious containers.Possible losses during storage of foods aremore affected by duration of storage than bystorage temperature. Blanching of fruits andvegetables helps prevent losses during frozenstorage.

Table 9-4 Vitamin A and Carotene Stability in Foods

Product

Vitamin AButter

Margarine

Nonfat dry milk

Fortified ready-to-eat cerealFortified potato chips

CaroteneMargarine

Lard

Dried egg yolk

Carbonated beverage

Canned juice drinks

Nutrient Content

1 7,000-30,000 lU/lb

1 5,000 lU/lb

1 0,000 lU/lb

4000 lU/oz700IUAIOOg

3 mg/lb

3.3 mg/lb

35.2mg/100g

7.6 mg/29 oz

0.6-1 .3 mg/8 fl oz

Storage Conditions

12 mo & 50C5 mo @ 280C6 mo @ 50C6 mo @ 230C3 mo @ 370C12 mo 9 230C6 mo @ 230C2 mo @ 230C

6 mo 9 50C6 mo 9 230C6 mo @ 50C6 mo 9 230C3 mo 9 370C12 mo 9 230C2 mo 9 3O0C2 mo 9 230C12 mo @23C

Retention (%)

66-9864-6889-10083-10094-10069-8983100

98891001009480949485-100

Source: From E. deRitter, Stability Characteristics of Vitamins in Processed Foods, Food Technol., Vol. 30, pp.48-51,54, 1976.

Vitamin A added to milk is more easilydestroyed by light than the native vitamin A.This is not because natural and synthetic vita-min A are different, but because these twotypes of vitamin A are dispersed differentlyin the milk (deMan 1981). The form in whichvitamin A is added to food products mayinfluence its stability. Vitamin A in beadletform is more stable than that added as a solu-tion in oil. The beadlets are stabilized by aprotective coating. If this coating is damagedby water, the stability of the vitamin is greatlyreduced (de Man et al. 1986).

Vitamin D

This vitamin occurs in several forms; thetwo most important are vitamin D2, or ergo-calciferol, and vitamin D3, or cholecalciferol.The structural formulas of these compoundsare presented in Figure 9-4. Vitamin D does

not occur in plant products. Vitamin D2occurs in small amounts in fish liver oils;vitamin D3 is widely distributed in animalproducts, but large amounts occur only infish liver oils. Smaller quantities of vitaminD3 occur in eggs, milk, butter, and cheese(Table 9-5).

The precursors of vitamins D2 and D3 areergosterol and 7-dehydrocholesterol, respec-tively. These precursors or provitamins canbe converted into the respective D vitaminsby irradiation with ultraviolet light. In addi-tion to the two major provitamins, there areseveral other sterols that can acquire vitaminD activity when irradiated. The provitaminscan be converted to vitamin D in the humanskin by exposure to sunlight. Because veryfew foods are good sources of vitamin D,humans have a greater likelihood of vitaminD deficiency than of any other vitamin defi-ciency. Enrichment of some foods with vita-min D has significantly helped to eradicaterickets, which is a vitamin D deficiency dis-ease. Margarine and milk are the foods com-monly used as carrier for added vitamin D.

The unit of activity of vitamin D is the IU,which is equivalent to the activity of 1 mg ofa standard preparation issued by the WHO.One IU is also equivalent to the activity of0.025 |ig of pure crystalline vitamin D2 orD3. The human requirement amounts to 400

Table 9-5 Vitamin D Content of Some Foods

Vitamin D fag/WOO gProduct Edible Portion)

Liver (beef, pork) 2-5Eggs 44Milk 0.9Butter 2-40Cheese 12-47Herring oil 2,500

Figure 9-4 Structural Formulas of (A) VitaminD2 and (B) Vitamin D3

B

A

to 500 IU but increases to 1,000 IU duringpregnancy and lactation. Adults who are reg-ularly exposed to sunlight are likely to have asufficient supply of vitamin D. Excessiveintakes are toxic.

Vitamin D is extremely stable, and little orno loss is experienced in processing and stor-age. Vitamin D in milk is not affected by pas-teurization, boiling, or sterilization (Hartmanand Dryden 1965). Frozen storage of milk orbutter also has little or no effect on vitamin Dlevels, and the same result is obtained duringstorage of dry milk.

The vitamin D potency of milk can beincreased in several ways: by feeding cowssubstances that are high in vitamin D activ-ity, such as irradiated yeast; by irradiatingmilk; and by adding vitamin D concentrates.The latter method is now the only commonlyused procedure. The practice of irradiatingmilk to increase the vitamin D potency hasbeen discontinued, undoubtedly because ofthe deteriorative action of the radiation onother milk components. Vitamin D is addedto milk to provide a concentration of 400 IU

per quart. Addition of vitamin D to marga-rine is at a level of 550IU per 100 g.

Tocopherols (Vitamin E)

The tocopherols are derivatives of tocol,and the occurrence of a number of relatedsubstances in animal and vegetable productshas been demonstrated. Cottonseed oil wasfound to contain a-, p-, and y-tocopherol,and a fourth, 5-tocopherol, was isolated fromsoybean oil. Several other tocopherols havebeen found in other products, and Morton(1967) suggests that there are four to-copherols and four tocotrienols. The toco-trienols have three unsaturated isoprenoidgroups in the side chain. The structure oftocol is given in Figure 9-5 and the struc-tures of the tocopherols and tocotrienols inFigure 9-6. The four tocopherols are charac-terized by a saturated side chain consisting ofthree isoprenoid units. The tocotrienols havethree double bonds at the 3', 7', and 1Y car-bons of the isoprenoid side chain (Figure

A

B

Figure 9-5 Structural Formula of (A) Tocol and (B) a-Tocopherol

9-6). The carbons at locations 4' and 8' inthe side chains of the tocopherols are asym-metric, as is the number 2 carbon in the chro-man ring. The resulting possible isomers aredescribed as having R or S rotation. The nat-ural tocopherols and tocotrienols are pre-dominantly RRR isomers. Morton (1967)has summarized the chemistry of the to-copherols as shown in Figure 9-7.

On oxidation, oc-tocopherol can form ameta-stable epoxide that can be irreversiblyconverted to oc-tocopherolquinone. Reduc-

tion of the quinone yields a quinol. To-copherolquinones occur naturally. Oxidationwith nitric acid yields the o-quinone or to-copherol red, which is not found in nature.Alpha-tocopheronic acid and a-tocopher-onolactone are some of the products ofmetabolism of tocopherol. Much of the bio-logical activity of the tocopherols is relatedto their antioxidant activity. Because a-to-copherol is the most abundant of the differ-ent tocopherols, and because it appears tohave the greatest biological activity, the oc-

Figure 9-6 Chemical Structure of the Tocopherols and Tocotrienols

Tocotrienol

Tocotrlenol

OfPT5

Tocotrienol

5,7,8 - Trimethyl5,8 - Dimethyl7,8 - Dimethyl8 - Methyl

R,

CH,CH,HH

R2

CH,HCH,H

R9

CH,CH,CH,CH1

Tocopherol

Tocopherol

aftTa

Tocopherol

5,7,8 - Trimethyl5,8 Dimethyl7,8 - Dimethyl8 - Methyl

R,

CH,CH,HH

R,

CH,HCH,H

R,

CH,CH,CH,CH,

tocopherol content of foods is usually con-sidered to be most important.

The biological activity of the tocopherolsand tocotrienols varies with the number andposition of the methyl groups on the chro-man ring and by the configuration of theasymmetric carbons in the side chain. The Rconfiguration at each chiral center has thehighest biological activity. Because the dif-ferent isomers have different activities, it isnecessary to measure each homolog and con-vert these to RRR-oc-tocopherol equivalents(Ct-TE). One oc-TE is the activity of 1 mg ofRRR-oc-tocopherol (Eitenmiller 1997). Thevitamin E activity of oc-tocopherol isomersand synthetic tocopherols is listed in Table9-6.

Tocopherols are important as antioxidantsin foods, especially in vegetable oils. With

few exceptions, animal and vegetable prod-ucts contain from about 0.5 to 1.5 mg/100 g;vegetable oils from 10 to 60 mg/100 g; andcereal germ oils, which are a very goodsource, from 150 to 500 mg/100 g. Vegetableoils have the highest proportion of oc-toco-pherol, which amounts to about 60 percent ofthe total tocopherols. Refining of vegetableoils, carried out under normal precautions(such as excluding air), appears to result inlittle destruction of tocopherol. The toco-pherol and tocotrienol content of selectedfats and oils and their primary homologs arelisted in Table 9-7. The seed oils containonly tocopherol. Tree oils, palm, palm ker-nel, coconut oil, and rice bran oil also con-tain major amounts of tocotrienols. Theprocessing of vegetable oils by deodorizationor physical refining removes a considerable

Figure 9-7 Chemistry of the Tocopherols. Source: From R.A. Morton, The Chemistry of Tocopherols,in Tocopherole, K. Lang, ed., 1967, Steinkopff Verlag, Darmstadt, Germany.

a-focopforomc acid a-focop/ierono/acfon*

o-qufnonf

e~ toccphtrolquinon*

quinol

#.-tocoph*rolmetastable

tpoxid*

irnvtrsibly onstanding

Table 9-6 Vitamin E Activity of cc-Tocopherollsomers and Synthetic Tocopherols

Name ILJ/mg

d-cc-tocopherol (2R4/R8/R) RRR-a- 1 49tocopherol

1 -a-tocopherol (2S4'R8'R) 0.46dl-a-tocopherol 1.10

all-rac-a-tocopherol2R4/R8/S-a-tocopherol 1.342S4'R8'S-oc-tocopherol 0.552S4'S8'S-a-tocopherol 1.092S4'S8'R-a-tocopherol 0.312R4'S8'R-a-tocopherol 0.852S4'S8'S-a-tocopherol 1.10d-a-tocopheryl acetate RRR-a- 1.36

tocopheryl acetatedl-a-tocopherol 1.00

all-rac-a-tocopherol acetate

Source: Reprinted with permission from R.R. Eiten-miller, Vitamin E Content of Fats and Oils: NutritionalImplications, Food Technol., Vol. 51, no. 5, p. 79, 1997, Institute of Food Technologists.

portion of the tocopherols, and these steam-volatile compounds accumulate in the fattyacid distillate (Ong 1993). This product is animportant source of natural vitamin E prepa-rations. Baltes (1967) carried out tests inwhich two easily oxidizable fats, lard andpartially hydrogenated whale oil, were stabi-lized with a-tocopherol and ascorbylpalmi-tate and citric acid as synergists. Withoutantioxidants, these fats cannot be used in thecommercial food chain. Amounts of a-toco-pherol ranging from 0.5 to 10 mg/100 g wereeffective in prolonging the storage life ofsome samples up to two years.

