QOPNA - Organic Chemistry, Natural and Agro-Food Products Research Unit, Department of Chemistry, University of Aveiro, 3810-193 Aveiro, Portugal.
IEETA - Institute of Electronics and Informatics Engineering of Aveiro and CIDMA - Center for Research & Development in Mathematics and Applications, University of Aveiro, 3810-193 Aveiro, Portugal.
Food Res Int. 2019 Jan;115:73-82. doi: 10.1016/j.foodres.2018.08.002. Epub 2018 Aug 3.
Microbial transglutaminase (MTG) is an enzyme largely used in the food industry, mainly to improve food texture. However, many globular proteins show low susceptibility to the action of this enzyme. High-pressure processing (HPP), being able to change protein conformation, may be a useful tool to increase the accessibility of globular proteins to the action of MTG. Nevertheless, HPP conditions need to be carefully optimized to avoid the expected decrease of enzymatic activity observed above certain conditions of pressure (P), treatment time (t) or temperature (T). Pressure inactivation of MTG under different HPP conditions (200-600 MPa; 20-40 °C; 10-30 min) was evaluated employing a face-centered composite design at four different pH values (4-7). The regression models obtained presented high coefficients of determination and high F values, although they could not explain some of the associated variability. At all the pH values tested, the three main factors (P, T, and t) significantly (p < 0.05) affected the activity of MTG. At least 20% of MTG was inactivated when low pressures (200 MPa) were used at pH 4 and 5, whereas a higher pressure above 400 MPa was needed to obtain a similar inactivation at pH 6 or 7. MTG pressure-inactivation followed first-order kinetics under all tested conditions. Inactivation rate constants decreased with increasing pressure at constant temperature and pH 4, with a positive activation volume (V), while the opposite was verified for the other pH values. Both activation energy (E) and V were dependent on pH, however, at the lower pH values, E and V did not vary significantly with pressure and temperature, respectively. Overall, MTG can be considered relatively resistant to pressure, particularly near its optimal pH.
微生物谷氨酰胺转氨酶（MTG）是一种广泛应用于食品工业的酶，主要用于改善食品质地。然而，许多球状蛋白对该酶的作用表现出较低的敏感性。高压处理（HPP）能够改变蛋白质构象，可能是增加球状蛋白对 MTG 作用的可及性的有用工具。然而，需要仔细优化 HPP 条件，以避免在压力（P）、处理时间（t）或温度（T）的某些条件下观察到的预期酶活性下降。在四个不同的 pH 值（4-7）下，采用面心复合设计评估了 MTG 在不同 HPP 条件（200-600 MPa；20-40°C；10-30 min）下的压力失活动力学。获得的回归模型具有较高的决定系数和较高的 F 值，尽管它们无法解释一些相关的可变性。在所有测试的 pH 值下，三个主要因素（P、T 和 t）显著（p<0.05）影响 MTG 的活性。当在 pH 4 和 5 下使用低压力（200 MPa）时，至少有 20%的 MTG 失活，而在 pH 6 或 7 下需要更高的压力才能获得类似的失活。在所有测试条件下，MTG 的压力失活遵循一级动力学。在恒定温度和 pH 4 下，失活速率常数随压力的增加而降低，具有正的活化体积（V），而在其他 pH 值下则相反。活化能（E）和 V 均依赖于 pH 值，然而，在较低的 pH 值下，E 和 V 分别随压力和温度的变化不大。总体而言，MTG 对压力相对具有抗性，特别是在其最适 pH 值附近。
