Oxidative and frying stabilities of soybean oils with altered fatty acid and/or lipoxygenase contents
Lipoxygenase (LOX)-null soybean lines, lacking LOX 2, LOX 2 and 3 and containing normal (>8.0%) or low (<3.0%) linolenate (18:3) contents were evaluated for their room-temperature storage stability, stability during frying, and oxidative stability in bread cubes stored after frying. Six genotypes of soybeans were extracted by both laboratory-scale and pilot plant-scale systems and were refined, bleached, and deodorized in the laboratory. Citric acid was added to oils during the cool-down stage of deodorization. For each system, two replications separated at the point of conditioning were evaluated for each genotype, including Century 84, L2-3, L2L3-2-4, A89-269043, A89-269043-L2, and A89-269043-L2L3;Peroxide values (PVs), fatty acid compositions, volatile compounds, and sensory evaluation were determined for several room-temperature storage conditions. To determine stability under frying conditions, each replicate (250 g) was heated to 180 ± 5°C in a minifryer. Bread cubes were fried at the beginning of heating and after 20 h of heating. Heating of the oils was continued for 10 h each day for 3 consecutive days. Sensory evaluation of the fried cubes, the peroxide values of oils extracted from the cubes, and the conjugated dienoic acid values and polymer values of the heated oils were measured. For both room-temperature and frying-temperature tests, soybean oils with low 18:3 contents were significantly more stable than were oils with normal 18:3 contents, regardless of the LOX contents of the beans;Additional soybean genotypes that contained different amounts of palmitate (16:0) and 18:3 were evaluated for oxidative stability. Soybean oils from Hardin 91, P9322, A91-282036, and HPLL were processed and analyzed. The fatty acid compositions, peroxide values, and cloud points were measured. The results showed that elevating 16:0 and/or lowering 18:3 increased the oxidative stability of soybean oils.