Sugar metabolism during postharvest storage of ‘Rongrien’ rambutan fruit at different stages of maturity

Rambutan (Nephelium lappaceum Linn.) variety ‘Rongrien’ fruit were harvested at four maturity stages based on rind ripeness color (green, orange yellow, orange red and red with green spintern tip) and fruit aril were analyzed for glucose, fructose and sucrose contents and invertase activity. Sucrose was the predominant sugar regardless of harvest maturity and increased with increasing ripeness stage. Glucose and fructose were much higher in green and orange yellow fruit than in orange red and red fruit. During storage at 25°C for 6 days, dramatic increases in glucose and fructose contents and decreases in sucrose content were noted in orange red and red fruit. Green and orange yellow fruit showed only increases in fructose content while glucose content did not vary much from the pre-storage level. Invertase activity did not correlate with changes in glucose, fructose and sucrose contents. The results indicate that sweetness of rambutan, one of the most important quality criteria, was the result of the balance of the three major sugar components dominated by sucrose in freshly harvested fruit and by glucose and fructose during postharvest storage.