The effects of non-fermented soybean milk (NFSM) and fermented soybean milk (FSM) intake on the faecal microbiota and metabolic activities in 10 healthy volunteers were investigated. Soybean oligosaccharides, raffinose and stachyose were utilized by bifidobacteria except for Bifidobacterium bifidum, but most strains of Escherichia coli and Clostridium perfringens could not use them. During the dietary administration of FSM, the number of bifidobacteria and lactobacilli in the faeces increased (p < 0.05), and clostridia decreased (p < 0.05). Moreover, the concentrations of faecal sulphide were decreased (p < 0.01) in the intake of FSM. During the dietary administration of NFSM, the number of bifidobacteria tended to increase. These results indicate that the consumption of soybean milk, especially FSM, is related to improvement of the intestinal environment.

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Tuberous roots of yacon (Smallanthus sonchifolius) accumulate about 10%, on a fresh weight basis, of inulin-type fructooligosacharides (FOSs), known as a food ingredient with various healthy benefits. However, we have a great difficulty to ensure these benefits because FOSs with a lower degree of polymerization (DP) decreased remarkably, and fructose increased when the tuberous roots were stored after harvesting even under previously recommended storage conditions of low temperature with high humidity. In the present study, to elucidate the involvement of FOS-metabolizing enzymes in FOS reduction during storage at 90% relative humidity and 8 degrees C, we extracted a crude protein from yacon tuberous roots and measured the activities of invertase (beta-fructofuranosidase, EC 3.2.1.26), sucrose:sucrose 1-fructosyltransferase (1-SST, EC 2.4.1.99), fructan:fructan 1-fructosyltransferase (1-FFT, EC 2.4.1.100), and fructan 1-exohydrolase (1-FEH, EC 3.2.1.80). The enzyme activities acting on sucrose, both invertase and 1-SST, were weakened after storage for a month. In addition, the activity of 1-FEH acting on short FOSs such as 1-kestose (GF(2)) and 1-nystose (GF(3)) was higher than that of 1-FFT. These results suggest that the continuous decline in FOSs of low DP during storage was dependent mainly on the 1-FEH activity. On the other hand, FOSs with a DP of >or= 9 only slightly decreased in stored yacon tuberous roots during storage, though distinct 1-FEH activity was observed in vitro toward a high-DP inulin-type substrate, indicating that highly polymerized FOSs content was unlikely to be closely connected with the 1-FEH activity.