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Food - Unit 03 Summary.docx

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Food Science
Course Code
FOOD 2010
Massimo Marcone

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UNIT 03: Food Chemistry: Major Components CHAPTER 4 (Pgs 91-119) 4.4. The Chemical and Functional Properties of Water  Functional properties: physical and chemical properties of food molecules that affect their behaviour in foods during formulation, processing, storage  include sensory and mechanical properties of foods o Determined by functional groups of food molecules  Water serves as fat replacer and zero-calorie ingredient  component of gels and emulsions, act as a medium for heat transfer, functions as plasticizer, accounts for food moisture, reactant or product in chemical reactions (condensation and hydrolysis)  Hydration: process by which water molecules surround and interact with solutes by acting as a solvent  Micelles: clusters of molecules in which the hydrophobic groups are directed away from water while the polar (charged) groups exposed on the external surface  Non-covalent interactions: interactions among water molecules and between water and food molecules Types Presence of water in foods:  Moisture: amount of water present in a food  water in foods called free water  Absorbed water/ structural water  Bound water/ structural water  exists in tight chemically bound situation  Water activity: measure of the availability of water molecules to enter into microbial, enzymatic, or chemical rxns  measure of relative humidity  determines shelf life of food  temperature- dependent o As % of bound water in food increases, water activity decreases o Calculated as ratio of water vapor pressure of the substance divided by vapor pressure of pure water at same temperature:  ɑ = P / P w 0  P = vapor pressure of the food  P0= vapor pressure of pure water at the same temperature  Relative humidity % (RH) = 100 x w  Moisture sorption isotherms: graphs of data that interrelate water (moisture) content of a food with its water activity at a constant temperature  indicates water activity at which food is stable and allows predictions of the effect of changes in moisture content ow ɑ  Water able to act as conductor of thermal energy to food molecules, process called heat transfer  Water acts as plasticizer: lowers glass transition temperaturG (T )  temperature at which change in physicochemical state and mobility of water and polymer molecule constituents of food occurs o Decrease in TGwith increasing water activity being linear o Plasticizer acts as food system softener, increasing food polymer molecular volume as well as mobility 4.5 The Chemical and Functional Properties of Food Acids  acetic acid contains carboxylic acid group and is thus organic acid  protein composed of amino acids and responsible for protein’s shape, functionality, nutritional quality  fats composed of fatty acids (ex. butyric acid is small carboxylic acid and has foul smell and present in rancid butter) o tartaric acid functions in leavening systems of many baked products and gives crisp flavour of citrus fruits  typical food acid is carboxylic or organic acid, containing carboxylic acid group (COOH) attached to remainder of molecule  acids that lack carboxylic acid group are inorganic acids o food acids added to sweetened beverages to extend and intensify sweet flavor o in dairy and baked products, acids impart desirable sour flavour  hygroscopicity: low attraction for moisture  functions of food acid related to molecular size and structure (ex. fumaric acids4C 4 4 is an alkene is less polar molecule than malic acid C 4 4 a5d is much less soluble in water)  just like all food acids, fumaric and malic acids are weak acids: mainly in form of –COOH but small amount has H separated, -- + dissociated to form COO + H  the lower the pK a the stronger the acid  Organic salts: compounds formed from organic acids in which hydrogen atom of acid group, COOH, replaced by metal ion  Buffer: solution of weak acid and its salt at pH where solution has ability to maintain that pH when quantities of base are added o Milk acid, lactic acid, anionic conjugate, lactate, form typical buffer system  Leavening: production of gas by yeast fermentation by reaction of acid with baking soda in batter and dough products, or by heating of salts o During fermentation, carbohydrates are converted to carbon dioxide gas and ethanol o Production of gases that create expansion in product causes “rise” in product  carbon dioxide gas, water vapor, air, ammonia, ethanol all leavening gas  Leavening acids: acids generate hydrogen ions that facilitate release of carbon dioxide from baking soda (sodium bicarbonate) o Gas release causes the expansion of a baking dough or batter product, due to increased pressure in gas nuclei o Baking soda, sodium bicarbonate (NaHCO ) 3sed in conjunction with leavening acids to produce leavening gas CO 2 alkaline substance Challenge! Food Systems  Food system: dispersion containing two phases: continuous phase and dispersed phase  3 basic dispersion types: 1) Solutions 2) Colloidal dispersions 3) Suspensions  Solutions: homogeneous mixtures in which one substance (solute) is dissolved in another (solvent)  Food colloids: surface active ingredients such as fatty acids, glycerides, phospholipids, polysaccharides and proteins  