Lipoxygenase 3 Reduces Hexanal Production from Soybean Seed Homogenates

Hexanal is a volatile aldehyde formed from disrupted soybean seeds such as during processing. This compound has an undesirable aroma that has limited some uses of soybean proteins in food products. Lipoxygenase, which oxidizes linoleic acid and leads to hexanal formation, exists in soybean seeds as three isozymes. It was thought that all three lipoxygenase isozymes contribute to hexanal production with isozyme 2 being the most effective. Our studies with near isogenic soybean lines deficient in the various lipoxygenase isozymes indicate that lipoxygenase 3 reduces hexanal formation in aqueous homogenates of soybean seed. Experiments with purified enzyme confirm that lipoxygenase 3 can decrease hexanal yield. Preliminary results suggest that lipoxygenase 3 reduces hexanal formation by converting the lipoxygenase product, 13-hydroperoxy-9,ll-octadecadienoic acid, into forms unavailable for conversion to hexanal. The different effects of lipoxygenase isozymes on the generation of hexanal have implications from the standpoints of food uses of plant products and in the physiological roles of particular lipoxygenase isozymes.