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 thirdgrade solvent extracted soybean oil, TG-SESBO). French fries were fried intermittently at 180-1858C for a total frying time of 32 h and at an interval time of 30 min. It was found that the initial amount of total TFAs was 0.29 g/100 g, 0.31 g/100 g, and 0.90 g/100 g 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 AE 0.17 g/100 g, 1.12 AE 0.10 g/100 g, and 1.70 AE 0.07 g/100 g, 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.Practical applications: A high intake of TFAs has been shown to lead to an increased risk of coronary heart disease. Plant oils, particularly soybean oil, have been widely used in the food industry in China. Frying is one of the most common methods to cook food. The formation of TFAs during frying has been shown to be closely related to the temperature and duration of the frying process. However, the effects of frying on the formation of TFAs in different soybean oils have not been well studied. In the present study, we demonstrated that increasing the number of frying cycles can cause an intensive increase in the concentration of TFAs in different types of soybean oil, but especially in PSBO.Abbreviations: FAME, fatty acid methyl ester; FG-SESBO, first-grade solvent extracted soybean oil; PSBO, pressed soybean oil; TFA, transfatty acid; TG-SESBO, third-grade solvent extracted soybean oil Eur.

Development of rice bran oil blends for quality improvement

“…The results showed that the linolenic acid was found absent in RBO + SOO (both ratios) after deep as well as shallow frying. Similarly, a recent study reported that linolenic acid present in soybean oil was less stable at high temperature (Hou, Jiang, & Zhang, 2012). The reduction in the USFA content during deep fat frying had also been reported in the previous studies (Che Man, Liu, Jamillah, & Rahman, 1999;Khatoon & Gopalakrishna, 2005).…”

Effects of frying on polar material and free fatty acids in soybean oils

“…Approximately 0.5 g frying oil was analysed in triplicates. The fatty acid composition was determined using GC as demonstrated by Hou et al (2012). Light petroleum/ diethyl ether mixture (90:10) was used to elute the nonpolar fraction.…”

“…AV was calculated as X = V 9 c 9 56.11/ m (V = volume in millilitres of standard volumetric potassium hydroxide solution; c = concentration of the standard volumetric potassium hydroxide solution; m = the mass in grams of the test sample). The fatty acid composition was determined using GC as demonstrated by Hou et al (2012).…”

“…Two types of soybean oilpressed soybean oil and solvent extracted soybean oilare commonly used for frying purposes and are therefore the main lipid sources in Chinese daily diet (Hou et al, 2012). Other authors have reported the effect of frying on PM, AV and composition of fatty acids in olive oil, sunflower oil, hydrogenated vegetable oil, corn oil and soybean oil (Romero et al, 2006;Librelotto et al, 2008;Karakaya & Simsek, 2010;Sunisa et al, 2011).…”

Improvement in thermal stability of soybean oil by blending with camellia oil during deep fat frying

“…decades have witnessed numerous attempts to improve its oxidative stability, including partial hydrogenation, the addition of antioxidants, modification of fatty acids, and blending with more saturated or monosaturated oils to reduce the amount of polyunsaturated fatty acids [11][12][13][14]. In these methods, partially hydrogenated oils offer better resistance to thermo-oxidative degradation, but increases saturated fatty acid and trans-fatty acid which already have been reported to increase the ratio of low-density-lipoprotein (LDL) to high-density-lipoprotein cholesterol (HDL) in the plasma and increase the risk of coronary heart disease (CHD), and play a part in atherosclerosis development [15,16].…”