The tocopherol content of some animaland vegetable products as reported by Thaler(1967) is listed in Table 9-8. Cereals and

cereal products are good sources of to-copherol (Table 9-9). The distribution oftocopherol throughout the kernels is not uni-form, and flour of different degrees ofextraction can have different tocopherol lev-els. This was shown by Menger (1957) in astudy of wheat flour (Table 9-10).

Processing and storage of foods can resultin substantial tocopherol losses. An exampleis given in Table 9-11, where the loss oftocopherol during frying of potato chips isreported. After only two weeks' storage ofthe chips at room temperature, nearly half ofthe tocopherol was lost. The losses were onlyslightly smaller during storage at freezertemperature. Boiling of vegetables in waterfor up to 30 minutes results in only minorlosses of tocopherol. Baking of white breadresults in a loss of about 5 percent of thetocopherol in the crumb.

The human daily requirement of vitamin Eis estimated at 30 IU. Increased intake ofpolyunsaturated fatty acids increases theneed for this vitamin.

Vitamin K

This vitamin occurs in a series of differentforms, and these can be divided into twogroups. The first is vitamin K1 (Figure 9-8),characterized by one double bond in the sidechain. The vitamins K2 have a side chainconsisting of a number of regular units of thetype

CH3

R-[CH2CH=CCH2]nH

where n can equal 4, 5, 6, 7, and so forth.Vitamin K1 is slowly decomposed by at-

mospheric oxygen but is readily destroyedby light. It is stable against heat, but unstableagainst alkali.

The human adult requirement is estimatedat about 4 mg per day. Menadione (2-methyl1,4-naphtoquinone) is a synthetic productand has about twice the activity of naturallyoccurring vitamin K.

Vitamin K occurs widely in foods and isalso synthesized by the intestinal flora. Goodsources of vitamin K are dark green vegeta-bles such as spinach and cabbage leaves, andalso cauliflower, peas, and cereals. Animalproducts contain little vitamin K1, except forpork liver, which is a good source.

The Vitamin K levels in some foods,expressed in menadione units, are given inTable 9-12.

WATER-SOLUBLE VITAMINS

Vitamin C (L-Ascorbic Acid)

This vitamin occurs in all living tissues,where it influences oxidation-reduction reac-tions. The major source of L-ascorbic acid infoods is vegetables and fruits (Table 9-13).

Source: Reprinted with permission from R.R. Eitenmiller, Vitamin E Content of Fats and Oils: Nutritional Implica-tions, Food Technol., Vol. 51, no. 5, p. 80, 1997, Institute of Food Technologists.

Table 9-7 Tocopherol (T) and Tocotrienol (T3) Content of Vegetable Oils and Their Primary Homologs

Fats and Oils

SunflowerCottonseedSafflowerSafflower high

linolenicSafflower high oleicPalm

Canola

CornSoybeanRice branPeanutOliveCocoa butterPalm kernelButterLardCoconut

Total T+T3(mg/100g)

46-6778

49-8041

3289-117

65

78-10996-1159-160

375.1203.4

1.1-2.30.6

1.0-3.6

OC-7E/10Og

35-6343

41-4641

3121-34

25

20-3417-20

0.9-4116

5.13.01.9

1.1-2.30.6

0.3-0.7

%T

100100100100

10017-55

100

95100

19-491001009938

10010031

%T3

OOOO

O45-83

O

5O

51-81OO1

62OO

69

Primary Homologs

oc-T, y-Toc-T, y-Toc-T, 5-T, Y-T p-TCC-T1 P-T

(X-T1 P-T, Y-Toc-T, oc-TS, 6-T3, oc-T, 6-

T3Y-T, (X-T, 8-T,Ct-TS(Tr)1 P-T(Tr)Y-T, oc-T, 8-T, Y-T3, 6-T3Y-T, 8-T, oc-TY-T3, ccT, (X-T3, p-T, p-T3Y-T, oc-T, 8-Toc-TY-T, 8-T, oc-T, cc-T3cc-T3, CC-TCC-Tcc-TY-T3, cc-T3, 8-T, cc-T, P-

T3

Table 9-8 Tocopherol Content of Some Animaland Vegetable Food Products

Total Tocopherol asProduct a-Tocopherol (mg/100 g)Beef liver 0.9-1.6Veal, lean 0.9Herring 1.8Mackerel 1.6Crab, frozen 5.9Milk 0.02-0.15Cheese 0.4Egg 0.5-1.5Egg yolk 3.0Cabbage 2-3Spinach 0.2-6.0Beans 1-4Lettuce 0.2-0.8 (0.06)Peas 4-6Tomato 0.9 (0.4)Carrots 0.2(0.11)Onion 0.3 (0.22)Potato ?(0.12)Mushrooms 0.08

Source: From H. Thaler, Concentration and Stabil-ity of Tocopherols in Foods, in Tocopherols, K. Lang,ed., 1967, Steinkopff Verlag, Darmstadt, Germany.

L-ascorbic acid (Figure 9-9) is a lactone(internal ester of a hydroxycarboxylic acid)and is characterized by the enediol group,which makes it a strongly reducing com-pound. The D form has no biological activ-ity. One of the isomers, D-isoascorbic acid,or erythorbic acid, is produced commerciallyfor use as a food additive. L-ascorbic acid isreadily and reversibly oxidized to dehydro-L-ascorbic acid (Figure 9-10), which retainsvitamin C activity. This compound can befurther oxidized to diketo-L-gulonic acid, in a

Table 9-9 Tocopherol Content of Cereals andCereal Products

Total Tocopherol as oc-Product Tocopherol (mg/1 OO g)Wheat 7-10Rye 2.2-5.7Oats 1.8-4.9Rice (with hulls) 2.9Rice (polished) 0.4Corn 9.5Whole wheat meal 3.7Wheat flour 2.3-5.4Whole rye meal 2.0-4.5Oat flakes 3.85Corn grits 1.17Corn flakes 0.43White bread 2.15Whole rye bread 1.3Crisp bread 4.0

Source: From H. Thaler, Concentration and Stabil-ity of Tocopherols in Foods, in Tocopherols, K. Lang,ed., 1967, Steinkopff Verlag, Darmstadt, Germany.

nonreversible reaction. Diketo-L-gulonic acidhas no biological activity, is unstable, and isfurther oxidized to several possible com-pounds, including 1-threonic acid. Dehydra-tion and decarboxylation can lead to theformation of furfural, which can polymerizeto form brown pigments or combine withamino acids in the Strecker degradation.

Humans and guinea pigs are the only pri-mates unable to synthesize vitamin C. Thehuman requirement of vitamin C is not welldefined. Figures ranging from 45 to 75 mg/day have been listed as daily needs. Contin-ued stress and drug therapy may increase theneed for this vitamin.

Vitamin C is widely distributed in nature,mostly in plant products such as fruits (espe-

Table 9-10 Tocopherol Content of Wheat and ItsMilling Products

Tocopherolmg/100g

Product Ash (%) (Dry Basis)

Whole wheat 2X35 5 04Flour 1 (fine) 1.68 5.90Flour 2 1.14 4.27Flour 3 0.84 3.48Flour 4 0.59 2.55Flour 5 0.47 2.35Flour 6 (coarse) 0.48 2.13Germ 4.10 25.0

Source: From A. Menger, Investigation of the Stabil-ity of Vitamin E in Cereal Milling Products and BakedGoods, Brot. Geback, Vol. 11, pp. 167-173,1957 (Ger-man).

cially citrus fruits), green vegetables, toma-toes, potatoes, and berries. The only animalsources of this vitamin are milk and liver.Although widely distributed, very high levelsof the vitamin occur only in a few products,such as rose hips and West Indian cherries.The concentration varies widely in differenttissues of fruits; for example, in apples, theconcentration of vitamin C is two to threetimes as great in the peel as in the pulp.

