Animal foods include livestock and poultry meat, eggs, aquatic products and milk. Animal food is the main source of high-quality protein, lipids, fat-soluble vitamins, B vitamins and minerals. From the point of view of food, meat refers to all parts of warm-blooded animals that are suitable for human consumption. It includes not only the bones and muscles of animals, but also many edible organs and organs, such as heart, liver, kidney, stomach, intestine, spleen, lung, tongue, brain, blood, skin and bone. Livestock and poultry meat refers to the meat of livestock and poultry. The former refers to the muscles and viscera of pigs, cows, sheep, rabbits, horses, mules, donkeys, dogs, deer and camels and their products, while the latter includes the muscles and products of chickens, ducks, geese, turkeys, quails, ostriches and pigeons. Livestock and poultry meat has high nutritional value and strong satiety. Can be processed and cooked into various delicious dishes, and is a food with high edible value. I. Main nutritional components and composition characteristics of livestock and poultry meat (I) The water content in water muscle is about 75%, which exists in the form of bound water, inelastic water and free water. The bound water accounts for about 5% of the total water content of muscle, which is closely combined with the electrostatic attraction of protein molecular surface and polar groups to water molecules to form a water molecule layer. Immobile water accounts for about 80% of the total water content of muscle, and exists among myofibrils, myofibrils and muscle membranes in the state of immobile water. Free water accounts for about 15% of the total muscle water, which exists in the extracellular space and can flow freely. (2) The content of protein in the meat of livestock and poultry in protein is 10% ~ 20%, which varies with the species, age, fatness and position of animals. In livestock meat, the average protein content of pork is about 13.2%. Beef is as high as 20%; Mutton is between pork and beef; The protein content of rabbit meat, horse meat, venison meat and camel meat is also around 20%. Dog meat is about 17%. In poultry meat, the protein content of chicken is relatively high, about 20%; Duck meat is about16%; Goose meat is about18%; The protein content of quail is as high as 20%. The protein content of meat in different parts of animals varies greatly due to the degree of fatness and thinness. For example, the protein content of pork tenderloin is about 2 1%, the rear buttock tip is about 15%, the rib meat is about 10%, and the breast meat is only 8%. Protein content of beef tenderloin is about 22%, hind leg meat is about 20%, rib meat is about 18%, and front leg meat is about 16%. The protein content of sheep foreleg meat is about 20%, hind leg meat is about 18%, and loin breast meat is about 17%. Protein content of chicken breast is about 20%, and protein content of chicken wings is about 17%. Generally speaking, heart, liver, kidney and other internal organs have higher protein content and less fat content. The protein content of different viscera is also different. In different internal organs of domestic animals, the content of protein in liver is higher, and the eggs in heart and kidney are 14% ~ 17%. Protein content in poultry viscera is high, and protein content in liver and heart is 13% ~ 17%. Protein of livestock and poultry meat is completely protein, which contains all kinds of essential amino acids. The proportion of essential amino acids is close to the requirement of human body, which is easy to be fully utilized by human body and has high nutritional value. It belongs to high-quality protein. The skin and tendons of livestock and poultry are mainly composed of connective tissue. The protein content of connective tissue is 35% ~ 40%, and most of them are collagen and elastin. For example, pigskin contains 28% ~ 30% protein, of which 85% is collagen. Because collagen and elastin lack essential amino acids such as tryptophan and methionine, they are incomplete protein. Therefore, foods made of pigskin and tendon (such as puffed pigskin, pigskin jelly, tendon, etc. ) has low nutritional value and needs to be supplemented with other foods to supplement essential amino acids. Bone is a kind of hard connective tissue, in which protein content is about 20% and collagen accounts for a large proportion, which is an incomplete protein. Bone can be processed into bone paste and added to meat products, making full use of protein. The content of protein in the blood of livestock and poultry is about pig blood 12%, cow blood 13%, sheep blood 7%, chicken blood 8% and duck blood 8%. Protein in animal plasma contains eight essential amino acids and histidine, which has high nutritional value, and its lysine and tryptophan content is higher than that of flour, so it can be added to various foods and meals as protein fortifier. Blood cells can be used to make sausages, and their amino acid composition is similar to collagen. When hydrolyzed with collagenase, the same peptide as collagen hydrolysate can be obtained. (3) The fat content varies greatly with animal species, age, fatness and location, ranging from 2% to over 89%. Among livestock meat, pork has the highest fat content, followed by mutton and beef. For example, the fat content of pig lean meat is 6.2%, sheep lean meat is 3.9%, and beef lean meat is only 2.3%. The fat content of rabbit meat is also low, which is 2.2%. In poultry meat, the fat content of turkey and quail is low, below 3%; The fat content of chicken and pigeon is