Abstract: Zhayu, a traditional Chinese fermented fish product with low salt content, high nutritional value, unique flavor and long-term storability, is made from medium-sized (2–4 kg) grass carp (Ctenopharyngodon idella). In order to reveal the evolution of bacterial flora during the fermentation process of Zhayu, changes in the bacterial community structure at 10 different time points from day 0 to day 180 of fermentation were analyzed by Illmina HiSeq high-throughput sequencing technique. Moreover, changes in texture characteristics, amino acid composition and fatty acid composition were also monitored. The results showed that during the whole fermentation process, 130 genera in 90 families in 60 orders in 30 classes in 10 phyla were found. In the early stage of fermentation (day 0 to day 10), the bacterial community diversity was rich, and there were more than 40 families with a relative abundance greater than 0.1%. The dominant families were Staphylococcaceae (48%), Enterococcaceae (9.46%), Cenarchaeaceae (5.57%), and Rhodobacteraceae (2.12%). From day 10 to day 50 of fermentation, the relative abundance of Bacillusaceae increased from 0.017% to 1.35%, Lactobacillaceae from 0.018% to 0.88%, Leuconostocaceae from 0.0% to 0.61%, Streptococcaceae from 0.002% to 0.32%, and Moraxellaceae from 0.006% to 0.31%; while Flavobacteriaceae, Oceanospirillaceae, Pseudoalteromonadaceae and Alteromonadaceae decreased rapidly, and Cenarchaeaceae decreased to zero. The dominant bacteria during this period were Staphylococcus, enterococci and lactic acid bacteria. In addition, Enterobacteriaceae tended to rapidly growth after 50 days of fermentation, which had a negative impact on the product quality. At the same time, it was found that the texture quality and the contents of amino acids and saturated fatty acids decreased with fermentation time, showing a significantly negative correlation at 0.01 level (bilateral). Therefore, the proper control of fermentation time is very important to ensure the product quality and safety of Zhayu.

Key words: Zhayu, solid-state fermentation, high-throughput sequencing, bacterial community dynamics, quality