Nutritive value of sweet potato protein produced from the residual products of sweet potato starch industry

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  • 甘藷汁液蛋白質の栄養価
  • サツマイモジュウエキ タンパクシツ ノ エイヨウカ

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1. Sweet potato proteins were prepared by acidifying and heating the residual juice of the sweet potato starch industry. The chemical compositions of the sweet potato protein dried by drum-drier were as follows: moisture, 8.73%; crude protein, 48.74%, ether extract, 7.40%; crude ash, 5.63%; nitrogen-free extracts, 29.50%.<br>2. The sweet potato proteins were colored either greenish brown or dark green and their absorption spectra in pH6.5 medium had a shoulder at 320-330 mμ, which suggested the presence of phenolic material. It was also shown that the proteins had an absorption maximum at 260mμ which was the characteristic of nucleic acid.<br>3. The sweet potato protein was deficient in methionine and lysine in comparison with whole egg protein. However, the content of most of the essential amino acids was higher than in soy-bean protein, particularly for methionine.<br>4. The major fatty acids found in the lipid of the sweet potato protein were linoleic and palmitic acids. These two scids made up 78% of the total acids.<br>5. Protein efficiency ratio (P. E. R.) of the sweet potato protein dried by drum-drier was 1.9 for weanling rats at the level of 10% dietary protein, but when the protein was fortified with methionine and lysine, P. E. R. value of 2.50 was obtained. It was recognized that the sweet potato protein fortified with methionine and lysine was closely equated with the soybean protein fortified with methionine as a protein source for growing rats.<br>6. The biological value and true digestibility of three types of sweet potato proteins prepared by different drying methods were determined with the nitrogen-balance method on young rats. The following figures were found for biological value and true digestibility: drying by acetone extraction, 72.0 and 82.3; drying by drum-drier, 74.6 and 79.4; drying in a current of hot air, 72.6 and 82.7. These results suggest that drying method had little influence on the nutritive value of sweet potato protein.

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