Chemical characteristics and microbial diversity of Ayu-narezushi from Gifu

Abstract

Based on the production method for funa-narezushi,' which has a long fermentation period, we established technology to manufacture "ayu-narezushi"made from ayu (Plecoglossus altivelis altivelis). The pH of raw ayu is 6.15. After 10 months of fermentation, the pH in the muscle portion of narezushi drops to between 4.20 and 4.70, and to between 4.00 and 4.65 in nare-meshi. The predominant microorganisms in ayu-narezushi were Lactobacillus sp. (2.57 ±0.2 × 104-1.13 ± 0.46× 109cfu/g), mold or yeast (2.95 ±0.07× 104-2.0 ± 0.0× 108cfu/g), and Bacillus sp. (2.83 ± 0.74 ×103-2.26±0.23 × 104cfu/g). Based on microflora analysis using a next-generation sequencer, the predominant bacteria in fermented ayu-hon-narezushi belonged to the genera Lactobacillus, Tetragenococcus and Staphylococcus. After 10 months of fermentation, the free amino acid content in nare-ayu-zushi increased seven-fold from that in raw ayu, and 10-to 15-fold in nare-meshi from that in meshi In particular, the glutamic acid and hydrophobic amino acid content increased in both the fish and the rice. We isolated Lactobacillus buchneri, L. parabuchneri and L. plantarum which produce/-aminobutyric acid (GABA) from glutamic acid during fermentation. It is thought that these microorganisms also produce GABA in nare-zushi.