Nutritive value of mixed proteins

Abstract

I.A fish meal, meat meal, soya-bean meal, groundnut meal and sunflower-seed meal of known amino acid composition were evaluated individually, and combined in all possible pairs, by the estimation of net protein utilization (NPU) and protein efficiency ratio (bodyweight gain:crude protein intake; PER) using rats. Each pair provided a total of 100 g protein/ kg diet made up so that the amounts of the constituents were (wlw) IOO:~, 80:20, 60:40, 20:So and 0 : 100. .Marked synergistic effects were noted only for mixtures of sunflower-seed meal with soya-bean, fish and meat meals.3. Chemical score ([amount of limiting amino acid/the rat's requirement for the same amino acid] x 100; CS), but not essential amino acid index; geometric mean for the ratio, amount of essential amino acid: the rat's requirement for that amino acid, for all ten essential amino acids ; EAAI), successfully predicted the rankings of all mixtures except groundnut meal-meat meal and groundnut meal-soya-bean meal, by both PER and NPU tests.4. Although there is broad agreement linking results of PER and NPU tests with results obtained by a more practical feeding trial in which the mixtures were evaluated as supplements to cereals, neither of these two standard tests is capable of predicting in every instance the advantages to be gained by mixing protein concentrates.An attempt has been made to relate the amino acid composition to the nutritive value for chicks of cereal-based diets containing pairs of protein concentrates com- amino acidlthe chick's requirement for the same amino acid] x 100; CS), frequently acted as a useful predictor of protein quality there were a number of instances in which it failed to do so, and this failure was attributed to short-comings in over-all amino acid balance in the diets concerned. The chick growth test used, total protein efficiency (g weight gain/g protein consumed; TPE), is a measure of the supplementary value of the protein concentrate, and further evaluations were carried out with similar mixtures to those used in the second part of the study described previously (Woodham & Deans, 1977), and using rat tests in which the mixed proteins were given alone, as the only protein sources. These standard tests were the protein efficiency ratio (body-weight gain:crude protein intake; PER) and the estimation of net protein utilization (NPU). METHODSPER. Male rats of the Rowett Hooded Lister strain, aged 19-21 d, were used. T h e technique was that described as the official method of the Association of Official Agricultural Chemists (Derse, 1960(Derse, , 1962(Derse, , 1965. Each diet was given to ten indivi-* Paper no. I : Br.