Protein quality in cereals and pulses

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Abstract
1. Two preceding papers in this series describe the application of microbiological and other in vitro tests in the evaluation of sorghum (Sorghum vulgarePers.), field beans (Vicia fabaL.) and barley, and in assessing the influence of polyethylene glycol (PEG 4000) on the nutritional availability of the methionine. The present paper gives for comparison the results of bioassays on some of the same test samples. Net protein utilization (NPU) in rats was measurd by the nitrogen balance method, and N digestibility in chickens by the ileal analysis procedure.2. In rat tests on sorghum, N in grain of high-tannin varieties was poorly digested. Supplementation of the test diets with 0.1 g PEG 4000/g protein gave a large improvement, which was partly offset by an apparent decrease in biological value (BV). With chickens N digestibility was even lower, and was similarly improved with PEG 4000. Treatment of high-tannin grain with ammonia solution was also effective in improving N digestibility.3. With low-tannin sorghum the amino acid digestibilities were uniformly high and were not affected by addition of PEG to the test diet. With high-tannin sorghums they were low and less uniform, and were much improved by PEG 4000.4. With field beans, the influence of the seed-coat tannin on protein utilization was much less pronounced than with sorghum. In chickens there was a significant effect (P< 0.05) of PEG 4000 on N digestibility in a high-tannin variety. With rats the effect was smaller and not significant.5. In four samples of barley, N digestibility was high (0.87–0.96) and was not further improved by PEG 4000. The BV of a high-lysine cultivar proved marginally inferior to that of a normal variety. Possible reasons for this are discussed.6. Over all, the results were closely consistent with those from microbiological tests withStreptococcus zymogenes.