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FOOD 2400 (3)
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Department
Food Science
Course
FOOD 2400
Professor
Yoshi Mine
Semester
Summer

Description
FOOD 2400 Summer 2012 Water • List some unique chemical and physical properties of water and ice • Describe some interaction of water with other molecules • Define what is meant by „water activity' • Explain the 3 regions represented in a sorption isotherm • Understand the importance of sorption isotherms to food stability • Define what is meant by „hysteresis' • Explain the differences between bound water and free water in food systems • Explain the process of ice crystallization • Explain the significance of nucleation and „seeding' during ice crystal formation • Explain the effect of cooling rate on ice crystal formation • Describe the changes which occur in foods during frozen storage; specifically freeze concentration and ice crystal damage. • Explain the concept of “glass formation” in foods and how this impacts on food stability • Explain the significance of water activity in relation to microbial growth/inhibition, chemical reactions, enzyme activity, and packaging requirements. Chemical and physical properties -high melting and boiling temperatures -large values for surface tension, dielectric constant, heat capacity and heat of phase transitions (fusion, vaporization, sublimation) -ice will conduct heat at a much faster rate than immobilized water -thermal diffusivities of water and ice indicate the rate solid and liquid forms of water undergo changes in temperature -ice's is 9 times greater than water -explains why tissue freezes 9 times quicker then they thaw Interaction of water with other molecules -able to influence noncovalent bonds (hydrogen, ionic, and apolar) that stabilize large molecules -hydrophilic substances interact strongly with water by ion-dipole and dipole-dipole interactions, causing changes in water structure and mobility -bound water = water which is very tightly associated with molecular structures -reduced molecular mobility -can't act as a solvent -structure is disrupted by the addition of dissociable solutes -water binding (hydration), tendency of water to associate with varying degree to hydrophilic substances; dependent on nature of non-aqueous constituents, salt, composition, pH and temperature -water holding capacity, ability of a matrix of molecules to entrap large amount of water to prevent exudation Describe water activity -better indicator of food stability than water content -aw = ERH = P/Po -P = partial pressure of water above the sample -Po = vapor pressure of pure water at the same temperature -ERH equilibrium relative humidity -its is an indication of how much water is available to participate in reactions for microbial growth 3 regions of sorption isotherm -plots of water activity vs water content in a food at a constant temperature -useful in predicting stability in foods with moisture content below 50% -can be gathered from dehydration (desorption) or rehydrating (adsorption) -adsorption used to observe hygroscopic products -desorption used to observe drying process -sigmoidal in shape and divided into 3 areas corresponding to different types or conditions of water in the food A - absorption of a monomolecular layer of water B - absorption of additional layers of water C - condensation of water in capillaries and pores of the material ZONE A -most strongly absorbed -most immobile in food -at -40oC this water is unfreezable -boundary between zones A and B is a monolayer of water (Langmuir water) -amount of water needed to form a monolayer over the accessible highly polar groups of dry matter ZONE B -known as multilayer water -water bounded to itself or to the solute water or through H-bonding -has solvent properties and acts as a plasticizing agent ZONE C -least strongly bound and most mobile -bulk phase water found in gels and cellular systems, and is physically entrapped -freezable, can act as a solvent, will allow chemical and microbial growth -most widely used isotherm is the BET, the monolayer coverage of water and water surface area can be calculated Importance of sorption isotherms to food stability Hysteresis -absorption and desorption curves are not always superimposable = hysteresis -depends on the nature of the food, physical changes (addition or removal of water, temperature, rate of desorption) -related to water condensing in capillaries of the food -when filling rate is controlled by the bulb of the capillary, when leaving flow is controlled