Nutritional evaluation, using rats, of diets based on cereals and ethanol-grown yeast

Abstract

Six experiments on growing rats were conducted to measure the nutritive value of diets based on cereals (wheat and barley, 1:1) and ethanol-grown yeast. Optimum protein provision in isonitrogenous diets (11.3% crude protein) determined on the basis of live weight gain, feed efficiency and protein efficiency ratio was found to be 60 and 40% for cereal and yeast protein, respectively, corresponding to a diet containing 84.5% cereals and 13.2% yeast (Experiments 1 and 2). The addition of single amino acids ( l-lysine, 0.05–0.15%; dl-methionine, 0.1–0.3%) or their combinations ( l-lysine + dl-methionine, 0.05 + 0.1%; 0.1 + 0.1%; 0.05 + 0.2%; and 0.1 + 0.2%) to the diet containing 13.2% yeast had no significant effect on either growth rate or feed efficiency (Experiments 3 and 4). A non-fortified diet alone proved to be comparable in nutritive value to a standard diet containing high-quality protein components. The diet with yeast providing 20% and cereals providing 80% of the total protein (5.55% yeast, 92.15% cereals) with combined supplement of amino acids ( dl-methionine 0.2% + l-lysine 0.2% + l-isoleucine 0.1% ; Experiment 5) promoted growth rate and feed efficiency similar to the standard diet, in spite of the fact that the experimental diet protein-content was about 3% lower. In a separate experiment (Experiment 6), similar results were achieved with the supplement of l-lysine alone (0.15% of the diet). As suggested by the results of model experiments on rats, the nutritive value of diets based on cereals and ethanol-grown yeast, possibly supplemented with amino acids, is comparable with that of diets containing animal protein components.