Fish sauce production relies on a natural fermentation process requiring 12-18 months for process completion. Virgibacillus sp. SK37 has been shown to be a potential strain for fish sauce acceleration. However, hydrolytic activity of proteinases bound at cell surface of this strain has not been well elucidated. Addition of 0.2 % CaCl(2) (w/w) in conjunction with starter cultures of Virgibacillus sp. SK 37 increased protein hydrolysis as measured by α-amino group content throughout fermentation (P < 0.05). Cell-bound proteinases from Virgibacillus sp. SK 37 were extracted into a free form by incubating the washed cells in Ca(2+)-free buffer at 37 °C for 2 h. Cell-bound proteinases revealed molecular mass of 19, 20, 22, 32, 34, and 44 kDa based on a synthetic peptide zymogram. The proteinases showed subtilisin-like serine characteristics with the highest activity at 50 °C and pH 8 and 11. Activity of the extracted proteinases increased ~4 times at ≥100 mM CaCl(2). In addition, CaCl(2) enhanced thermal stability of the extracted proteinases. Enzymes showed proteolytic activity in either the absence or presence of 10 and 25 % NaCl toward fish muscle, soy protein isolate, and casein substrates. Cell-bound proteinases were likely to play an important role in protein hydrolysis during fish sauce fermentation.

译文

鱼露生产依赖于自然发酵过程,需要12-18个月才能完成过程。Virgibacillus sp。SK37已被证明是鱼露加速的潜在菌株。然而,尚未很好地阐明该菌株细胞表面结合的蛋白酶的水解活性。添加0.2% CaCl(2) (w/w) 与Virgibacillus sp. SK 37的发酵剂培养物一起增加了蛋白质水解,如在整个发酵过程中通过 α-氨基含量测量 (P <0.05)。通过将洗涤过的细胞在不含Ca(2) 的缓冲液中于37 °C孵育2小时,将来自Virgibacillus sp. SK 37的细胞结合蛋白酶提取为游离形式。根据合成肽酶谱,细胞结合蛋白酶的分子量为19、20、22、32、34和44 kDa。蛋白酶表现出枯草杆菌蛋白酶样丝氨酸特征,在50 °C和pH 8和11时活性最高。提取的蛋白酶的活性在 ≥ 100 mM CaCl(2) 时增加了约4倍。此外,CaCl(2) 增强了提取的蛋白酶的热稳定性。在不存在或存在10和25% NaCl的情况下,酶对鱼肌肉,大豆分离蛋白和酪蛋白底物表现出蛋白水解活性。在鱼露发酵过程中,细胞结合的蛋白酶可能在蛋白质水解中起重要作用。

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