Hydrolytic activity of Virgibacillus sp. SK37, a starter culture of fish sauce fermentation, and its cell-bound proteinases
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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 % CaCl2 (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 Ca2+-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 CaCl2. In addition, CaCl2 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.
KeywordsVirgibacillus sp. Moderately halophilic bacterium Cell-bound proteinase Fish sauce fermentation
This work was supported by a research grant from the National Science and Technology Development Agency (NSTDA), Thailand under research agreement No. BT-B-01-FT-19-5014 and Suranaree University of Technology under a Food Protein Research Unit Grant Agreement.
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