Protein Notes - STKM 1012 - PDF

STKM 1012 BASIC FOOD SCIENCE AND NUTRITION PROTEIN NOORUL SYUHADA Department of Food Sciences Faculty of Science and Technology UKM Protein is one of the major components of body tissues and an essential nutrient for growth. P...

STKM 1012 BASIC FOOD SCIENCE AND NUTRITION PROTEIN NOORUL SYUHADA Department of Food Sciences Faculty of Science and Technology UKM Protein is one of the major components of body tissues and an essential nutrient for growth. Proteins constitute approx. 16% of the body weight. Protein is available from a variety of foods and ample in the Malaysian diet. Protein is made up of amino acids (building block – subunit) joined together by peptide bonds  Amino Acid Basic elements: carbon (C), hydrogen (H), oxygen (O) and nitrogen (N) Chemically build up of amino acid (AA) Carboxyl group (COOH) - acidic Hydrogen atom (H) Amino group (NH2) - base Side chain (R) Two types amino acid: 1. Essential amino acid (EAA) = – cannot be synthesized by the body, obtain from diet 2. Non-essential amino acid (NEAA) – can be synthesized by the body Types of amino acids Essential Non-essential Histidine Alanine Isoleucine Arginine Leucine Asparagine Lysine Aspartic acid Methionine Cysteine Phenylalanine Glutamic acid Threonine Glutamine Tryptophan Glycine Valine Proline Serine Tyrosine Hydrogen bonding Amino acids are the building blocks for proteins, joined together by peptide bonds between the carboxyl and the amino group of the next amino acid in line.  FOUR Protein Structure Bethe Alphait t 00  Primary structure of protein synthesis hydrolysis Peptide bond Amino acid Amino acid  Secondary structure of proteins Non-linear - - - Amino acid linked either in alpha-helix or beta- sheet configuration within a polypeptide  Coiled in spring-like, stabilized by formation of hydrogen orG disulphide bonds Amino acid  Tertiary structure of proteins tod Protein tertiary structure is the three- dimensional shape of a protein. The tertiary structure will have a single - polypeptide chain "backbone" with one or more protein secondary structures. Amino acid side chains may interact and bond in a number of ways.  Quaternary structure of proteins The quaternary structure of a protein is the=> association of several protein chains or subunits into a closely - packed arrangement. oc Each of the subunits has its own primary, secondary, 6 and tertiary structure.  helnerdrogen ne by pond The subunits are held together by hydrogen bonds - and van der Waals forces between nonpolar side chains. Eg:CGlobular in shape (albumin & milk casein), or fibrous (collagen)  PROTEIN SHAPE soluble - Globular proteins - & - Fibrous proteins - ↓ givnature  era PROTEIN SHAPE: sombre- Globular Proteins I folded Rounded in shape (spherical) Soluble in water The chains are usually folded so that hydrophobic groups are on the inside, while the hydrophilic~ groups are on the outside. This makes many globular proteins soluble in water.  The water molecules could penetrate easily within the proteins due to: Not closely packed No organised arrangement Easily dispersed in water / salt solutions to form COLLOIDS ~ Examples: Ovalbumin – egg white - Caseinogen – milk - Haemoglobin - myoglobin - Quantumany PROTEIN SHAPE: - Fibrous Proteins - Elongated – twisted like a rope They are straighter (inelastic proteins) or coiled in a spiral (elastic proteins) GenerallyG insoluble Molecules are closely packed and organised arrangement  Insoluble in water Not greatly affected by acids, alkalis or moderate heat Example: Gluten – wheat Elastin – connective tissue in meat Keratin – hair and wool  C G gluten  PROTEIN CLASSIFICATION Complete Protein Protein with all essential AA (at the right ratio and - quantity) O Sources are mainly from animals: eggs, milk, cheese and meats Incomplete Protein Proteins without one or more essential AA Mostly from plants: cereal, nuts, legumes, seeds  FUNCTIONS OF PROTEINS 1. Primary roles for proteins in the body include being structural proteins, enzymes, hormones, transport proteins and immunoproteins. 2. Growth, building and maintenance of tissues  Supply of EAA in suitable ratio and quantity for synthesizing protein  Maintenance of body tissues is essential because the body is constantly undergoing wear and tear, and proteins and amino acids provide continuous repairs 3. Specific physiology functions Methionine – important to form choline, precursor of > acetylcholine (a neurotransmitter in brain) - Tryptophan – precursor of vitamin B (niacin) Phenylalanine – precursor of tyrosine (hormone) Antibody – immunity system defenda a Protein * 4. Proteins defend the body against diseases. - When the body detects invading antigens, it manufactures antibodies, which are large protein molecules designed specifically to combat them. - 5. Energy 8  Supply of 4kcal/g energy  Around 50% of total protein from diet can be used as fuel for energy Factors affecting protein needs 1. Growth level (Age) More protein is needed during growth period Babies, infant, children Pregnant women (~ 70 to 100 g protein per day). 2. Diet Type of protein consumed –complete or not Sparing effect must be enough Digestibility and absorption of protein is influenced by preparation and cooking. 