Food Chemistry

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2011 May

Chapter 1-IntroductionOutline

What is Food Chemistry

History of Food Chemistry

Approach to the Study of Food Chemistry

What is Food Chemistry

In underdeveloped regions of the world In developed regions of the world Food chemistry, a major aspect of food science,

deals with the composition and properties of food and the chemical changes during handling, processing, and storage.

Food chemistry is intimately related to chemistry, biochemistry, physiological chemistry, botany, zoology, and molecular biology.

History of Food Chemistry

Carl Wilhelm Scheele (1742-1786)

Antoine Laurent Lavoisier (1743-1794)

Sir Humphrey Davy (1778-1829)

Justus Von Liebig (1803-1873)

Approach to the Study of Food Chemistry

Determining those properties that are important characteristics of safe, high-quality foods

Determining those chemical and biochemical reactions that have important influences on loss of quality and/or wholesomeness of foods

Integrating the first two points so that one understands how the key chemical and biochemical reactions influence quality and safety

Applying this understanding to various situations encountered during formulation, processing, and storage of food

Quality and Safety Attributes Safety is the first requisite of any food Quality attributes of food and some alterations during

processing and storage

Attribute AlterationTexture Loss of solubility; Loss of water-holding capacity; Toughening;

SofteningFlavor Development of Rancidity (hydrolytic or oxidative); Cooked or

caramel flavors; Other off-flavors; Desirable flavorsColor Darkening; Bleaching; Development of other off-colors;

Development of desirable colors (e.g., browning of baked goods)Nutritive value

Loss, degradation or altered bioavailability of proteins, lipids, vitamins, minerals

Safety Generation of toxic substances; Development of substances that are protective of health; Inactivation of toxic substances

Chemical and biochemical reactions

Many reactions can alter food quality or safety The more important classes of these reactions

Types of reaction ExamplesNonenzymic browning Baked goodsEnzymic browning Cut fruitsOxidation Lipids (off-flavors), vitamin degradation, pigment

decoloration, proteins (loss of nutritive value)Hydrolysis Lipids, proteins, vitamins, carbohydrates, pigmentsMetal interactions Complexation (anthocyanins), loss of Magnesium

from chlorophyll, catalysis of oxidation

Chemical and biochemical reactions

Types of reaction Examples

Lipid isomerization Cis trans, nonconjugated conjugated

Lipid cyclization Monocyclic fatty acids

Lipid polymerization Foaming during deep fat frying

Protein denaturation Egg white coagulation, enzyme inactivation

Protein cross-linking Loss of nutritive value during alkali processing

Polysaccharide synthesis In plants postharvest

Glycolytic changes Animal tissue postmortem, plant tissue postharvest

Effect of reactions on food quality and safety

Primary causative event

Secondary event Attribute influenced

Hydrolysis of lipids Free fatty acids react with protein

Texture, flavor, nutritive value

Hydrolysis of polysaccharides

Sugars react with proteins Texture, flavor, color, nutritive value

Oxidation of lipids Oxidation products react with many other constituents

Texture, flavor, color, nutritive value, toxic substances can be generated

Bruising of fruit Cells break, enzymes are released, oxygen accessible

Texture, flavor, color, nutritive value

Effect of reactions on food quality and safety

Primary causative event

Secondary event

Attribute influenced

Heating of green vegetables

Cell walls and membranes lose, integrity, acids are released, enzymes become inactive

Texture, flavor, color, nutritive value

Heating of muscle tissue

Proteins denature and aggregate, enzymes become inactive

Texture, flavor, color, nutritive value

Cis and Trans conversions in lipids

Enhanced rate of polymerization during deep rat frying

Excessive foaming during deep fat frying, diminished bioavailability of lipids

Analysis of situations encountered during the storage and processing of food

The variables that are important during the storage and processing of food

The variables that are important during the storage and processing of food

Product factors Chemical properties of individual constituents; oxygen content; pH; Water activity; Tg; Wg

Environmental factors

Temperature; time; composition of the atmosphere; chemical; physical or biological treatments imposed; exposure to light; contamination; physical abuse

Carbohydrates

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Outline

Definition

Classification

Functions

Definition and Classification Carbohydrates are polyhydroxyl compounds (-OH) that

contain a carbonyl group (-C=O) Empirical formula is Cx(H2O)y, especially C2H4O2, C3H6O3

and CH2O, and C5H10O4 and C6H12O5. Carbohydrates include two types, based on functional group.

