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, L~, L3, L1 -}-L3, or L 2 -}-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 L 2 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 L 2 isozyme may reduce offflavors in soy products.Soybean oil contains between 7 and 9% linolenic acid (18:3) and about 55% linoleic acid (18:2}. Oxidation of these fatty acids during processing and storage of soybeans poses a significant problem to the food industry. Breakdown products from fatty acids have been associated with grassy-beany and rancid flavors (1,2}. These oxidation products are considered responsible, at least in part, for reduced consumer acceptability of soy products. The flavor problems can occur in protein as well as oil products because the undesirable compounds are reactive and can bind covalently to proteins during processing {3,4}.Considerable indirect evidence has implicated seed lipoxygenase as a major factor contributing to the oxidation of lipids during processing, thereby lowering product quality {3,5}. This enzyme catalyzes the hydroperoxidation of cis-cis pentadienes and is present in relatively large quantities {about 2% of the protein} in soybean seeds (6). The hydroperoxides formed by lipoxygenase activity and their breakdown products are known to exhibit off-flavors {3,7}. Furthermore, lipoxygenase inactivation by heat during processing has been correlated with the improvement of sensory evaluation scores (8}. Heat treatments are widely used 1Cooperative research between USDA/ARS and the Purdue Agricultural Experiment Station.to inactivate lipoxygenase, but they are expensive, can produce undesirable alterations of the proteins and themselves can add to the flavor profile of soy products.Three lipoxygenase isozymes, denoted L1, L2 and L3, are present in soybean seeds (6}. They differ from one another in reaction products, p...
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 F 2 and F5 seeds from selfed plants indicated that absence of Lo3 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 X PI 408 251. The latter parent contains L-3 but lacks L-1. We propose that the dominant allele be called Lxs, whereas the recessive one be designated Ix3.
A cultivar lacking the glycinin subunit A5A4B3 ('Raiden') was crossed with one lacking the α'-subunit of β-conglycinin ('Keburi'). Analysis of F2 and F3 progeny indicated that the missing bands of the A5A4B3 and the α'-subunit were each controlled by a recessive allele of two independently segregating genes. Gene symbols Gy 4/gy 4 and Cgy 1/cgy 1 were proposed for the genes which confer the presence or absence of the glycinin and conglycinin subunits, respectively.
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