Info about Agriculture

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Occurrence in Foods and Nutritional Implications

All animal foods, such as meat, fish, milk, and eggs, are protein-rich, whereas most plant foods are not. Leguminous seeds, like beans and nuts, where protein and lysine are high, are an exception. These proteins, however, are deficient in the sulfur-containing amino acids, particularly methionine. The proteins found in cereal grains (seeds of maize grain, rice, sorghum), in turn, are deficient in lysine and tryptophan, but not so in methionine. Leafy vegetables are somewhat richer than root vegetables, whereas fruits are very low in protein. The proteins of seeds of pseudocereals like quinoa (Chenopodium quinoa Willd.) and maranthus grain (Amaranthus sp.) have amino acid profiles that combine the characteristics of both legumes and cereals. Humans can synthesize only 10 of the 20 amino acids required for protein synthesis. They must obtain the rest from their diet if they are to remain healthy.


Interestingly, the metabolisms of children and adults are slightly different. The growing child has a greater requirement for arginine and histidine than the adult, whereas adults synthesize sufficient arginine for their daily requirement. Consistent with food composition data, proteins rather than free amino acids are the main source of dietary nitrogen. Some special diets, however, require the use of predigested proteins or free amino acids. About 75% of amino acid metabolism in normal healthy adults is devoted to protein synthesis. This protein is essential for normal growth, repair, and defense, including the production of active enzymes, plasma protein, muscle creatine and, in females, reproduction and synthesis of milk proteins. The remaining 25% of nitrogen metabolism produces intermediates of the tricarboxylic acid (TCA) cycle, hormones, and neurotransmitters.