Soybean protein aggregation induced by lipoxygenase catalyzed linoleic acid oxidation

Aggregation of lipid-reduced soybean proteins (LRSP) was investigated by chemical analysis, spectroscopy, electrophoresis, SEC-HPLC and light scattering. Soybean proteins obtained from the model systems consisting of LRSP and different levels of linoleic acid and lipoxygenase (RSP 4 and 5) showed increased turbidity, protein oxidation, surface hydrophobicity but decreased sulfhydryl and disulfide contents. SDS-PAGE of RSP 4 and 5 revealed remarkable difference of electrophoretic bands for 7S subunits, comparing with those samples without linoleic acid and lipoxygenase. Fluorescence spectroscopy suggested other covalent linkages than disulfide bonds formed during the formation of aggregates. SEC-HPLC and laser light scattering indicated that aggregates with high molecular weight and large particle size existed in samples of RSP 4 and 5. The experimental evidences suggest that the aggregates were formed via non-covalent interactions, but covalent bonds were also involved.