Aldoses and ketoses Carbohydrates include three types, based on single sugar unit.

Monosaccharides : 1 unit Oligosaccharides : 2-20 units (Disaccharides: 2 units) Polysaccharides : >20 units

Aldoses Ketoses

Monosaccharides Monosaccharide isomerization

OligosaccharidesC1,2 glycosidic bond

C1,4 glycosidic bond

1

1

sucrose

maltose

Polysaccharides

cellulose

amylose

Aldoses

chiral carbon atom epimer

C4 epimer for Glucose

C2

C2 epimer for Glucose

C4

Chiral carbon atom

Glyceraldehyde (1)

Glucose (4)

Enantiomers Enantiomers are stereoisomers that are complete

mirror images of each other, much as one's left and right hands are "the same" but opposite.

Only the D-isomer is found in living organisms.

L-glyceraldehyde D-glyceraldehyde

D/L enantiomers

D-glucose L-glucose

Ketoses

C5 epimer for Fructose

C5C

Chain and ring types

anomeropposite side anomersame side

/ anomer

2

6

5

4

3

1

1

2

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Drawing

Pyranose ring is more stable than furanose ring

Pyranose ring Furanose ring

Configuration and conformation Configurations are the permanent geometry that

results from the spatial arrangement of its bonds. Conformations are the arrangement of the parts of an

object. Two polymers which have the same chemical

composition but can only be made identical by breaking and reforming bonds are said to be two configurations of that polymer (e.g. L/D, /).

Two polymers which differ only by rotations about single bonds are said to be two different conformations of that polymer (e.g. chair/boat form).

Functions Carbohydrates provide necessary caloric intake and

nutrition.

Carbohydrates are widely used as important sweeteners and preservers.

Carbohydrates provide favorite colors and flavors.

Carbohydrates have good viscosity, gelatinization and stabilization.

Lipids

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Outline Definition

Classification

Functions and roles

Physical properties

Chemical reactions

Quality analyses

Lipids Definition: Any of a group of substances that in

general are soluble in organic solvents, but are not soluble in water. Mostly made up of C, H and O, Some P, N and S.

Classification Fatty acids Glycerol PhospholipidWaxes Sterols

Fatty acids Structure

(Water-soluble tail)Polar end - Hydrophilic end

(Fat-soluble tail)Non-polar end - Hydrophobic end

Saturated and Unsaturated fatty acids Saturated fatty acids

Saturated fatty acids do not contain any double bonds or other functional groups along the chain.

Saturated fatty acids are straight chains Unsaturated fatty acids

Monounsaturated fatty acidsMonounsaturated fatty acids have one double bondMonounsaturated fatty acids are widespread in the

living world where they occur mostly as the cis-isomer. Polyunsaturated fatty acids

Polyunsaturated fatty acids have two or more double bonds, especially conjugated fatty acids

Saturated and Unsaturatedfatty acids

Cis and Trans fatty acids Nomenclature Two different ways to make clear where the double bonds are

located in molecules: Cis/trans-x: The double bond is located on the xth

carbon-carbon bond, counting from the carboxyl terminus. The cis or trans notation indicates whether the molecule is arranged in a cis or trans conformation. In the case of a molecule having more than one double bond, the notation is, for example, cis-9, cis-12 or cis-9,12.

-x : A double bond is located on the xth carbon-carbon bond, counting from the , methyl end of the chain. Sometimes, the symbol is substituted with a lowercase letter n, making it n-9/-9, n-6/-6 or n-3/-3.

Numbering

Fatty acids can be represented by a simply numerical expression consisting of two terms separated by a colon.

