Effects of frying on the trans-fatty acid formation in soybean oils

Abstract

To evaluate the effects of repeated deep-frying on the trans-fatty acid (TFA) formation in soybean oils, simultaneous frying experiments were carried out. French fries were prepared using three different types of soybean oil (pressed soybean oil, PSBO; first-grade solvent extracted soybean oil, FG-SESBO; and third-grade solvent extracted soybean oil, TG-SESBO). French fries were fried intermittently at 180-185°C for a total frying time of 32h and at an interval time of 30min. It was found that the initial amount of total TFAs was 0.29g/100g, 0.31g/100g, and 0.90g/100g in PSBO, TG-SESBO, and FG-SESBO, respectively. Before the frying started, the C18:1,t-9, trans-linoleic acid (TLA), trans-linolenic acid (TLNA), and total TFA content of the PSBO and TG-SESBO were significantly lower than in the FG-SESBO (p<0.05). However, in the frying oil samples, the final concentration of total TFA in the PSBO, TG-SESBO, and FG-SESBO were 1.79±0.17g/100g, 1.12±0.10g/100g, and 1.70±0.07g/100g, which was 6.17-, 3.61-, and 1.89-fold higher that in fresh oil, respectively. The highest increasing slopes of C18:1,t-9, TLA, TLNA, and total TFA were observed in the PSBO. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.