Kinetics of inactivation of quality-deteriorating enzymes and degradation of selective phytoconstituents in pink guava pulp during thermal processing.

Thermal inactivation kinetics of peroxidase (POD), polyphenol oxidase (PPO), pectin methyl esterase (PME) and ascorbate oxidase (AO) were studied over the temperature range of 45-85 °C along with the degradation kinetics of ascorbic acid (AA) and lycopene in Psidium guajava pulp. POD, PPO, PME and AO followed first-order kinetics whereas AA degradation data was explained by pseudo first-order kinetics. Lycopene degradation was suitably fitted in an exponential model, indicating continuous degradation of lycopene and higher degradation at higher temperature. Activation energy (Ea) of POD, PPO, PME, and AO was 63.79 ± 1.28, 60.36 ± 1.21, 63.22 ± 1.06 and 106.33 ± 8.51 kJ/mol, respectively. AA had Ea (95.82 ± 1.92 kJ/mol) higher than lycopene (54.92 ± 1.10 kJ/mol). PME (Z = 39.4 ± 0.1 °C) showed highest heat stability while AO (Z = 14.3 ± 1.1 °C) was least stable amongst the enzymes studied. AA (Z = 23.5 ± 0.5 °C) was weakest amongst the phytoconstituents in guava pulp and its retention was challenged during thermal processing. The thermal resistance of quality deteriorating enzyme of guava was found to be higher than that of the common spoilage organisms such as Saccharomyces cerevisiae and Lactobacillus plantarum reported for processed fruit products. Thus, this research hints towards the need for more robust thermal processing for inactivation of quality deteriorating enzymes.