Food types and frying frequency affect the lipid oxidation of deep frying oil for the preparation of school meals in Korea

200 soybean oils used in school meals for deep frying were investigated to elucidate factors influencing lipid oxidation in the oils. The mean levels of moisture along with primary and secondary lipid oxidation products were significantly different among the oils used by the six schools. When comparing lipid oxidation products of frying oils used for four different food groups (vegetables, fish, meat or carbohydrate-rich foods), differences were found among them, with the values for the carbohydrate-rich group being the lowest. The vegetable group was higher in the contents of conjugated dienes and trienes, and lower for those of hydroperoxides and malondialdehyde. The mean values of malondialdehyde and p-anisidine value for the fish group were greater than those of the other groups. The levels of conjugated trienes and malondialdehyde increased with the frying frequency. These findings indicate that food types and frequency of frying play a role in determining the oil oxidation in deep fried foods in schools.