Changes in Organic Acids, Sugars, and Headspace Volatiles during Fruit Ripening of Soursop (Annona muricata L.)

Abstract

Abstract Sequential changes in starch, sugars, organic acids, and headspace volatiles were determined on single soursop fruits from harvest to fruit breakdown. Sucrose increased 4-fold; maximum concentration occurred 3 days after harvest, then declined to 40% of the peak value. Fructose and glucose increased slowly to a peak 5 days after harvest. The ratio of sucrose, glucose, and fructose, respectively, at the edible ripe stage was 4.3:3.0:3.2. There was a 7-fold increase in malic acid and a 3-fold increase in citric acid. Both acids peaked 3 to 4 days after harvest, then declined. About half of the organic acids were present as salts. Headspace volatile production paralleled ethylene evolution. Volatile production began to increase 3 days after harvest and peaked 2 days later. This peak corresponded with the peaks in total sugars, organic acids, and the edible ripe stage when individual fruit results were compared on the basis of the start of the climacteric respiratory increase. After the peak in volatile production, there was a dramatic drop over the next 3 days in major fruity esters produced, with a gradual increase in volatiles, which probably imparted the off-odor of the overripe fruit. The activities of amylase, polygalacturonase, and cellulase increased during ripening. Starch breakdown leading to sugar and organic acid production occurred before any rise in ethylene production. This breakdown of starch may be an important initiating event in the ripening of soursop fruit.