by the capillary Ice crystallization -first step is nucleation nuclei crystals of ice crystals form -ice crystals will grow around the nuclei -supercooling = pure water cooled below its melting temperature, no nucleation. when a small ice crystal is added to the supercooled liquid, nucleation beings and temperature rises to the melting temperature -low degrees of supercooling = crystallization is slow -when lower temperatures are used process is quicker -speed of crystallization determines the number and size of ice crystals -fast cooling = high rate of nucleation, slow crystal growth rate = fine crystal structure -slow cooling = low rate of nucleation, fast crystal growth rate = fewer but larger ice crystals -seeding (addition of nuclei to liquids prior to freezing) can be used to increase the number of initial nuclei present and to encourage a finer crystalline structure Changes which occur in frozen foods during storage (Freeze concentration and ice crystal damage) -freeze concentration -concentration of non-aqueous constituents in the unfrozen phase -during freezing water from solution is transferred into ice crystals and non aqueous constituents become more concentrated in a diminished quantity of unfrozen water -unfrozen phase can have changes in pH, ionic strength, viscosity, freezing point, surface and interfacial tension, redox potential -low temperature decreases reaction rates, but freeze concentration can increase non-enzymatic reactions (oxidative reactions and protein insolubility) -ice crystal damage -due to decompartmentalization, enzymes and substrates may come together, thus catalyzing a reaction. thus some enzymatic reaction may increase -recrystallization, melting and refreezing of ice crystals with slight temperature fluctuations can cause damage to the food Glass Formation and impact on food stability -can be formed in frozen foods, but it is not ice formation -glass is a very viscous liquid -can form when the temperature of a liquid is lowered (usually at very high cooling rates) -temperature much lower than for crystallization -no nucleation or crystal growth, instead the molten liquid changes to a glassy state -at high moisture system can go rubbery before glassy -the rubbery state can be detrimental to food stability since molecular mobility is high and therefore reaction rates are higher than in glassy state -glass can form in a partially frozen food some liquid water is removed, the remaining aqueous solution in a food becomes increasingly concentrated in dissolved solids. if glass temperature is reached, remaining water is transformed into glass. known as cryoprotection -increase in water content decreases the transition temperature in foods, related to plasticizing effect of water plasticizers weaken intermolecular forces between molecules and therefore increase the plasticity and flexibility of food polymers Significance of water activity in relation to microbial growth/inhibition, chemical reactions, enzyme activity, and packaging requirements -molds and yeast grow at water activity between 0.7 and 0.8 (upper limit of capillary water) -bacteria grow when water activity reaches 0.8 (lower limit of loosely bound water) -only lipid oxidation is not limited in the monolayer region (water activity 0 and 0.2) -lipid oxidation is high because of increased mobility of oxygen and free radicals in the absence of water -maillard, vit B degradation, microbial growth exhibit rate maxima at intermediate to high aw values -water activity and microbial growth/food spoilage is closely correlated -IMF (intermediate moisture foods) moisture content (20-40%) [cakes, cookies] -aw between 0.6-0.9 -stabilized by combining principles of water activity with pH, heat and preservatives -sorption isotherms can be used to select suitable packaging -ex hygroscopic foods must be packaged in watertight packages because they absorb water readily for other foods packaging must serve to prevent moisture loss from the product Lipids Upon completion of this unit, you should be able to: • Understand conventional nomenclature designations for fatty acids and glycerides • Explain the significance of double bonds, chain length, and cis/trans configuration of fatty acids with respect to the chemical and physical characteristics of lipids (YOU KNOW THIS !!! ) • Compare/contrast lipid distribution patterns in various raw material sources and discuss the significance of their similarities and differences • Describe the stereospecific numbering system used for glycerides (i.e. sn-1, sn-2 and sn-3) • Recognize the basic