3. Diseases Health problems will increase protein need Higher body temperature will increase the metabolic rate and tissues damage Extensive tissues building up is required Protein requirement measurement # 1) Protein Quantity The methods used as basis for estimating protein requirements are Factorial method and Nitrogen (N) balance method - Considering protein required for maintenance and growth (maintenance of 0.66 g/kg body weight/day and a protein efficiency utilisation of 58%). 4-  Factorial method Nitrogen-balance technique  Determine the difference  Calculate protein requirements for physiological condition such as between the intake of nitrogen growth, pregnancy or lactation, in and the amount excreted in which nitrogen is not only needed urine, faeces and sweat, for maintenance but also for the together with minor losses by deposition of protein in newly other routes. formed tissue or secretions (milk). Status Seen in Zero Healthy adult nitrogen f https://academic.oup.com/jn/article/128/12/ balance 2609S/4724458 Positive - When new tissue is being built, nitrogen as in infancy and childhood -- balance - pregnancy and lactation - - Negative - infection or traumatic injury -- nitrogen - under-nutrition when protein balance intake is too low or is of poor quality Recommended Nutrient Intake (RNI) for Malaysia g / 2) Protein quality Protein quality refers to how well or poorly a given - protein can be absorbed from a diet and utilised by the body. - Specifically, it refers to how well the essential amino acid profile of a protein satisfies their functions in the body, as well as the digestibility of the protein and bioavailability of the amino acids. The common methods of evaluating protein quality: 1. Biological value 2. Protein efficiency ratio 3. Chemical score of protein 4. Protein digestibility 5. Protein digestibility corrected amino acid score (PDCASS) 6. Digestible indispensable amino acid score (DIAAS).  > How - 1. Biological value (BV) Afficienoa - measure on how efficiently food protein being absorbed from the gastrointestinal tract and can be turned into body tissues. - BV calculated by dividing the amount of nitrogen retained for the body’s use by the nitrogen absorbed from food and multiplied by 100 (expressed as % of nitrogen utilized). 2. Protein efficiency ratio - Protein efficiency ratio (PER) is another means of measuring a food’s protein quality. - The PER of a food reflects its biological value, since both basically measure protein retention by body tissues. - Plant proteins, because of their incomplete nature, generally yield lower PER values, whereas the values for animal proteins are higher, often above 2.0. 3. Chemical score of protein - Chemical score estimates the protein quality of a food. - The amount of each essential amino acid provided by a gram of the food protein is divided by an “ideal” amount for that amino acid per gram of food protein. - The lowest amino acid ratio calculated for any essential amino acid is the chemical score. - Scores vary from 0 to 1.0. 4. Protein digestibility - The degree to which a protein is digested influences its nutritional value. - Animal proteins are digested more efficiently than = plant proteins. - This is because digestive enzymes have greater difficulty entering plant cells, which are surrounded by cellulose and woody substances. if it's broken well , can Yield small of protein particle - The method of cooking also affects digestibility. i. Heat alters the structure but not the amino acid content of protein molecules. ii. Over-heating, however, may destroy some amino acids or may cause the formation of products resistant to digestive enzymes. iii. Cooking with water improves the digestibility of wheat and rice proteins. - The digestibility of protein is normally expressed in relation to that of egg, milk, meat or fish, which are used as reference proteins (digestibility = 100). 5. Protein Digestibility Corrected Amino Acid Score (PDCAAS) - Widely used measure of protein quality - This is used in place of Protein Efficiency Ratio (PER) evaluations for foods intended for children over 1 year of age and for non-pregnant adults. - To calculate the PDCAAS of a protein, its chemical score is determined. - For e.g. wheat has a chemical score of 0.47. The score is then multiplied by the digestibility of the protein (generally, 0.9 to 1.0), in turn yielding the PDCAAS. - The maximum PDCAAS value is 1.0, which is the value of milk, eggs, and soy protein. 6. Digestible Indispensable Amino Acid Score (DIAAS) - DIAAS determines amino acid digestibility at the end of the small intestine, which provides a more precise estimate of the amounts of amino acids absorbed by the body and the contribution of protein to human amino acid and nitrogen requirements.  lack of protein Protein Deficiency Protein-energy malnutrition Non developing countries – poverty and tradition in distribution of food in the family Caused death to children under 5 years. Kwashiorkor Marasmus Shortage of calorie and Shortage of protein quality and quantity protein Semi starved But enough calorie Thin, diarrhea, Symptom: dehydrated Edema Thin, weak muscles Pigmentation – hair and skin