Abstract: Juice sac granulation is a major quality deterioration of harvested pumelo fruit. This study investigated the effect of heat treatment on the fruit quality of Guanxi honey pumelo during postharvest storage and its inhibitory effect on juice sac granulation, and explored the appropriate conditions. Furthermore, this study analyzed the correlation between the inhibitory effect and the metabolism of lignin synthesis and polysaccharide degradation in the cell wall. Spraying with 35, 42, 49 and 56 ℃ water was employed as postharvest handling. The appropriate temperature was selected based on the granulation index and the contents of moisture, total soluble solids and titratable acid during cold storage, and its impacts on the lignin content, lignin synthetic enzyme activities, cell wall polysaccharide contents and cell wall polysaccharide-degrading enzyme activities in fruit juice sacs were evaluated. The results suggested that compared with other treatments, spraying with water at 42 ℃ for 15 min effectively retarded the increase in juice sac granulation index and the decrease in moisture content, and maintained the contents of total soluble solids and titratable acid. Meanwhile, it suppressed the activity of phenylalnine ammonialyase, cinnamyl alcohol dehydrogenase and peroxidase in the juice sac, delaying the increase in lignin content; and inhibited the activities of cellulase, pectin methylesterase, polygalacturonase and β-galactosidase, delaying the increase in cellulose and hemicellulose contents, the decline in covalently bound pectin content and the accumulation of ion-soluble pectin and water-soluble pectin in the juice sac during storage. The above results indicated that spraying with water at 42 ℃ could retard juice sac granulation and maintain the quality of harvested Guanxi honey pumelo fruit, and the inhibitory effect on juice sac granulation might be associated with inhibited enzyme activities related to lignin synthesis and cell wall polysaccharide degradation, resulting in delayed juice sac fibration, lignification and pectin degradation, which maintained the cell wall composition and structure.

Key words: Guanxi honey pumelo fruit; heat treatment; juice sac granulation; lignification; cell wall polysaccharide