* Essential fatty acids (EFA): -3 and -6 fatty acids cant be constructed within human or animals from other components and therefore must be obtained from the diet.

Acylglycerols

Monoacylglycerol Diacylglycerol

Triacylglycerol

Triacylglycerols (TAG)

Glycerol Fatty acids TAG

Acylglycerols Glycerol esters of fatty acids make up to 99% of the liquid

of animal and plant origin, have been traditionally called fats and oils. This distinction is based on whether the material is solid or liquid at room temperature.

Classification Milk fats Lauric acids Vegetable butters Animal fats Oleic-linoleic acids Linolenic acids Marine oils

Nomenclature The sn system is applicable to both synthetic and natural

fats. sn-1 is R1sn-2 is R2 and sn-3 is R3 (top-to-bottom)

1-stearoyl-2-oleoyl-3-myristoyl-sn-glycerolsn-glycerol-1-stearate-2-oleate-3-myristatesn-18:0-18:1-16:0

sn-1

sn-2sn-3

sn: used immediately preceding the termglycerol, indicates that the sn-1, sn-2, and sn-3 positions are listed in that order

Phospholipids phospholipids are used for any lipid containing phosphoric acid as a mono- or diester.

phosphoric acid

Waxes

Fatty acid + Long chain alcohol Important in fruits: Natural protective layer in fruits, vegetables, etc. Added in some cases for appearance and

protection.

Beeswax(myricyl palmitate)

Spermaceti(cetyl palmitate)

Male & female sex hormones Bile acids Adrenal corticosteroids Cholesterol

Sterols

Lipid properties Physical properties

Melting point (MP) (40-55 oC)Long chain fatty acids pack better than short chain ones MPlong > MPshort

Saturated fatty acids pack better than unsaturated ones MPsat. > MPunsat. Hydrogenation increase the MP.

Trans fatty acids pack better than cis ones MPtrans. > MPcis.

Physical propertiesMPconjugated double bond > MPnon-conjugated

double bond MP has relationship with digestibility.MP37 oC, digestibility = 97.98%; MP 37 oC-50 oC,

digestibility = 90%; 50 oC, indigestible. Boiling point (BP) (180-200 oC)

BP increases with increased carbon chain of fatty acidsSaturated fatty acids and unsaturated ones have similar

BP. Density

fat< Density

water

Chemical properties Lipolysis

Hydrogenation

Autoxidation Interesterification

Hydrolysis Types of hydrolysis Saponification (base catalyzed) Acid hydrolysis Enzymatic hydrolysis (lipase catalyzed) Interesterification

Hydrolysis products Small quantities of free fatty acids

Contribute flavors to cheese, milk, chocolateCause off-flavors in milks, fruits and vegetables

Interesterification Interesterification-Rearrange fatty acids so they

become distributed randomly among triglycerolmolecules of fat

Basic catalyst such as NaOHKOHNaOCH3organic base Mechanism

Interesterification

Acid catalyst such as sulfuric acid and sulfonic acidMechanism

Interesterification Hydrogen Addition of hydrogen across double bonds Produces triglycerides with higher melting points Liquid fats convert to semi-solid fats or soft fats convert

into firmer fat Improves oxidative stability Produces Trans fats

Trans fatty acids Refer to triglycerides containing unsaturated fatty acids in

trans conformation. Found in partially hydrogenated fats or oils Health problems

Increase cardiovascular disease. Eating just 5 grams of it per day increases the risk of heart disease 25 %.

Increase risks of other chronic diseases, such as cancer, obesity, and diabetes.

FDA adopted new food labeling Label gives weight of trans fat. The regulation allows trans fat levels of less than 0.5

grams per serving to be labeled as 0 grams per serving.

