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Production of a Milk‐Clotting Enzyme by Glutinous Rice Fermentation and Partial Characterization of the Enzyme
Author(s) -
Zhao Xiao,
Wang Ji,
Zheng Zhe,
Zhao Aimei,
Yang Zhennai
Publication year - 2015
Publication title -
journal of food biochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.507
H-Index - 47
eISSN - 1745-4514
pISSN - 0145-8884
DOI - 10.1111/jfbc.12108
Subject(s) - fermentation , food science , chemistry , enzyme assay , enzyme , skimmed milk , biochemistry
Fermentation parameters affecting a milk‐clotting enzyme ( MCE ) production by glutinous rice fermentation were evaluated using selected rice starters called J iuqu. The MCE was produced under the following conditions: rice inoculation starter at 3%, fermentation time of 5 days, temperature at 30 C , initial rice medium pH of 5.0, rice concentration of 70% and rotation speed of 120 rpm. The enzyme preparation obtained by 70% ethanol precipitation of the culture supernatant had milk‐clotting activity ( MCA ) of 6,160 S u/g and a C / P ratio (the ratio between MCA and proteolytic activity) of 10.81 at a recovery rate of 44.82%. The molecular mass of the MCE was 39.7 kDa . MCE production was optimal at 35 C and a pH of 5.4. The presence of N a + , K + , Mg 2+ , Ca 2+ and Al 3+ stimulated enzyme activity. The K m and V max values were 22.90 g/ L and 21.11 m L /s, respectively, with skim milk as the substrate. Practical Applications In the last two decades, different sources of milk‐clotting enzymes ( MCE s) have been explored to meet the increasing demand for cheese production worldwide. This study describes a MCE isolated by ethanol fractionation from glutinous rice wine fermented by J iuqu. The MCE , with a relatively high C / P ratio, is potentially applicable as a coagulant in cheese making. The property of thermal instability of the enzyme is advantageous as it would be inactivated during curd scalding (at about 50 C ), thus formation of bitter‐taste peptides caused by residual proteolytic activity of the enzyme during cheese ripening could be prevented. In addition, the optimal temperature (35 C ) of the MCE is within the range of temperature (30–35 C ) generally used during milk coagulation processes. Therefore, the results suggest that a MCE that could have potential application in cheese production may be obtained by glutinous rice fermentation under the conditions of this study.