1 Beam Test Results of USTC LMRPC modules (50cm) Yongjie Sun presnted by Hongfang Chen.
10252021 By Shu-Chen Hsieh
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10252021 By Shu-Chen Hsieh 1
Transcript of 10252021 By Shu-Chen Hsieh
10252021 By Shu-Chen Hsieh
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➢Physicochemical properties of amino
acids
➢Chemical reactivity of amino acids
➢Processing induced changes in
proteins
➢Enzymatic modification of proteins
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Physicochemical properties of
amino acids
Structure of amino acids Carboxyl group
Amino
group
Hydrogen
atom
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Glycine
Aliphatic amino acids
(Val) (Leu) (Ile)
(Gly)[G]
[V] [L] [I]
CH3
Alanine (A)
(Ala) 6
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Aromatic amino acids
(Phe) (Tyr) (Trp)[F] [Y] [W]
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Acidic amino acids and their
amides
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Basic amino acids
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Sulfhydryl amino acids
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Formation of cystine
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The heterocyclic pyrrolidine ring restricts the geometry of polypeptides
Cyclic amino acids
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(Ser) [S] (Thr) [T]
Hydroxyl amino acids
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Derived natural amino acids
O-phosphoserine (casein) 4-hydroxylysine (collagen)
N-Methyllysine (myosin) 4-methylproline
(apple)
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Derived AAs from processing
From heated milk15
◼Aspartame is a
dipeptide methyl ester
(aspartylphenylalanine
methyl ester), an
artificial sweetener
◼About 200 times
sweeter than table
sugar
◼Used in diet drinks
Aspartame
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Stereochemistry of amino acids
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Chiral center
Solid wedges: bonds
coming forward
Shaded wedges: receding
bonds
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◼19 of the 20 common amino acids have a chiral α-
carbon atom (exception: Gly)
◼Mirror image pairs of amino acids are designated
L (levo) and D (dextro)
◼Proteins are assembled from L-amino acids
(a few D-amino acids occur in nature)
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◼Amino acid “residues” compose peptide chains
◼Peptide chains are numbered from the N (amino)
terminus to the C (carboxyl) terminus
◼Example: (N) Gly-Arg-Phe-Ala-Lys (C)
(or GRFAK)
◼Formation of peptide bonds eliminates the ionizable
a-carboxyl and a-amino groups of the free amino
acids
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◼Nonpolar: aliphatic, aromatic
◼Polar non charged: hydroxyl, sulfhydryl
◼Polar charged: acidic, basic
Polar-hydrophilic
Nonpolar-hydrophobic
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Acid-base properties of amino acids
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Henderson-Hasselbach equation
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◼Under normal cellular conditions amino acids
are zwitterions (dipolar ions):
Amino group = -NH3+
Carboxyl group = -COO-
◼A zwitterion is a molecule with
equal numbers of positive and
negative charges - thus the net
charge is zero
◼An ampholyte is a molecule containing
groups with both acidic and basic pKa
values
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pI
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pKa1pKa2
pKa326
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H+
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◼Hydrophobicity can be defined as the excess energy of a
solute dissolved in water compared to that in an organic
solvent under similar conditions
◼ The most direct and simplest way to estimate
hydrophobicity of AA side chain is experimental
determination of free energy changes for dissolution of
AAs side chains in water and in an organic solvent, such
as octanol or ethanol.
◼AAs side chains with large positive free energy
(oct→water ) are hydrophobic; they would be prefer to be
in an organic phase rather than in an aqueous phase.
Hydrophobicity of amino acids
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Residue area (Å 2)
0 50 100 150 200 300250
The hydrophobicity of nonpolar residues
is linearly correlated to their surface area
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Optical properties of amino acids
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Reaction with ninhydrin
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Chemical reactivity of amino
acids
Reaction with O-phthaldialdehyde
Emission 450 nm
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Reaction with fluorescamine
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◼Food processing and storage can either
transduce benefic or detrimental effects on food
◼Detrimental effects mainly come from
➢ Loss of essential amino acids
➢Toxic substances formation
Processing induced changes in proteins
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Chemical processing
◼Heating
◼Cooling
◼Drying
◼Application of chemicals
◼Irradiation
◼Fermentation
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High temperature heat treatment
>200oC
◼Destruction of amino acids: eg.
