Effect of low methoxyl (LM) pectin complexation on the thermal and proteolytic inactivation of lysozyme: A kinetic study

Using isothermal heating or proteolytic hydrolysis, inactivation of lysozyme was studied in the presence of different low methoxyl (LM) pectin concentrations. Kinetic studies were carried out in order to evaluate the effect of the LM pectin complexation on the heat and proteolysis sensitivities of lysozyme when it is used as preservative in heat treated foods or foods containing proteolytic enzymes, respectively. The thermal inactivation of “free” lysozyme followed first-order kinetics and D-values decreased with increasing temperature indicating a more rapid lysozyme inactivation at higher temperatures. The calculated Z-value in the studied temperature range (75–95 °C) was 9.3 °C. The influence of LM pectin complexation on the inactivation kinetics of lysozyme (0.714 g·L−1) was shown to be dependent on the LM pectin concentration (0–1 g·L−1). Lysozyme complexed with a small amount of LM pectin (0.05 g·L−1) showed an increase in its thermal stability, especially at 75 and 80 °C. However, an increase in the LM pectin concentration increased the lysozyme sensitivity to heat treatment. On the other hand, the addition of proteolytic enzymes to the LM pectin/lysozyme complexes gave the opposite effect: higher LM pectin concentrations were more effective to protect lysozyme against hydrolysis by proteases. These results were interpreted in terms of lysozyme entrapment in an LM pectin chain network via electrostatic interactions resulting in stabilization or sensitization effect according to LM pectin concentration.