OXIDATIVE STABILITIES OF SOYBEAN OILS THAT LACK LIPOXYGENASES

Lipoxygenase (LOX)-null soybean lines that lack LOX 2, or LOX 2 and 3, and contain normal (8.0-8.6%) or low (2.0-2.8%) linolenate (18:3) amo unts were evaluated for their oil qualities and storage stabilities. S oybean oils of six genotypes were extracted by both laboratory-scale a nd pilot-plant systems and were refined, bleached, and deodorized in t he laboratory. Citric acid was added to oils during the cool-down stag e of deodorization. Two replications, separated at the point oi condit ioning, were evaluated for each genotype. Under storage conditions of 55-60 degrees C in the dark, soybean oils with low 18:3 contents were significantly (P less than or equal to 0.05) more stable as measured b y peroxide values than were oils with normal 18:3 contents, regardless of the LOX content of the beans. The volatile analysis showed few dif ferences between oils with low and high 18:3 contents or among oils fr om beans that lack different LOX enzymes. After 16 d of storage, the a mount of 1-octen-3-ol was significantly greater in oils with low 18:3 content, and soybean oils from beans with normal LOX content had a sig nificantly (P less than or equal to 0.05) lower amount of 1-octen-3-ol than did the oils that lacked LOX enzymes. Storage at 35 degrees C un der light showed no differences in volatile amounts or sensory evaluat ions after 14 d of storage. During storage, peroxide values tended to be lower in oils from beans with normal 18:3 content and in oils from beans with normal LOX content. Generally, the absence of LOX 2 or LOX 2 and 3, although having a small effect on lipid oxidation, was not as important to oil quality as was the 18:3 content.