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 a result of 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* and b* ‐values will address the challenges of sugarcane juice preservation. RESULTS Sugarcane billets were blanched at variable time–temperature combinations in the range 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 life ( t ½ ) dropped from 16.5 to 3.47 min and decimal reduction time ( D ‐values) dropped from 54.83 to 11.52 min. Thus reactions were temperature‐sensitive. Thermodynamic studies indicated an endothermic (positive enthalpy values, Δ H > 0; 78.10 kJ mol −1 ) and reversible process (negative entropy values Δ S < 0; −0.044 kJmol −1 K −1 ). Michaeli–Menten constant ( K m ) and maximum velocity ( V max ) of PPO activity were determined by adding variable lemon juice concentrations in sugarcane juice. As the Km values increased (from 5.53 to 15.81 m m ) and V max values decreased (from 666.67 to 384.61 UmL −1 ), a Lineweaver–Burk plot suggested decreased PPO affinity of sugarcane juice. CONCLUSION The results of the present study indicate that studies on chemical kinetics and thermodynamics (PPO, TPC and L , a* and b* ‐values) of blanched sugarcane cane juice shall mitigate challenges of sugarcane juice preservation.