University of Ghent, Faculty of Agricultural and Applied Biological Sciences

Department of Organic Chemistry

Influence of processing on minor components in vegetable oils

Prof. dr. ir. Roland Verhé

2

General introduction

Composition crude oilNutritional importance

Oils and fats

• delivering energy (9 kcal/g)

• essential fatty acids (ω3, ω6)

• fat soluble vitamins (Vitamine A, D, E, K)

• sensorial and rheological appreciation of foods

• Triglycerides (>98%) and partial acylglycerides, free fatty acids

• Tocopherols, phytosterols, phospholipids, waxes, metals, colouring pigments

• Odour, flavour components

3

Overview vegetable oil refining

Chemical refiningChemical refining Physical refiningPhysical refining

Degumming

Bleaching

Steam refining Deodorization

Degumming

Neutralisation

Bleaching

Deodorization

Refined OilRefined Oil

SOAPS

GUMS

FFA

Crude OilCrude Oil

FFA

distillate

4

Vegetable oil quality characteristics

Currently : minor componentsTraditional parameters

bland taste

light colour

good oxidative stability

+ : Functional minor components

tocopherols, phytosterols,

oryzanol, coenzyme Q10

→ application in functional foods

- : Harmful contaminantspesticides, PAH’s, PCB’s

5

Tocopherols

O

HO

R1

R2R3

CH3CH3

CH3 CH3 CH3

LOO

Chemical structureName R1 R2 R3

α-toco CH3 CH3 CH3

γ-toco H CH3 CH3

δ-toco H H CH3

Non-polar and polar oxidation products

Natural source : vegetable oils, corn oil 1100 ppm, soya oil 900 ppm

Nutritional importance : → Vitamin E, prevention of free radical damage in vivo e.g. cardiovascular diseases, cancers, neurological disorders (Alzheimer,...)

Application : dietary supplements

6

Phytosterols

Chemical structure : – flexible side chain at C17

(sitosterol, campesterol, stigmasterol,…)– sterols versus stanols

HO

β-sitosterol

Nutritional importance : phytosterols lower plasma cholesterol and LDL cholesterol

Natural source : vegetable oils and cereals

Function : Essential component of the membranes

Application : in functional foods (e.g. margarine's,…)

7

Objective study

Refining process

Phytosterols & Tocopherols

Crude oil

Technology AnalysisChemistry

Observations → chemical modification → explanations

Naturallypresent

0.02-0.9%

modification

8

Occurrence of tocopherolsand phytosterols in vegetable

oils : free or bounded

9

Natural occurrence

OCH3

C16H33

HOFreeData available

Tocopherols

OCH3

C16H33

O

O

Esterified

Confuse data

→ synthesis of tocopheryl esters

→ development of analytical procedure (HPLC - UV)

→ tocopheryl esters are absent in crude vegetable oils

10

Natural occurrence

HO

β-sitosterol

• Tocopherols

→ only free tocopherols occur naturally in vegetable oil

• Phytosterols occur

• free

11

Natural occurrence

β-sitosteryl-oleate

C O

O

O

β-sitosteryl ferulate (γ-oryzanol)HO

H3CO

O

• Tocopherols

→ only free tocopherols occur naturally in vegetable oil

• Phytosterols occur

• free

•esterified to fatty acid

•esterified to phenolic acids•e.g. rice bran oil

12

Natural occurrence

O

β-sitosteryl-D-glucoside

O

OH

OH

CH2OH

• Tocopherols

→ only free tocopherols occur naturally in vegetable oil

• Phytosterols occur

• free

• esterified to fatty acid

• esterified to phenolic acid

• linked to sugar

O

β-sitosteryl-(6'O-oleoyl)-D-glucoside

O

OH

OH

CH2C

O

O

13

Total sterol analysis• Has been widely studied• Involves a saponification

• Little data is available on level of free and esterified phytosterols

Analysis free - esterified sterols• Free and esterified sterols were separated on polarity by silica gel chromatography, followed saponification and GC quantification

•Development and validation of analytical method

Steryl esters → free sterols

14

Free and esterified phytosterols

0 200 400 600 800 1000

Rapeseed (refined)Rapeseed (crude)

Corn (refined)

