Enzymatic Activity and Flavor Compound Production in Fermented Silver Carp Fish Paste Inoculated with Douchi Starter Culture

Silver carp fish pastes inoculated with or without a douchi starter culture containing live Aspergillus oryzae were fermented for 30 days to produce two different fermented products, designated CulF and ConF, respectively. Protein degradation and flavor compound production during the course of fermentation were monitored. Proteolytic activity, generally higher in CulF than in ConF (P < 0.05) and dominated by acidic and serine proteases, declined to an overall minimum after 30 days. Myosin in the CulF and ConF extractives was completely degraded after 1 and 5 days, respectively. The content of free amino acids and low molecular weight (<1.3 kDa) peptides rose rapidly in CulF and progressively in ConF (P < 0.05). Ethanol, silanediol, pyrazine, phenol, and formic acid were prevalent volatile compounds in CulF, whereas butanol, butanoic acid, and acetic acid were abundant in ConF. Therefore, douchi-inoculated fermentation is an attractive process to produce savory fish pastes.