Food Chemistry 2023 with 100% correct questions and answers

4 basic food molecules carbohydrate protein lipid water percentage of water in food 0-95% oil is ____ % water 0% meat is ___ % water 70% free water water that is easily separated from food Bound water water incorporated into chemical nature of other nutrients why is water polar? electrically unsymmetrical positive H negative O 1 kilocalorie amount of energy needed to raise temp of 1kg of water by 1°C what substance takes the most energy to heat water specific heat amount of heat required to raise temp of 1g of substance by 1°C specific heat of water 1 freezing point of water 0°C 32°F Boiling point of water 100°C 212°F heat of solidification the temperature at which a substance converts from a liquid to a solid state heat of solidification of water 80calories of heat lost per gram of water why water expands when frozen molecular packing determined by requirement for even distribution of hydrogen bonds melting point temperature at which a solid changes to a liquid melting point of water returning 80calories of heat to each gram of ice heat of vaporization amount of heat required to convert liquid to gas amount of energy needed to boil/vaporise water 540 calories what increases the boiling point of water adding solute what decreases the boiling point of water elevation due to less pressure being applied to water, easier for steam to leave what do pressure cookers do increase atmospheric pressure, increasing boiling point Functions of water heat transfer solvent Dispersions Food preservation Chemical Reactions 3 types of dispersions solution colloidal suspension solution homogenous mixture of a solute (being liquid, solid or gas) dissolved in a solvent (being liquid, solid or gas) eg. soft drink Colloidal dispersion particles are between 2nm and 1µm = too large to go into solution, but not large enough to precipitate out eg. jelly, gravy, custard, mayonnaise Suspension particles are larger than 1µm and remain suspended in continuous phase eg. cornstarch in water by removing water you are removing food for microorganisms Aw water activity water activity amount of available (free water) in food ranges from 0-1 what lowers water activity adding sugar & salt - water orientates around these molecules making it unavailable chemical formula of carbohydrate Cn(H20)n n can be from 2 to thousands where are carbohydrates primarily found green plants formed during photosynthesis 4 types of carbohydrates monosaccharides disaccharides oligosaccharides polysaccharides monosaccharides glucose fructose galactose ribose arabinose glucose found in blood found in its free form in fruit, honey and vege found in repeating units in starch and glycogen fructose fruit sugar found in fruit and honey used in soft drinks sweetest of all sugars not good for use in: candy = too sticky baked goods = overbrowning ice-cream = lower freezing point galactose seldom found alone in nature part of lactose forms galatonic acid which is component of pectin Ribose 5 carbon sugar component of nucleotides part of ATP & DNA Arainose forms structure of vegetable gums and fibre Disaccharides (2 monosaccharides) sucrose maltose lactose Sucrose common table sugar 1 glucose + 1 fructose Maltose malt sugar 1 glucose + 1 glucose Lactose milk sugar 1 glucose + 1 galactose 5% of milk content lactase breaks down lactose into monosaccharides glucose & galactose lactase deficiency lactose intolerance Oligosaccharides (3-10 monosaccharides) Raffinose Stachyose polysaccharides (many monosaccharides) Glycogen starch fibre (undigestible) Rafinose 3 monosaccharides galactose + glucose + fructose Stachyose 4 monosaccharides 2 galactose + 1 glucose + 1 fructose Oligosaccharide digestion not digested in small bowel, move to large intestine where they are fermented by bacteria which produce gas. oligosaccharide uses bulking agent in low kj diet food fat replacers in beverages starch amylose amylopectin increases ability to form a gel more amylose present in starch amylose straight glucose chain amylopectin branched glucose chain Fibre undigested portion of carbohydrate which remains after expose to digestive enzymes types of fibre cellulose hemicellulose pectic substances vege gums inulin lignin cellulose one of most abundant compounds on earth long chains of repeating glucose present in every plant cell wall unable to be broken down by human digestion hemicellulose mixture of monosaccharides broken down by baking soda pectic substances assist with gel formation protopectin, pectin & pectic