Total soluble solids, ethanol insoluble fraction, pH, titratable acidity, total phenols, total ethanol-soluble sugars, ascorbic acid, respiration, and ethylene production were determined sequentially in individual soursop fruits from the day of harvest until the start of fruit breakdown. Total soluble solids increased from about 10° Brix to near 16° Brix during 3 days of ripening. Fruit pulp pH declined from 5.8 to 3.6 with a concomitant increase in titratable acidity over the same ripening period. Penetration force was high, generally greater than 7.5 kg, in the preclimacteric stage and then declined to less than 0.5 kg during ripening. Total phenols declined during ripening to one-third of the preclimacteric levels, while total ethanol-soluble sugars and ascorbic acid increased twofold and elevenfold, respectively. The maximum respiration rate was 108 ml/kg·hr. Ethylene production increased 24–48 hr after the fruit climacteric was initiated. The optimum eating stage occurred at day 5 to 6 from harvest at the peak of ethylene production. At a later stage, the fruit was more bland with a slight off-odor; this correlated with a decline in the titratable acidity and total phenols.
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Robert E. Paull (1982) studied this question.