Abstract:

The objective of this study is to elucidate the effect of exogenous oxalic acid on ripening, softening and
preservation process of postharvested sugar apple (Annona squamosa L.) and provide a new method to preserve sugar apple
fruits. After being dipped in 5 mmol/L oxalic acid solution for 20 min, sugar apple fruits (Annona squamosa L. cv. African
Pride) were stored at 15 ℃, and the physiological parameters related to delaying ripening, softening and cracking process
were measured. The results showed that oxalic acid treatment decreased the softening rate and delayed the increase of total
soluble solids (TSS). Compared with the control, the cracking rate of the treatment group was reduced and the activities
of both pectin methylesterase (PE) and polygalacturonase (PG) were significantly inhibited. Oxalic acid treatment could
promote the activities of superoxide dismutase (SOD) and peroxidase (POD) at the later period of storage, and decrease the
loss of soluble protein and vitamin C significantly. In addition, oxalic acid treatment could also decrease polyphenol oxidase
(PPO) activity and malondialdehyde (MDA) content. Correlation analysis showed that the physiological parameters of PE
activity and PG activity were significantly correlated with the softening and cracking process. Therefore, exogenous oxalic
acid treatment can delay the ripening and senescence rate of sugar apple fruits.

Key words: sugar apple, oxalic acid, ripening process, storability