Hexanal synthesis in isolated soy proteins

Sodium erythrobate (2.3 mM) and dithiothreitol (6.5 mM) caused headspace hexanal from aqueous slurries of commercial isolated soy proteins (ISP) to increase by as much as 13-fold compared with headspace hexanal in the controls. When linoleic acid was also added, headspace hexanal levels from commercial and laboratory-prepared ISP were further increased by as much as 18- and 136-fold, respectively, compared with the levels in the controls. When ¹³C-labeled linoleic acid was added to aqueous mixtures of laboratory-prepared ISP along with reducing agents, 96% of the resulting hexanal contained the ¹³C isotope. Commercial ISP samples had about 40% of the isotopically labeled carbon incorporated into hexanal. These large increases in hexanal were almost completely prevented by heating the aqueous ISP to 100 °C or above prior to adding the reducing agent and linoleic acid. Adding cysteine or sodium sulfite reduced headspace hexanal levels from aqueous ISP slurries by more than 88%. Thiol blockers, iodoacetic acid and N-ethylmaleimide, did not affect hexanal levels.