Polyamines have beneficial properties to prevent aging-associated diseases. Raw soybean has relatively high polyamine contents; and the fermented soybean natto is a good source of polyamines. However, detailed information of diversity of polyamine content in raw soybean is lacking. The objectives of this study were to evaluate differences of polyamines among raw soybeans and select the high polyamine-containing cultivar for natto production. Polyamine contents were measured chromatographically in 16 samples of soybean, which showed high variation among soybeans as follows: 93-861 nmol/g putrescine, 1055-2306 nmol/g spermidine, and 177-578 nmol/g spermine. We then confirmed the high correlations of polyamine contents between raw soybean and natto (r = 0.96, 0.95, and 0.94 for putrescine, spermidine, and spermine, respectively). Furthermore, comparison of the polyamine contents among 9 Japanese cultivars showed that 'Nakasen-nari' has the highest polyamine contents, suggesting its suitability for enhancement of polyamine contents of natto.

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__________________We applied the low acid phosphatase producer Aspergillus oryzae KBN8048 or its mutants to non-heated soybean paste. In a rice koji trial, acid phosphatase activity was lower than that of A. oryzae EM-2, a market strain for miso brewing, when sodium phosphate concentrations up to 20 mM were added at the beginning of incubation. The soybean paste was brewed at 30 °C for 60 days, using rice koji, followed by the addition of 0.2 % inosinic acid and incubation at 4 °C. The inosinic acid required 7 weeks and 1 week to decrease by 50 % with KBN8048 and EM-2, respectively. When KBN8048 was incubated at 30 °C for 1 week, more inosinic acid was retained than when the same was done using EM-2. These observations indicate that addition of A. oryzae KBN8048 strains to non-heated soybean paste was effective for inhibiting the degradation of inosinic acid.