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Food Chemistry
Wenjuan QuJiangsu University
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
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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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2011 May
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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
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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
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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.
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Lipids
Wenjuan QuJiangsu University
2011 May
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
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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
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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
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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
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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.
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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.
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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
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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.
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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
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Amino acid, peptide & protein
Wenjuan QuJiangsu University
2011 May
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
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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.
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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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2011 May
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
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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
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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
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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
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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
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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
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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
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Benefits of Vitamin KBenefits of Vitamin K
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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
%
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949
Food Pyramid Food Pyramid
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Food Chemistry-English version.pdfmorden food chemistry-5.pdf