Thermoxidative and hydrolytic changes in sunflower oil used in fryings with a fast turnover of fresh oil

Abstract

The modification of a sunflower oil used for 75 repeated deep‐fat fryings of potatoes, with a fast turnover of fresh oil during frying, was evaluated by measuring the total polar components isolated by column chromatography. The total polar components increased rapidly during the first 20 fryings from 5.09±0.21 (mean±SD) mg/100 mg unused oil to 15.99±0.40, followed by minor but also significant changes until the thirtieth frying (17.99±0.41 mg/100 mg oil). The level did not increase further with continued frying. Further, the polar fraction was examined by high‐performance size‐exclusion chromatography. Triglyceride polymers increased from 0.10±0.01 mg/100 mg unused oil to 1.65±0.13 and 3.44±0.17 mg/100 mg oil at the twentieth and seventy‐fifth fryings, respectively. Triglyceride dimers also increased significantly from 0.75±0.12 mg/100 mg unused oil to 6.25±0.28 (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. Oxidized triglycerides also significantly increased, but at the twentieth frying reached a near‐steady state of 6.26 mg/100 mg oil. Diglycerides 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 thermoxidative alteration of the oil were found during the first twenty fryings, followed by minor changes and by a tendency to reach a near‐steady state throughout the successive fryings.

Influence of fatty acid composition on the formation of polar glycerides and polar fatty acids in sunflower oils heated at frying temperatures.

“…Quantitative results obtained for the main groups of glyceridic compounds indicate the primacy of the formation of polymerization compounds (TGD plus TGP) which contribution to polar compounds was normally higher than 50% (numbers into brackets in Tables I and II) and even surpassed 70% for the most altered sample (SO in Table II). These results are in good agreement with those reported for oils with similar levels of polar compounds having been subjected to thermoxidation or frying under very distinct conditions (Arroyo et al, 1992;Cuesta et al, 1993;Dobarganes et al, 1993;Márquez-Ruiz et al, 1995;Pozo-Díaz et al, 1995), thus indicating that the variables of the treatment affect mainly the total degradation level.…”

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“…The results obtained from all of the above described experiences are in agreement with those found by different authors which reported an increase of the polar content with the number of fryings (Fedelli, 1988;Sánchez-Muniz etaL, 1989;Cuesta etaL, 1991;Cuesta etaL, 1993;Sánchez-Muniz, 1993).…”

Thermal degradation of groundnut oil during continuous and intermittent frying

“…It is well discussed in the literature that formation of polymers is aggravated with increased frying temperature and total number of fryings. (Choe and Min 2007;Cuesta et al 1993). However, in the present study the significant increase (P<0.05) of viscosity in the intermittent frying oil is noteworthy and can be attributed to the fact that solubility of oxygen increases as the oil cools down from frying temperature (as discussed before).…”