Vitamin C is the least stable of all vitaminsand is easily destroyed during processing andstorage. The rate of destruction is increasedby the action of metals, especially copper

Table 9-11 Tocopherol Losses DuringProcessing and Storage of Potato Chips

Tocopherol(mg/100 g) Loss (%)

Oil before use 82 Oil after use 73 11Oil from fresh chips 75 After two weeks at 39 48

room temperatureAfter one month at 22 71

room temperatureAfter two months at 17 77

room temperatureAfter one month at 28 63

-120CAfter two months at 24 68

-12.0C

and iron, and by the action of enzymes.Exposure to oxygen, prolonged heating inthe presence of oxygen, and exposure to lightare all harmful to the vitamin C content offoods. Enzymes containing copper or iron intheir prosthetic groups are efficient catalystsof ascorbic acid decomposition. The mostimportant enzymes of this group are ascorbicacid oxidase, phenolase, cytochrome oxi-dase, and peroxidase. Only ascorbic acid oxi-dase involves a direct reaction among en-zyme, substrate, and molecular oxygen. Theother enzymes oxidize the vitamin indirectly.Phenolase catalyzes the oxidation of mono-

Figure 9-8 Structural Formula of Vitamin K1

Table 9-12 Vitamin K in Some Foods (Expressedas Menadione Units per 100 g of Edible Portion)

Product Units/1 OO g

Cabbage, white 70Cabbage, red 18Cauliflower 23Carrots 5Honey 25Liver (chicken) 13Liver (pork) 111Milk 8Peas 50Potatoes 10Spinach 161Tomatoes (green) 24Tomatoes (ripe) 12Wheat 17Wheat bran 36Wheat germ 18

Table 9-13 Vitamin C Content of Some Foods

Ascorbic AcidProduct (mg/1 OO g)

Black currants 200Brussels sprouts 10OCauliflower 70Cabbage 60Spinach 60Orange 50Orange juice 40-50Lemon 50Peas 25Tomato 20Apple 5Lettuce 15Carrots 6Milk 2.1-2.7Potatoes 30

L-ASCORBIC ACID D-ASCORBIC ACID

L-ARABOASCORBIC ACIDD-ISOASCORBIC ACID(ERYTHORBIC ACID)

Figure 9-9 Structural Formulas of L-Ascorbic Acid and Its Stereoisomers

and dihydroxy phenols to quinones. Thequinones react directly with the ascorbicacid. Cytochrome oxidase oxidizes cyto-chrome to the oxidized form and this reactswith L-ascorbic acid.

Peroxidase, in combination with phenoliccompounds, utilizes hydrogen peroxide tobring about oxidation. The enzymes do notact in intact fruits because of the physicalseparation of enzyme and substrate. Mechan-ical damage, rot, or senescence lead to cellu-lar disorganization and initiate decomposition.Inhibition of the enzymes in vegetables isachieved by blanching with steam or by

Table 9-14 Effect of Blanching Method onAscorbic Acid Levels of Broccoli

Ascorbic Acid (mg/100 g)

Factor Effect Reduced Dehydro Total

"Raw 94 0 4 0 98.2Water blanch 45.3 5.7 51.0Steam blanch 48.8 7.4 56.2

Source: From D. Odland and M.S. Eheart, AscorbicAcid, Mineral and Quality Retention in Frozen BroccoliBlanched in Water, Steam, and Ammonia-Steam, J.Food ScL, Vol. 40, pp. 1004-1007, 1975.

electronic heating. Blanching is necessarybefore vegetables are dried or frozen. In fruitjuices, the enzymes can be inhibited by pas-teurization, deaeration, or holding at lowtemperature for a short period. The effect ofblanching methods on the ascorbic acid con-tent of broccoli was reported by Odland andEheart (1975). Steam blanching was foundto result in significantly smaller losses ofascorbic acid (Table 9-14). The retention ofascorbic acid in frozen spinach depends onstorage temperature. At a very low tempera-ture (-290C), only 10 percent of the initiallypresent ascorbic acid was lost after one year.At -12, the loss after one year was muchhigher, 55 percent. The presence of metalchelating compounds stabilizes vitamin C.These compounds include anthocyanins andflavonols, polybasic or polyhydroxy acidssuch as malic and citric acids, and polyphos-phates.

Ascorbic acid is oxidized in the presenceof air under neutral and alkaline conditions.At acid pH (for example, in citrus juice), thevitamin is more stable. Because oxygen isrequired for the breakdown, removal of oxy-gen should have a stabilizing effect. For theproduction of fruit drinks, the water shouldbe deaerated to minimize vitamin C loss. Thetype of container may also affect the extent

Figure 9-10 Oxidation of L-Ascorbic Acid

L-ASCORBICACID

DEHYDRO-L-ASCORBICACID

DIKETO-L-GULONICACID

of ascorbic acid destruction. Use of tin cansfor fruit juices results in rapid depletion ofoxygen by the electrochemical process ofcorrosion. In bottles, all of the residual oxy-gen is available for ascorbic acid oxidation.To account for processing and storage losses,it is common to allow for a loss of 7 to 14 mgof ascorbic acid per 100 mL of fruit juice.Light results in rapid destruction of ascorbicacid in milk. It has been shown (Sattar anddeMan 1973) that transparent packagingmaterials permit rapid destruction of vitaminC (Figure 9-11). The extent of ascorbic aciddestruction is closely parallel to the develop-ment of off-flavors. The destruction of ascor-bic acid in milk by light occurs under theinfluence of riboflavin as a sensitizer. Thereaction occurs in the presence of light andoxygen, and the riboflavin is converted tolumichrome.

Factors that affect vitamin C destructionduring processing include heat treatment andleaching. The severity of processing condi-tions can often be judged by the percentageof ascorbic acid that has been lost. Theextent of loss depends on the amount ofwater used. During blanching, vegetablesthat are covered with water may lose 80 per-cent; half covered, 40 percent; and quartercovered, 40 percent of the ascorbic acid. Par-ticle size affects the size of the loss; forexample, in blanching small pieces of car-rots, losses may range from 32 to 50 percent,and in blanching large pieces, only 22 to 33percent. Blanching of cabbage may result ina 20 percent loss of ascorbic acid, and subse-quent dehydration may increase this to a totalof 50 percent. In the processing of milk,losses may occur at various stages. From aninitial level of about 22 mg/L in raw milk,

Figure 9-11 Effect of Exposure Time at Light Intensity of 200 Ft-C on the Loss of Ascorbic Acid inMilk. Packaging materials: (1) clear plastic pouch, (2) laminated nontransparent pouch, (3) carton, (4)plastic 3-quart jug. Source: From A. Sattar and J.M. deMan, Effect of Packaging Material on Light-Induced Quality Deterioration of Milk, Can. lnst. Food ScL Technol J., Vol. 6, pp. 170-174, 1973.

EXPOSURE TIME hours

L-A

SC

OR

BIC

A

CID

%

lo

ss

the content in the product reaching the con-sumer may be well below 10 mg/L. Furtherlosses may occur in the household duringstorage of the opened container.

The processing of milk into various dairyproducts may result in vitamin C losses. Icecream contains no vitamin C, nor doescheese. The production of powdered milkinvolves a 20 to 30 percent loss, evaporatedmilk a 50 to 90 percent loss. Bullock et al.(1968) studied the stability of added vitaminC in evaporated milk and found that adding266 mg of sodium ascorbate per kg was suf-ficient to ensure the presence of at least 140mg/L of ascorbic acid during 12 months ofstorage at 210C. Data on the stability of vita-min C in fortified foods have been assembledby deRitter (1976) (Table 9-15).

There are many technical uses of ascorbicacid in food processing. It is used to preventbrowning and discoloration in vegetablesand fruit products; as an antioxidant in fats,fish products, and dairy products; as a stabi-lizer of color in meat; as an improver offlour; as an oxygen acceptor in beer process-ing; as a reducing agent in wine, partiallyreplacing sulfur dioxide; and as an addednutrient. The vitamin is protected by sulfurdioxide, presumably by inhibiting polyphe-nolase.

Vitamin B1 (Thiamin)

This vitamin acts as a coenzyme in themetabolism of carbohydrates and is presentin all living tissues. It acts in the form of thi-amin diphosphate in the decarboxylation ofoc-keto acids and is referred to as cocarboxy-lase. Thiamin is available in the form of itschloride or nitrate, and its structural formulais shown in Figure 9-12. The molecule con-tains two basic nitrogen atoms; one is in theprimary amino group, the other in the quater-

Table 9-15 Vitamin C Stability in Fortified Foodsand Beverages after Storage at 230C for 12Months, Except as Noted

Retention

No. ofSam- Mean Range

Product pies (%) (%)

Ready-to-eat cereal 4 71 60-87Dry fruit drink mix 3 94 91-97Cocoa powder 3 97 80-100Dry whole milk, air 2 75 65-84

packDry whole milk, gas 1 93

packDry soy powder 1 81 Potato flakes1 3 85 73-92Frozen peaches 1 80 Frozen apricots2 1 80 Apple juice 5 68 58-76Cranberry juice 2 81 78-83Grapefruit juice 5 81 73-86Pineapple juice 2 78 74-82Tomato juice 4 80 64-93Vegetable juice 2 68 66-69Grape drink 3 76 65-94Orange drink 5 80 75-83Carbonated beverage 3 60 54-64Evaporated milk 4 75 70-82

1 Stored for 6 months at 230C.2Thawed after storage in freezer for 5 months.

Source: From E. deRitter, Stability Characteristicsof Vitamins in Processed Foods, Food Technol., Vol.30, pp. 48-51,54, 1976.

nary ammonium group. It forms salts withinorganic and organic acids. The vitamincontains a primary alcohol group, which isusually present in the naturally occurringvitamin in esterified form with ortho-, di-, or

triphosphoric acid. In aqueous solution, thecompound may occur in different forms,depending on pH. In acid solution, the equi-librium favors the formation of positive ions(Figure 9-13). The thiol- form is favored inalkaline medium. This form can react withcompounds containing sulfhydryl groups toform disulfide bridges. It has been suggestedthat thiamin occurs in some foods linked toprotein by disulfide bridges.

Small quantities of thiamin are present inalmost all foods of plant and animal origin.Good sources are whole cereal grains; organmeats such as liver, heart, and kidney; leanpork; eggs; nuts; and potatoes (Table 9-16).Although thiamin content is usually mea-

sured in mg per 100 g of a food, another unithas been used occasionally, the IU corre-sponding to 3 jug of thiamin-hydrochloride.The human daily requirement is related tothe carbohydrate level of the diet. A mini-mum intake of 1 mg per 2,000 kcal is consid-ered essential. Increased metabolic activity,such as that which results from heavy work,pregnancy, or disease, requires higher intake.

Thiamin is one of the more unstable vita-mins. Various food processing operationsmay considerably reduce thiamin levels.Heat, oxygen, sulfur dioxide, leaching, andneutral or alkaline pH may all result indestruction of thiamin. Light has no effect.The enzyme is stable under acid conditions;

Figure 9-12 Structural Formula of Thiamin. Hydrochloride: X = Cl , HCl; Mononitrate: X = NO3 .

