Enhancing miso production with optimized puffed-rice koji and its biological function evaluation

In order to enhance enzyme activities of koji and further improve the health benefits and nutritional value of miso, puffed rice was used to prepare koji with optimization of fermentation utilizing response surface methodology (RSM), and the optimized puffed rice koji was used to produce miso and low-salt miso. Results showed that β-glucosidase activity increased by 1.98-fold after RSM optimization. The optimized puffed rice koji also showed the highest β-amylase and protease activities (237.1 and 968.8 units/g, respectively) compared to rice koji (108.7 and 637.4 units/g, respectively). Moreover, miso made from puffed-rice koji presented a much higher polyphenol content, antioxidant activity, and aglycone conversion. These findings clarified the relationship between changes in enzyme activities in koji and the important components of miso, and also advance solid-state fermentation research and development of functional miso.