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Biochemical Characterization of an Extracellular Heat‐Stable Protease from Serratia liquefaciens Isolated from Raw Milk
Author(s) -
Baglinière François,
Salgado Rafael Locatelli,
Salgado Cleonice Aparecida,
Vanetti Maria Cristina Dantas
Publication year - 2017
Publication title -
journal of food science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.772
H-Index - 150
eISSN - 1750-3841
pISSN - 0022-1147
DOI - 10.1111/1750-3841.13660
Subject(s) - protease , casein , raw milk , skimmed milk , food science , proteases , chemistry , dithiothreitol , serratia , psychrotrophic bacteria , enzyme , hydrolysis , substrate (aquarium) , biochemistry , microbiology and biotechnology , chromatography , pseudomonas , biology , bacteria , genetics , ecology
The protease Ser2 secreted by the psychrotrophic strain Serratia liquefaciens L53, a highly proteolytic strain isolated from Brazilian raw milk was purified and characterized. Using azocasein as substrate, Ser2 exhibited activity in a wide range of pH (5 to 10) and temperature (4 to 60 °C). The optimal activity was detected at pH 8.0 and at a temperature of 37 °C. This protease, still active at 4, 7, and 10 °C, was strongly inhibited by chelating agents and by dithiothreitol, a reducing agent. These results confirmed that Ser2 belongs to the peptidase family M10 and requires Ca 2+ , Zn 2+ , and disulfide bridges for stability. This protease is able to hydrolyze three kinds of casein in the preferential order of κ→ β→ α‐casein. Highly heat‐stable in skimmed, semi‐skimmed, and whole milk at 140°C with D ‐values of 2.8, 3.9, and 4.5 min, respectively, Ser2 showed a residual activity between 87 and 100 percent after heat‐treatment of 65 °C for 30 min, 72 °C for 20 s, and 140 °C for 4 s that are commonly used in dairy industries. As the protease AprX that is mainly secreted by Pseudomonas genus, Ser2 could be one of the main causes of UHT milk destabilization during storage.