Studies on the Deterioration of the Frying Oils. V
The Type and Induction Period of the Deterioration of Soybean Oil
1963 Volume 12 Issue 4 Pages 214-219
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1963 Volume 12 Issue 4 Pages 214-219
It has been found there exist two types in the deterioration of frying oils, and they are named J and S types from their respective deterioration types. J is original deterioration type which appear in most oils, while some oils belong to S type inhere unstable factors such as that they were stored in undesirable condition or color reversion were developed fastly in them. Each type has always its induction and subsequent weariness periods (so called TSUKARE), and latter develops rapidly after the former period. The TSUKARE (weariness) has been ordinally identified by the change of foaming conditions to be occurred during frying. However, it often occurred that the induction period was not seen, because the sampling is generally made on a periodical basis in the evaluation test of frying stability.
In this study, the potato chips (at the rate of 1 kg an hour) were fried at 190°C by using 1.5 kg of five kinds of soybean oil. Those sampling for the objective test were fixed on the basis of the foaming conditions, giving up the periodical sampling.
The results of this experiment were as follows :
1) The change in iodine value, carbonyl value, viscosity and ultra violet absorption spectra have been found extremly useful in evaluating the induction and subsequent weariness period, but the others (refractor, color and acid value) were not so helpful.
2) The absorption band of conjugated dienoic acid (at about 230 mμ), which showed a broad range and increased slowly during the induction period, were developed intensely and rapidly with progress of the TSUKARE (weariness). On the other hand, it was also found that those absorptions of conjugated trienoic acid (at 259, 268, 279 mμ) were very clearly indicated during induction period, but tended to disappear in the order of 259, 279, 268 mμ as the TSUKARE advances.
3) After the TSUKARE appeared in the frying, the sampling must be done frequently to take hold of progress in the induction and weariness periods.