Lipid autoxidation Effects of lipid autoxidation

Flavor quality lossRancid flavor Changes of color and textureConsumer acceptance

Nutritional quality lossEssential fatty acidsVitamins

Health risksGrowth retardation Heart diseasesProducing free radicals

Lipid autoxidation Lipid autoxidation - free radical reactions. Initiation, Propagation and Termination

Initiation Initiation of autoxidation occurs when hydrogen atom at -

methylene group in double bonds of unsaturated fatty acids is removed to form an alkyl radical (R)

Initial generation of free radicals is slow Initiated by singlet oxygen (1O2)

Metastable, excited energy state of O2Two unpaired electrons in same orbital

Initiation mechanisms Oxygen raised to excited state by light.

Inactive by blanching (short energy potooxidation) Promoted by pigments (sensitizers)

e.g. chlorophyll, riboflavin Oxygen raised to excited state by enzymes lipoxygenase Inactivate by blanching (heating to denature enzymes) Oxygen raised to excited state by metal ions (e.g. Fe, Co,

Cu) Naturally in food or from metal equipment Using chelating agents (e.g. EDTA) to prevent

oxidation.

Hydroperoxide formation Hydroperoxide decomposition

Autoxidation mechanismInitiation

Oxidation mechanism

Propagation

Bad way Good way

Termination

Oxidation mechanism

Hydroperoxidedecomposition

Factors influencing lipid oxidation rate Fatty acid composition

number, position and geometry of double bonds affect the oxidation rate.

Saturated triglycerides are stable at room temperature Unsaturated fatty acids are promotions of lipid oxidation Relative oxidation rates : Arachidonic : linolenic: linoleic

: oleic= 40:20:10:1 Conjugated double bonds are more reactive than non-

conjugated ones. Cis configuration is more reactive than trans one.

Free fatty acid percent Free fatty acids react faster than triglycerides.

Factors influencing lipid oxidation rate Oxygen concentration:

At low oxygen pressure, oxygen pressure is positive to oxidation rate

Under enough oxygen supply, oxygen pressure has no effect Temperature

Oxidation rates increase with increased temperatures specific surface area

Oxygen rate is positive to specific surface area Water activity

Oxidation rate is high at aw < 0.1, such as rancidity in dehydrate foods

Metal ions (e.g. Fe, Co, Cu)

Factors promoting or suppressing lipid oxidation rate

Antioxidant enzymes Singlet Oxygen Quenching of Tocopherols

Metal Ions EDTA Antioxidant mechanism

Synthetic antioxidants Natural antioxidants Vitamin C Tocopherol Quercetin Anthocyanin Radical scavenging antioxidants break free radical

chain reaction by donating hydrogen to free radicals

Lipid quality analyses Acid value Saponification value Iodine value Peroxide value Ester value 9 Constant values express the characteristics of oil

compositione.g. iodine value, saponification value

9 Variable values express the changes in oil property e.g. acid value, peroxide value

Acid Value (AV) Definition: Number of mg of KOH required to

neutralize the Free Fatty Acids (FFA) in 1 g of fat. Acid vale (AV) expresses the number of free fatty

acid (FFA) in oil.

g fat

Saponification Value (SV) Saponification - Hydrolysis of ester (Tri-acylglycerol,

TAG) under alkaline condition. Definition : Number of mg of KOH required to saponify 1

g of fat

a

b

FFA (%) =AV/SV100%

Saponification Value SV expresses the oil characteristics and molecular weight

of TAG. Higher SV means lower molecular weight of TAG. For fat and oil, the SV is normally around 200.

Ester value (EV) Definition : Number of mg of KOH required to saponify

glyceride in 1 g of fat.

Iodine Value (IV) Definition: Number of iodine (g) absorbed by 100 g of oil.

1 g of fat adsorbed 1.5 g of iodine, iodine value is ?

Iodine Value =

Number of Double Bonds per Molecule

Molecular weight and iodine value can calculate the number of double bonds. The unknown compound has molecular weight of 878 and iodine value of 173. Determine thenumber of double bonds in the unknown compound.

Iodine Value

Peroxide Value (POV) Definition: Number of ml of standard Na2S2O3

required to titrate 1 g of fat or express by iodine content (%).

Peroxide value (POV) expresses the degree of oxidation in the initial period.

