揚物油のアワ立ちに関する研究-5-
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概要
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1. The object of this study is to find the factors which affect to the change in the foaming properties in deep fat frying and to make clear the quantitative relations, commonly appliable to all frying oils, between the foaming properties and these factors.<BR>2.50g or 100g of linseed oil, safflower oil, olive oil, palm oil, soybean oil, rapeseed oil and castor oil in 300 cc beakers were heated at 200°C or 220°C for about 10 hrs. At every interval of 30 minutes, a piece of potato was dipped in the oil and the state of foaming was recorded. Thus, we prepared the sample of which a half part of the surface was covered by foams when a piece of potato was dipped in, and the sample, in which entire surface was covered by foam, in respect to the each oil. We designated as the half-foaming oils for the former and as the whole-foaming oils for the latter, respectively.<BR>The viscosities of these samples were determined at 25°C and 200°C. These foaming oils were fractionated by column chromatographic method into 3 fractions, using silicagel treated with <I>n</I>-hexane containing 5% of <I>i</I>-propyl ether as the absorbent. Foaming oil samples were eluted with 15% <I>i</I>- propyl ether in hexane to yield first fraction (F<SUB>1</SUB>); 60% <I>i</I>-propyl ether in hexane to yield the second fraction (F<SUB>2</SUB>) and with ethyl ether to yield the third fraction (F<SUB>3</SUB>). It was reported in our previous paper that F<SUB>3</SUB> was mainly composed of oxidative-polymerized matter and this was main substances which caused foaming of thermally oxidized soybean oils.<BR>3. The rate of increase in viscosity were varied according to the type of oils and the heating conditions. Taking the same kind of oils, the samples having the same viscosity showed the same foaming tendencies, even though they were prepared under different conditions. But the samples which showed the same foaming tendency but originated from different oils did not show the same viscosities. Thus, we failed to find any such relation between the rate of increase in viscosity or the absolute value of viscosity at 200°C and the foaming tendencies in various oils.<BR>The half-foaming oils originating from various oils contained 810% of F<SUB>3</SUB> fractions and the whole-foaming oils contained 1214% of F<SUB>3</SUB> farctions. The contents of F<SUB>3</SUB> seemed to influence the foaming properties of frying oils.
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