The Japanese pear (Pyrus pyrifolia Nakai) cv. ‘Rinka’ exhibits severe symptoms of vascular bundle browning (VBB) in the flesh tissue within a week when stored at 4°C. This study examined the impact of pre-storage heat treatments at 30, 35, and 40°C, as well as delayed storage (DS), for which harvested pears are held at 25°C for 7 days before cold storage, on the incidence of VBB. The results showed that heat treatments at 35 or 40°C for one or two days significantly reduced the incidence of VBB during cold storage. Specifically, the pears treated at 40°C for two days exhibited no detectable VBB after being stored at 4°C for 15 days. There were no significant differences in the quality, such as the soluble solids content and firmness, between the treated and untreated pears, although the percentage weight loss was higher after 15 days of cold storage in the treated pears (2.14–2.79%), compared with that in the control (0.92–1.12%). These results indicate that heat treatments extend the storage life of Rinka pears under low-temperature conditions. The efficacy of DS was also observed, but to a lesser extent. Moreover, optical microscopy revealed the accumulation of phenolic compounds and an increase in polyphenol oxidase (PPO) activity in the vascular bundles and the surrounding cells of the affected flesh tissue, whereas these changes were observed exclusively in the vascular bundles of healthy flesh tissue.
Hayama et al. (Thu,) studied this question.