Peroxide Value

Amino acid, peptide & protein

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Amino acids The -carbon is the carbon to which a functional group is

attached.

Groups of amino acids Amino acids can be classified into several categories based

on the side chains Aliphatic amino acids Aromatic amino acids Hydroxy amino acids Acidic amino acids Basic amino acids Amide amino acids Sulfur-containing amino acids Secondary amino acids

Aliphatic amino acids

Aromatic amino acids Hydroxy amino acids

Acidic amino acids

The side chains contain a carboxyl group Negatively charged (acid) at neutral pH Carboxyl groups function as nucleophiles in some enzymatic

reactions

Amide amino acids

Hydrophillicnitrogenous bases Positively charged (basic) at neutral pH

Basic amino acids Sulfur-containing amino acids

Secondary amino acids Groups of amino acids Amino acids can be classified into several categories based on

the degree of interaction of the side chains with water: Hydrophobic amino acids: Phe, Leu, Ile, Val, Ala, Met,

Pro, Trp, Tyr. Polar and uncharged amino acids: Ser, Thr, Gly, Asn, Cys Positively charged amino acids: Lys, Arg, His. Negatively charged amino acids: Asp, Glu.

Chemical properties pI

pI For amino acids with more than two ionizable groups, such as

lysine for example, the same formula is used, but this time the two pKa's used are those of the two groups that lose and gain a charge from the neutral form of the amino acid.

pI

Flavors

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General philosophy Definition: The term flavor has evolved to a usage

that implies an overall integrated perception of all of the contributing senses (smell, taste, sight, feeling, and sound) at the time of food consumption.

Classification Smell-odors and flavors Taste Nonchemical senses-sight, sound, and feeling

Methods for flavor analysis Isolation technique Distillation technique Fused-silica capillary column technique GC-MS technique HPLC technique

Sensory assessment of flavors Formal panels Determination of detection thresholds Odor units (OU) Aroma extract dilution analysis (AEDA) Characterizing or character-impact compounds

Taste and nonspecific saporoussensations Taste substance: sweet, bitter, sour, and salty Sweet modality Bitter taste modality Salty and sour taste modalities

Flavor enhancers Astringency Pungency Cooling

Vegetables, fruit, and spice flavors Sulfur-containing volatiles Unique sulfur compound in Shiitake muchrooms Methoxy alkyl pyrazine volatiles Enzymically derived volatiles Volatiles from branched-chain amino acids Flavors derived from the Shikimic acid pathway Volatile terpenoids in flavors Citrus flavors Flavors of herbs and spices

Flavors development Flavors from lactic acid-ethanol fermentation Flavor volatiles from fats and oils Flavor volatiles in muscle foods and milk Volatiles in fish and seafood flavors Development of process of reaction flavor volatiles Thermally induced process flavors Volatiles derived from oxidative cleavage of

carotenoids

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VitaminsVitamins

Food chemistryFood chemistryQu Wenjuan

2010 September

2

OutlineOutline

z Chemistry and nutrition of vitamins z Water-soluble vitaminsz Fat-soluble vitamins

z General causes for of vitamin loss in food z Variation in vitamin contentz Postharvest changes in vitamin content of foodsz Preliminary treatments: trimming, washing, millingz Effects of blanching and thermal processing z Losses of vitamins following processing z Influence of processing chemicals and other food

components

3

Vitamins Vitamins

z A diverse group of organic compounds that are nutritionally essential micronutrients

z necessary for growth, vitality, health, general well being, and for the prevention and cure of many health problems and diseases

z Functions in vivoz Coenzymes or their precursorsz Components of the antioxidative defense system

Vc, Carotenoids, VEz Factors involved in genetic regulation z Speciallied functions

VA in visions, ascorbic acids in hydroxylation reactions

4

FatFat--soluble vitaminssoluble vitamins

z Classification z Vitamin A, Vitamin D, Vitamin E, Vitamin K

z Structure and general properties

z Stability and modes of degradationz Bioavailabilityz Analytical methods

5

Vitamin A (Retinol)Vitamin A (Retinol)

