Biological evaluation of proteins: a new aspect

Abstract

The growth method of comparing the nutritive value of proteins, namely the estimation of protein efficiency ratio (P.E.R.) has long been popular because of its simplicity despite its well-known drawbacks (Mitchell, 1944).Among the more serious disadvantages of this method are: (a) no allowance is made for maintenance requirements of the test animal, (6) the result varies with food intake, and (c) the assumption that the gain in body-weight is indicative of the protein tissue laid down is not always valid.A modification is described whereby a control group of animals fed on a protein-free diet is included in the experiment, and the difference between the weights of this group and the test group is used in the calculation instead of merely weight gain. This procedure allows for maintenance requirements and also permits the evaluation of poor proteins which do not promote growth (and of which, consequently, P.E.R. cannot be measured). The results obtained are independent of food intake. T h e third criticism mentioned above is shown to be of minor significance under our experimental conditions. EXPERIMENTAL Animals and diets. The rats and diets and amino-acid mixtures were as described previously (Bender, 1956).Body water. The whole carcasses, without evisceration or cleaning of the gut, were dried to constant weight in a hot air oven at 1 0 5~.

Protein Evaluation of Foods

“…Bender and Doell (1957) pointed out that gain in body weight is constant in composition is not valid. They argued further that the result may vary with the level of protein in the diet, and that the results are influenced by food intake.…”

“…However weight loss of the rat fed a non protein diet id equivalent to the protein needed for maintenance. In an argument put forward by Mclaughlan and Keith (1975) to criticize the slope ratio method of Bender and Doell (1957), they assumed a straight line relationship involving the weight loss of the non-protein group of rats proposed by Bender and Doell (1957), and other levels of dietary protein. The results of the slope-ratio method, otherwise known as the net protein retention value (NPR), at any point of the curve, remained constant, while on the other hand the protein efficiency ratio varied along the curve.…”

“…Another modified assay also known as the slope ratio method, which is an extension of the previous method of Bender and Doell (1957), was put forward by Hegsted and Chang (1957) to avoid problems resulting from non-linear response. This slope-ratio assay is a multiple dose (protein level) method, which they termed relative nutritive value (RNV).…”

“…The method ascribes a value of zero to protein that do not that permit growth. To correct the dependence of protein efficiency ratio on food intake Bender and Doell (1957) proposed the use of a slope ratio method whereby weight loss of a control group of animals given a protein free diet as well as the weight gain of the test group are considered. This slope-ratio method was put forward in an attempt to overcome some of the problems in the protein efficiency ratio.…”

Impacto de la dieta sobre la inducción de infección con quistes de Giardia lamblia en ratas Sprague-Dawley

“…A cada una de las dietas preparadas se les analizó el contenido de humedad y de proteína, siguiendo los métodos descritos por el AOAC. 14 …”