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Lipoxygenase-mediated oxidation of fatty acids has long been implicated in the production of off-flavors in soybean products. This assumption was tested by use of preparations from soybean lines nearly isogenic to the cultivar Century that lack the lipoxygenase isozyme or isozyme combinations L1, L2, L3, L1 + L3, or L2 + L3. Near-isogenic lines were used to ensure that any effects observed were due to elimination of lipoxygenase isozymes, and not to other unrecognized genetic differences between lines. Full-fat soy flour and unblanched soymilk preparations from the lines were evaluated by a six-member taste panel for eight flavor and/or aroma attributes common to soybeans. By comparison to near-isogenic controls, removal of the L2 isozyme from soymilk preparations produced significantly lower scores for beany, rancid and oily flavor and aroma attributes, as well as higher scores for dairy and cereal flavor and aroma attributes. Similar trends were noted for soy flour flavor attributes. Thiobarbituric acid (TBA) numbers, a measure of lipid oxidation, were lower in homogenized soy flour suspensions from lines lacking L2. Removal of the L1 and L3 isozymes did not result in improved flavor scores or lower TBA numbers. Total oil content and the fatty acid profile of the near isolines did not vary appreciably. The results indicated that genetic removal of the L2 isozyme may reduce off-flavors in soy products.

This study describes a major gene which controls lipoxygenase-3 (L-3) activity in soybean [Glycine max (L.) Merr.]. Cultlvars ‘Wasenatsu’ (PI 417 458) and ‘Ichigowase’ (PI 205 085) were found to L-3 by both immunological and electrophoretic methods. The inheritance of this trait was determined from progeny of crosses between Wasenatsu and either ‘Century’ or ‘Raiden’, two cultlvars that contain high levels of L-3. Segregation ratios in F₂ and F₃ seeds from selfed plants indicated that absence of L-3 was due to a single allele that was recessive to the one controlling the presence of the enzyme. Comparable results have been obtained using progeny from the cross Ichigowase ✕ PI 408 251. The latter parent contains L-3 but lacks L-1. We propose that the dominant allele be called Lx₃, whereas the recessive one be designated lx₃.