CH3

CH3H3COH

CH3CH3

Retinol

z also called retinolz Unsaturated hydrocarbons, found in trans form naturallyz A basic structural unit of the molecule a five-carbon isoprene segmentz All trans isomers have the greatest vitamin A activity

6

CarotenoidsCarotenoids

z Carotenoids contribute significant vitamin A activity to foods

z Of ~600 carotenoids, ~50 have some provitamin Aactivity which partially converted to vitamin A in vivo. Naturally in trans form.

z -carotene exhibits the gratest pro-vitamin A activity. About 50% of the vitamin A activity.

z Singlet oxygen (1O2) scavenger

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- Carotene and Retinol

CH 3

CH 3

CH 3 CH 3 CH 3

CH 3 CH 3 CH 3

H 3 C

CH 3

H 3 C CH 3

CH 3

CH 3 CH 3

H 3 C CH 3

CH 3

CH 3 CH 3CH 2OH

Oxidation

C HO

Retainal

Retinol (Vitamin A)

- 2H

Provitamin A

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Benefits of Vitamin ABenefits of Vitamin A

DEFICIENCY SYMPTOMS:May result in night blindness; increased susceptibility to infections; rough, dry, scaly skin; loss of smell & appetite; frequents fatigue; lack of tearing; defective teeth & gums' retarded growth.

Vitamin A excess, also called hypervitaminosis A, is a toxic condition produced by a high intake of vitamin A, generally 150,000 g daily over a period of several months.

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Sources of Vitamin A and betaSources of Vitamin A and beta--carotenecarotene

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Stability of Vitamin A and Stability of Vitamin A and --carotenecarotenez Geometric isomerizationz Target: the unsaturated chainz trans cisz Heat or light can induce isomerization

z Oxidationz Belong to lipids, so lipid oxidation also happens to

both

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Vitamin DVitamin D

z Although about 10 compounds have vitamin D activity, the two most important ones are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3).

z Vitamin D3 represents the dietary source, while vitamin D2 occurs in yeasts and fungi.

Vitamin D3

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Benefits of Vitamin DBenefits of Vitamin D

DEFICIENCY SYMPTOMS: May lead to rickets, tooth decay, softening of bones, improper healing of fractures, lack of vigor, muscular weakness, inadequate absorption of calcium, retention of phosphorous in the kidneys

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Sources of Vitamin DSources of Vitamin D

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Vitamin EVitamin E ((TocopherolsTocopherols))

O

HO

R1

R2R3

CH3

CH3 CH3 CH3CH3

Trivial Name Chemical Name R1 R2 R3

-Tocopherol 5,7,8-Trimethyltocol CH3 CH3 CH3-Tocopherol 5,8-Dimethyltocol CH3 H CH3-Tocopherol 7,8-Dimethyltocol H CH3 CH3-Tocopherol 8-Methyltocol H H CH3

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Benefits of Vitamin EBenefits of Vitamin E

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Source of Vitamin ESource of Vitamin E

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Oxidation of Vitamin EOxidation of Vitamin E

z Good stability in the absence of oxygen and oxidizing lipids

z Stable to heatz As antioxidantsz Scavenge free radical, e.g. 1O2, . OH, ROO .

z Hydrogen donating ability : > > > - Tocopherol

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Resonance of Resonance of -- TocopherolTocopherol RadicalsRadicals

33

R, RO , or ROO

-Tocopherol

O

O

CH3

H3C

CH3C16H

CH3

O

HO

CH3

H3C

CH3

CH3 CH3 CH3CH3

RH , ROH , ROOH

R, RO , or ROO

O

CH3

CH3

H3C

CH3

C16H33OOH

H2O

O

CH3

CH3

H3C

CH3

C16H33O++ ROO-

H O C16H33CH3

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O

CH3

3C

O

CH3

CH3

H3C O

OH

CH3

C16H

-Tocopherylquinone

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Regeneration by Vitamin CRegeneration by Vitamin C

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Vitamin KVitamin K

z Vitamin K1, or phylloquinone, is synthesized by plants; the members of the vitamin K2 are of microbial origin.

z Photochemical degradation

21

Benefits of Vitamin KBenefits of Vitamin K

22

Sources of Vitamin KSources of Vitamin K

Vitamin K deficiency is seldom naturally encountered in higher animals because the vitamin is usually adequately supplied in the diet, besides being synthesized by intestinal bacteria.

