文章基本信息

标题：Characterisation of polyphenol oxidase and peroxidase and the role in browning of loquat fruit
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作者：Zhang X. ; Shao X.
期刊名称：Czech Journal of Food Sciences
印刷版ISSN：1212-1800
电子版ISSN：1805-9317
出版年度：2015
卷号：33
期号：2
页码：109-117
DOI：10.17221/384/2014-CJFS
出版社：Czech Academy of Agricultural Sciences
摘要：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 (Δ E ^#= 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.
关键词：Eriobotrya japonica ; PPO; POD