Thermal inactivation kinetic of pectin methylesterase and cloud stability in sour orange juice

• PME is known as a pasteurization index in sour orange juice.
• The optimal thermal treatment based on PME inactivation improves the turbid appearance of the juice.
• Different fractions of PME with different thermal resistance were found during thermal treatment.
• Corrected come up time was used to estimate the time of sour orange juice pasteurization.
• Thermal treatment led to increment in cloud value by reduction in PME activity.

Heat treatment is a common method to improve cloud stability of high acid food products such as sour orange juice. Inactivation of pectin methylesterase enzyme (PME), naturally found in citrus, is known as a heat treatment index for these products. In this work, the kinetics of PME thermal inactivation and cloud stability in sour orange juice were investigated. The fresh sour orange juice was heated in a controlled water bath at 60, 70, 80 and 90 °C for different times depending on applied temperature. Time–temperature data was simultaneously recorded using a data-logger. The inactivation kinetics of PME was calculated in terms of thermal resistance parameters (D & Z values), activation energy, enthalpy, entropy and free energy. The obtained Z-value (36.90 °C), activation energy (62.61 ± 0.84 kJ/mol) and free energy (93.52–96.37 kJ/mol) revealed the high stability of PME during the heat treatment. Based on thermal resistance of PME, heating times were corrected by considering the come-up time effectiveness. The results showed that cloud value of heated juice increased by PME inactivation during heat treatment.