CHEMICALS THAT MAKE UP PROTEINS Carbon Hydrogen Oxygen Phosphorus Nitrogen SulphurFunctions Growth and Maintenance Energy – 1g of pure protein provides 17KJ (4kcal) Formation of enzymes, antibodies and some hormones (thyroxin)
SOURCES OF PROTEINS Milk and Cheese (HBV) Meat and Fish (HBV) Eggs (HBV) Bread and Cereals (LBV) Vegetables (LBV) Nuts (LBV)
PROTEIN DEFICIENCY KwashiorkorCommon in children after weaningLow protein and high carbohydrate diet SymptomsStunted Growth, Muscle Wasting, Bloated abdomen, Oedema (fluid in tissues causes swelling), causes Anaemia. TreatmentA balanced diet – more vitamins and minerals for PEM (protein – energy malnutrition). Lowers risk of getting disease due to fertilisers.
CHEMICAL STRUCTURE Proteins are large molecules and are built up of long chains of units called AMINO ACIDS There are over 80 amino acids but only around 20 are found in food protein.Structure Acidic Part Alkaline Part
CHEMICAL STRUCTURE Amino acids are Amphoteric because each amino acid contains at least one amino group (NH2) and one acidic group (COOH) which display both base (alkaline) and acidic properties. 500 amino acids make a protein molecule A peptide link is formed when the amino group of one amino acid reacts with the acidic group of an adjacent amino acid. Condensation Polymerisation is when a molecule of water is eliminated during the formation of the peptide link. When TWO amino acids join together they form a Dipeptide. When long chains of amino acids join together they form a Polypeptide.
THE BIOLOGICAL VALUE OF PROTEIN Biological Value of protein is used as a measure of protein quality. Foods that contain all essential amino acids are of better quality than foods that do not. High Biological Value foods (HBV) are: Meat, Fish, Eggs, Milk and Cheese. Low Biological Value foods (LBV) are: Bread, Cereals, Nuts and Pulses. Complementation foods are proteins containing different essential amino acids (i.e. HBV and LBV foods) are eaten together e.g.Beans on toast Bread and CheeseRice Pudding Macaroni Cheese
DENATURATION AND COAGULATION DenaturationWhen the physical structure of the protein is altered in an irreversible way.The protein becomes less soluble and more viscous e.g. whisking egg whites CoagulationThe hardening or setting of a protein e.g. frying an egg
DENATURATION CAN BE BROUGHT BY VARIOUSMEANS: Action of HeatMany proteins coagulate when heated e.g. eggEgg white coagulates at 60 C and egg yolk coagulates at 66 CDenatured proteins are readily attacked by digestive enzymes to make the food more digestible. Presence of AcidMilk sours due to bacteria present in milk which ferment lactose, producing lactic acid.The pH of milk lowers causing the milk protein to coagulate.
DENATURATION CAN BE BROUGHT BY VARIOUSMEANS: Addition of SaltSodium Chloride coagulates some proteinsIn cheese making, salt is added to curd to increase firmness and suppress growth of micro-organisms.If salt is added to cooking water used for boiling eggs, the white will not escape as readily if the shell is cracked. Addition of Rennina.k.a. Rennet – an enzyme which coagulate protein and use to make Junket which clots/ coagulates milk.Rennin is also used together with a bacterial starter culture to form a curd in cheese manufacture.
DENATURATION CAN BE BROUGHT BY VARIOUSMEANS: Mechanical ActionDuring whisking of egg white causes a partial coagulation of protein.Protein molecules unfold and form a reinforcing network round the air bubbles – this stabilises the foam.Used in food production e.g. meringues and soufflés.
MAILLARD REACTION A.K.A. Non-enzymic browningIt is a browning reaction which occurs during roasting, baking, grilling and frying of many foods.A chemical reaction takes place between:The amino group of a free amino acidA free amino group on a protein chainThe carbonyl group of a reducing sugar e.g. glucose.