structure of a phospholipid • Name some compounds found in the unsaponifiable fraction of fats • You do not need to memorize the names of specific fatty acids found in specific foods. Knowledge of general trends is sufficient. Here are some examples: (1) rather than memorizing that meats primarily contain palmitic, oleic and stearic acids, it is sufficient to know that meats contain a lot of long chain saturates; (2) marine oils contain highly unsaturated, long chain fatty acids, which have important nutritional consequences because of their omega-3 designations. • Describe the reaction mechanisms responsible for oxidative rancidity (namely, autoxidation, photoxidation, and flavour reversion) • List some intermediates and by-products of autoxidation, and discuss the significance of these compounds to rancidity • Describe some desirable and undesirable consequences arising from lipoxygenase activity • Discuss factors influencing the rate of lipid oxidation in foods • Describe the consequences of oxidative and non-oxidative decomposition of lipids upon exposure to high temperatures and frying • Discuss the mechanisms of action and characteristics of common antioxidants • Describe some desirable and undesirable consequences of lipase activity • Describe the general mechanisms for hydrogenation, and explain how the process can be controlled. Identify some products of the reaction, and discuss the significance of these products in food systems • Describe the interesterification reaction and how it can be used to produce unique products • Describe the properties associated with alpha, beta, and beta prime fat crystal forms, and explain their significance to foods • Explain the purpose of the various processing stages in the refining of crude fats and oils • Describe characteristics of various types of emulsions, and discuss the principles of emulsion stabilization • Discuss, very generally, the health implications of dietary lipids • Describe examples of novel fats and oils, and fat replacers Shorthand Description of Fatty Acids and Glycerides -Two numbers separated by a colon -first number indicates the number of carbon atoms -second number indicates the number of double bonds Example= 16:0 palmitic acid -Info may be given for unsaturated fatty acids - Example= 18:1c9 (oleic acid, cis isomer at carbon 9) -Some carbons chains may be counted backwards -Example= 18:2n-6 (linolenic acid, omega-6) -Triglycerides can be abbreviated using the first letters of the common names of the component fatty acids Example = SSS for tristearin Component Fatty Acids -Land Animals -saturated, long-chain fatty acids -Ruminant Milk Fat -saturated, 4-10 chain fatty acids -Marine Oils -unsaturated, long-chain fatty acids -Seedfats -unsaturated fatty acids (chain length can vary) Component Glycerides -sn = stereospecific numbering -3 carbon atoms designated sn-1 (from the top) to sn-3 (at the bottom) Phospholipids -have a lipophilic and hydrophilic portion -are removed from oils to be used as emulsifiers in certain food products Unsaponifiables -fat is boiled with alkali to form "soaps", which dissolve in the water layer with glycerol and phosphates. -Fractions that form soaps are saponifiables and the ones that do not are unsaponifiables -consists of sterols, terpenic alcohols, aliphatic alcohols, squalene, and hydrocarbons -mainly sterols (cholesterol [animals], phytosterols [plants] etc) Autoxidation -described as rancidity -can be affected by: -amount of oxygen present -degree of unsaturation of the lipids -presence of antioxidants -presence of prooxidants (esp copper) and organic compounds (heme- containing, or lipoxidase) -nature of packaging material -light exposure -temperature of storage -can be divided into 3 steps: -INITIATION -hydrogen is abstracted from olefinic compound to yield a free radical -takes place at the carbon atom next to the double bond and can be brought about by the action of light or metals -PROPAGATION -once a free radical has been formed, it will combine with oxygen to form a peroxy-free radical, which can in turn abstract hydrogen from another unsaturated molecule to yield a peroxide and a new free radical -TERMINATION -free radicals combine to form nonradical products Photoxidation -oxidation with singlet oxygen -main step involves a self-catalytic free radical mechanism that accounts for the chain reaction of hydroperoxide ROOH formation and decomposition -initiation occurs by direct attack of oxygen in thetriplet state -the singlet oxygen is the active species in photo-oxidative deterioration as it is more