may exist as charged particles (ions), as molecules, or clusters of these (aggregates)  Emulsion: colloidal dispersion of 2 liquids, usually oil and water, that are immiscible o If oil is dispersed in water: called oil-in-water emulsion (O/W)  ex. raw, unprocessed milk (contains large fat globules that clump together and rise to layer on top of water phase: creaming) o If water dispersed in oil: called water-in-oil emulsion (W/O)  ex. butter (contains 2 liquid phases that are allowed to solidify)  Amphiphilic molecules: contain hydrophilic and hydrophobic regions in structure (ex. monoglycerides, phospholipids, sorbitan monostearates)  increase viscosity of continuous phase of emulsion, which enhances emulsion stability by inhibiting droplet merging and phase separation  Foam: dispersed phase is gas  lower surface tension and gelling ability, gelatin maintains foam stability by increasing viscosity and prevents crystallization of sucrose  ex. colloidal dispersion (whipped cream - multifunctional ingredient such as gelatin used)  Gel: 2 phase system in which liquid is dispersed in solid  colloid gel form when colloid molecules or particles associate in liquid such that solvent becomes immobile ex. colloidal dispersion (legume proteins, coagulated by heat, acid, enzymes into tofu gel  salt soluble meat proteins, animal proteins – gelatin)  Sol: opposite of gel  solid dispersed in a liquid  starch suspension in water becomes sol when heated due to process of gelatinization  cooling, gelatinized starch sol converts into gel (gravy) CHAPTER 5 (Pgs 120-153) 5.1 Food Carbohydrates  Organic alcohol: simple sugar  molecule that contains carbon atoms attached to – OH (alcohol) groups  Monosaccharide o 3 carbon atoms: trioses o 5 carbon atoms: pentoses o 6 carbon atoms: hexoses  ex. glucose, fructose, galactose (al6 C12 6 )  Fructose: exists as 5 member ring structure  sweeter and more soluble than glucose  considered ketoses because carbonyl group at carbon atom 2 is in form of ketone  Glucose: exists as a 6 member ring structure  most common in foods  considered aldose because carbonyl group (–C=O) at carbon atom 1 is in form of aldehyde  Galactose: occurs in disaccharide lactose  Disaccharide: monosaccharides are building blocks  2 monosaccharides joined together  bond in the structure is glycosidic bond o Sucrose: composed of glucose and fructose  common table sugar and used in food preparation in its crystalline o Lactose: composed of glucose and galactose  found only in milk and dairy products o Maltose: composed of 2 glucose units Functional Properties of Sugar:  Sugar molecules contain –OH alcohol group ( solubility and sweetness) and –C=O (reducing activity and the Maillard browning reaction that causes color and flavour changes)  Reducing sugars: sugars that contain aldehyde or ketone carbonyl group  act as reducing agents  ex. all monosaccharides and certain disaccharides o React with other substances through oxidation-reduction to produce reduced substance plus the oxidized sugar molecule o Dextrose equivalent (DE): measure of % of glycosidic bonds hydrolyzed in simple sugars indicating level of reducing sugar present  Higher the DE = more soluble and greater reducing ability.)  Browning: 2 types: 1) Maillard browning: non enzymatic  simple sugars but sucrose  browning of foods as result of Millard reaction o browning reaction between a simple sugar and amino acid to form melanoidins o 3 steps: a) Condensation Reducing sugar + amino acid ↔ glycosylamine. b) Rrearrangement Glycosylamine ↔ Amadori compounds [colourless]  pyrazines c) Polymerization Colourless intermediate compounds ↔ brown melanoidins 2) Carmelization: formation of brown caramel pigments as result of applying heat energy to O sugars  Need at least of a temperature of 200 C  Crystallization: formation of crystalline structure implies organized 3D arrays of unit cells into solid form o Depends on moisture, temperature, concentration of sugar o Crystal: solid made up of units in repeating pattern o 2 steps: a) Transfer of sugar molecule to surface of a crystal b) Incorporation of sugar into crystalline structure  Humectant: substance that has affinity for moisture o able to hydrogen bond with water molecules, making less water available for microbial growth  Inversion: hydrolysis of sucrose to its component monosaccharides is carried out if a sweeter product is desired than sucrose alone o mixture of two monosaccharides endproducts, called inverted sugar, typically created in food products through deliberate application of enzyme invertase  Oxidation and Reduction: Oxidation in sugars causes a less sweet sugar o Reduction causes formation of sugar alcohols, alternative sweetners  Glucome + hydrogen  sorbitol  Fructose + hydrogen  mannitol  Maltose + hydrogren  maltitol  Sweetness and texturizing: Sweetness of sugars  Fructose > sucrose > glucomse > maltose > galactose > lactose o Competition for water by sugar affects texture o Starch gelatinization is delayed due to sugars o Effect is to reduce viscosity and gel strength of starch thickened mixtures like pudding o Sugars also act as tenderizers in cakes and baked products Polysaccharides and their Functional Properties  Oligosaccharides: 10 or fewer sugar units  Beta-glucans: polysaccharides of glucose similar to cellulo0se, but less linear, occurring
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