THERMOOXIDATIVE AND HYDROLYTIC CHANGES IN SUNFLOWER OIL USED IN FRYINGS WITH A FAST TURNOVER OF FRESH OIL

The modification of a sunflower oil used for 75 repeated deep-fat fryi ngs of potatoes, with a fast turnover of fresh oil during frying, was evaluated by measuring the total polar components isolated by column c hromatography. The total polar components increased rapidly during the first 20 fryings from 5.09 +/- 0.21 (mean +/- SD) mg/100 mg unused oi l to 15.99 +/- 0.40, followed by minor but also significant changes un til the thirtieth frying (17.99 +/- 0.41 mg/100 mg oil). The level did not increase further with continued frying. Further, the polar fracti on was examined by high-performance size-exclusion chromatography. Tri glyceride polymers increased from 0.10 +/- 0.01 mg/100 mg unused oil t o 1.65 +/- 0.13 and 3.44 +/- 0.17 mg/100 mg oil at the twentieth and s eventy-fifth fryings, respectively. Triglyceride dimers also increased significantly from 0.75 +/- 0.12 mg/100 mg unused oil to 6.25 +/- 0.2 8 (mg/100 mg oil) at the twentieth frying and to 7.09 +/- 0.31 mg/100 mg oil at the thirtieth frying, with no further significant changes. O xidized triglycerides also significantly increased, but at the twentie th frying reached a near-steady state of 6.26 mg/100 mg oil. Diglyceri des and free fatty acid levels, related to hydrolytic alteration, did not increase with continued fryings. The results indicate that during deep-fat frying of potatoes with fast turnover of fresh sunflower oil, more thermoxidative than hydrolytic processes take place. A dramatic leap of total polar content and a change of compounds related to therm oxidative alteration of the oil were found during the first twenty fry ings, followed by minor changes and by a tendency to reach a near-stea dy state throughout the successive fryings.