Impact of Thermo-sonication on Pectin Methylesterase (PME) Inactivation & Cloud Stability of Nagpur Mandarin Juice

Abstract

Nagpur mandarin is well known globally for its excellent nutritional benefits and flavour. These all characteristics get affected during storage due to a lack of knowledge & processing techniques. One of the most important parameters which decide the quality of fruit juice during storage is cloud stability, which gets affected during storage due to the action of an enzyme named pectin methylesterase. Pectin methylesterase enzyme (PME) is a heat-resistant enzyme that impacts the juice quality by decreasing the cloud stability. Thermosonication is a technique to reduce the PME activity in juice by utilizing the principle of heat and ultrasound. Therefore, an experiment was carried out to inactivate the PME utilizing the ultrasound combined with higher temperature known as thermosensation on Nagpur mandarin (Citrus reticulata Blanco) juice. This study was initiated to calculate the effect of thermosensation treatment on the pectin methylesterase enzyme (PME) activity along with the effect of thermosensation on cloud stability in comparison with various thermal pasteurization treatments. Juice samples were thermosonicated at temperatures of 50 ℃, 55 ℃, 60 ℃, and 63 ℃ for 25, 20, 15 and 10 min respectively at a constant frequency of 40 kHz. Juice samples were also thermally pasteurized at 65 ℃, 75 ℃, 85 ℃, and 95 ℃ for 80, 60, 40, and 20 sec. Samples were analyzed after treatment at 0 days and 7 days of refrigerated storage at 4 ℃. Result indicated that thermosensation at 63 ℃ for 10 min at 40 kHz frequency showed much reduced PME activity with inactivation of 72.56% over control whereas thermal pasteurization at 95 ℃ showed inactivation of 69.31%. The same treatment also showed maximum cloud activity as compared to control and thermally pasteurized juice samples. Hence thermosensation can be used as an alternative processing technique for the inactivation of PME and cloud stability.