acid found within and between cell walls of fruit & vege natural cementing agent vegetable gums used to thicken, gel, stabilise and emulsify help with body, texture, viscosity and mouthfeel inulin repeating fructose units with end glucose unit soluble fibre used by food industry lignin one fibre that is not a carbohydrate long chain of phenolic alcohols backbone of hemicellulose xylose mannose galactose side chains of hemicellulose arabinose glucuronic acid galactose protopectin and pectic acid found in unripe & overripe fruit vegetable gum sources plant - arabic, karaya, tragacanth seed - locust bean, guar seaweed - agar, alginates inulin sources asparagus, artichoke, garlic, chicory root starch functions thickener edible film sweetener carbohydrate functions sweetness solubility crystallisation odour moisture absorption texture fermentation preservation number of Amino acids 22 how many amino acids must be obtained form diet 9 complete protein from animal protein source incomplete protein from plant protein source protein complementation 2 incomplete proteins, each containing amino acids missing in the other are combined to make complete protein eg. rice has methionine and no lysine and beans have lysine and no methionine and should be eaten together amino acid structure carbon + amine + acid + hydrogen + R group primary protein structure amino acid sequence secondary protein structure chains fold to form alpha helix and beta sheets tertiary protein structure 3D folding of secondary structures into larger molecule quaternary protein structure multiple protein subunits protein functions hydration denaturation coagulation enzymatic browning maillard reaction buffering coagulation of proteins clotting/precipitation into a semi-solid, happens after denaturation as side groups are exposed and proteins are unfolded allowing more interactions denaturation of proteins with heat, pH extremes, alcohol & physical disturbance breaks bonds between amino acid side chains resulting in unfolding hydration of proteins proteins dissolve in and attract water they form gels eg. gluten must be hydrated Enzymes speed up chemical reactions used in cheese production - rennin meat tenderisation - papain colour of tea/coffee - polyphenol oxidase in baked products to improve flour quality and staling types of enzymes hydrolases - catalyse hydrolytic reactions lyases - break away small molecules form substrate transferases - transfer a group from one substrate to another ligases - catalyse bonding of molecules isomerases - transfer groups to yield isomeric forms Proteins as buffers acts as buffers as they are amphoteric (can act as acid or base) and can accept or donate H NH2 can accept H COOH can donate H isoelectric point point when protein charge is neutral Enzymatic Browning phenolic compound + oxygen = melanin (brown/black colour) eg. cut apple Maillard Reaction sugar + protein + heat = browning eg. toast fat solid at room temperature mainly from animal sources oil liquid at room temperature mainly from plant sources triglycerides 95% of lipids 1 glycerol + 3 fatty acids saturated fat carbon chain of fatty acid saturated with hydrogen no double bonds in meat, dairy, coconut, palm monounsaturated fat 1 double bond in carbon chain in olives, peanuts, avocado polyunsaturated fat 2+ double bonds in carbon chain in fish, vegetable oils what effects melt temperature carbon chain length number of double bond trans fats hydrogenation of bend carbon chain of unsaturated fat linked with increased CVD phosopholipids similar structure to triglyceride with 1 fatty acid replaced by phosphorus containing compound have hydrophobic & hydrophilic end sterols interconnected carbon rings important in human body animal sterol cholesterol plant sterol plant sterol esters lower LDL levels fat functions taste mouthfeel shortening power satiety heat transfer appearance texture heat transfer of fat some fat more suitable for frying than others depends on: cost flavour length of fatty acid chain smoke point smoke point temperature at which an oil begins to smoke dye to release of free glycerol, followed by breakdown of glycerol to acrolein avoid cooking what type of fat? omega 3 if temperature is too low when cooking with oil: increased fat absorption by food resulting in soggy food if temperature is too high when cooking with oil: fat deterioration & discolouration increased fat absorption by food due to increased viscosity of fat optimal temperature when cooking with fat 191°C / 375°F what should you not use to put out a fat