RSTK
◼Mutagenic compounds generation:
aminoimidazoazaarene
Heterocyclic amines39
◼Improving digestibility
◼Inactivating enzyme eg lipoxygenase
◼Inactivating inhibitors of digestive
enzymes eg ovomucoid
◼Destroying toxins eg enterotoxin from
Staphylococcus aureaus
◼Inactivating antinutritional factor eg lectin
60‐90oC, 1h, partial denaturation
Moderate heat treatment
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PER: protein efficiency ratio
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紅肉遭WHO列為致癌物業者跳腳（20151027 法國世界報）
IARC的主任威爾德博士表示，紅肉雖有營養價值，人們仍應避免過多攝取。該機構的統計表明，常人每日一旦多攝取100公克的紅肉，大腸癌的風險就高出17%；如果是加工肉品，更只要50公克就會高出18%。目前全球癌症的死亡人口中，每年有5萬人可以咎因於紅肉飲食，而這又大都集中於富裕國家。所謂的紅肉，包括：牛肉、小牛肉、豬肉、羔羊、山羊肉、馬肉等。加工肉品則指使用過鹽漬、催熟、發酵、燻烤等各種製程的肉類。尤其是高溫烹調時肉品表面產生的多環芳烴和雜環胺，生肉中的血紅素鐵、臘肉使用的硝酸鹽／亞硝酸鹽，彼等的致癌性都讓科學家不敢輕忽。
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IARC: international agency for research on cancer
Racemization
◼High [OH] > Low[OH]
◼protein > AAs
◼Preference for DSCFENT
◼Decreased digestibility
◼Generation of toxic products eg
D-proline
Cysteine
phosphoserine
Chemical alteration of amino acids
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Compositional changes during
extraction and fractionation
◼Isoelectric precipitation-lost of the Met, Trp in
coconut protein isolates
◼Ultrafiltration and ion exchange-lost of
foaming property of whey protein
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Protein cross-linking (1/2)
1000X faster than lysine
Cysteine
Ammonia
sulfites
◼Decreased the
digestibility
◼Reduce the biological
availability of essential
amino acids
Lysinoalanine Lanthionine45
Excessive heating of
pure protein or
proteinaceous food
low in carbohydrate
content
◼Decreased digestibility
◼Decreased bioavailability
Protein cross-linking (2/2)
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Ionizing radiation
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➢Bactericidal agents
➢Detoxification
➢Bleaching
◼The use of oxidizing agents in foods
◼Oxidative compounds produced in processing
➢Free radicals
➢Peroxidation of lipids
➢Photooxidation
➢Nonenzymatic browning of foods
Effects of oxidizing agents
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Oxidation of methionine
Biological unavailable
Strong oxidizing conditions
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Oxidation of cysteine and cystine
Biological unavailable
Biological available
Biological unavailable
Biological available
At acidic pH
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Oxidation of Tryptophan
Severe oxidizing
condition
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Photooxidation of Tryptophan
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Occurrence of this type of cross-link has been found in natural proteins ,
such as elastin, keratin, and collagen, and more recently in dough
Oxidation of Tyrosine
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Maillard reactionReaction between amines and carbonyl compounds (C=O)
at elevated temperature, which will decompose and
eventually condense into insoluble brown products known
as melanoidins
Carbonyl-amine reactions
◼Loss of lysine
◼Oxidation of some amino acids. WHYM
◼Decrease of protein solubility
◼Lower digestibility
◼Mutagens formation eg products of CK
◼Amino reductones: antioxidative activity
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Schiff’s base
Strecker degradation
Distinctive aroma
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Gossypol
Glutaraldehyde
aldehydes
◼Insolubilization
◼Loss of digestibility and bioavailability of lysine
◼Loss of functional properties of proteins
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Acrylamide
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AGE (advanced glycation end-product)
AGEs are formed both outside and inside the body.
Specifically, they stem from glycation reaction, which
refers to the addition of a carbohydrate to a protein
without the involvement of an enzyme.
In humans, histones in the cell nucleus are richest in
lysine, and therefore form the glycated protein N(6)-
Carboxymethyllysine (CML)
AGEs affect nearly every type of cell and molecule in the
body and are thought to be one factor in aging and some
age-related chronic diseases
Dietary AGE can form in food during cooking, particularly
in dry cooking such as frying, roasting and baking, far less
so in boiling, stewing, steaming and microwaving. 59
Reaction with lipids
Oxidation of unsaturated lipids leads to formation of alkoxy and peroxy
free radicals. These free radicals in turn react with proteins, forming a
variety of cross-linked products
◼Decreased nutritional value
◼Off flavor60
Reaction with Halogenated solvent
◼ Halogenated organic solvent are often used to extract
oil and some antinutritive factors from oil seed products
◼ The products of the reaction between protein and
halogenated might be toxic eg extraction with
trichloroethylene results in the formation of small
amount of S-dichlorovinyl-L-cysteine
◼ Might cause the alkylation of KHC eg methyl bromide,
thus decrease the nutritional value
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CK Highly reactive
Reaction with
polyphenol
HMW: High molecular weight
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Reaction with Nitrites
Formation of N-nitrosoamines can be decreased by ascorbic acid and
erythorbate
Improve color
Prevent bacteria growth63
◼Bioavailability of cysteine is not altered
◼Unfolding of protein may happen
Reaction with sulfites
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Enzymatic hydrolysis
Partial hydrolysis of proteins using proteolytic enzymes is one
of the strategies for improving the functional properties. Protein
hydrolystes have many uses in specialty food such as geriatric
foods, nonallergenic infant formula, sports drinks, and diet
foods
Enzymatic modification of proteins
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◼Food protein with allergenicity
Cow’s milk
➢Casein
➢Lactoglobulin
➢lactalbumin
Soy proteins
Gluten
Egg proteins
Peanut proteins
◼Hydrolysis of casein up to 55% DH (degree of
hydrolysis) decreases its allergenicity by about 50% ARI
(allergenicity reduction index)
Hydrolysates make proteins less allergic
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◼Peptides with a mean residue hydrophobicity of
>1.4 Kcal/mol are bitter.
◼Hydolysates of highly hydrophobic proteins
(casein, soy protein, and corn protein)-very bitter.
◼Hydolysates of highly hydrophilic proteins
(gelatin)-less bitter.
Solutions?
The bitterness emanates from certain peptides
released during hydrolysis
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Plastein reaction
◼The plastein reaction refers to a set of reactions
involving initial proteolysis, followed by
resynthesis of peptide bonds by a protease.
◼The enzyme, especially papain and
chymotrypsin, acts both as a protease and an
esterase under certain conditions.
◼The plastein reaction can be exploited to
improve the nutritional quality.
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Protein cross-linking
Transglutaminase
◼Improve nutritional quality71
◼Physicochemical properties of Amino acids✓Structure of amino acids✓Stereochemistry of amino acids✓Acid-base properties of amino acids✓Hydrophobicity of amino acids✓Optical properties of amino acids◼Chemical reactivity of amino acid◼Processing induced changes in proteins◼Enzymatic modification of proteins
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