electrophilic than oxygen in its triplet state and reacts with moieties of high density (double bonded carbon) -the resulting hydroperoxides can cleave to initiate a conventional free radical chain reaction -singlet oxygen can be generated in many ways -natural pigments in food -in fat-containing foods have substances that can act as photosensitizers to product singlet oxygen -chlorophyll-a and other pigments -can be quenched by -B-carotene -BHA -BHT Flavour Reversion -type of oxidative rancidity that can occur in fats with linolenic acid -characterized by grassy, painty, and fishy off-flavours -flavours from volatile oxidation products that result from the terminal pentene radical of linolenic acid Formation of Intermediates (hydroperoxides) -depends on the starting material -oleate - hydrogen abstractions at C8 and C11 giving two allylic radical intermediates. Oxygen attacks to form 8,9,10 & 11 allylic hydroperoxides. (with 9 and 10 in higher quantities) -linoleate - 20 times more susceptible to oxidation than oleate. H abstraction produces a pentadienyl radical intermediate upon reaction with oxygen to give 9,13-diene hydroperoxides -linolenates - Hydrogen abstraction at the two active methylene groups of C11 and C14 to give two pentadienyl radicals. Oxygen attack at the carbon end of each radical gives 9-,12-,13-, and 16- hydroperoxides Lipoxygenase Activity -also called LOX group of enzymes which can cause oxidation of lipids -wideley distributed in veg and animal kingdom Positives -development of the aroma of a tomato LOX is kept separately than its substrate (polyunsaturated fats) When cut they come together the smell gets stronger Decompartmentalization occurs as fruit ages as well -LOX can improve the rheology of wheat flour doughs. Absorption of atmosphere oxygen during dough mixing improves the rheological properties of the dough because oxidized lipids help change the rheological properties of gluten Negatives -the off-flavour development in soybeans and soybean products is dependent on the action of the various endogenous LOX which cause decomposition, resulting in hydroperoxides and rancid flavours -Accumulation of unblanched frozen peas causes off-flavours. LOX can have a bleaching effect on beta-carotene, xanthophylls and chlorophylls, therefore destroying vitamins through oxidation. -lipases may release fatty acids providing substrates for those LOX enzymes requiring free fatty acid as a substrate Rate of Lipid Oxidation 1. Fatty Acid Composition -number, position and geometry of double bonds can affect the rate -cis oxidize more than trans 2. Free Fatty Acids VS Corresponding Acylglycerols -Oxidize faster when free than when esterified to glycerol 3. Oxygen -if supply is unlimited, rate of oxidation is independent of oxygen pressure -at low oxygen pressure, rate is proportional to pressure 4. Temperature -increases as temperature increases -also influences oxygen pressure, higher temp = higher oxygen pressure 5. Surface Area -Increases in proportion of SA -If SA/Volume increases, decreasing the oxygen pressure is less effective to slow the rate of oxidation 6. Moisture -depends on a w -low water activity (less than 0.1) = oxidation is quick - aw0.3 = oxidation is minimum as, catalytic activity of metal catalysts reduced, free radicals quenched, promoting non-enzymatic browning, impeding access of oxygen to food. -higher water activity = rate increases as a result of mobilization of catalysts 7. Pro-Oxidants -Transition Metals (esp with 2 or more valency states) (-Ca +2,Fe +2 +, Cu+ 2) with suitable redox potential between them -cobalt, iron, copper, manganese, nickel 8. Radiant Energy -visible and ultraviolet radiation can promote generation of free radicals, leading to autoxidation 9. Enzymes (Lipoxygenase) -see above 10. Antioxidants -natural (tocopherols) and synthetic (BHA, BHT) that act to prevent oxidation Consequence of oxidative and non-oxidative decomp of lipids upon exposure to High Temperatures and Frying -during frying, water is continually released into the oil, which hastens hydrolysis to yield increased amounts of free fatty acids -oxidative stability of the new mixture may be different from that of the original frying fat -chemical changes -increase in frying oil viscosity (result of polymer formation) -increase free fatty acid content -development of a dark colour (due to polymeric compounds) -increased tendency of the oil to foam (due to compounds which migrate from the food into the oil) -can affect sensory properties (oxidation products) but nutritional value (formation of