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The effects of soy flour from LOX null mutant isolines and purified LOX isozymes on the rheological and breadmaking properties of a commercial hard wheat flour were investigated. Wheat flours were fortified with either 3% soy mutant flours alone, or in the presence of 0.2% and 1% linoleic acid. Purified LOX 2 isozyme had the greatest effect among LOX isozymes on dough extensibility and strength. Linoleic acid substrate addition reduced dough extensibility and strength. The L2L3 null isoline mutant for L1 resulted in the largest increase in bread volume. A reduction in bread firmness occurred after 5 day storage for all three single null mutant-containing samples in the presence of 1.0% linoleic acid substrate.

Lipoxygenases are implicated in improvement of bread quality after addition of enzyme active soy flour. However, differences among the three major isozymes in soybeans in terms of impact on bread characteristics are not known. Differences exist among soybean lipoxygenase isozymes in terms of stability and generation of volatile flavor and aroma. Soybean flour with different lipoxygenase isozymes present might affect bread dough volatiles or defatting may affect activity of the isozymes. Full fat or defatted soy flour could be added to bread dough. Defatting selectively reduced lipoxygenase 2 activity with little effect on lipoxygenases 1 and 3. Addition of full fat soy flour from mutant isolines indicated that as with soybean homogenates, lipoxygenase 2 is mostly responsible for undesirable aroma compounds. Much higher levels of volatile alcohols were found in soy flour amended bread dough than in soy flour homogenates alone.