Chemical kinetics and thermodynamics of PPO activity, colour changes and microbial degradation during blanching of the sugarcane billets.

BACKGROUND: Sugarcane juice, which has a short shelf life, is a popular thirst-quenching and rejuvenating beverage worldwide. The limited shelf life is due to changes in polyphenol oxidase (PPO) activity, total plate count (TPC) and color attributes (L*, a* and b* values). We hypothesized that chemical kinetics and thermodynamics of blanched sugarcane cane juice causing alterations in PPO, TPC and L, a*, b* values shall address the challenges of sugarcane juice preservation.

RESULT: Sugarcane billets were blanched at variable time-temperature combinations in the range of 0-20 min and 70-90°C. Reaction rates increased with increasing temperature; PPO activity, TPC and colour followed first order kinetics. PPO activity had an activation energy (Ea) of 81 kJ mol-1 . The half time (t ½) values dropped from 16.5 min to 3.47 min and decimal reduction time (D-values) dropped from 54.83 min to 11.52 min. Thus reactions were temperature-sensitive. Thermodynamic studies indicated an endothermic (positive enthalpy values, ΔH > 0; 78.10 kJmole-1 ) and reversible process (negative entropy values ΔS < 0; -0.044 kJmole-1  K-1 ). Michaelis - Menten constant (Km ) and maximum velocity (Vmax ) of PPO activity were determined by adding variable lemon juice concentrations in sugarcane juice. As Km values increased (from 5.53 mM to 15.81 mM) and Vmax values decreased (from 666.67 to 384.61 UmL-1 ), Lineweaver Burk Plot suggested decreased PPO affinity of sugarcane juice.

CONCLUSION: The results indicated that studies on chemical kinetics and thermodynamics (PPO, TPC and L, a*, b* values) of blanched sugarcane cane juice shall mitigate challenges of sugarcane juice preservation. This article is protected by copyright. All rights reserved.