trans fats) -compounds formed 1. Volatiles - result from the decomposition of hydroperoxides, and include saturated, and unsaturated aldehydes, ketones, hydrocarbons, lactones, alcohols, acids and esters 2. Nonpolymeric Polar Compounds - produced from various pathways involving alkoxyl radicals 3. Dimeric and Polymeric Acids, and Dimeric and Polymeric Glycerides - compounds result from thermal and oxidative free radical combinations. Polymerization results in an increase in the viscosity of the frying oil 4. Free Fatty Acids - arise from the hydrolysis of triacylglycerols in presence of heat and water. Free fatty acids are very susceptible to oxidation resulting in volatile formation. High quality oil has a low free fatty acid, and thus fatty acid test is used as a test to determine quality of the frying oil. -Control Measures 1. Use of a good quality oils with consistent stability 2. Use lowest frying temperature possible 3. Filter oil to remove food products 4. Replace oil 5. Use of antioxidants 6. Frequent testing of oil throughout the frying process -thermal decomposition 1. Saturated Fatty Acids a) thermal non-oxidative reaction -very high temperatures are required -detectable breakdown products consist mostly of hydrocarbons, acids and ketones b) thermal oxidative reaction - more stable than unsaturated -when heated in air at temperatures above 150 C they will undergo oxidation -major breakdown products including carboxylic acids, 2-alkanones, n-alkanals, lactones, n-alkanes, and l-alkenes 2. Unsaturated Fatty Acids a) thermal non-oxidative reaction -formation of dimeric compounds with temperatures above 220 C o -other substances of low molecular weight are also formed b) thermal oxidative reaction -most often encountered in foods during the heating of fats and oils -at high temperatures, it occurs rapidly producing major compounds that are similar to those produced as a result of room temperature autoxidation -at elevated temperatures, hydroperoxide decomposition and secondary oxidation occur at extremely rapid rates Mechanisms of action and Characteristics of Antioxidants - Modes of action 1. Inhibition of free radicals in the initiation step OR 2. Interrupting propagation of the free radical chain through donation of hydrogen atoms -believed that the second method is more predominant, even though a free radical is formed, it is less likely to react with oxygen, than free fatty acid radicals -Characteristics of Antioxidants 1. Tocopherols -vitamin E derivatives -primary antioxidants in vegetable oils -work best at low levels, at high levels they act as pro-oxidants 2. Propyl Gallate -effective to phenolic structure and 3 OH groups -effective in retarding lipoxygenase oxidation of linoleic acid -in presence of iron, propyl gallate discolours at alkaline pH but is lost during baking or frying 3. Butylated Hydroxyanisole (BHA) and Butylated Hydroxytolunene (BHT) -widely used commercially -weak antioxidants in vegetable oils, but are effective in combination with other primary antioxidants -BHA has phenolic odour when exposed to high heat Lipase Activity -Enzymes that hydrolyze ester linkages of emulsified triacylglycerols at and oil/water interface -widely distributed in nature -Steps -Triacylglycerol TO -1,2 diacylglycerol and 2,3 diacylglycerol TO -2-monoacylglycerol -however there are exceptions -there are specificities with lipases acylglycerol - preferential hydrolysis of low molecular TAG's positional - ex pancreatic lipase hydrolyzes only primary position esters of TAG's fatty acid - occur when one type of fatty acid is more rapidly hydrolyzed than another type, when both are attached to the same positions of like TAG molecules phospholipase A1 - hydrolyzes at sn-1 position phospholipase A2 - hydrolyzes at sn-2 (implicated in toughening of frozen fish) (aroma in fresh veggies) phospholipase B - hydrolyzes sn-1 of lysolecithin phospholipase C - hydrolyzes at sn-3 phospholipase D - choline hydrolyzing enzyme, hydrolyzes at sn-4 to give phosphatidic acid POSITIVES -can add desired flavour to cheese NEGATIVES -enzymes can form free fatty acids in meat meaning they must be rendered to inactivate this General Mechanisms for Hydrogenation -control process -products of reactions -significance of products in food systems -objectives 1. convert liquid oils into semisolid or plastic fats to produce shortenings and margarines 2. Improve the oxidative stability of the oil -oil is first mixed with a suitable catalyst (usually nickel), heated to the desired temperature (140-225 C), then exposed to hydrogen at