Improving the quality of fermented soybean products using low-frequency airborne ultrasonicated Koji

Abstract

The aim of this study was to compare three fermented soybean products (soybean paste, red pepper paste, and soy sauce) prepared with non-treated (NK) and ultrasonicated Koji (UK, at 30 kHz). The physicochemical properties and ABTS radical scavenging activity were investigated during fermentation. The pH values of soybean products containing UK were found to be slightly more acidic compared to the NK-containing products after fermentation, whereas the titratable acidity gradually increased during the fermentation period. Hunter L-values of all soy sauce samples (UK and NK) decreased rapidly after fermentation, but the application of UK did not affect the color quality of the final product. All soybean products prepared with UK showed higher amino-type nitrogen contents than products prepared with NK owing to the high enzymatic activities of UK. The ABTS radical scavenging activity of soybean paste prepared with UK was significantly higher compared to the NK-containing sample at day 50. In conclusion, the application of UK showed significant potential to enhance the physicochemical qualities and antioxidant activity of fermented soybean products, suggesting its promising use as an ingredient in fermented soybean products.