EFFECT OF OIL REPLENISHMENT DURING DEEP-FAT FLYING OF FROZEN FOODS INSUNFLOWER OIL AND HIGH-OLEIC ACID SUNFLOWER OIL

Frying stability of sunflower oil (SO) with 23% oleic acid and 61% lin oleic acid, and of high-oleic acid sunflower oil (HOSO) with 74% oleic acid and 13% linoleic acid was studied during 20 discontinuous deep-f at fryings of various frozen foods, with or without frequent replenish ment of the used oil with fresh oil. Alterations of both oils were mea sured by column, gas-liquid and high-performance size-exclusion chroma tography. Total polar content and compounds, related to thermoxidative changes, and diacylglycerides, related to hydrolytic changes, increas ed in all oils during frying but reached higher levels in SO than in H OSO. Nevertheless, the increased levels of diacylglycerides observed m ay result from the frozen potatoes prefried in palm oil. Oleic acid in HOSO and linoleic acid in SO significantly decreased, but the fatty a cid modifications that occurred during the repeated fryings were not o nly related to thermoxidative alteration but also to interactions betw een the bath oil and the fat in the fried products. Data from this stu dy also indicated that HOSO performed more satisfactorily than SO in r epeated fryings of frozen foods. Moreover, frequent addition of fresh oil throughout the deep-frying process minimized thermoxidative and hy drolytic changes in the frying oils and extended the frying life of th e oils.