Trans fat is a unsaturated fatty acid with trans configuration and separated double bonds. Analytical methods have been introduced to analyze trans fat content in foods including infrared (IR) spectroscopy, gas chromatography (GC), Fourier transform-infrared (FT-IR) spectroscopy, reverses-phase silver ion high performance liquid chromatography, and silver nitrate thin layer chromatography. Currently, FT-IR spectroscopy and GC are mostly used methods. Trans fat content in 6 vegetable oils were analyzed and processing effects including baking, stir-frying, pan-frying, and frying on the formation of trans fat in corn oil was evaluated by GC. Among tested vegetable oils, corn oil has 0.25 g trans fat/100 g, whereas other oils including rapeseed, soybean, olive, perilla, and sesame oils did not have detectable amount of trans fat content. Among cooking methods, stir-frying increased trans fat in corn oil whereas baking, pan-frying, and frying procedures did not make changes in trans fat content compared to untreated corn oils. However, the trans fat content was so low and food label can be declared as ‘0’ trans based on the regulation of Ministry of Food ad Drug Safety (MFDS) (< 2 g/100 g edible oil).
Isoflavone extracts from soybeans and soyfoods were treated with riboflavin photosensitization and changes in antioxidant activities of isoflavone extracts under riboflavin sensitization were determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS), and ferric reducing antioxidant power (FRAP) assays. Extracts rich in malonyl derivatives, β-glucosides, and aglycones were prepared from raw, ovendried, and almond-incubated soybeans, and the fermented soyfoods cheongukjang and natto. As the period of visible light irradiation increased to 120 min, the total isoflavone content determined using HPLC decreased in all samples. Aglycones in almond-incubated extracts decreased by 77.5% after 120 min, and β-glucosides in oven-dried extracts decreased by 52.0%. The radical scavenging activity based on DPPH and ABTS assays significantly (p<0.05) decreased in most extracts, compared with controls. The reducing power in aglycone-and β-glucoside-rich extracts increased, whereas the reducing power in extracts with high malonyl forms was not significantly (p>0.05) increased after riboflavin sensitization.
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