Figure 9-13 Behavior of Thiamin in Aqueous Solutions. Source: Reprinted with permission from J.Schormuller, The Composition of Foods, 1965, Springer.

alkaline

Pseudobasepositive ions

acid

Thiol form

Table 9-16 Thiamin Content of Some Foods

Thiamin(mg/100g)

Product Edible Portion

Almonds 0.24Corn 0.37Egg 0.11Filberts 0.46Beef heart 0.53Beef liver 0.25Macaroni (enriched) 0.88Macaroni (not enriched) 0.09Milk 0.03Peas 0.28Pork, lean 0.87Potatoes 0.10Wheat (hard red spring) 0.57Wheat flour (enriched) 0.44Wheat flour (not enriched) 0.08

at pH values of 3.5 or below, foods can beautoclaved at 12O0C with little or no loss ofthiamin. At neutral or alkaline pH, the vita-min is destroyed by boiling or even by stor-age at room temperature. Even the slightalkalinity of water used for processing mayhave an important effect. Bender (1971)reports that cooking rice in distilled waterreduced thiamin content negligibly, whereascooking in tap water caused an 8 to 10 per-cent loss, and cooking in well water caused aloss of up to 36 percent.

Some fish species contain an enzyme thatcan destroy thiamin. Sulfur dioxide rapidlydestroys thiamin. For this reason, sulfurdioxide is not permitted as an additive infoods that contain appreciable amounts ofthiamin.

Baking of white bread may result in thia-min loss of 20 percent. Thiamin loss in milk

processing is as follows: pasteurization, 3 to20 percent; sterilization, 30 to 50 percent;spray drying, 10 percent; and roller drying,20 to 30 percent. Cooking of meat causeslosses that are related to size of cut, fat con-tent, and so on. Boiling loss is 15 to 40 per-cent; frying, 40 to 50 percent; roasting, 30 to60 percent; and canning, 50 to 75 percent.Similar losses apply to fish. Because thiaminand other vitamins are located near the branof cereal grains, there is a great loss duringmilling. White flour, therefore, has a greatlyreduced content of B vitamins and vitamin E(Figure 9-14). Not only is thiamin contentlowered by milling, but also storage of wholegrain may result in losses. This depends onmoisture content. At normal moisture levelof 12 percent, five months' storage results ina 12 percent loss; at 17 percent moisture, a30 percent loss; and at 6 percent moisture, noloss at all. Because of the losses that arelikely to occur in cereal grain processing andin the processing of other foods, a programof fortification of flour is an important factorin preventing vitamin deficiencies. Table9-17 lists the nutrients and recommendedlevels for grain products fortification (NationalAcademy of Sciences 1974b). A summary ofdata relating processing treatment to thiaminstability has been given by deRitter (1976)(Table 9-18).

Vitamin B2 (Riboflavin)

The molecule consists of a d-ribitol unitattached to an isoalloxazine ring (Figure9-15). Anything more than a minor changein the molecule results in a loss of vitaminactivity. Aqueous solutions of riboflavin areyellow with a yellowish-green fluorescence.The vitamin is a constituent of two coen-zymes, flavin mononucleotide (FMN) andflavin adenine dinucleotide (FAD). FMN is

riboflavin-5'-phosphate and forms part ofseveral enzymes, including cytochrome creductase. The flavoproteins serve as elec-tron carriers and are involved in the oxida-tion of glucose, fatty acids, amino acids, andpurines.

Very good sources of riboflavin are milkand milk products; other sources are beefmuscle, liver, kidney, poultry, tomatoes, eggs,green vegetables, and yeast (Table 9-19).

Riboflavin is stable to oxygen and acid pHbut is unstable in alkaline medium and is

Figure 9-14 Relation Between Extraction Rate and Proportion of Total Vitamins of the Grains Retainedin Flour. Source: Reprinted with permission from W.R. Aykroyd and J. Doughty, Wheat in HumanNutrition, 1970, Food and Agriculture Organization of the United Nations.

Extraction rate (%)

Propo

rtion o

f vita

min r

etaine

d (%)

Table 9-17 Nutrients and Levels Recommendedfor Inclusion in Fortification of Cereal-GrainProducts1

Level

Nutrient (mg/lb) (mg/100g)

Vitamin A2 22 O48Thiamin 2.9 0.64Riboflavin 1.8 0.40Niacin 24.0 5.29Vitamin B6 2.0 0.44Folic acid 0.3 0.07Iron 40 8.81Calcium 900 198.2Magnesium 200 44.1Zinc 10 2.2

1Wheat flour, corn grits, cornmeal, rice. Othercereal-grain products in proportion to their cereal-graincontent.

2Retinol equivalent.

Source: Reprinted with permission from NationalAcademy of Sciences, Recommended Dietary Allow-ances, 8th rev. ed., 1974, National Academy of Sci-ences.

very sensitive to light. When exposed tolight, the rate of destruction increases as pHand temperature increase. Heating underneutral or acidic conditions does not destroythe vitamin.

The human requirement for riboflavin var-ies with metabolic activity and body weightand ranges from 1 to 3 mg per day. Normaladult requirement is 1.1 to 1.6 mg per day. Inmost cases, the riboflavin of foods is presentin the form of the dinucleotide, the phospho-ric acid ester, or is bound to protein. Only inmilk does riboflavin occur mostly in the freeform.

Under the influence of light and alkalinepH, riboflavin is transformed into lumiflavin,

Table 9-18 Thiamin Stability in Foods

Reten-Product Treatment tion (%)

Nine canned Processing 31-89vegetables

Four canned Storage, 2-3 mo 73-94vegetables @ room

temperatureCereals Extrusion cooking 48-90Fortified ready-to- Storage, 12 mo @ 10O

eat cereal 230CBread (white, Commercial 74-79

whole wheat) bakingDevil's food cake Baking 0-7

(PH9)

Source: From E. deRitter, Stability Characteristics ofVitamins in Processed Foods, Food Technol., Vol. 30,pp. 48-51,54, 1976.

an inactive compound with a yellowish-green fluorescence. Under acid conditions,riboflavin is transformed into another inac-tive derivative, lumichrome, and ribitol. Thiscompound has a blue fluorescence. The trans-

Figure 9-15 Structural Formula of Riboflavin.Riboflavin: R = OH; Riboflavin phosphate: R =PO3NaOH.

Table 9-19 Riboflavin Content of Some Foods

Riboflavin (mg/100 g)Product Edible Portion

Beef oTeCabbage 0.05Eggs 0.30Chicken 0.19Beef liver 3.26Chicken liver 2.49Beef kidney 2.55Peas 0.29Spinach 0.20Tomato 0.04Yeast (dry) 5.41Milk 0.17Nonfat dry milk 1.78

formation into lumiflavin in milk results inthe destruction of ascorbic acid.

The light sensitivity of riboflavin results inlosses of up to 50 percent when milk isexposed to sunlight for two hours. The natureof the packaging material significantlyaffects the extent of riboflavin destruction. Itappears that the wavelengths of light respon-sible for the riboflavin destruction are in thevisible spectrum below 500 to 520 nm. Ultra-violet light has been reported to have nodestructive effect on riboflavin (Hartman andDry den 1965). Riboflavin is stable in drymilk for storage periods of up to 16 months.Pasteurization of milk causes only minorlosses of riboflavin.

Vitamin B6 (Pyridoxine)

There are three compounds with vitaminB6 activity. The structural formula of pyri-

doxine is presented in Figure 9-16. Theother two forms of this vitamin are differentfrom pyridoxinethey have another substit-uent on carbon 4 of the benzene ring. Pyri-doxal has a -CHO group in this position andpyridoxamine has a -CH2NH2 group. Allthree compounds can occur as salts. VitaminB6 plays an important role in the metabolismof amino acids, where it is active in the coen-zyme form pyridoxal-5-phosphate. The threeforms of vitamin B6 are equally active inrats; although it can be expected that thesame applies for humans, this has not beendefinitely established.

Vitamin B6 is widely distributed in manyfoods (Table 9-20), and deficiencies of thisvitamin are uncommon. The recommendedallowance for adults has been established at2 mg per day. The requirement appears toincrease with the consumption of high-pro-tein diets.

Vitamin B6 occurs in animal tissues in theform of pyridoxal and pyridoxamine or astheir phosphates. Pyridoxine occurs in plantproducts.

Pyridoxine is stable to heat and strongalkali or acid; it is sensitive to light, espe-cially ultraviolet light and when present inalkaline solutions. Pyridoxal and pyridoxam-

Figure 9-16 Structural Formula of Pyridoxine

Table 9-20 Vitamin B6 Content of Some Foods

Product Vitamin B6 (\ig/g)

Wheat 3.2-6.1Whole wheat bread 4.2White bread 1.0Orange juice 0.52-0.60Apple juice 0.35Tomatoes 1.51Beans, canned 0.42-0.81Peas, canned 0.44-0.53Beef muscle 0.8-4.0Pork muscle 1.23-6.8Milk, pasteurized 0.5-0.6Yeast 50

ine are rapidly destroyed when exposed toair, heat, or light. Pyridoxamine is readilydestroyed in food processing operations.

Because it is difficult to determine thisvitamin in foods, there is a scarcity of infor-mation on its occurrence. Recent data estab-lish the level in milk as 0.54 mg per liter.Other sources are meats, liver, vegetables,whole grain cereals, and egg yolk.

The effects of processing on pyridoxinelevels in milk and milk products have beenreviewed by Hartman and Dryden (1965).No significant losses have been reported to

result from pasteurization, homogenization,or production of dried milk. Heat steriliza-tion of milk, however, has been reported toresult in losses ranging from 36 to 49 per-cent. Losses occur not only during the heattreatment but also during subsequent storageof milk. These storage losses have beenattributed to a conversion of pyridoxal topyridoxamine and then to a different form ofthe vitamin. Wendt and Bernhart (1960) haveidentified this compound as fe/s^-pyridoxaldisulfide (Figure 9-17). This compound isformed by reaction of pyridoxal and activesulfhydryl groups. The latter are formed dur-ing heat treatment of milk proteins. Exposureof milk to daylight in clear glass bottles foreight hours resulted in a vitamin B6 loss of21 percent.

