Protein quality in cereals and pulses. 1. Application of microbiological and other in vitro methods in the evaluation of rice (Oryza sativa L.), sorghum (Sorghum vulgare Pers.), barley and field beans (Vicia faba L.)

Protein quality in cereals and pulses. 3. Bioassays with rats and chickens on sorghum (Sorghum vulgare Pers.), barley and field beans (Vicia faba L.). Influence of polyethylene glycol on digestibility on the protein in high-tannin grain

1. Two preceding papers in this series describe the application of microbiological and other in vitro tests in the evaluation of sorghum (Sorghum vulgare Pers.), field beans (Vicia faba L.) 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 measured 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 improvemnet, 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 less than 0.05) of PEG 4000 on N idgestibility 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 with Streptococcus zymogenes.

Protein quality in cereals and pulses. 2. Influence of polyethyleneglycol on the nutritional availability of methionine in sorghum (Sorghum vulgar Pers.), field beans (Vicia faba L.) and barley

1. Polyethyleneglycol (PEG 4000) was examined for its influence on relative nutritional value (RNV) and available methionine in sorghum (Sorghum vulgare Pers.), field beans (Vicia faba L.) and barley, as measured microbiologically with Streptococcus zymogenes. The results were assessed in relation to the content of tannins in the test samples. 2. In grain of hybrid sorghum the RNV averaged 87 (range 79--92) for six low-tannin varieties and 41 (30--53) for eleven high-tannin varieties. The corresponding available methionine values averaged 17.0 (15.7--18.9) and 8.9 (6.7--11.0) g/kg protein. Addition of PEG 4000 to the test samples increased the average RNV of the high-tannin varieties from 41 to 78, and the average available methionine content from 8.9 to 16.2 g/kg protein. 3. With seed of ten coloured flowered varieties of field beans, treatment with PEG gave a small but consistent increase in the available methionine content, which resulted from the inactivation of tannins in the testa. 4. In twenty-three samples of barley grain, treatment with PEG had no effect on the values obtained for available methionine. 5. Treatment of high-tannin sorghum grain with ammonia has been reported to inactivate the tannins and increase the nutritional value for rats and chicks. This finding was confirmed. The present study showed that ammonia and PEG 4000 were equally effective in enhancing the nutritional quality as measured in the microbiological tests.