pressure up to 60 psig and agitated. When the hydrogenated oil is cooled and the catalyst removed by filtration -hydrogenation mechanism 1. Carbon metal complex (S-M) is formed at either end of the olefinic bond 2. Intermediate complex (S-M) is then able to react with an atom of catalyst- absorbed hydrogen (M-H) to form an unstable half-hydrogenated state, in which the double bond (olefin) is attached to the catalyst by only one link and is thus free to rotate 3. The half-hydrogenated compound (S-M-H) may now either a) react with another hydrogen atom and dissociate from the catalyst to yield the saturated product OR b)lose a hydrogen atom to the nickel catalyst to restore the double bond 4. The regenerated double bond can be either in the same position as in the non-hydrogenated compound, or a positional and/or geometric isomer of the original double bond may be formed -products that form depend on the path of the half hydrogenated intermediate -because of isomerization to the trans configuration, hydrogenation can affect the nutritional value of the fat -omega-3, omega-6 fats acids... not utilized in the body as essential fatty acids -only cis fatty acids are retained in the body as a source of essential fatty acids -in most case only partially hydrogenated leaving double bonds intact -selectivity = relative rate of hydrogenation of the more unsaturated fatty acids as compared to that of the less unsaturated acids -to determine selectivity is the concentration of hydrogen absorbed on the catalyst -high concentration of hydrogen = less selectivity and vice versa -increase temperature increases speed of reaction, and increased selectivity -intensity of agitation, hydrogen pressure, kind of concentration of catalyst can also influence selectivity -more selectivity = can minimize the formation of fully saturated compounds -less selectivity = more trans isomers, nutritional concern -hydrogenation catalysts can be poisoned during hydrogenation prevent by -starting oil should be -refined -bleached -low in soaps -dry -hydrogen should be -dry -free of sulfur -free of carbon dioxide -free of ammonia poisoning results in decreased reaction rate, increased trans isomer formation Interestification (and how if can be used to produce unique products) -involves rearranging the fatty acids so that they become distributed randomly among the triacylglycerol molecules of the fat -the unique fatty acid distribution patterns of some natural fats limit their industrial applications, changing these distribution patterns by interestification may improve the consistency of such fats and improve their usefulness -random distribution is not always desirable -can be slightly controlled if maintained at a temp below its melting point -known as directed interestification -can result in selective crystillization of trisaturated glycerides -crystals can precipitate, meaning oil can become shortening without hydrogenation -if precipitation of glycerol is removed the product will remain liquid at low temperatures -can occur without a catalyst at temperatures above 300 C o o -usually carried out using catalysts at temperatures as low as 50 C in times as short as 30 mins -greatest application of interestification is in the manufacture of shortening and production of lard -shortening made from lard can be grainy so interestification is used to make a smoother consistency Alpha, beta and Beta' Fat Crystal Forms (and significance) -crystallization - process by which liquid converts to a solid -slow and exothermic and expand when they crystallize -NOTE glassy state does not form -melting point/range -can be used to characterize fats -depend on fatty acid chain length, unsaturation, double bond configuration, and arrangement of fatty acids on the glycerol backbone -solid fat content -can be measured by dilatometry or pulsed nuclear magnetic resonance -amount an size of crystals determine physical properties of the product -fat crystals are held together by van de Waals forces, which can be broken, however upon standing bonds reform (property known as thixotropic) -cooling rate determines the solid fat content and crystal size and shape -when crystallization is rapid or temperature is lower than the melting temperature, nucleation will predominate over crystal growth -with slow cooling or low degree of supercooling, crystal growth predominates over nucleation = less but larger crystals -polymorphism = existence of more than one crystal form (in order of stability) -alpha -beta prime -beta -to go from a more stable to a less stable polymorph to a less