Corn oil (crude)Frituur (sunflower)

Sunflower (refined)Cotton (crude)

Cotton (refined)

Soya (refined)Peanut (refined)

Olive oil (cold pressed)

soybean (crude)Walnut (refined)

Palm oil (refined)Olive oil (cold pressed)

Coconut (crude)

Palm oil (crude)Red palm olein (crude)

sterol content (mg/100g) esterified free

15

Influence of refining on free and esterified

phytosterols in soybean oil

16

Influence of refining on soybean

0 50 100 150 200 250 300 350

Sterol concentration (mg/100 g)

Crude

Degummed

Neutralized

Bleached

Deodorized

Chemical refining

Esterified sterols Free sterols

0 50 100 150 200 250 300 350

Sterol concentration (mg/100 g)

Crude

Degummed

Bleached

Deodorized

Physical refining

Esterified sterols Free sterols

17

Chemical neutralisation of soybean

Time 30 min, temperature 45°C

0

50

100

150

200

250

300

350

sterol mg/100g

feed 2.5 5 10 12.5 15

strength NaOH (%)

0% excess NaOH

free esterified

18

Bleaching of soybean oil

050

100150200250300350400

sterol mg/100g

feed 2.8 3.1 3.1 3.2 3.6 3.6 4.15 6

pH bleaching earth (10% suspension in water)

1% earth, 100°C, 30 min

free esterified

19

Steradienes - disteryl ethers

• Steradienes : sterol dehydration productsR

HO

R

phytosterol steradienetemperature

bleaching earth

-H2O

• Disteryl ethers : sterol condensation productsR

O

R

→ ratio dehydration / condensation : 10/1

20

Steradienes - bleaching

• Steradiene formation is mainly influence by– bleaching temperature– degree of acid activation of the bleaching earth

0

5

10

15

20

25

2.5 3.5 4.5 5.5

pH suspension bleaching earth / water (10%)

rela

tive

ster

adie

ne in

crea

se

30 min, 80°C, 1% earth30 min, 100°C, 1% earth30 min, 100°C, 2% earth

21

Deodorization of soybean oil

0

50

100

150

200

250

300

350

Sterol mg/100g

Feed 220°C 230°C 240°C 250°C 260°C

Deodorization temperature (°C)

Chemical refining (FFA feed=0.1%)

Esterified sterols Free sterols

0

50

100

150

200

250

300

350

Sterol mg/100g

Feed 220°C 230°C 240°C 250°C 260°C

Deodorization temperature (°C)

Physical refining (FFA feed=1.1%)

Esterified sterols Free sterols

22

Steradiene - deodorization

• Steradienes are distillated and condensed in the deodoriser distillate ( 90 - 600 ppm steradienes in soya distillate)

• Degree of sterol dehydration is mainly influenced by deodorization temperature

60

100

140

180

220

215 220 225 230 235 240 245

Temperature (°C)

Tota

l ste

radi

ene

(ppm

)

Temperature(°C)

Free sterolDehydration (%)

220 0.05230 0.1240 0.23250 0.4260 1.06

23

Influence of processing on tocopherols

24

Stability of tocopherolsObjective : assess the stability of tocopherols at high temperature

deodorization

Distillate

Refined oilBleached oil

Tocopherol mass balance during deodorization

Toco bleached oil = toco refined oil + toco distillate + ??

Observation :Tocopherol loss of 20-30% in the tocopherol mass balance

Explanation : analytical - incomplete condensation -thermal breakdown - oxidative degradation

25

Stability of tocopherols

• Fundamental study

Reference :

With TBHQ : (1500ppm)

N2 flush :

Tocopherol loss (%)

Conclusion : thermal stability, probably oxidative degradation

⇒ major tocopherol oxidation products?

