Evaluation of Heat Treated Fryig Oils. III.

Components in Subfractions of Polar Fatty Acid Methyl Esters from Heat Treated Soybean Oil.

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Polar fractions of fatty acid methyl esters (PFA) prepared from soybean oil heated 30 h by frying whale meat (Wh) and potato (Po) were subjected to fractionation by TLC and silicagel column chromatography (CC), monitoring each fraction for its UV-absorbance (at 233 nm). Highly UV-active fractions were analyzed by GLC and GC-MS to compare with the chromatographic patterns obtained from Wh and Po and to comprehend the nature of UV-active components. The fractions with R_ƒ in a range of 0.230.96 by TLC (developed with petroleum ether-diethyl ether-ethanol 50 : 50 : 2) contributed nearly 90% of the total UV-absorption of PFA and amounted 5669%(on the weight basis) of PFA. These fractions showed strong intensities of absorption at 790795 and 765770 cm^-1 in the IR region. The chromatograms obtained from both samples were quite similar, indicating similar nature of components being involved in both samples. The most remarkable UV-active subfractions obtained by CC (R_ƒ 0.810.96) as well as five subsequent fractions (R_ƒ up to 0.73) were found to be composed of short chain esters, chiefly C₁₁C₁₅, having UV-active conjugated systems such as diene, enal (or enone), and formylenol. Compounds having a carbonyl or a hydroxyl group in their mid-chains were also detected in GLC fractions eluted at high temperatures. On the other hand, a subfraction with its R_ƒ 0.590.67 was found to be composed of chiefly C₁₈ compounds either in an normal chain or cyclohexyl form having the conjugated systems as mentioned above and also a keto or hydroxyl group. Other compounds found were 8-phenyloctanal, C₆ and C₈-esters carring in their molecules the 5-oxo-1-cyclopentenyl residue, and dioctyl phthalate.