HIGH-TEMPERATURE STABILITY OF SOYBEAN OILS WITH ALTERED FATTY-ACID COMPOSITIONS

One canola oil and six soybean oils with different fatty acid compositions were heated intermittently, and bread cubes were fried in them to determine the stability of the oils. Two of the soybean oils were commercial varieties Hardin and BSR 101. The other soybean oils were from experimental lines developed at Iowa State University, and included A17 with 1.5% linolenate (18:3) and 15.1% palmitate (16:0), A16 with 1.9% 18:3 and 10.6% 16:0, A87-191039 with 1.8% 18:3 and 29.1% oleate (18:1) and A6 with 27.7% stearate (18:0). The soybean seeds were cold-pressed and crude canola oil was obtained without additives. Oils were refined, bleached and deodorized under laboratory conditions with additions. Each oil (300 mL) was heated to 180 +/-5-degrees-C in a minifryer. Bread cubes were fried at the beginning of heating, and half of the cubes were used for analyses. The second half was analyzed after storage at 60-degrees-C for seven days. Heating of the oils was continued for 20 h, cooled for 10 h, and then reheated for another 20 h, after which additional bread cubes were fried and analyzed. Results of sensory evaluation of the fried cubes, the peroxide values (PV) of oils extracted from the cubes and the conjugated dienoic acid values of the oils showed that the A17, A16, A87-191039 and A6 oils had better stabilities than did Hardin, BSR 101 and canola oils. The initial 18:3 contents of oils predicted their oxidative and flavor stabilities under heating and frying conditions (for PV vs. 18:3, r = 0.89, P = 0.008; for flavor quality vs. 18:3, r = -0.93, P = 0.002; for flavor intensity vs. 18:3, r = -0.91, P = 0.004).