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WaterWater--soluble vitaminssoluble vitamins

z Vitamin C (ascorbic acid)z B vitaminsz thiamin (vitamin B1), riboflavin (vitamin B2), vitamin

B6, niacin (nicotinic acid, vitamin B3), vitamin B12, folic acid, pantothenic acid, and biotin.

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Ascorbic AcidAscorbic Acid

z A carbohydrate-like compoundz Acidic and reducing properties ----contributed by 2,3-

enediol moietyz Highly polarz pKa1=4.04 @ 25 oC , ionization of the C3 hydroxyl group

L-ascorbic acid

2,3-enediol

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Benefits of Vitamin CBenefits of Vitamin C

DEFICIENCY SYMPTOMS: May lead to soft & bleeding gums, swollen or painful joints, slow-healing wounds & fractures, bruising, nosebleeds, tooth decay, loss of appetite, muscular weakness, skin hemorrhages, capillary weakness, anemia, impaired digestion.

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Sources of Vitamin CSources of Vitamin C

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Oxidation of LOxidation of L--ascorbic acidascorbic acid L-dehydroascorbic acid loses reducing power

All have vitamin C activity except 2,3-diketogulonic acid because they are almost completely reduced to L-ascorbic acid in body

Two electrons oxidation and hydrogen dissociation

AA DHAA DKGLoss of

reducing power

Neutral or alkaline pH

Brown pigments

Maillard reaction

No vitamin activity

Vitamin C Activity

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Oxidation of LOxidation of L--ascorbic acidascorbic acid

z Highly susceptible to oxygenz Catalytic effects of metal ions (Cu2+, Fe3+)z Heat and light accelerate the oxidation processz Neutral or alkaline condition favors oxidation of L-

ascorbic acid

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LL--ascorbic acid as antioxidantsascorbic acid as antioxidants

z Mechanism: its availability for energetically favourable oxidation.

z Reactive oxygen species oxidize (take electrons from) ascorbate first to monodehydroascorbateand then dehydroascorbate.

z The reactive oxygen species are reduced to water while the oxidized forms of ascorbate are relatively stable and unreactive.

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Thiamin Thiamin

z Primidine + methylene + thiazole

N

S

N

NH3C

CH2

NH2

CH3

CH2CH2OHpyrimidine thiazole

Methylenebridge

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Benefits of ThiaminBenefits of Thiamin

DEFICIENCY SYMPTOMS: Systemic thiamine deficiency can lead to myriad problems including neurodegeneration, wasting and death.

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Sources of ThiaminSources of Thiamin

Thiamine is found naturally in the following foods, each of which contains at least 0.1 mg of the vitamin per 28-100 g: Green peas, Spinach, Liver, Beef, Pork, Nuts, Pinto beans, Bananas, Soybeans, Goji berries, Whole-grain and Enriched Cereals, Breads, Yeast ,the aleurone layer of unpolished rice, and Legumes.

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Degradation of ThiaminDegradation of Thiamin

z pHz Neutral or greater pH values favor its degradation

z Sulfiting agent (SO3-2)z ,US federal regulation prohibits the use of sulfiting

agents in foods that are significant sources for thiamin

z Water activityz Stable at low water activity

z Sensitivity to heat is depending on water activity and pH

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Riboflavin (Vitamin BRiboflavin (Vitamin B22))

z All derivatives of riboflavin are given the name flavinsz The flavin derivatives FAD and FMN are synthesised from dietary

riboflavin (vitamin B2) and ATP. They function as coenzymes in alarge of flavin-dependent enzymes in oxidation-reduction reactions in bodies.