similar, ranging from 14% to 17%. The fat content of ducks and geese is about 20%. The fat composition of livestock meat is mainly saturated fatty acids, mainly composed of stearic acid, palmitic acid and oleic acid, with a high melting point. Poultry meat fat contains more linoleic acid, has a low melting point and is easy to digest and absorb. The cholesterol content in lean meat is low, about 70mg per 100g. Fat meat is about 90% higher than lean meat, and it is higher in viscera, generally about 3-5 times that of lean meat. The cholesterol content in brain is the highest, reaching more than 2000 mg per100g. The content and composition of essential fatty acids are an important aspect to measure the nutritional value of edible oil. Animal fat contains significantly less essential fatty acids than plant fat, so its nutritional value is lower than plant fat. Among animal fats, the content of essential fatty acids in poultry fat is higher than that in livestock fat; The essential fatty acid content of pig fat is higher than that of ruminants such as cattle and sheep. Generally speaking, the nutritional value of poultry fat is higher than that of livestock fat. (4) Carbohydrate The carbohydrate content is 1% ~ 3%, with an average of 1.5%, which mainly exists in muscle and liver in the form of glycogen. Animals were overtired before slaughter, the glycogen content decreased, and the storage time after slaughter was too long. In addition, due to the action of enzyme, glycogen content decreased, lactic acid increased correspondingly, and pH value decreased. (5) The mineral content is generally 0.8% ~ 1.2%. The content of lean meat is higher than that of fat meat, and the viscera is higher than that of lean meat. The iron content is about 5 mg/ 100 g, and pig liver is the most abundant. Iron in livestock and poultry meat mainly exists in the form of heme, which has high digestion and absorption rate. Viscera is also rich in zinc and selenium. The selenium content of bovine kidney and pig kidney is dozens of times that of other general foods. In addition, livestock meat also contains more phosphorus, sulfur, potassium, sodium, copper and so on. Although the content of calcium is not high, its absorption and utilization rate is high. The liver of poultry is rich in many minerals, and the average level is higher than that of poultry meat. The content of iron in liver and blood is very rich, as high as 10 ~ 30 mg/ 100 g, which is the best dietary source of iron. Birds' hearts and internal organs are also mineral-rich foods. (VI) Vitamins Livestock and poultry meat can provide a variety of vitamins, mainly B vitamins and vitamin A. The content of internal organs is more than that of muscles, and the liver is the most abundant, especially vitamin A and vitamin B2. The content of vitamin A in bovine liver and sheep liver is the highest, and the content of vitamin B2 in pig liver is the richest (Table 2-2- 1). There is also more vitamin E in poultry meat. (7) Extracts refer to water-soluble substances except protein, salts and vitamins, including nitrogen-containing extracts and nitrogen-free extracts. 1. Nitrogen-containing extracts Nitrogen-containing extracts are non-protein nitrogen-containing substances, accounting for 1.65% of muscle chemical components and 1 1% of total nitrogen-containing substances. They mostly exist in free state and are the main components of meat flavor. These substances can be divided into the following categories. (1) Nucleotide: adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), etc. (2) Guanidine compounds: including guanidine, methylguanidine, creatine and creatinine, in which the creatine content is relatively high. In addition to the above nitrogen-containing compounds, there are purines, free amino acids, carnitine, urea, amines and so on. 2. Nitrogen-free extract Nitrogen-free extract is a leachable organic compound containing no nitrogen, including sugars and organic acids, accounting for 65,438+0.2% of muscle chemical composition. There are few sugars in muscle, mainly glycogen, glucose, glucose -6- phosphate, fructose and ribose. Ribose is a component of nucleic acid in cells; Glucose is the energy source of muscle contraction; Glycogen is a polymer of glucose, which is the main form of sugar in muscle. However, after animal slaughter, muscle glycogen is gradually decomposed into glucose, and glycolysis produces lactic acid. The organic acids in muscle are mainly lactic acid produced by glycolysis, in addition to glycolic acid, succinic acid and a small amount of glycolysis intermediates. 2. Rational Utilization of Livestock and Poultry Meat protein has high nutritional value and contains a lot of lysine, so it should be eaten with cereals to give play to the complementary role of protein. In order to give full play to the nutritional function of livestock and poultry meat, we should also pay attention to dispersing livestock and poultry meat into every meal to prevent centralized consumption. Animal meat is high in fat and cholesterol, and fat is mainly composed of saturated fatty acids. Eating too much can easily lead to obesity and hyperlipidemia, so the proportion in the diet should not be too much. However, the fat of poultry meat contains more unsaturated fatty acids, so the elderly and patients with cardiovascular diseases should choose poultry meat. Viscera contains many vitamins, such as iron, zinc, selenium and calcium, especially liver, which is rich in vitamin B2 and vitamin A, so you should eat them regularly. 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