Abstract
In the previous paper, we compared the lengths of foam extension with the extent of deterioration of frying oils, and it was observed that the foam was more extended according to the deterioration of oils. And the rats fed with different degrees of foam extension showed growth depression from oils with foam extension 32mm. In this paper, relationship between foam extension and foam height of oils, and/or carbonyl and anisidine values were investigated. The determinations of foam extension and foam height were carried out according to the method reported previously (J. Jap. Soc. Nutr. and Food Sci.,16,425 (1964), Science of Cookery,20,384 (1987)). Carbonyl and anisidine values, contents of oxidized fatty acids (oxidized fatty acids mean fatty substances insoluble in petroleum ether separated from fatty acids after saponification of frying oils) and tocopherol were determined by JOCS official method 2.4.22-73,2.4.26-81, AOCS official and tentative method G3-53, and HPLC, respectively.
Foam tendency, carbonyl and anisidine values, percent of oxidized fatty acids and decomposition of tocopherol in oils increased during heating. It was revealed that 32mm of foam extension corresponded to 21mm of foam height and carbonyl value 40. Foam tendency of frying oils was apparently increased by addition of oxidized fatty acids separated from the heating oils.