stable form requires melting and recrystallization of the fat -polymorphic form is dependent on purity, temperature, rate of cooling, presence of crystalline nuclei, type of solvent, composition of its fatty acids, and positional distribution -fats with limited number of TAG's, few polymorphs and tend to be beta -fats with random and more TAG's, more polymorphs and transform slowly from one form to another -polymorphic fats are used primarily in shortenings and margarines whose quality is dependent on 1. incorporated air 2. plasticity and consistency 3. solid/liquid ratio example: B' can incorporate lots of small air bubbles B can incorporate few large bubbles Purpose of various Processing stages in refining -fractionation, three reasons : 1. remove high melting components that would make an oil cloudy (winterization) 2. obtain two or more fractions of fat with different melting characteristics from one fat 3.produce fractions that possess unique physical properties and can therefore be used as specialty or confectionary fats -dry fractionation (from the melt) -carried out on a large scale with palm oil OR -dissolving fat into a solvent -during fractionation, both cooling and agitation rates must be carefully controlled -ideally large crystals are produced -some TAG's are hard to separate if they have similar melting temperatures (solid solution formation) -can also be influences by solubilization of TAG's in other TAG's -entrainment can hinder fractionation (physical trapping of liquid oil in the crystallized fat) -tempering -temperatures during melting are controlled to be in the state they are most useful Characteristics of Emulsions and Emulsion Stabilization Major types of emulsifiers 1. Oil in Water ex: milk, cream, salad dressing, mayonnaise, ice cream 2. Water in Oil ex: butter and margarine 3. Meat Emulsion fat is dispersed phase, continuous phase are salts, soluble and insoluble protein particles, muscle and connective tissue -emulsion detabilization 1. Creaming or sedimentation - action of gravity on phases that differ in density 2. Flocculation or clustering - inadequate electrostatic charge at the globule surface is the main cause of clustering. Following flocculation, fat globules move as groups 3. Coalescence - most serious, involves rupture of interfacial film, joining of globules and reduction in interfacial area -emulsion stabilization -synthetic -ionic or non-ionic -natural -HLB developed to help in the selection of proper emulsifiers for certain applications. Characterizes the relative simultaneous attraction of an emulsifier for water and oil -indication of how an emulsifier will behave not how efficient it is -foods that contain many natural emulsifiers 1. phospholipids 2. proteins 3. water soluble gums 4. monoacylglycerols Novel Fats and Oils, Fat Replacers -can be developed with specific nutritional and/or functional properties -fat replacers, mimic characteristics with less calories Carbohydrates • Describe the general structural configuration of monosaccharides, oligosaccharides and polysaccharides • Explain the differences between D- and L- designations for monosaccharides • Distinguish between alpha- and beta- anomeric forms of monosaccharides • Explain what is meant by a "reducing sugar" • Define "mutarotation" and "enolization" • Describe reactions involved in caramelization and Maillard browning • Discuss factors which influence growth of sugar crystals • Describe the structure of branched starch (amylopectin) and linear starch (amylose) • List examples of sugar alcohols • List examples of applications for celluloses, hemicellulose, pentosans, and lignin in foods • Describe the general structure of cyclodextrins and present an example of an application for cyclodextrins • Describe the structural characteristics of high and low-methoxyl pectins • Discuss the differences in gel properties between high and low-methoxyl pectins • Give examples of commercial applications for pectic enzymes • Explain functional properties associated with commonly used gums, and identify synergistic effects when specific gums are used together in food systems Structure monosaccharides, oligosaccharides, polysaccharides -monosaccharide = 1 unit of carbohydrates -oligosaccharides = 2-10 units of carbohydrates are joined -polysaccharide = more than 10 units of carbohydrates D- and L- designations - D- is for dextrorotatory - L- is for levorotatory -different by position of OH on the assymetric carbon -D has OH to right -L has OH to the left Alpha- and beta- anomeric monosaccharides -closely related monosaccharide -isomers that differ from one another only in configuration are called anomers -two forms are called alpha-, and beta- -in the Fischer projections OH points to right in alpha, left in beta. Reducing Sugar -contains a free hemiacetal group that can react to produce carbonyl function -ability to reduce metal ions such as silver or copper while the sugar is oxidized to carboxilic acid -glucose is because its carbonyl group is available -sucrose the reducing groups are linked -its important in the Maillard browning reaction Functions of Carbs in Foods -hydrophilicity -they attract water due to numerous OH groups present that interact with water by H-bond -water-binding capacity (humectancy) -ex glycerol -binding of flavour ligands -retain volatile flavour compounds -sugar-water + flavourant = sugar-flavourant + water -carbohydrate browning products & food flavours -non-oxidative browning reactions yield a variety of volatile flavourants -sweetness -varies with configuration and physical conditions Mutoration, Enolization and Dehydration 1. Mutoration -process by which pure isomers of reducing sugars adopt an equilibrium composed of various species -first reaction to occur to sugars when they are dissolved -temperature dependent -acids and alkalis are catalysts and increase the rate 2. Enolization -formation of enediol -occurs through open chain formation form -catalyzed by alkali -reactions are reversible, known as Lobry de Bruyn-Alberda van Ekenstein reactions 3. Dehydration and Thermal degradation reactions -occur at high temperatures -both catalyzed by acid or base Caramelization and Maillard Browning -caramelization -result of directly heating carbohydrates or in concentrated syrups -facilitated by small amounts of acids and certain salts -increased temperatures and pH increase the reaction -STAGES -thermolysis and formation of anhydro sugars -increase in colour due to conjugated double bonds which absorb light and in polymerization from the condensation of unsaturated rings -three stages of crystallization dehydration - after 35 mins 200C formation of caramelAn - 55 mins later formation of caramelEN - 55 mins later -two useful purposes -produces caramel flavour syrups -produces caramel colours -Maillard see proteins Factors influencing growth of sugar crystals -tendency of crystallization depends on type of sugar and crystallizing conditions -including temperature, solution supersaturation, presence of impurities -non-reducing crystallize easily compared to reducing sugars -can lead to textural problems in EX like ice cream Starch and Amylose + Amylopectin Explain how the branched or linear structure of starches affects functional properties in foods -see FOOD 2700 Describe changes which occur to starch granules and molecules in solution upon gelatinization and retrogradation -see FOOD 2700 Discuss the effects of various types of starches upon gelatinization and retrogradation, and give some examples of applications in foods See FOOD 2700 Describe the characteristics and functional properties of common modified starches -acid modified starch -produced by holding starch granules below gelatinization temperature in an acidic medium, acid hydrolyzes glycosidic linkages in starch without breaking up any granules -dried and used as powder, produces low viscosity fluids that are easy-to- handle and can be easily poured into molds and set into firm gels -cross-bonded starch -produced by forming covalent links between adjacent starch chains. cross-links prevent starch granules from swelling normally and provide greater stability to heat agitation, and damage from hydrolysis, and reduced tendency to rupture -function as stabilizers and thickeners, resistance to gelling and retrogradation, show good freeze-thaw stability and do not synerese on standing -substituted starches -prepared by reaction some of the OH groups with reagents that introduce different substituents into the starch molecule -make it harder for the starch molecules to associate and form a gel -linear regions are prevented from forming crystalline regions -oxidized starches -prepared by treating starch with hypochlorite -result is hydrophilic nature of the starch is increased leading to greater interactions with water and fewer starch-starch interactions -starch dextrinization -can be carried out by heating dry starch powders, often in presence of hydrochloric or phosphoric acid -result in formation of dextrins which are used for coatings and as binders because of their film-forming properties
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