The Composition of Fatty Acids in Frying Oils and the Hydrolysis during Deep Fat Frying

Abstract

Soybean and hydrogenated soybean oils were treated by the water spraying and heating system as a model of deep fat frying in the presence or the absence of air. In the presence of air, the acid value of hydrogenated soybean oil increased very much as compared with that of soybean oil, but in the absence of air, the two oils showed almost the same increase of acid value (Fig.-1). These results give a suggestion that some factors to promote the hydrolysis were formed in the hydrogenated soybean oil by thermal oxidation. When these oils were thermally oxidized by bubbling dry air at 180°C, it was also recognized that increase of acid value in hydrogenated soybean oil was obviously greater than that in soybean oil (Table-4). The fact that saturated fatty acid esters are apt to produce acidic substances by thermal oxidation was further confirmed by the thermal oxidation of various fatty acid esters (Table-6, 7).Consequently, the reason why hydrogenated or saturated fats are very sensitive to the hydrolysis during deep fat frying, probably depends on a process that acidic substances which produced in these fats by thermal oxidation promote their hydrolysis in the presence of water.