Abstract
The relationship between the decomposition of peroxide on oxidized oils by heating in an atomosphere of carbon dioxide and carbonyl value (conventional method by 2, 4-dinitrophenylhydrazine) were investigated.
1) Soy bean oil were aerated at 150°, 160° and 170°C for 180 minutes and required samples were heated in an atomosphere of carbon dioxide at respective temperature for equal time as in the case of previous aeration. Their peroxide values were then measured at regular intervals for 30 minutes.
The result suggested that, in the thermal oxidation, the quantitative proportion of formation and decomposition of peroxide value existed in a very constant level throughout for 180 minutes at each temperature; i.e., about 45m eq/kg at 150°C, 35m eq/kg at 160°C and 28m eq/kg at 170°C.
2) Oxidized soy been oil (P.O.V. 364), rape seed oil (P.O.V. 262) and lard (P.O.V. 172) were prepared by aeration at 98°C, then they were heated at 60, 98, 150 and 200°C in the atomosphere of carbon dioxide. Almost amounts of peroxide were decomposed fastly (about 20min) at 200°C, but did not decomposed when heated at 60°C for 8 hours. However, when peroxide were concentrated more higher (P.O.V. 600700), decomposition occured but very slowly even at 60°C. During the early stage of peroxide decomposition in each case at 98°C and 150°C, a considerable rates of decomposition were observed, but in the later stage, the rates were slow and usually decreased. Each decomposition at 98°C and 150°C showed closely parallel curve and showed just opposite to the curve of typical induction period in autoxidation.
3) The results of this investigation showed several aspects.
a) Although the decomposition of peroxide may occure from such causes as temperature, time and catalysts, the accumulation of peroxide itself is a cause of accelerated decomposition.
b) Peroxide formed in the autoxidation interferes to the determination of carbonyl value, but which formed as the result of frying dose not.
c) Estimation of carbonyl value may serve as a reliable index of frying deterioration of oils.
