Characterisation of polyphenol oxidase and peroxidase and the role in browning of loquat fruit

Xinglong Zhang and Xingfeng Shao
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Xinglong Zhang: Department of Food Science and Engineering, Ningbo University, Ningbo, Zhejiang, P.R. China
Xingfeng Shao: Department of Food Science and Engineering, Ningbo University, Ningbo, Zhejiang, P.R. China

Czech Journal of Food Sciences, 2015, vol. 33, issue 2, 109-117

Abstract: 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 Km= 47.11 mmol/l for PPO with catechol as the substrate and Km = 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 (search for similar items in EconPapers)
Date: 2015
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Citations: View citations in EconPapers (2)

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Persistent link: https://EconPapers.repec.org/RePEc:caa:jnlcjf:v:33:y:2015:i:2:id:384-2014-cjfs

DOI: 10.17221/384/2014-CJFS

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