Dr. Elsaid A. Eldaly Prof. Prof. of Meat Hygiene Food control Dept. Faculty of Veterinary Medicine Zagazig University 9/28/2013
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Chemical Composition and nutritional value of meat The proximate composition of a typical, adult mammalian muscle postmortem, after the onset of rigormortis, but before degradative changes commence, is 75% water, 19% protein, 2.5% lipids, 1.2% carbohydrate and 2.3% of miscellaneous non-protein substances (Table 1) 9/28/2013
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Table (1)Chemical composition of typical adult mammalians muscle after rigor mortis but before degradative changes post-mortem Components Wet% weight 1.Water --------------------------------------- 75.0 2. Protein --------------------------------------19.0 (a)Myofibrillar 11.5 *Myosin *Actin *connectin (titin) *N2 line protein (nebulin) * tropomyosins *troponins, C, I and T * α, β and γ actinins * myomesin, (M-line protein) and C-proteins *desmin, filamin, F-and I-proteins, etc. 9/28/2013 ٣
(b) Sarcoplasmic 5.5 *glyceraldehyde phosphate dehydrogenas *aldolase * creatine kinase * other glycolytic enzymes * myoglobin *haemoglobin and other unspecified extracellular proteins (c) Connective tissue and organelle 2.0 *collagen * elastin *mitochondrial etc. (including cytochrome c and insoluble enzymes 9/28/2013
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3. Lipid 2.5 4. Carbohydrate 1.2 *lactic acid * glucose-6-phosphate * Glycogen *glucose, traces of other glycolytic intermediates 5. Misellaneous soluble non-protein substances 2.3 a.Nitrogenous 1.65 *Creatinine *inosine monophosphate *di-and tri-phosphopyridine nucleotides *amino acids * carnosine, anserine (b) Inorganic 0.65 total soluble phosphorus Potassium,sodium ,magnesium,calcium, zinc, 9/28/2013 trace metals
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6. Vitamins: various fat-and water soluble vitamins, quantitatively minute ________________________________________________
1- Muscle or meat proteins Muscle or meat proteins can be divided into three different fractions on the basis of function and solubility (i) Sarcoplasmic or water-soluble (ii) Myofibrillar or salt soluble- and (iii) Connective tissue 9/28/2013
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(i) Sarcoplasmic proteins: The sarcoplasmic fraction consists of those proteins found in the sarcoplasm, or the fluid surrounding and bathing myofibrills. Sarcoplasmic proteins are often referred to as water-soluble proteins, because they are commonly extracted with water
ii) Myofibrillar protein: Myofibrillar proteins are also known as contractile proteins, they play a main role in muscle contraction and locomotion in the living animals
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The principale proteins in the myofibrillar fraction include myosin, actin (75-80% of myofibrillar proteins) and the combination form of actomyosin. In addition, the myofibrillar fraction includes tropomyosin (8-10%), troponin(8-10%), the actinins ( and forms 2-2.5% of each) and other minor regulatory proteins. The myofibrillar or so called salt-soluble proteins are commonly extracted with potassium chlorid, usually at an ionic 9/28/2013 ٨ strength (0.3).
(iii) Connective tissue proteins This fraction includes two distinctly different proteins, collagen and elastin, and also another, reticulin, which is less well-defined than the former two (a) Collagen: It is the principle component of the connective tissue fraction. It is found widely distributed in the body and comprises 20-25% of the total protein. It is the principle protein in bone, tendon, and skin. With prolonged heat treatment the temperature converts collagen to 9/28/2013 soluble gelatin.
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(b) Elastin: It is a minor component of most tissues but is found in appreciable amounts in the ligaments of the vertebrae and in the walls of large arteries. It has a yellow appearance and fluorescence as bluish white fibers under ultraviolet light.
(c) Reticulin The third recognized protein component of connective tissue is reticulin. It is chemically very similar to collagen. 9/28/2013 ŮĄŮ
2- The lipids of meat Lipids in meat are of three discrete types: subcutaneous, intermuscular and intramuscular The lipids are mostly composed of triglycerides (70%) which are fats and oils, both of which are water-insoluble but soluble in ethyl ether. The lipids also includes phospholipids, saturated and unsaturated fatty acids and other fatsoluble substances, including cholesterol. 9/28/2013 ŮĄŮĄ
3- Carbohydrate Carbohydrate is represented mainly by glycogen (animal starch about 0.5-1.3%) which has a major influence on muscle changes after slaughter. Most of it is converted by glycolysis into lactic acid which causes the pH of the meat to drop from approximately 7.2 to 5.5. 4- Non-protein nitrogen: 5- Minerals: 6- Vitamins :The vitamins can be classified as fatsoluble and water-soluble. The fat-soluble group includes A, D, E and K; the water soluble group contains the B-complex vitamins and vitamin C. Generally, meat is an excellent source of B complex vitamins and is poor in the fat-soluble group 9/28/2013 and vitamin C (ascorbic acid). ٥٢
II. Nutritional value of meat: The biological value of meat protein is 0.75 (human milk = 1.0, wheat protein = 0.50) and the net protein utilization is( 80) (egg = 100, wheat flour=52). The digestibility of
meat protein, like that of milk and egg is 94-97, compared with 78-88 for plant protein. The cholesterol and saturated fatty acid content of meat have both been associated with predisposition to heart disease. The cholesterol content of ca 65-75
mg/100g (lean muscle) is not excessively high, although consumption of large quantities of meat obviously leads to a high total intake. Cholesterol content of kidney (ca. 400 mg/100g) brain (2000 mg/100g) and liver (ca. 430 mg/100g) is significantly higher than that of the meat itself. Degree of saturation varies with species, beef and mutton fat are more saturated than pork fat, which in turn is far more 9/28/2013 saturated than poultry fat.
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