Food canning results in losses of vitaminB6 of 20 to 30 percent. Milling of wheat mayresult in losses of up to 80 to 90 percent.Baking of bread may result in losses of up to17 percent.

A review of some stability data of vitaminB6 as prepared by deRitter (1976) is given inTable 9-21.

Niacin

The term niacin is used in a generic sensefor both nicotinic acid and nicotinamide

Figure 9-17 Structural Formula of fcw-4-Pyridoxal Disulfide

(Figure 9-18). Nicotinamide acts as a com-ponent of two important enzymes, NAD andNADP, which are involved in glycolysis, fatsynthesis, and tissue respiration. Niacin isalso known as the pellagra preventive factor.The incidence of pellagra has declined but isstill a serious problem in parts of the NearEast, Africa, southeastern Europe, and inNorth American populations that subsist on

corn diets. When corn is treated with alkalior lime, as for the tortilla preparation in Cen-tral America, the amount of available niacincan be greatly increased. Tryptophan can beconverted by the body into niacin. Manydiets causing pellagra are low in good-qual-ity protein as well as in vitamins. Corn pro-tein is low in tryptophan. The niacin of cornand other cereals may occur in a bound form,

Figure 9-18 Structural Formulas of (A) Nicotinic Acid and (B) Nicotinamide

Source: From E. deRitter, Stability Characteristics of Vitamins in Processed Foods, Food Technol., Vol. 30, pp.48-51,54,1976.

Table 9-21 Vitamin B6 Stability in Foods

Product

Bread (added B6)Enriched corn meal

Enriched macaroni

Whole milk

Infant formula, liquid

Infant formula, dryBoned chicken

Treatment

Baking12 mo @ 380C + 50% relative

humidity12 mo @ 380C + 50% relative

humidity

Evaporation and sterilizationEvaporation and sterilization

+ 6 mo @ room temperatureProcessing and sterilization

Spray dryingCanningIrradiation (2.79 megarads)

Retention (%)

100

90-95

100

SaccharomycesCarlsbergensis

3018

Chick5544

Rat6541

33-50 (natural)84 (added)

69-835768

called niacytin, that can be converted intoniacin by alkali treatment.

The human requirement of niacin is re-lated to the intake of tryptophan. Animalproteins contain approximately 1.4 percentof tryptophan, vegetable proteins about 1percent. A dietary intake of 60 mg of tryp-tophan is considered equivalent to 1 mg ofniacin. When this is taken into account,average diets in the United States supply500 to 1,000 mg tryptophan per day and 8 to17 mg niacin for a total niacin equivalent of16 to 33 mg. The RDA for adults, expressedas niacin, is 6.6 mg per 1,000 kcal, and notless than 13 mg when caloric intake is lessthan 2,000 kcal.

Table 9-22 Niacin Content of Some Foods

Niacin (mg/100 g)Product Edible Portion

Barley (pearled) 3.1Beans (green, snap) 0.5Beans (white) 2.4Beef (total edible) 4.4Beef kidney 6.4Beef liver 13.6Chicken (dark meat) 5.2Chicken (light meat) 10.7Corn (field) 2.2Haddock 3.0Milk 0.1Mushrooms 4.2Peanuts 17.2Peas 2.9Potatoes 1.5Spinach 0.6Wheat 4.3Yeast (dry) 36.7

Good dietary sources of this vitamin areliver, kidney, lean meat, chicken, fish, wheat,barley, rye, green peas, yeast, peanuts, andleafy vegetables. In animal tissues, the pre-dominant form of niacin is the amide. Niacincontent of some foods are listed in Table9-22.

Niacin is probably the most stable of the Bvitamins. It is unaffected by heat, light, oxy-gen, acid, or alkali. The main loss resultingfrom processing involves leaching into theprocess water. Blanching of vegetables maycause a loss of about 15 percent. Processes inwhich brines are used may cause losses of upto 30 percent. Processing of milk, such aspasteurization, sterilization, evaporation,and drying have little or no effect on nico-tinic acid level. Virtually all the niacin inmilk occurs in the form of nicotmamide. Inmany foods, application of heat, such asroasting or baking, increases the amount ofavailable niacin. This results from the changeof bound niacin to the free form.

Vitamin B12 (Cyanocobalamine)

This vitamin possesses the most complexstructure of any of the vitamins and is uniquein that it has a metallic element, cobalt, in themolecule (Figure 9-19). The molecule is acoordination complex built around a centraltervalent cobalt atom and consists of twomajor partsa complex cyclic structure thatclosely resembles the porphyrins and a nu-cleotide-like portion, 5,6-dimethyl-l-(oc-D-ribofuranosyl) benzimidazole-3'-phosphate.The phosphate of the nucleotide is esterifiedwith l-amino-2-propanol; this, in turn, isjoined by means of an amide bond with thepropionic acid side chain of the large cyclicstructure. A second linkage with the largestructure is through the coordinate bondbetween the cobalt atom and one of the nitro-

gen atoms of the benzimidazole. The cyanidegroup can be split off relatively easily, forexample, by daylight. This reaction can bereversed by removing the light source. Thecyano group can also be replaced by othergroups such as hydroxo, aquo, and nitroto.Treatment with cyanide will convert thesegroups back to the cyano form. The differentforms all have biological activity.

Cyanocobalamine is a component of sev-eral coenzymes and has an effect on nucleicacid formation through its action in cycling5-methyl-tetrahydrofolate back into the folatepool. The most important dietary sources ofthe vitamin are animal products. Vitamin B12is also produced by many microorganisms. Itis not surprising that vitamin B12 deficiencyof dietary origin only occurs in vegetarians.

The average diet in the United States isconsidered to supply between 5 and 15 |Hg/day. In foods, the vitamin is bound to pro-teins via peptide linkages but can be readilyabsorbed in the intestinal tract. The RDA is 3|ig for adults and adolescents.

Few natural sources are rich in vitaminB12. However, only very small amounts arerequired in the diet. Good sources are leanmeat, liver, kidney, fish, shellfish, and milk(Table 9-23). In milk, the vitamin occurs ascobalamine bound to protein.

Vitamin B12 is not destroyed to a greatextent by cooking, unless the food is boiled inalkaline solution. When liver is boiled inwater for 5 minutes, only 8 percent of thevitamin B12 is lost. Broiling of meat mayresult in higher losses. Pasteurization causes

Figure 9-19 Structural Formula of Cyanocobalamine

Table 9-23 Vitamin B12 Content of Some Foods

Product Vitamin B12

Beef muscle 0.25-3.4 jig/1 OO g

Beef liver 14-152 (ig/1 OO gMilk 3.2-12.4 |ig/LShellfish 600-970 p.g/1 OO g (dry wt)Egg yolk 0.28-1.556 jig/1 OO g

only a slight destruction of vitamin B12 inmilk; losses range from 7 to 10 percentdepending on pasteurization method. Moredrastic heat treatment results in higher losses.Boiling milk for two to five minutes causes a30 percent loss, evaporation about 50 percent,and sterilization up to 87 percent. The loss indrying of milk is smaller; in the production ofdried skim milk, the vitamin B12 loss is about30 percent. Ultra-high-temperature steriliza-tion of milk does not cause more vitamin B12destruction than does pasteurization.

Folic Acid (Folacin)

Folic acid is the main representative of aseries of related compounds that containthree moieties: pterin, /7-aminobenzoic acid,and glutamic acid (Figure 9-20). The com-mercially available form contains one glutamic

acid residue and is named pteroylglutamicacid (PGA). The naturally occurring formsare either PGA or conjugates with varyingnumbers of glutamic acid residues, such astri- and heptaglutamates. It has been sug-gested that folic acid deficiency is the mostcommon vitamin deficiency in North Amer-ica and Europe. Deficiency is especiallylikely to occur in pregnant women.

The vitamin occurs in a variety of foods,especially in liver, fruit, leafy vegetables, andyeast (Table 9-24) (Hurdle et al. 1968; Stre-iff 1971). The usual form of the vitamin inthese products is a polyglutamate. The actionof an enzyme (conjugase) is required to lib-erate the folic acid for metabolic activity;this takes place in the intestinal mucosa. Thefolacin of foods can be divided into two maingroups on the basis of its availability to L.casei: (1) the so-called free folate, which isavailable to L. casei without conjugase treat-ment; and (2) the total folate, which alsoincludes the conjugates that are not normallyavailable to L. casei. About 25 percent of thedietary folacin occurs in free form. Thefolate in vegetables occurs mainly in the con-jugated form; the folate in liver occurs in thefree form.

The RDA for folacin is 400 (Ig for adults.There is an additional requirement of 400|iig/day during pregnancy and 200 |iig/dayduring breastfeeding.

