米ヌカ内における油脂分の酸価調節に関する研究 (第6報)

酸価上昇反応における油脂分の性状変化

抄録

Treating a large quantity of different kinds of rice bran in large tubes of thin steel plate, an examination was made on the effect of lipase on the hydrolytic velocity of fatty matter, on the variation of oil content and on its transformation due to the lapse of reaction time by measuring different kinds of constants and by fractional distillation. Of the fatty acids that constitute rice bran oil, an investigation was conducted to determine which fatty acid was selectively hydrolyzed.
As a result it was found that the diameter of steel tubes and the location showed no difference on effect as was in the case of our fundamental research. As reaction time lasts longer free fatty acid content increases, but the amount of unsaponifiable matter, iodine value and peroxide value remain at almost definite values, and only a small amount of hydroxy acid is produced. When free fatty acid content is 75%, acetyl value becomes 4550, but when free fatty acid content is more or less than 75%, acetyl value decreases. It is presumed from this tendency of increase and decrease of acetyl value that the hydrolytic mechanism of fatty matter by lipase comes about by stepwise. In the case of the first step of reaction, an experimental formula exists between free fatty acid content and specific gravity or refractive index. In the case of the latter step of reaction wherein free fatty acid decreases after increasing once, however, no experimental formula exists. This comes from the formation of ethyl ester. As a result of analysis, by distillation under reduced pressure, the composition of the fatty matter after 140 hours' reaction time, the presence of ethyl ester was confirmed. It is considered that from the carbohydrate that co-exists in rice bran, ethanol is formed by alcohol fermentation, which in turn, produces ethyl ester by the synthetic action of lipase. No ethyl ester existed, however, in a sample oil after 7080 hours' reaction. The oil content decreases initially about 0.10.2% but after that there is a tendency of a slight increase. Of the fatty acids that constitute rice bran oil, those that are to be subjected to selective hydrolysis by lipase are palmitic, oleic and linolic acids in order.