Antioxidant and Neuroprotective Effects of Doenjang Prepared with Rhizopus, Pichia, and Bacillus

Abstract

A new type of <i>doenjang</i> was manufactured by mixing soaked soybean, <i>koji</i> (<i>Rhizopus oryzae</i>), <i>cheonggukjang</i> (<i>Bacillus amyloliquefaciens</i> MJ1-4 and <i>B. amyloliquefaciens</i> EMD17), and <i>Pichia farinosa</i> SY80 as a yeast, salt, and water, followed by fermentation with <i>koji</i> that was made by fermenting whole wheat with <i>R. oryzae</i>. The mixed culture <i>doenjang</i> was designed to have a more palatable flavor and stronger biological activities than the conventional product. The extract of mixed culture <i>doenjang</i> showed higher antioxidant activity than the commercial <i>doenjang</i> as evaluated by the ferric reducing antioxidant power assay although it was not significantly different from the commercial product in 2,2-diphenyl-1-picrylhydrazyl and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) radical scavenging activities. Further, the mixed culture <i>doenjang</i> reduced intracellular reactive oxygen species levels and protected cells from glutamate-induced cytotoxicity more efficiently in human hippocampal HT22 neuroblastoma cells than the commercial <i>doenjang</i>. In conclusion, a newly-developed mixed culture <i>doenjang</i> had a strong antioxidant activity <i>in vitro</i> and cultured cell model systems, exhibited a potential to prevent oxidative stress-associated disorders although animal and clinical studies are needed to confirm its <i>in vivo</i> efficacy.