Figure 9-20 Structural Formula of Folic Acid

Table 9-24 Folate Content of Some Foods

FolateProduct fag/g)

Beef, boiled 0.03Chicken, roasted 0.07Cod, fried 0.16Eggs, boiled 0.30Brussels sprouts, boiled 0.20Cabbage, boiled 0.11Lettuce 2.00Potato, boiled 0.12Spinach, boiled 0.29Tomato 0.18Orange 0.45Milk 0.0028Bread, white 0.17Bread, brown 0.38Orange juice, frozen reconstituted 0.50Tomato juice, canned 0.10

Many of the naturally occurring folates areextremely labile and easily destroyed bycooking. Folic acid itself is stable to heat inan acid medium but is rapidly destroyedunder neutral and alkaline conditions. Insolution, the vitamin is easily destroyed bylight. Folate may occur in a form more active

than PGA; this is called folinic acid or citro-vorum factor, which is N5-formyl-5, 6, 7, 8-tetrahydro PGA (Figure 9-21). The folate ofmilk consists of up to 20 percent of folinicacid. It has been reported that pasteurizationand sterilization of milk involve only smalllosses or no loss. Hurdle et al. (1968) re-ported that boiling of milk causes no loss infolate; however, boiling of potato results in a90 percent loss and boiling of cabbage a 98percent loss. Reconstitution of dried milkfollowed by sterilization as can occur withbaby formulas may lead to significant folacinlosses. Fermentation of milk and milk prod-ucts may result in greatly increased folatelevels. Blanching of vegetables and cookingof meat do not appear to cause folic acidlosses. Table 9-25 contains a summary offolate stability data prepared by deRitter(1976). Citrus fruit and juices are relativelygood sources of folic acid, which is presentmostly as the reduced 5-methyl tetrahydro-folate (monoglutamate form). There are alsopolyglutamate derivatives present (White etal. 1991).

Pantothenic Acid

The free acid (Figure 9-22) is very unsta-ble and has the appearance of a hygroscopic

Figure 9-21 Structural Formula of Folinic Acid

Source: From E. deRitter, Stability Characteristics ofVitamins in Processed Foods, Food Technol., Vol. 30,pp. 48-51,54, 1976.

oil. The calcium and sodium salts are morestable. The alcohol (panthenol) has the samebiological activity as the acid. Only the dex-trorotatory or D form of these compoundshas biological activity. Pantothenic acidplays an important role as a component ofcoenzyme A, and this is the form in which itoccurs in most foods.

Pantothenic acid occurs in all living cellsand tissues and is, therefore, found in mostfood products. Good dietary sources includemeats, liver, kidney, fruits, vegetables, milk,egg yolk, yeast, whole cereal grains, and nuts(Table 9-26). In animal products, most of thepantothenic acid is present in the bound

Table 9-26 Pantothenic Acid Content of SomeFoods

Pantothenic AcidProduct fag/g)

Beef, lean 10Wheat 11Potatoes 6.5Split peas 20-22Tomatoes 1Orange 0.7Walnuts 8Milk 1.3-4.2Beef liver 25-60Eggs 8-48Broccoli 46

form, but in milk only about one-fourth ofthe vitamin is bound.

There is no recommended dietary allow-ance for this vitamin because of insufficientevidence to base one on. It is estimated thatadult dietary intake in the United Statesranges from 5 to 20 mg/day, and 5 to 10 mg/day probably represents an adequate intake.

The vitamin is stable to air, and labile todry heat. It is stable in solution in the pHrange of 5 to 7 and less stable outside thisrange. Pasteurization and sterilization ofmilk result in very little or no loss. The pro-duction and storage of dried milk involveslittle or no loss of pantothenic acid. Manu-

Table 9-25 Folic Acid Stability in Foods

Product

CabbagePotatoesRiceBeef, pork,

and chickenVarious

foods

Treatment

Boiled 5 minBoiled 5 minBoiled 15 minBoiled 15 min

Cooked

Retention ofFolic Add

Free (%)

3250

Figure 9-23 Structural Formula of Biotin

facture of cheese involves large losses duringprocessing, but during ripening the pan-tothenic acid content increases, due to syn-thesis by microorganisms. Blanching of veg-etables may involve losses of up to 30 per-cent. Boiling in water involves losses thatdepend on the amount of water used.

Biotin

The structural formula (Figure 9-23) con-tains three asymmetric carbon atoms, andeight different stereoisomers are possible.Only the dextrorotatory D-biotin occurs innature and has biological activity. Biotinoccurs in some products in free form (vege-tables, milk, and fruits) and in other productsis bound to protein (organ meats, seeds, andyeast). Good sources of the vitamin are meat,liver, kidney, milk, egg yolk, yeast, vegeta-bles, and mushrooms (Table 9-27).

Biotin is important in a number of meta-bolic reactions, especially in fatty acid syn-thesis. The biotin supply of the human or-ganism is only partly derived from the diet.

An important factor in biotin's availabilityis that some of the vitamin is derived fromsynthesis by intestinal microorganisms; thisis demonstrated by the fact that three to six

Table 9-27 Biotin Content of Some Foods

Product Biotin fog/1 OO g)

"Milk 1.1-3.7Tomatoes 1Broad beans 3Cheese 1.1-7.6Wheat 5.2Beef 2.6Beef liver 96Lettuce 3.1Mushrooms 16Potatoes 0.6Spinach 6.9Apples 0.9Oranges 1.9Peanuts 34

times more biotin is excreted in the urinethan is ingested with the food. The dailyintake of biotin is between 100 and 300 (Ig.No recommended dietary allowance hasbeen established. Biotin is deactivated byraw egg white. This is caused by the glyco-protein avidin. Heating of avidin will destroythe inactivator capacity for biotin.

Data on the stability of biotin are limited.The vitamin appears to be quite stable. Heattreatment results in relatively small losses.The vitamin is stable to air and is stable atneutral and acid pH. Pasteurization and ster-ilization of milk result in losses of less than10 percent. In the production of evaporatedand dried milk, losses do not exceed 15 per-cent.

VITAMINS AS FOOD INGREDIENTS

In addition to their role as essential micro-nutrients, vitamins may serve as food ingre-

Figure 9-24 Prevention of Lipid Free RadicalFormation by Ascorbyl Palmitate. Source: FromM.L. Liao and P.A. Seib, Selected Reactions ofL-Ascorbic Acid Related to Foods, Food Tech-noL, Vol. 41, no. 11, pp. 104-107, 1987.

dients for their varied functional properties(Institute of Food Technologists 1987). Vita-min C and vitamin E have found widespreaduse as antioxidants. In lipid systems, vitamin

E may be used as an antioxidant in fats thathave little or no natural tocopherol content.Ascorbic acid in the form of its palmitic acidester, ascorbyl palmitate, is an effective anti-oxidant in lipid systems. Ascorbyl palmitateprevents the formation of lipid free radicals(Figure 9-24) and thereby delays the initia-tion of the chain reaction that leads to thedeterioration of the fat (Liao and Seib 1987).Ascorbyl palmitate is used in vegetable oilsbecause it acts synergistically with naturallyoccurring tocopherols. The tocopherols arefat-soluble antioxidants that are used in ani-mal fats. Ascorbic acid reduces nitrous acidto nitric oxide and prevents the formation ofN-nitrosamine. The reaction of nitrous acidand ascorbic acid is given in Figure 9-25(Liao and Seib 1987). Ascorbic acid is alsowidely used to prevent enzymic browning infruit products. Phenolic compounds are oxi-dized by polyphenoloxidase to quinones.The quinones rapidly polymerize to formbrown pigments. This reaction is easily re-versed by ascorbic acid (Figure 9-26).

LIPID RADICALASCORBYL PALMITATERADICAL

ASCORBYLPALMITATE

FREERADICAL

PARTIAL STRUCTUREOF LIPID

2-NITRITE ESTEROF L-ASCORBIC ACID

NITRICOXIDE

L-ASCORBICACID

L-ASCORBATE RADICAL

Figure 9-25 Reaction Between Nitrous Acid and Ascorbic Acid. Source: From M.L. Liao and P.A.Seib, Selected Reactions of L-Ascorbic Acid Related to Foods, Food Technol, Vol. 41, no. 11, pp.104-107, 1987.

The carotenoids p-carotene and p-apo-8-carotenal are used as colorants in fat-basedas well as water-based foods.

Other functions of ascorbic acid are inhibi-tion of can corrosion in canned soft drinks,

REFERENCES

Baltes, J. 1967. Tocopherols as fat stabilizers. In To-copherol, K. Lang, ed. Darmstadt, Germany: Stein-kopff Verlag.

Bender, A.E. 1971. The fate of vitamins in food pro-cessing operations. In Vitamins, ed. M. Stein. Lon-don: Churchill Livingstone.

Bullock, D.H., et al. 1968. Stability of vitamin C inenriched commercial evaporated milk. J. Dairy ScL51:921-923.

Combs, G.F. 1992. The vitamins: Fundamental aspectsin nutrition and health. San Diego: Academic Press.

deMan, J.M. 1981. Light-induced destruction of vita-min A in milk. J. Dairy ScL 64: 2031-2032.

deMan, J.M., et al. 1986. Stability of vitamin A bead-lets in nonfat dry milk. Milchwissenschaft 41:468^69.

protection of flavor and color of wine, pre-vention of black spot formation in shrimp,stabilization of cured meat color, and doughimprovement in baked goods (Institute ofFood Technologists 1987).

deRitter, E. 1976. Stability characteristics of vitaminsin processed foods. Food TechnoL 30: 48-51, 54.

Eitenmiller, R.R. 1997. Vitamin E content of fats andoils: Nutritional implications. Food TechnoL 51, no.5:78-81.

Gross, J. 1987. Pigments in fruits. London: HarcourtBrace Jovanovich.

Hartman, A.M., and Dryden, L.P. 1965. Vitamins inmilk and milk products. Am. Dairy Sci. Assoc.Champaign, IL.

Hurdle, A.D.F., et al. 1968. A method for measuringfolate in food and its application to a hospital diet.Am. J. Clin. Nutr. 21: 1202-1207.

Institute of Food Technologists. 1987. Use of vitaminsas additives in processed foods. Food TechnoL 41,no. 9: 163-168.

BROWNPIGMENTS

PHENOLICCQMPOUMD

0-QUINONE

L-ASCORBICACID

DEHYDROASCOR3ICACID

Figure 9-26 Reduction of Ortho-Quinone by Ascorbic Acid During Enzymic Browning. Source: FromM.L. Liao and RA. Seib, Selected Reactions of L-Ascorbic Acid Related to Foods, Food TechnoL, Vol.41, no. 11, pp. 104-107,1987.

