藤黄微球菌(Micrococcus luteus)KDF1胞外蛋白酶酶学性质与水解大豆蛋白产物研究

The extracellular protease from Micrococcus luteus KDF1: properties and characterization of its hydrolysates from soy protein

对1株分离于克东腐乳的优势菌株藤黄微球菌（Micrococcus luteus）KDF1胞外蛋白酶的酶学性质及其水解大豆分离蛋白（soybean protein isolates，SPI）产生的氨基酸图谱进行研究。以酪蛋白为底物，利用酶学技术研究了温度、pH、NaCl、乙醇和金属离子对藤黄微球菌（Micrococcus luteus）KDF1胞外蛋白酶的活性和稳定性的影响。研究表明藤黄微球菌（Micrococcus luteus）KDF1胞外蛋白酶的最适反应温度为40℃，在20—40℃范围内具有良好的稳定性；最适反应pH为9．0，在pH7．0～9．0范围内具有良好的稳定性；在9％（w／v）NaCl和8％（w／v）乙醇中分别表现出良好的催化活性和稳定性；Ca^2＋和Mg^2＋可显著增强藤黄微球菌（Micrococcus luteus）KDF1胞外蛋白酶的催化活性。利用氨基酸分析技术检测藤黄微球菌（Micrococcus luteus）KDF1胞外蛋白酶水解SPI产生的氨基酸图谱，结果表明总游离氨基酸、必需氨基酸和风味氨基酸含量明显增加。上述结果表明藤黄微球菌（Micrococcus luteus）KDF1胞外蛋白酶在酶法促熟和酶法发酵腐乳领域有潜在的应用价值。

The enzymatic properties of extracellular protease from predominant strain Micrococcus luteus KDF1 isolated from Kedong sufu and the amino acid profiles of its hydrolysates from soybean protein were researched. Using casein as substrate, the effects of temperature, pH, NaCl, ethanol and metal ions on activity and stability of the extra- cellular protease from Micrococcus luteus KDF1 were studied by means of enzymatic technology. The extracellular protease from Micrococcus luteus KDF1 exhibited maximal activity at 40℃ or at pH 9.0, and high stability at 20 - 40 ℃ or at pH 7.0 - 9.0. The high stability and activity of extracellular protease from Micrococcus luteus KDF1 were exhibited in both 9 % NaCI and 8 % ethanol. The activity of extracellular protease from Micrococcus luteus KDF1 was significantly enhanced by the presence of Ca^2＋ and Mg^2＋ ions. Hydrolysis of soybean protein isolates with extracellular protease from Micrococcus luteus KDF1 increased the level of total free amino acids, essential amino acids and flavor amino acids. The results showed that extracellular protease from Micrococcus luteus KDF1 seemed to be good candidate enzyme for acceleration of fermented soybean food ripening.