fire water storage of fats & oils fats should be stored in the fridge oils should be stored at room temperature, away from sunlight rancidity deterioration of fat what causes rancidity exposure to oxygen exposure to heat and sunlight what prevents rancidity vitamin e sol colloidal dispersion of a solid in a liquid four basic building blocks of food (elements) carbon hydrogen oxygen nitrogen some other elements found in food calcium sulfur phosphorus iron zinc magnesium sodium chlorine some other molecules encountered in food alcohols vitamins plant pigments organic acids polyphenols some techniques applied to food in processing/storage Increasing temperature/adding heat Decreasing temperature/removing heat Adding acids or alkaline ingredients Mechanical/physical force eg. cutting, chopping, pounding, whisking, stirring Addition of water Removal of water what are changes that occur to food molecules through process Proteins - denature; break into smaller chains CHO - gelatinization; dissolve (sugar); crystallize; break into smaller chains Fats - melt; solidification; emulsification with water flame point temperature where streaks of fire come from surface of oil antioxidant compound that inhibits oxidation which can cause rancidity main antioxidant in fat is vitamin e cis bent chain with hydrogens branching on the opposite sides of each other trans bent chain is straightened by moving hydrogens to the same side trans-fat have detrimental health consequences acrolein fat reaches smoke point it begins to break down. 1st into glycerol and free fatty acids 2nd glycerol is further broken down into acrolein which has an unpleasant odour emulsion liquid dispersed in another liquid continuous phase the fluid phase of a colloid within which particles (disperse phase) are dispersed disperse phase the particle phase which is distributed within a fluid (continuous phase) emulsifier has water-loving (hydrophilic) and water-fearing (hydrophobic) properties and can disperse in water of oil interface a thin layer between different substances eg. when water and oil separate there is an interface between them surface tension unbalanced molecular cohesive forces at or near the surface, as a result of which the surface tends to contract and exhibit properties resembling those of a stretched elastic membrane. how is spreadability related to composition of fat? higher saturated fat = firmer spread unless there are additives, whipped with air margarine often easier to spread due to higher oil content - unsaturated fat when deep frying a coating provides: food keeps it's structure and integrity why is egg and flour used to coat before frying? eggs provides sticking agent increases browning provides flavour why would you choose to use a flavoured oil instead of a vegetable oil? to provide added flavour to items such as salad dressings why is mayonnaise potentially dangerous? contains raw eggs - risk of salmonella why is butter more calorie dense than margarine? butter is saturated fat, molecules are more tightly packed. margarine is unsaturated and whipped with air why does stir frying absorb less fat? high heat and short amount of cooking doesn't allow food to absorb as much oil why can't mayonnaise be made with butter would harden in fridge - not a true emulsion why is mayonnaise made with egg yolk not white? egg white is foamy and contains no fat which means it doesn't contribute to the emulsion how does sugar impact on gel formation? sugar competes for water, decreasing gelling rate how does acid affect gel? creates shorter chains, resulting in softer gel gelatinisation increase in volume, viscosity and translucency of starch granules when they are heated in liquid how does gelatin work? long thin protein strands of gelatin allow it to form a gel, these protein molecules are surrounded by water molecules form a network by creating cross-links (bonds) among themselves. the water is trapped within these protein strands. synersis weeping or extraction of liquid form a gel example: escape of liquid to the bottom of a meringue or pores filled with liquid within a meringue from underbeating beading tiny syrup droplets on surface of baked meringue results from undissolved sugar or overcooking (over-coagulation) component of egg white responsible for foam formation protein - albumen ferrous sulphide ring grey/green colour surrounding yolk of hard boiled egg when under the pressure of boiling hydrogen sulfide gas in the egg white reacts with the iron present in the yolk resulting in a ferrous sulfide (grey residue)