A new biological method for estimating food protein nutritive value

Abstract

I . A new method has been devised for the nutritional evaluation of food protein quality. The method is analogous to the classical determination of net protein utilization (NPU). The suggested new criterion, the protein utilization by the liver (LPU), expresses the amount of food nitrogen 'retained' in the liver as a percentage of the food nitrogen intake.2. Five different foods, casein, soya-bean protein isolate, maize gluten, wheat gluten, cottonseed meal alone or with supplements of amino acids, a total of thirteen samples, were tested for LPU and NPU in groups of six rats. The correlation coefficient between values for LPU and NPU for all seventy-eight rats was + 0.85 and was highly significant.Many detailed reviews of conventional methods of protein evaluation are found in the literature (Allison, 1949(Allison, ,1959(Allison, ,1964 Frost, 1959;Rippon, 1959;Campbell, 1963 (Allison, 1964) showed that the susceptibility of different organs to changes in the quality of nutritional proteins is in the order: blood > liver > muscle > kidney > brain. Guggenheim (1964) tried to use as criterion average daily gain of liver N which he expected to be correlated with dietary protein quality, but it did not fulfil expectations.Henry, Kosterlitz & Quenouille (1953) described a liver N method based on gain in liver N per I O O g initial body-weight. The correlation with N balance methods was generally good, provided the nutritive value of the protein was not greater than that of casein; with this method the variance was large and dependent on the length of the experiment (Henry, Cormack & Kosterlitz, 1961).The objective of this paper is to propose a new short method for protein evaluation, protein utilization by the liver (LPU), based on estimation of the changes in N content of the liver in relation to the N consumption; the method introduces a control group to account for N consumption for maintenance. 1967).* E X P E R I M E N T A L Materials and methodsWeanling rats of the Charles River C.D. strain were divided into groups of six, three males and three females, each group having the same average weight. The rats were kept in individual cages in an air-conditioned room (24O, 50-60% relative humidity) for 10 days.The diets, designed according to the Association of Official Agricultural Chemists (1965), contained 10% protein and were offered ad lib. Water intake was unrestricted.The proteins studied were: vitamin-free casein--goyo protein (N x 6-3); commer- All diets tested contained either these proteins alone or supplemented with the respective limiting amino acid or acids. Those animals not receiving diets supplemented with essential amino acids received a mixture of non-essential amino acids (DL-alanine 12 yo, L-glutamine 54.5 yo, glycine 12%, L-proline 10-5 yo, DL-serine I I yo)to compensate for the addition of the essential amino acids. The control groups were given protein-free diets.At the end of the experimental periods the rats were weighed and killed, their livers removed and weighed and food consumption was ...

Methods of Protein Digestive Stability Assay - State of the Art

“…A variation of these methods suggests the determination not of the animal weight, but rather of amount of a specific tissue (liver, muscle, etc. ), laid down while feeding on a test protein (Bender 1958;Mokady et al 1969). These include protein retention efficiency and liver protein utilization.…”