Change of Saccharides in Soybeans during Manufacturing of Natto

Abstract

Natto is a Japanese traditional food made from whole soybeans by the fermentation of Bacillus natto. The change of soybeans saccharides in both quality and quantity was investigated by the gaschromatographic and photometric analysis during manufacturing of natto. Raw soybeans imported from China for natto manufacturing, contained 7.05% sucrose, 1.15% raffinose, 6.34% stachyose, 0.07% myo-inositol and 0.98% starch on dry base. During soaking and steaming, oligosaccharides, myo-inositol and starch were partially lost in soaking water or cooking drain and a part of the oligosaccharides was decomposed. During fermentation, sucrose decreased down to about one seventh, and both raffinose and stachyose decreased to about one third of the starting levels within 10 hours after starting fermentation. Along with the reduction of the sugars, manninotriose, melibiose, glucose and fructose increased up to 2.04% in 12hrs, 1.62% in 8hrs and 0.27% in 8hrs, respectively. Thereafter glucose and fructose decreased rapidly, whereas other oligosaccharides decreased slowly. Levan, viscous polysaccharides produced by Bacillus natto, increased along with the reduction of soybeans oligosaccharides. Neither liberation of galactose nor saccharification of starch were obserbed during fermentation. After maturing, the final products still contained 0.41% stachyose, 1.18% manninotriose, 0.16% melibiose, 0.49% levan and 0.64% starch on dry base.