Liao, M.-L., and P.A. Seib. 1987. Selected reactions ofL-ascorbic acid related to foods. Food Technol 41,no. 11: 104-107, 111.

Menger, A. 1957. Investigation of the stability of vita-min E in cereal milling products and baked goods.Brot. Gebdck 11: 167-173 (German).

Morton, R.A. 1967. The chemistry of tocopherols. InTocopherol, ed. K. Lang. Darmstadt, Germany:Steinkopff Verlag.

National Academy of Sciences. 1974a. Recommendeddietary allowances, 8th rev. ed. Washington, DC.

National Academy of Sciences. 1974b. Proposed forti-fication policy for cereal-grain products. Washing-ton, DC.

Odland, D., and M.S. Eheart. 1975. Ascorbic acid,mineral and quality retention in frozen broccoliblanched in water, steam and ammonia-steam. J.Food ScL 40: 1004-1007.

Ong, A.S.H. 1993. Natural sources of tocotrienols. InVitamin E in health and disease, ed. L. Packer and J.Fuchs. New York: Marcel Dekker.

Rouseff, R.L., and S. Nagy. 1994. Health and nutri-tional benefits of citrus fruit components. FoodTechnol. 48, no. 11: 126-132.

Sattar, A., and J.M. deMan. 1973. Effect of packagingmaterial on light-induced quality deterioration ofmilk. Can. Inst. Food ScL Technol. J. 6: 170-174.

Streiff, R.R. 1971. Folate levels in citrus and otherjuices. Am. /. Clin. Nutr. 24: 1390-1392.

Thaler, H. 1967. Concentration and stability of toco-pherols in foods. In Tocopherol, ed. K. Lang. Darms-tadt, Germany: Steinkopff Verlag

Wendt, G., and E.W. Bernhart. 1960. The structure of asulfur-containing compound with vitamin B6 activ-ity. Arch. Biochem. Biophys. 88: 270-272.

White, D.R., et al. 1991. Reverse phase HPLC/ECdetermination of folate in citrus juice by direct injec-tion with column switching. J. Agr. Food Chem. 39:714-717.

INTRODUCTION

The possibility of harmful or toxic sub-stances becoming part of the food supplyconcerns the public, the food industry, andregulatory agencies. Toxic chemicals may beintroduced into foods unintentionally throughdirect contamination, through environmen-tal pollution, and as a result of processing.Many naturally occurring food compoundsmay be toxic. A summary of the varioustoxic chemicals in foods (Exhibit 11-1) waspresented in a scientific status summary ofthe Institute of Food Technologists (1975).Many toxic substances present below certainlevels pose no hazard to health. Some sub-stances are toxic and at the same time essen-tial for good health (such as vitamin A andselenium). An understanding of the proper-ties of additives and contaminants and howthese materials are regulated by governmen-tal agencies is important to the food scientist.Regulatory controls are dealt with in Chapter12.

Food additives can be divided into twomajor groups, intentional additives and inci-dental additives. Intentional additives arechemical substances that are added to foodfor specific purposes. Although we have lit-tle control over unintentional or incidentaladditives, intentional additives are regulated

by strict governmental controls. The U.S.law governing additives in foods is the FoodAdditives Amendment to the Federal Food,Drug and Cosmetic Act of 1958. Accordingto this act, a food additive is defined as fol-lows:

The term food additive means any sub-stance the intended use of which results,or may reasonably be expected to result,directly or indirectly in its becoming acomponent or otherwise affecting thecharacteristics of any food (includingany substance intended for use in pro-ducing, manufacturing, packing, pro-cessing, preparing, treating, packaging,transporting, or holding food; and in-cluding any source of radiation intendedfor any such use), if such a substance isnot generally recognized, among expertsqualified by scientific training and expe-rience to evaluate its safety, as havingbeen adequately shown through scien-tific procedures (or, in the case of a sub-stance used in food prior to January 1,1958, through either scientific proce-dures or experience based on commonuse in food) to be safe under the condi-tion of its intended use; except that sucha term does not include pesticides, color

Additives and Contaminants

CHAPTER 11

additives and substances for which priorsanction or approval was granted.

The law of 1958 thus recognizes the fol-lowing three classes of intentional additives:

1. additives generally recognized as safe(GRAS)

2. additives with prior approval3. food additives

Coloring materials and pesticides on rawagricultural products are covered by otherlaws. The GRAS list contains several hun-dred compounds, and the concept of such alist has been the subject of controversy (Hall1975).

Before the enactment of the 1958 law, U.S.laws regarding food additives required that afood additive be nondeceptive and that anadded substance be either safe and thereforepermitted, or poisonous and deleterious and

therefore prohibited. This type of legislationsuffered from two main shortcomings: (1) itequated poisonous with harmful, and (2) theonus was on the government to demonstratethat any chemical used by the food industrywas poisonous. The 1958 act distinguishesbetween toxicity and hazard. Toxicity is thecapacity of a substance to produce injury.Hazard is the probability that injury willresult from the intended use of the substance.It is now well recognized that many compo-nents of our foods, whether natural or added,are toxic at certain levels but harmless oreven nutritionally essential at lower levels.The ratio between effective dose and toxicdose of many compounds, including suchcommon nutrients as amino acids and salts,is of the order of 1 to 100. It is now manda-tory that any user of an additive must petitionthe government for permission to use thematerial and must supply evidence that thecompound is safe.

Exhibit 11-1 Toxic Chemicals in Foods

NATURAL

normal components of natural foodproducts

natural contaminants of natural foodproducts-microbiological origin: toxins-nonmicrobiological origin: toxicants

(e.g., Hg, Se) consumed in feeds byanimals used as food sources

MAN-MADE

agricultural chemicals (e.g., pesticides,fertilizers)

food additives chemicals derived from food packag-

ing materials chemicals produced in processing of

foods (e.g., by heat, ionizing radiation,smoking)

inadvertent or accidental contaminants-food preparation accidents or mis-

takes-contamination from food utensils-environmental pollution-contamination during storage or

transport

An important aspect of the act is the so-called Delaney clause, which specifies thatno additive shall be deemed safe if it is foundto induce cancer in man or animal. Such spe-cial consideration in the case of cancer-pro-ducing compounds is not incorporated in thefood laws of many other countries.

INTENTIONAL ADDITIVES

Chemicals that are intentionally introducedinto foods to aid in processing, to act as pre-servatives, or to improve the quality of thefood are called intentional additives. Theiruse is strictly regulated by national and inter-national laws. The National Academy of Sci-ences (1973) has listed the purposes of foodadditives as follows:

to improve or maintain nutritional value to enhance quality to reduce wastage to enhance consumer acceptability to improve keeping quality to make the food more readily available to facilitate preparation of the food

The use of food additives is in effect a foodprocessing method, because both have thesame objectiveto preserve the food and/ormake it more attractive. In many food pro-cessing techniques, the use of additives is anintegral part of the method, as is smoking,heating, and fermenting. The National Acad-emy of Sciences (1973) has listed the follow-ing situations in which additives should notbe used:

to disguise faulty or inferior processes to conceal damage, spoilage, or other

inferiority to deceive the consumer

if use entails substantial reduction inimportant nutrients

if the desired effect can be obtained byeconomical, good manufacturing prac-tices

in amounts greater than the minimumnecessary to achieve the desired effects

There are several ways of classifying in-tentional food additives. One such methodlists the following three main types of addi-tives:

1. complex substances such as proteins orstarches that are extracted from otherfoods (for example, the use of casein-ate in sausages and prepared meats)

2. naturally occurring, well-defined chem-ical compounds such as salt, phos-phates, acetic acid, and ascorbic acid

3. substances produced by synthesis,which may or may not occur in nature,such as coal tar dyes, synthetic (3-caro-tene, antioxidants, preservatives, andemulsifiers

Some of the more important groups ofintentional food additives are described inthe following sections.

Preservatives

Preservatives or antimicrobial agents playan important role in today's supply of safeand stable foods. Increasing demand for con-venience foods and reasonably long shelf lifeof processed foods make the use of chemicalfood preservatives imperative. Some of thecommonly used preservativessuch as sul-fites, nitrate, and salthave been used forcenturies in processed meats and wine. Thechoice of an antimicrobial agent has to bebased on a knowledge of the antimicrobial

spectrum of the preservative, the chemicaland physical properties of both food and pre-servative, the conditions of storage and han-dling, and the assurance of a high initialquality of the food to be preserved (Davidsonand Juneja 1990).

Benzoic Acid

Benzoic acid occurs naturally in manytypes of berries, plums, prunes, and somespices. As an additive, it is used as benzoicacid or as benzoate. The latter is used moreoften because benzoic acid is sparsely solu-ble in water (0.27 percent at 180C) andsodium benzoate is more soluble (66.0 g/100mL at 2O0C). The undissociated form of ben-zoic acid is the most effective antimicrobialagent. With a pKa of 4.2, the optimum pHrange is from 2.5 to 4.0. This makes it aneffective antimicrobial agent in high-acidfoods, fruit drinks, cider, carbonated bever-ages, and pickles. It is also used in marga-rines, salad dressings, soy sauce, and jams.

Parabens

Parabens are alkyl esters of /?-hydroxyben-zoic acid. The alkyl groups may be one ofthe following: methyl, ethyl, propyl, butyl, orheptyl. Parabens are colorless, tasteless, andodorless (except the methyl paraben). Theyare nonvolatile and nonhygroscopic. Theirsolubility in water depends on the nature ofthe alkyl group; the longer the alkyl chainlength, the lower the solubility. They differfrom benzoic acid in that they have antimi-crobial activity in both acid and alkaline pHregions.

The antimicrobial activity of parabens isproportional to the chain length of the alkylgroup. Parabens are more active againstmolds and yeasts than against bacteria, and

more active against gram-positive than gram-negative bacteria. They are used in fruit-cakes, pastries, and fruit fillings. Methyl andpropyl parabens can be used in soft drinks.Combinations of several parabens are oftenused in applications such as fish products,flavor extracts, and salad dressings.

