The stability of frying oils can be evaluated in several methods, heating, aeration and frying tests, amongst, the most practical is the frying test.
In this paper, investigation was made for problem arising in frying test and for the procedure to evaluate frying stability of each oil.
The frying methods were as follows :
Continuous frying method : The oil lost during frying is not supplied. This is a fundamental test to evaluate the frying stability of each oil.
Replenish frying method : At the end of each frying period 10% weight oil of original is removed and fresh oil of equal weight is replaced. This is considered of importance because this method is most commonly used at present. This method coupled with the continuous frying method makes it useful to compare with the replenish efficiency and especially to determine the relative effectiveness of stabilizers.
Test was made by these methods using soybean (S), rapeseed (R) and soybean oils added with two kind stabilizers (0.5S, 1.0S). As the result of this experiments, the order of stabilization was 1.0S>0.5S>R>S in both method, but the replenish efficiency was indicated in the following order, 0.5S>1.0S>R≥S. As to the estimated effectiveness of stabilizers, 1.0S has been proved of greater stability than 0.5S as a result of the continuous method, but in the replenish method there was little or no difference between the two and marked replenish efficiency was appeared at 0.5S.
For the same sample oil, iodine, carbonyl and absorbancy values (at 233mμ) appeared at the end of each induction period were almost identical in both methods. Therefore, the basis for the evaluation of stability should be judged from the length of induction period which is measured with iodine, carbonyl values and absorbancv at 233mμ.
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