Czech J. Food Sci., 2015, 33(2):109-117 | DOI: 10.17221/384/2014-CJFS

Characterisation of polyphenol oxidase and peroxidase and the role in browning of loquat fruitFood Chemistry

Xinglong ZHANG, Xingfeng SHAO

Department of Food Science and Engineering, Ningbo University, Ningbo, Zhejiang, P.R. China

Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from a new loquat fruit cultivar (Ninghaibai) and characterised using reliable spectrophotometric methods. In both cases, the optimum pH for PPO was 4.5 and 5 for POD, and their optimum temperatures were 30 and 35°C, respectively. Both enzymes followed Michaelis-Menten kinetics, showing K_m= 47.11 mmol/l for PPO with catechol as the substrate and K_m = 153.00 mmol/l for POD with guaiacol as the substrate. PPO was much more thermolabile than POD, losing more than 40% of relative activity after 30 min of heating at 40°C. PPO activation energy was much lower than POD activation energy (ΔE^# = 39.74 and 94.65 kJ/mol for PPO and POD, respectively): Both enzymes activities showed decreasing patterns as the compound concentration in the assay medium increased. 4-hexylresorcinol (4-HR), oxalic acid, and l-cysteine showed strongly inhibitive effects on the enzymes. Changes in L*, a*, and b* values were chosen to describe the browning of loquat pulp. Only PPO displayed a higher negative correlation with L* values, which indicated that PPO plays an important role in the browning of stored loquat cv. Ninghaibai.

Keywords: Eriobotrya japonica; PPO; POD

Published: April 30, 2015  Show citation