Flavin adenine dinucleotide(FAD)

Flavin mononucleotide (FMN)

Riboflavin

ribose

adenine

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OxidationOxidation--reduction behavior of reduction behavior of flavinsflavins

Oxidized form

Bright yellowReduced form

Colorless

FAD FADH2

2e-, 2H+

In physiological condition, FAD/FADH2involve in electron-transfer reaction

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Benefits of RiboflavinBenefits of Riboflavin

DEFICIENCY SYMPTOMS: sore throat, swelling of mucous membranes, mouth or lip sores, anemia, and skin disorders.

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Sources of RiboflavinSources of Riboflavin

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Niacin (Vitamin B3)Niacin (Vitamin B3)

z Niacin is the generic term for nicotinic acid and derivatives.z The most stable of vitamins

z Not affected by light, no thermal loss of vitamin acitivity during food processingz Heat converts nicotinamide to nicotinic acid, both have vitamin B3 activity

z Coenzyme forms of Niacinz NAD, NADP---in many dehydrogenase reactions.

Nicotinic acid

Nicotinamide

Nicotinamide adenine dinucleotide (NAD)

Nicotinamide adenine dinucleotide

phosphate (NADP)

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Benefits of NiacinBenefits of Niacin

DEFICIENCY SYMPTOMS: cracked and red lips, inflammation of the lining of mouth and tongue, mouth ulcers, cracks at the corners of the mouth (angular cheilitis), and a sore throat. A deficiency may also cause dry and scaling skin, fluid in the mucous membranes, and iron-deficiency anemia. The eyes may also become bloodshot, itchy, watery and sensitive to bright light.

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Sources of NiacinSources of Niacin

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Vitamin B6Vitamin B6z A group of compounds having the vitamin activity of prodoxinez A cofactor in many reactions of amino acid metabolism, including

transamination, deamination, and decarboxylation. z Necessary for the enzymatic reaction governing the release of glucose from

glycogen.

z Light-induced degradationz Thermal degradationz Thermal interconversion

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Benefits of Vitamin B6Benefits of Vitamin B6

The classic clinical syndrome for B6 deficiency is a seborrheic dermatitis-like eruption, atrophic glossitis with ulceration, angular cheilitis, conjunctivitis, intertrigo, and neurologic symptoms of somnolence, confusion, and neuropathy

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Sources of Vitamin B6Sources of Vitamin B6

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FolateFolate (Vitamin B9) (Vitamin B9)

z A group of compounds having chemical structure and nutritional activity similar to folic acid

z Stabilility denpending on food systems. Complicated environmental factors (catalysts, oxidants, pH, buffer ions, etc. )

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Benefits of Benefits of FolateFolate (Vitamin B9) (Vitamin B9)

Folic acid deficiency may cause poor growth, gray hair, swollen tongue (glossitis), mouth ulcers, peptic ulcer, and diarrhea. It may also lead to certain types of anemias.

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Sources of Sources of FolateFolate

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General Causes of Losses in FoodGeneral Causes of Losses in Food

z Postharverst changes in vitamin content of foodsz Enzymes contribute to changes of vitamin content

z Preliminary treatments: trimming, washing, millingz Discarding stem, skin, or othersz Water-soluble vitaminsz Leaching

z Effects of blanching and thermal processingz Vc, Thiamin, Niacin, etc

z Losses of vitamin during storage after processingz Influence of processing chemicals and other food

componentsz Hypochlorous acid (HOCl), hypochlorite anion (OCl-), Cl2, SO2,

Nitrite, etc

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VitaminsVitamins--Losses during processingLosses during processing

30107Niacin

4857Thiamin

533319Ascorbicacid

Blanching & retortblanchingFresh cookedVitamin

%

Jiangsu University

Jiangsu University

Jiangsu University

949

Food Pyramid Food Pyramid

Jiangsu University

Jiangsu University

Jiangsu University

Food Chemistry-English version.pdfmorden food chemistry-5.pdf