Hydrolytic activity of Virgibacillus sp. SK37, a starter culture of fish sauce fermentation, and its cell-bound proteinases.
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.
School of Food Technology, Institute of Agricultural Technology, Suranaree University of Technology, Nakhon Ratchasima, 30000, Thailand.
Sornchai
S
Sinsuwan
Sureelak
S
Rodtong
Jirawat
J
Yongsawatdigul
D000818:Animals; D001426:Bacterial Proteins / Q000302:isolation & purification / Q000378:metabolism; D002122:Calcium Chloride / Q000494:pharmacology; D004795:Enzyme Stability / Q000187:drug effects; D005285:Fermentation / Q000187:drug effects; D029941:Fish Proteins / Q000378:metabolism; D005399:Fishes; D005516:Food Microbiology; D005524:Food Technology; D006868:Hydrolysis; D010447:Peptide Hydrolases / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D058679:Virgibacillus / Q000187:drug effects / Q000201:enzymology*
D001426:Bacterial Proteins; D029941:Fish Proteins; D010447:Peptide Hydrolases; D002122:Calcium Chloride