Quality and safety of natto fermented with <i>Bacillus subtilis</i> BJ3-2 using kidney beans from Guizhou

Abstract With the continued development of the kidney bean industry and increased kidney bean production, processing methods need to be developed and optimised for kidney beans. This study focused on the nutritional qualities of seven varieties of raw materials of Guizhou kidney bean and the characteristic and safety factors of kidney bean natto (KBN), including amino acid nitrogen, mucus yield, natto kinase activity, and biogenic amines (BAs). The kidney beans demonstrated good adaptability to natto processing. After fermentation, the average protein content of the seven kidney beans increased by about 3.37 g/100. Among the varieties, YuQiuDou (YQD, P520522025) demonstrated the best adaptability to fermentation. The nutritional composition of YQD kidney beans was as follows: total starch (53.55 g/100 g), protein (23.84 g/100 g), resistant starch (27.00 g/100 g), and α-amylase inhibitor (6.39 U/g). The mucilage yield of YQD natto was determined to be 20.57%, while the NK activity exhibited by YQD natto was measured at 0.2992 ± 0.002 Tos-Arg-OMe. The BAs detected in KBNs were 7.62–33.92 mg/kg (lower than the United States Food and Drug Administration limit of ≤50 mg/kg), and spermine was predominant. This study provides guidance and a reference for the future development of kidney bean products and the selection of raw materials.