Analysis for availability of amino acid supplements in foods and feeds: biochemical and nutritional implications.

Abstract

In formulated diets based on cereal grains, lysine and/or methionine are usually deficient as well as often being the first amino acids limiting the nutritional value of such diets. Deficiency of these two amino acids in nutritional practice is compensated by synthetic L-lysine and DL-methionine supplementation or by the introduction of various protein sources - rich in lysine and methionine. Among all essential amino acids lysine is most liable and subject to damage during the processing of foods and feeds which can cause the "deepening" of the lysine deficiency not on the total but on the physiologically-available lysine basis. Hence, the simultaneous lysine deficiency and biological "sufficiency" problem is discussed using examples of practical diets in which a balance of biologically-active substances was achieved by the formulation and optimalisation according to the needs of animals, taking into account physiological lysine "accessibility" - "availability". Growth rate, nitrogen balance data and chemical composition of the tissue in long term trials are the most valid indication justifying the quantity of amino acid supplements to the practical diets. Prediction of the practical results of dietary amino acid balance from various short-term chemical and biological tests can give misleading results. Their application in nutritional practice is restricted to particular types of foods/feeds, and to specific processing systems and test conditions. Observations of the appearances of most limiting, dietary amino acids in the blood after the meal do not provide a complete nutritional characteristics of practical rations due to complex regulatory mechanisms in protein and amino acid metabolism much of which are not yet fully understood.