Changes of hexanal content in fermented soymilk: Induced by lactic acid bacterial fermentation and thermal treatment

To study the causes of beany off-flavor regeneration after fermented soymilk was thermal treated. Hexanal was soymilk beany off-flavor and analyzed using headspace solid phase microextraction. The hexanal removal and regeneration during fermentation and heat treatment of soymilk and soy protein solutions were analyzed. Soymilk contained both free and protein-bound hexanal. Both 7 S and 11 S could bind to hexanal, and the amount of bound hexanal to 11 S was approximately five times that to 7 S. pH decreased to approximately 4.5 or enzymatic hydrolysis could effectively weaken the binding of hexanal to soy protein, but not capable of dissociating them. Further heat treatment was required for hexanal volatilized from protein. Lactic acid bacteria could completely remove free hexanal, but the removal ability of protein-bound hexanal was weak, which varied among bacterial species. The results will be valuable for improving flavor qualities of fermented soymilk and its beverage products. This result revealed the mechanism behind the fact that the off-flavor of heated fermented soymilk was difficult to be removed. Thus, the results will be valuable for improving flavor qualities of fermented soymilk and its beverage products. Practical applications This result revealed the mechanism behind the fact that the off-flavor of heated fermented soymilk was difficult to be removed. Thus, the results will be valuable for improving flavor qualities of fermented soymilk and its beverage products.

Automated summary

This study investigated the causes of beany off-flavor regeneration after thermal treatment of fermented soymilk. It was found that both free and protein-bound hexanal were present in soymilk. Enzymatic hydrolysis and pH reduction could weaken the binding of hexanal to soy protein, but not completely dissociate them. Further heat treatment was required to volatilize hexanal from the protein. Lactic acid bacteria could remove free hexanal, but had weak ability to remove protein-bound hexanal.