The effect of low-temperature storage on the activity of polyphenol oxidase in Castanea henryi chestnuts

Chestnuts of Castanea henryi (Skan) Rehd. et Wils were stored at 4 and −20 °C for a duration of 6 months. The effects of such storage treatments on the polyphenol oxidase (PPO) activity and total free phenolics content were investigated. Total phenolics content showed uneven distribution in C. henryi chestnuts. The chestnut PPO was isolated and characterized in terms of optimum temperature (40 °C), optimum pH (5.0), substrate specificity (catechol most efficient) and relative molecular weight (69.0 kDa). The PPO specific activity decreased from ca. 1180 to 340 U mg−1 for chestnuts stored at 4 °C and to ca. 300 U mg−1 for those stored at −20 °C. The PPO activity and the storage temperatures in this investigation showed a significant (P < 0.05) correlation. Moreover, the total phenolics content in both embryonic bud and endosperm decreased more during storage at −20 °C than at 4 °C. We therefore found a statistically significant correlation (P < 0.05) between the phenolics content and the PPO activity in chestnuts stored at these temperatures.