The bacterial community and the metabolic activities involved at the flavor-forming stage during the fermentation of shrimp sauce were investigated using metatranscriptome and 16S rRNA gene sequencings. Results showed that the abundance of Tetragenococcus was 95.1%. Tetragenococcus halophilus was identified in 520 of 588 transcripts annotated in the Nr database. Activation of the citrate cycle and oxidative phosphorylation, along with the absence of lactate dehydrogenase gene expression, in T. halophilus suggests that T. halophilus probably underwent aerobic metabolism during shrimp sauce fermentation. The metabolism of amino acids, production of peptidase, and degradation of limonene and pinene were very active in T. halophilus. Carnobacterium, Pseudomonas, Escherichia, Staphylococcus, Bacillus, and Clostridium were also metabolically active, although present in very small populations. Enterococcus, Abiotrophia, Streptococcus, and Lactobacillus were detected in metatranscriptome sequencing, but not in 16S rRNA gene sequencing. Many minor taxa showed no gene expression, suggesting that they were in dormant status.

The epiphytic Lactobacillus acidophilus SW01 isolated from shrimp waste (SW) was used in SW fermentation. During the fermentation the lag phase of SW01 was hardly observed. The pH of the fermentation broth decreased to 3.86 within 12 h and reached the lowest point at 3.73 after 48 h. This indicates a quick and deep acidification process by SW01. Besides, SW01 was observed to have high protease activity. As a result, the minerals and protein in SW were quickly removed with their contents decreasing to 0.73% and 7.8% respectively after 48 h fermentation. In the pilot scale fermentation, the pH was 3.99 and 3.86 respectively after 12 and 24 h fermentation. The mineral and protein contents were 0.98% and 8.44% respectively after 48 h fermentation. The residue of the fermented SW contains less than 1% minerals and can be easily transformed into chitin by a mere bleaching treatment.Highlights► An epiphytic Lactobacillus acidophilus SW01 was used in shrimp waste fermentation for chitin production. ► L. acidophilus SW01 produced sufficient lactic acid and enough protease in shrimp waste. ► L. acidophilus SW01 remarkably improved the removal of minerals and protein from shrimp waste. ► After fermentation the mineral content in shrimp waste was below 1%. ► Result of pilot scale fermentation was close to that of laboratory experiments.