Compositional differences, antioxidant activity, angiotensin-converting enzyme inhibition, and sensory characteristics of kamaboko fermented in wheat, rice, brown rice, and soybean koji

Fermentation of kamaboko in koji with wheat (KW), rice (KR), brown rice (KB), or soybean (KS) was performed by simulation of tofuyo processing. Moisture and protein content decreased with fermentation, while other detected compounds increased significantly. Ash content increased from 12.9 g/100 g in kamaboko to 17.9–20.2 g/100 g (KW, KR, and KB) and 26.8 g/100 g (KS) after 4 weeks of fermentation. Mineral and fatty acid composition varied. After 8 weeks of fermentation, KW, KR, and KB exhibited total free amino acids, sugar, and phenolic content of 2804–3396 mg/100 g, 43.5–55.3 g/100 g, and 207–263 mg/100 g, while KS showed 12,300 mg/100 g, 11.3 g/100 g, and 539 mg/100 g, respectively. Radical scavenging and angiotensin-converting enzyme (ACE) inhibitory activity increased significantly following fermentation. KS showed the strongest 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging activity and ACE inhibition. Sensory analysis revealed that KW, KR, and KB were significantly more favorable than KS, with significantly stronger sweetness and weaker smell, saltiness, and aftertaste. These results indicate that wheat, rice, and brown rice koji -fermented products are acceptable as food, and that the soybean koji -fermented product is a useful source of bioactive compounds such as peptides and phenolics.