Sorbic Acid

Sorbic acid is a straight-chain, trans-transunsaturated fatty acid, 2,4-hexadienoic acid.As an acid, it has low solubility (0.15 g/100mL) in water at room temperature. The salts,sodium, or potassium are more soluble inwater. Sorbates are stable in the dry form; theyare unstable in aqueous solutions because theydecompose through oxidation. The rate ofoxidation is increased at low pH, by increasedtemperature, and by light exposure.

Sorbic acid and sorbates are effectiveagainst yeasts and molds. Sorbates inhibityeast growth in a variety of foods includingwine, fruit juice, dried fruit, cottage cheese,meat, and fish products. Sorbates are mosteffective in products of low pH includingsalad dressings, tomato products, carbonatedbeverages, and a variety of other foods.

The effective level of sorbates in foods isin the range of 0.5 to 0.30 percent. Some ofthe common applications are shown in Table11-1. Sorbates are generally used in sweet-ened wines or wines that contain residualsugars to prevent refermentation. At the lev-els generally used, sorbates do not affectfood flavor. However, when used at higherlevels, they may be detected by some peopleas an unpleasant flavor. Sorbate can bedegraded by certain microorganisms to pro-duce off-flavors. Molds can metabolize sor-bate to produce 1,3 pentadiene, a volatilecompound with an odor like kerosene. Highlevels of microorganisms can result in the

degradation of sorbate in wine and result inthe off-flavor known as geranium off-odor(Edinger and Splittstoesser 1986). The com-pounds responsible for the flavor defect areethyl sorbate, 4-hexenoic acid, 1-ethoxy-hexa-2,4-diene, and 2-ethoxyhexa-3,5-diene.The same problem may occur in fermentedvegetables treated with sorbate.

Sulfites

Sulfur dioxide and sulfites have long beenused as preservatives, serving both as antimi-crobial substance and as antioxidant. Theiruse as preservatives in wine dates back toRoman times. Sulfur dioxide is a gas that canbe used in compressed form in cylinders. It isliquid under pressure of 3.4 atm and can beinjected directly in liquids. It can also beused to prepare solutions in ice cold water. Itdissolves to form sulfurous acid. Instead ofsulfur dioxide solutions, a number of sulfitescan be used (Table 11-2) because, when dis-solved in water, they all yield active SO2.

The most widely used of these sulfites ispotassium metabisulfite. In practice, a valueof 50 percent of active SO2 is used. Whensulfur dioxide is dissolved in water, the fol-lowing ions are formed:

SO2 (gas) -> SO2 (aq)SO2 (aq)

+ - H2O -> H2SO3H2SO3 - H

+ + HSO3- (K1 = 1.7 x 1(T2)

HSO31 -> H+ + SO3

21 (K2 = 5 x IO"6)

2HSO3- -> S2O52- + H2O

All of these forms of sulfur are known as freesulfur dioxide. The bisulfite ion (HSO3") canreact with aldehydes, dextrins, pectic sub-stances, proteins, ketones, and certain sugarsto form addition compounds.

Table 11-1 Applications of Sorbates as Antimicrobial Agents

Products

Dairy products: aged cheeses, processed cheeses, cottage cheese, cheesespreads, cheese dips, sour cream, yogurt

Bakery products: cakes, cake mixes, pies, fillings, mixes, icings, fudges, toppings,doughnuts

Vegetable products: fermented vegetables, pickles, olives, relishes, fresh saladsFruit products: dried fruit, jams, jellies, juices, fruit salads, syrups, purees, concen-

tratesBeverages: still wines, carbonated and noncarbonated beverages, fruit drinks, low-

calorie drinksFood emulsions: mayonnaise, margarine, salad dressingsMeat and fish products: smoked and salted fish, dry sausagesMiscellaneous: dry sausage casings, semimoist pet foods, confectionery

Levels (%)

0.05-0.30

0.03-0.30

0.02-0.200.02-0.25

0.02-0.10

0.05-0.100.05-0.300.05-0.30

Source: Reprinted with permission from J.N. Sofos and RF. Busta, Sorbic Acid and Sorbates, in Antimicrobials inFoods, P.M. Davidson and A.L. Branen, eds., p. 62,1993, by courtesy of Marcel Dekker, Inc.

The addition compounds are known asbound sulfur dioxide. Sulfur dioxide is usedextensively in wine making, and in wine acet-aldehyde reacts preferentially with bisulfite.Excess bisulfite reacts with sugars. It is pos-sible to classify bound SO2 into three forms:aldehyde sulfurous acid, glucose sulfurousacid, and rest sulfurous acid. The latter holdsthe SO2 in a less tightly bound form. Sulfitesin wines serve a dual purpose: (1) antisepticor bacteriostatic and (2) antioxidant. Theseactivities are dependent on the form of SO2present. The various forms of SO2 in wineare represented schematically in Figure 11-1.The free SO2 includes the water-soluble SO2and the undissociated H2SO3 and constitutesabout 2.8 percent of the total. The bisulfiteform constitutes 96.3 percent and the suifiteform 0.9 percent (all at pH 3.3 and 2O0C).The bound SO2 is mostly (80 percent)present as acetaldehyde SO2, 1 percent asglucose SO2, and 10 to 20 percent as restSO2. The various forms of suifite have differ-ent activities. The two free forms are the onlyones with antiseptic activity. The antioxidantactivity is limited to the SO3

2" ion (Figure11-1). The antiseptic activity of SO2 ishighly dependent on the pH, as indicated inTable 11-3. The lower the pH the greater the

antiseptic action of SO2. The effect of pH onthe various forms of sulfur dioxide is shownin Figure 11-2.

Sulfurous acid inhibits molds and bacteriaand to a lesser extent yeasts. For this reason,SO2 can be used to control undesirable bac-teria and wild yeast in fermentations withoutaffecting the SO2-tolerant cultured yeasts.According to Chichester and Tanner (1968),the undissociated acid is 1,000 times moreactive than HSO3~ for Escherichia coli, 100to 500 times for Saccharomyces cerevisiae,and 100 times for Aspergillus niger.

The amount of SO2 added to foods is self-limiting because at levels from 200 to 500ppm the product may develop an unpleasantoff-flavor. The acceptable daily intake (ADI)is set at 1.5 mg/kg body weight. Becauselarge intakes can result from consumption ofwine, there have been many studies on re-ducing the use of SO2 in wine making.Although some other compounds (such assorbic acid and ascorbic acid) may partiallyreplace SO2, there is no satisfactory replace-ment for SO2 in wine making.

The use of SO2 is not permitted in foodsthat contain significant quantities of thia-mine, because this vitamin is destroyed bySO2. In the United States, the maximum per-

Chemical

Sulfur dioxideSodium suifite, anhydrousSodium suifite, heptahydrateSodium hydrogen suifiteSodium metabisulfitePotassium metabisuifiteCalcium suifite

Formula

SO2Na2SO3

Na2SO3-? H2ONaHSO3Na2S2O5K2S2O5CaSO3

Content of Active SO2

100.00%50.82%25.41%61.56%67.39%57.63%64.00%

Table 11-2 Sources of SO2 and Their Content of Active SO2

mitted level of SO2 in wine is 350 ppm.Modern practices have resulted in muchlower levels of SO2. In some countries SO2 isused in meat products; such use is not per-mitted in North America on the grounds thatthis would result in consumer deception. SO2is also widely used in dried fruits, where lev-els may be up to 2,000 ppm. Other applica-tions are in dried vegetables and dried potato

Table 11-3 Effect of pH on the Proportion ofActive Antiseptic SO2 of Wine Containing 100mg/L Free SO2

pH Active SO2 (mg/L)

~22 3?!o2.8 8.03.0 5.03.3 3.03.5 1.83.7 1.24.0 0.8

products. Because SO2 is volatile and easilylost to the atmosphere, the residual levelsmay be much lower than the amounts origi-nally applied.

Nitrates and Nitrites

Curing salts, which produce the character-istic color and flavor of products such asbacon and ham, have been used throughouthistory. Curing salts have traditionally con-tained nitrate and nitrite; the discovery thatnitrite was the active compound was made inabout 1890. Currently, nitrate is not consid-ered to be an essential component in curingmixtures; it is sometimes suggested thatnitrate may be transformed into nitrite, thusforming a reservoir for the production ofnitrite. Both nitrates and nitrites are thoughtto have antimicrobial action. Nitrate is usedin the production of Gouda cheese to preventgas formation by butyric acid-forming bac-teria. The action of nitrite in meat curing is

Figure 111 The Various Forms of SO2 in Wine and Their Activity. Source: Reprinted with permis-sion from J.M. deMan, 500 Years of Sulfite Use in Winemaking, Am. Wine Soc. /., Vol. 20, pp. 44-46, 1988, American Wine Society.

I antjoxidont

activeantiseptic

acetaldehyde SO2

rest SO2

bound SO2

TOTAL SO 2

free SO2

HSOj

giucose su?

considered to involve inhibition of toxin for-mation by Clostridium botulinum, an impor-tant factor in establishing safety of curedmeat products. Major concern about the useof nitrite was generated by the realizationthat secondary amines in foods may react toform nitrosamines, as follows:

analytical procedures are difficult, there is asyet no clear picture of the occurrence of nitro-samines. The nitrosamines may be either vol-atile or nonvolatile, and only the latter areusually included in analysis of foods. Nitro-samines, especially dimethyl-nitrosamine, havebeen found in a number of cases when curedmeats were surveyed at concentrations of afew |Ltg/kg (ppb). Nitrosamines are usuallypresent in foods as the result of processingmethods that promote their formation (Hav-ery and Fazio 1985). An example is the spraydrying of milk. Suitable modifications ofthese process conditions can drasticallyreduce the nitrosamine levels. Considerablefurther research is neces