α-tocopherol (2000ppm)dissolved in triolein andheated to 245°C, 5-6 mbar for 80 min, no steam injection

9

3

0

Tocopherol oxidation• Previous tocopherol oxidation studies :

• oxidation of α-tocopherol dissolved in a solvent• oxidation initiators : K3FeCN6, FeCl3, tBOOH, AIBN• oxidation at room temperature • formation of several known oxidation products

O

HO

R

α-tocopherol O O

OO

RR

OO

Rα-tocopherol spirotrimeer

R

O

OOO OH

R

α-tocopheroldimer quinone

O

O OH

R

α-tocopherolquinone

RO

HO

R

O

O

27

Tocopherols

• Identification of oxidation products in triglycerides

O

O OH

R

O

7,8-epoxy-α-tocopherolquinone

O

O OH

R

α-Tocopherolquinone

O

O OH

O

R

4a,5-Epoxy-α-tocopherolquinone

- synthesis of most important tocopherol oxidation products

- used as standards for the identification of tocopheroloxidation products formed in triolein

Tocopherols are antioxidants → prone to oxidation

Concentration of tocopherol oxidation products?

28

Stability of tocopherol during thermoxidation stress

• Objective :- Modeling of α-tocopherol degradation in function of heating time, temperature and triacylglycerol unsaturation

- Quantification of α-tocopherol oxidation products formed

• Experimental :- Statistical central composite design- Addition of α-tocopherol standard (1000 ppm) to

technical grade triolein and tripalmitin- Heating : 5g of oil in OSI tubes, no air bubbling

29

Modeling of α-tocopherol oxidation products during thermoxidation in triolein

and tripalmitin

0

10

20

30

175 200 225

Temp (°C),Time=2h,OOO/PPP=50/50

toco

pher

ol (%

)

0

1

2

3

4

5

poly

mer

(%)

α-tocopherol ( ), epoxy-α-tocopherolquinone ( );

α-tocopherolquinone ( ), total triacylglycerol, polymer (•)

30

Modeling of α-tocopherol oxidation products during thermoxidation in triolein

and tripalmitin

α-tocopherol ( ), epoxy-α-tocopherolquinone ( );

α-tocopherolquinone ( ), total triacylglycerol, polymer (•)

0

10

20

30

25 50 75

Triolein (%), Time=2h, Temp=200°C

toco

pher

ol (%

)

0

1

2

3

polym

er (%

)

31

Deodoriser distillate : characterisation and

technology to improve quality

32

Analytical characterisation major componentsfree free fatty acids

physical refining : > 70%chemical refining : < 60%

monoglyceridesdiglyceridestriglyceridessqualenetocopherols and phytosterols

physical refining : 2-5%chemical refining : 10-25%

Characterisation of deodoriser distillate

33

Deodorization technology

• Observation :– chemical distillate : high tocopherol and

phytosterol content → high economic value

– physical distillate : high free fatty acid content → low economic value

• Objective :– develop new deodorization technology to improve

the quality of physical deodoriser distillate

34

Deodorization technology

• Methodology :– condensation of free fatty acids in a first distillate

fraction– condensation of tocopherols and phytosterols in a

second distillate fraction

→ by optimisation of the temperature profile

35

Improved deodorization technology : conclusion

Free fatty

acids

tocopherols phytosterols

Chemical 10-24 10-15 10-17

Physical 76-87 2-5 2-7

Distillate 1 90-96 1-2 1-2

Distillate 2 37-67 8-10 10-15

36

General conclusion

The new and fundamental view followed in this research indicates thattocopherols and phytosterols are stable components, however several transformation reactions can take place of which the ratio is influenced by the technological conditions

37

Acknowledgement

Jose Miguel MontiagudoStephan reverseauAna PonsAleksandra SzulczewskaUrsulla SosinsksaRevilija MozuraityteJose Ayala Vila

Ana Belen Cano Dries Cauwenbergh Elena CortesMaria ForcadaLucia Guardiola Garcia Tilemachos GoumperisSofia Ioannidou

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Characterisation of deodorizer distillate2. Rheological characterisation

viscosity is determined byChemical distillate : phytosterols

Physical distillate : free fatty acids

01020304050607080

0 1 2 3 4 5

Steryl ester content (%)

Visc

osity

(cP

or 1

.10-3

Pa.

s)

50°C

60°C

70°C

80°C ×

39

Characterisation of deodorizer distillate2. Rheological characterisation

viscosity is determined byChemical distillate : phytosterols

Physical distillate : free fatty acids

010203040506070

30 40 50 60 70 80

Free fatty acid content (%)

Visc

osity

(cP

or 1

.10-3

Pa.

s)

50°C

60°C

70°C

80°C ×