To know the functions, sources & biological value of protein (4.2a,c) Year 13 Proteins (p13-15) Aims To know the functions, sources & biological value of protein (4.2a,c) To understand the role of protein as part of a well balanced diet (4.2a) To be able to make a high quality Sponge Fruit Flan (4.4 b eggs, 4.4 c whisking)

Concept of nutrition Balanced diet DRV EAR RNI GDA Malnutrition Key terms Concept of nutrition Balanced diet DRV EAR RNI GDA Malnutrition

Key terms Concept of nutrition – nutrition is the study of the nutrients in food, how the body uses nutrients & the relationship between diet, health & disease’. (now also includes wider social issues and impact on food consumption) Balanced diet – A diet that contains all the nutrients in the correct proportions to meet a person’s needs. Affected by: Age, Gender, Body build, State of health DRV – Dietary reference values EAR – Estimated average requirement RNI – Reference nutrient intake RI – Reference intake (replaced GDA) Malnutrition – a deficiency, excess or imbalance of nutrients that causes adverse effects on health & wellbeing

Proteins Essential in human diet Only nutrient supplying NITROGEN Nitrogen vital for cell formation & growth Built from AMINO ACIDS Molecules containing an amine group (NH2) & an acid group (COOH) CARBON HYDROGEN OXYGEN + NITROGEN Some contain sulphur & phosphorous (CHONPS) 20 different amino acids Joined in various combinations (like building blocks)

Structure of Amino Acids All same structure H R C COOH (carboxyl group weakly acidic) NH2 (amino group Varies between one amino acid & another

Amino Acids Have ability to link together Form PROTEIN CHAINS One AMINO ACID reacts with ACIDIC CARBOXYL GROUP of next Water is eliminated Link that occurs between AAs = PEPTIDE LINK (CONH) Long chains that form = POLYPEPTIDE CHAINS

R R O H 0 NH2 C C N C C H OH H H OH H2O CONDENSATION = WATER REMOVED Polypeptide Chains R R O H 0 NH2 C C N C C H OH H H OH H2O CONDENSATION = WATER REMOVED H2O Added = Hydrolysis

Reverse Action Called Hydrolysis One molecule of water added Causes protein to break into AMINO ACIDS Happens during digestion

Protein Molecules Consist of several adjacent polypeptide chains Can be FOLDED,COILED OR CROSS LINKED at intervals Simple protein = insulin (pancreatic hormone) = 50 amino acids Complicated protein = haemoglobin = 500 amino acids

1. Globular Proteins – proteins consisting of coiled chain Structure of Proteins 3 types 1. Globular Proteins – proteins consisting of coiled chain - water soluble - easily denatured - e.g. ALBUMEN & GLOBULIN - occur in milk & egg white

Structure of Proteins 2. Fibrous Proteins – polypeptide chains twisted into springs - like coils & zig zags - elastic property - e.g. ELASTIN (protein in meat tendons) - GLUTEN (protein in flour) - zig zag structure produces tough non elastic protein - eg COLLAGEN found in connective tissue

Structure of Proteins protein - e.g. PIGMENT 3. Conjugated proteins – chemically combined with a non protein - e.g. PIGMENT PIGMENT + PROTEIN = HAEMOGLOBIN - classed according to non protein group e.g. PHOSPHOPROTEINS – contain phosphate groups such as CASEIN in milk Cross links joining polypeptide chains can be H bonds, salt links & most importantly DISULPHIDE links – give great toughness & steady shape e.g. GLUTEN in flour

Denaturisation When protein molecules UNTWIST Causes loss of structure & function IRREVERSIBLE Caused by 1. Heat – most frequent cause. - especially albumen in eggs - causes linking bonds to break - protein loses H2O binding power - considerable shrinkage Protein coagulates - molecules packed more tightly which causes –skin to form on milk Custard to curdle or egg white to harden If heat applied slowly & not raised above 60ºF curdling should not occur

Denaturisation 2. Mechanical action – e.g. whipping, shaking - when egg white is whisked breaks cross links & denatures. 3. Some Chemicals ACIDS – lemon juice added to milk – lactic acid formed When milk is sour may bring about coagulation of milk protein ALCOHOL & VINEGAR – preservative effect on food – denature enzymes which cause destruction of food.

Essential Amino Acids Body can manufacture some Amino Acids 8 which it can’t = ESSENTIAL AMINO ACIDS Further 2 are required by growing children Protein needed for growth and repair Also secondary energy source

Biological Value Proteins Tells us how nourishing a protein is 2 types HIGH BIOLOGICAL VALUE e.g. meat, eggs, cheese, fish. Contain all essential amino acids in proportion required by human body Most of nitrogen available for growth & repair Eggs have highest B.V 100%, Milk 95%, Meat & fish 80 – 90% LOW BIOLOGICAL VALUE – deficient in one or more essential amino acid Usually from vegetable sources e.g. beans, bread, nuts, peas (fresh & processed), whole cereals SUPPLEMENTARY VALUE (complimentary) When mixed together e.g. beans on toast, hummus & pitta bread, Dahl & chapati – biological value increased Individually beans & bread LBV but eaten together provide HBV BIOLOGICAL VALUE = % ABSORBED PROTEIN that is converted to body protein

Homework Protein test – Friday 8th July Monday 27th – Scotch eggs, mayonnaise & coleslaw