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Chapter 5

Chapter 5- Food Chemistry 2, Carbohydrates, Lipids, Proteins.docx

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Department
Food Science
Course Code
FOOD 2010
Professor
Massimo Marcone

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Chapter 5: Food Chemistry 2, Carbohydrates, Lipids, Proteins 5.1 Food Carbohydrates -structure of sugars -all contain CHO -simple sugars (fructose, glucose, galactose are monosaccharides) and (lactose, sucrose, maltose are disaccharides) also termed organic alcohols. -monosaccharides -3 carbons are triose -5 carbons are pentose -6 carbons are hexose -disaccharides -monosaccharides are the building blocks -2 monosaccharides form one disaccharides -sucrose (fructose, glucose) -lactose (galactose, glucose) -maltose (glucose, glucose) -functional properties of sugar -reducing sugars (sugars that contain aldehyde or ketone carbonyl group. They react through oxidation-reduction to produce reduced substance plus the oxidized sugar molecule. All monosaccharides and most disaccharides are reducing sugars. Dextrose equivalent [DE] measure of % of glycosidic bonds hydrolyzed in simple sugars, indicating the level of reducing sugar present. Higher the DE = more soluble and greater reducing ability.) -browning (Maillard browning and caramelization. Maillard browning is nonenzymatic [simple sugars but sucrose] browning reaction between a simple sugar and amino acid to form melanoidins. Happens in 3 steps. 1: condensation of reducing sugar and amino acid gives glycosylamine. 2: rearrangement glycosylamine becomes amadori compounds [colourless] and then pyrazines. 3: polymerization, the colourless intermediate compounds from the brown melanoidin pigments. There is also carmelization, which is the formation of brown caramel pigments as a result of applying heat energy to sugars. Need at least of a temperature of 200 C. There is no single compound identified as caramel, it depends on the substance what is called caramel.) -crystallization (sugars can exist in soluble [as syrup] and crystalline states. Formation of a crystalline structure implies organized 3D arrays of unit cells into a solid form. A crystal is a solid made up of units in a repeating pattern. When the sugar is purified crystallization is the key step. Happens in 2 stages. The first one is transfer of sugar molecule to surface of a crystal and the second is the incorporation of sugar into the crystalline structure. Crystallization in hard candies is desirable, however in ice cream it would make it more gritty.) Chapter 5: Food Chemistry 2, Carbohydrates, Lipids, Proteins -humectancy (humectant = affinity for moisture. They hydrogen bond with water molecules, making less water available for microbial growth.) -inversion (hydrolysis of sucrose to its monosaccharides is carried out if a sweeter product is desired than sucrose alone. The mixture of two monosaccharides endproducts, called inverted sugar, is typically created in food products through the deliberate application of the enzyme invertase) -oxidation and reduction (oxidation causes a less sweet sugar. Reduction of a disaccharide forms a sugar alcohol, which is a alternative sweetener. Glucose + Hydrogen = sorbitol. Fructose + Hydrogen = mannitol. Maltose + Hydrogen = maltitol.) -sweetness and texturizing (Fructose>Sucrose>Lactose. in order from most sweet to least sweet. Competition for water by sugar and other substances, can change texture. Starch gelatinization is delayed due to sugars. The effect is to reduce the viscosity and gel strength of starch thickened mixtures like pudding. Sugars also act as tenderizers in cakes and baked products.) -Polysaccharides and their funcitonal properties -complex carbs -10 or fewer sugar units are called oligosaccharides -beta-glucans similar to cellulose but less linear. (oatrim [a by-prodcut] can be used as a fat replacer and texturizing ingredient) -cellulose (indigestible for humans. A non-caloric microparticulate form of cellulose available in food industry, when dispersed, forms a network of particles with mouthfeel and flow properties similar to fat. So it can be a fat replacer.) -dextrins and maltodextrins (dextrins are polysaccharides derived from starch, linear arrays of glucose units. Produced commercially by hydrolyzing amylose portion of starch. Heat is used to carry out the reaction. Can be used as fat replacers. Dextrans have a alpha 1-6 linkage compared to alpha 1-4 linkage in dextrins. Dextrans are food gums. Maltodextrins are polysaccharide fragments derived from starch hydrolysis. They can be used as a fat replacer, texture modifier or bulking agent.) -Fructoogligosaccharides ([FOS] are naturally occurring sugars consisting of multiple units of sucrose joined one, two or three fructose molecules via glycosidic bond to the fructose portion of the sugar molecule. Also known as prebiotics, they promote growth of bacterial organisms believed to be beneficial in health.) -Inulin: Dietary Fibre (its a FOS that acts as a dietary fibre, occuring naturally in some plants. Composed of a chain of fructose units with a terminal glucose unit. Not digestible, and it can provide a creamy mouthfeel through texture modification, as well as be a fat and sugar replacer, and it can be a bulking agent. Chapter 5: Food Chemistry 2, Carbohydrates, Lipids, Proteins -Pectic Substances (found in plant cell wall. protopectin in immature fruit. Then it becomes pectin and then pectic acid. see FOOD 2700 notes for more) -Starch (polysaccharide derived from plant sources, has branched[amylopectin] and unbranched[amylose] regions occurring in starch granules. see FOOD 2700 notes for gelatinization and retrogradation) -Vegetable Gums (substances derived from plants that distrivute in water as colloidal dispersions. Composed of long-chain polymers of various hexoses and pentoses. Virtually noncaloric so are good fat replacer. They have a high solubility, pH stability and gelling ability are the desired characteristics of a food gum. 5.2 Food Lipids -structures and types of lipids -fats and oils (triacylglycerols or triglycerides is a glycerol and 3 fatty acid chains.) -saturated and unsaturated (double bonds or not) -cis and trans fats (all unsaturated trans is more linear, and cis is more of a kink) -melting point -the temperature where solid fat becomes liquid fat -unsaturated cis is more liquid -unsaturated trans, and saturated are more solid -flavour compounds -either the fat itself has specific flavour -or the atoms they react with. IE reversion flavour mild-off flavour developed by refined oils that have been exposed to oxygen. They are less intense compared to those associated with oxidative rancidity. -polar lipids -found in membranes of plant and animal tissue -ex: glycerophospholipids -glycerol, 2 fatty acids, hydrophilic part containing phosphate group -ex: lecithin -pigments (see chap 6
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