Textbook Notes (363,608)
Canada (158,467)
Food Science (195)
FOOD 2010 (187)

Food - Unit 03 Summary.docx

10 Pages
Unlock Document

University of Guelph
Food Science
FOOD 2010
Massimo Marcone

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:  ɑw= P / P0  P = vapor pressure of the food  P 0 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  Emulsion is type of colloidal dispersion, system containing two liquids or phases that normally don’t mix: dispersed phase and a continuous phase  presence of water phase is prerequisite for emulsion  Water acts as important vehicle for heat transfer in foods during food processing operations and in food preparation  Water molecules always possess kinetic energy - as long as temperature is above 0 K (-273 C)O  Addition of heat (thermal) energy, kinetic energy of water molecules increases  Temperature increase of water as it is heated is proportional to its kinetic energy increase  Water able to act as conductor of thermal energy to food molecules, process called heat transfer  Increasing amount of water in food can have quality repercussions  can act as solvent, change state with temperature and exhibit motion within food system o Frozen foods: stabilize movement of water is desirable from quality standpoint o Freeze-thaw cycles in stored foods can result in production of concentrated and diluted portions of previously homogeneous food product when freeze-thaw stability poor  Water acts as plasticizer: lowers glass transition temperature (G )  temperature at which change in physicochemical state and mobility of water and polymer molecule constituents of food occurs o Decrease in T Gith 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 acid4 C4H4O is an alkene is less polar molecule than malic acid 4 4 5 and 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 pKa, the stronger the acid  acids can soften flour doughs  carboxylic acid groups establish “reducing conditions” in dough, donating H  hydrogen adds to sulfur atoms present in disulfide bonds, converting them back to –SH  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 )3used 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 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 > gl
More Less

Related notes for FOOD 2010

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.