Protein quality in cereals and pulses

Abstract

1. Polyethyleneglycol (PEG 4000) was examined for its influence on relative nutritional value (RNV) and available methionine in sorghum (Sorghum ulgare 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.