SORBITOL AND OTHER CARBOHYDRATE VARIATION DURING GROWTH AND COLD STORAGE OF McINTOSH APPLE FRUITS

Abstract

Fruits of McIntosh apple, Malus pumila Mill., were analyzed at 10-day intervals for sorbitol, sucrose, glucose, fructose, raffinose, and starch throughout development on the tree, both day (10 a.m.) and night (10 p.m.), and while in storage. The highest concentrations (mg/g fresh weight) of sorbitol occurred during early fruit growth with values of 4.36 and 5.38 mg/g on June 6 and 16, respectively, followed by a decreasing trend in concentration through until July 6 (1.85 mg/g) and persistently low levels, varying between 1.23 and 2.85 mg/g throughout the remainder of the season. The fructose content was relatively low during early fruit growth with values of 7.24 and 6.71 mg/g on June 6 and 16, respectively, after which it rose substantially and increased progressively to 49.60 mg/g at the end of the season. The concentrations of glucose (0.72–4.02 mg/g), sucrose (0.27–1.87 mg/g), and raffinose (0–0.77 mg/g) were relatively low throughout the growing season as were generally those of raffinose during storage. Starch increased to maximum concentrations (5.83–8.80 mg/g) during the summer months, decreased towards the end of the season, and disappeared early in storage. Day/night analyses of fruits throughout the season yielded distinct patterns in the day/night ratio of sorbitol that were concurrent with the periods of major shifts in sorbitol and fructose levels during fruit development. During the storage period, the general trend in the concentrations of sorbitol and sucrose showed increases of 1.63–4.44 and 0.67–7.22 mg/g, respectively. The concentrations of fructose (19.59–82.50 mg/g) and glucose (6.36–72.38 mg/g) were relatively high but markedly variable throughout the storage period. Fructose was present generally in greater quantities than glucose.