This study attempted to culture koji mold
Aspergillus oryzae on seaweeds including
Pyropia yezoensis,
Sarugassum horneri,
Saccharina japonica,
Ecklonia stolonifera,
Eucheuma muricatum, and
Ascophyllum nodosum. The seaweeds were added with water, starter strains of
A. oryzae, and incubated for 3 days at 30-34.5℃. The mold growth was observed for all the seaweed samples at the range of 0.3-10.7 mg of N-acetylglucosamine per gram dry matter of culture, but the growth was limited when the ash content of the seaweeds exceeded 20% w/w. The growth of contaminant bacteria was high at 10
7-10
9 cfu/g levels as for some of the seaweed cultures and regarded as a problem before utilization as a food item. The three prepared lots of nori cultures were dominated by gram positive bacteria including
Staphylococcus gallinarum beside the koji mold based on metagenomic analysis. The nori cultures showed enzymatic activities in protease and α-amylase, while cultures of
Sar. horneri and
Sac. japonica showed only protease activity. The water content-water activity relationship suggested that the suitable water content for mold solid-state culture is at 50-70% w/w levels to give the water activity value of 0.96-0.97. Preparation of seaweed koji was suggested by culturing koji mold on seaweeds (desalted, 50-70% moisture) regulating bacterial growth.
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