Abstract
Trans fats, unsaturated fatty acids with at least one double bond in the trans configuration, have received a great amount of attention in the field of oleo chemistry and safety. In this work, the cis-trans isomerization of unsaturated fatty acids in edible oils has been successfully developed using simple and cheap p-toluenesulfinic acid as catalyst. The effects of reaction time, temperature, catalyst loading, and the amounts of water and antioxidants on the cis-trans isomerization have been systematically investigated. The results indicate that the amount of water (0–20 wt %) and antioxidants (0–200 mg/kg) had no significant effect on this cis-trans isomerization of unsaturated fatty acids in edible oils. The final products (trans fats) from the cis-trans isomerization reaction were characterized by both GC and React IR. The yield of trans double bonds from the isomerized fat can reach 79.6% after heating at 100 oC for 90 min without changing either the location of the double bonds or the degree of unsaturation. In addition, this convenient method has been applied to various vegetable oils (e.g., olive oil, camellia seed oil, corn oil, sesame oil, sunflower oil and soybean oil) and nearly 80.0% yields of TFA were generated, which shows a promising method to provide trans-fat products for research related to oleo and food chemistry.
Highlights
It is a known fact that fatty acids, which contain saturated fatty acids and unsaturated fatty acids, are one of the most important components of edible oils (Kurt, 2018)
The cis-trans isomerization of unsaturated fatty acids in edible oils is not expected in most cases because an excessive intake of trans fatty acids (TFAs) has been associated with the increased risk of coronary heart disease (CHD), sudden death, diabetes mellitus and increased markers for systematic inflammation (Duffy et al, 2006; Hulshof et al, 1999; Lemaitre et al, 2006)
The proposed mechanism for trans carboncarbon double bond formation in edible oils using p-toluenesulfinic acid as catalyst is presented in Scheme 1
Summary
It is a known fact that fatty acids, which contain saturated fatty acids and unsaturated fatty acids, are one of the most important components of edible oils (Kurt, 2018). Most of the natural unsaturated fatty acids in edible oils are non-conjugated acids with a cis structure. TFAs are produced from cis-unsaturated fatty acids during the heating of oils at high temperatures (> 200 oC) and the hydrogenation process in the presence of hydrogen and metal-catalysts (e.g., Ni, Cu) (Liu et al, 2017). Hydrogenated vegetable oils have been widely used in the food industry for a long period of time to produce different oil-based foods, such as cakes, cookies, french fries and margarine, because of their longer shelf-life, oxidative stability and other particular physical properties (Cizmeci et al, 2005; García et al, 2017; Iida et al, 2015; Mozaffarian et al, 2006). The deep frying process (160–180 oC) using unsaturated vegetable oils (e.g., soybean oil, sunflower oil, canola oil) would lead to an increase in trans fatty acids when the operation time was more than 20 h (Farag et al, 2010; Tsuzuki et al, 2010)
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