We have investigated on conditions for extraction of urea from rice-
koji to determine urea content in
koji.
The most appropriate condition for extraction of urea is as follows: rice-
koji is solubilized at 55°C by a saccharifying enzyme (e.g.Gluc S etc.) following heat inactivation of enzymes of
koji, and then the amount of urea is determined by the enzymatic assay. Alternatively, the condition under which urea is extracted with distilled water at room temperatureis sufficient for comparing urea contents in various
koji samples.
When we estimated urea content in rice-
koji during
koji preparation under these conditions, most of urea contained in rice was consumed by
koji mold (
Aspergillus oryzae) for its germination in early stage and thereafter the amount of urea in
koji increased as
koji mold showed vigorous mycelial growth.
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