Physico-chemical properties of longan fruit during development and ripening

- Longan fruit growth follows a smooth sigmoidal type during fruit development.
- Sucrose is the primary accumulated sugar at maturity stage of longan fruit.
- Sucrose accumulation is associated with a decline of AI, NI, and SS-C and an increase of SPS.
- Fruit quality indexes and antioxidant activity are gradually increased with fruit development.

As a non-climacteric fruit, longan does not continue to ripen until harvest due to pericarp browning and aril breakdown. The patterns of fruit growth and changes in physico-chemical properties of longan fruits ('cv. Shixia') after post-anthesis (DPA) were investigated over two different year seasons, with the aim to identify a reliable maturity index for harvest. Fruit growth, based on fruit weight, volume and diameter, followed a smooth sigmoidal type of curve for eleven selected periods. Vc contents showed an ascending trend in aril. A similar variation was also demonstrated in the ratio of TSS/TA and activities of PPO and POD. However, MDA in aril showed less accumulation than that in pericarp, though the change trends of MDA were similar in both of tissues. By contrast, sucrose was the primary accumulated form in the later growth stage of longan fruit. Increases in the proportion of sucrose were associated with a decline of AI, NI, and SS-C activities and an increase of SPS activity approximately 70 DPA. Information on fruit morphology and physico-chemical properties is benefit for better understanding of the physiological maturity status of longan. Based on charateristics of different indexes, TSS/TA and sucrose contents revealed increasing trend with advancing maturity and reached the steady status during 100-110 DPA. So their indexes was applied to determine the physiological mature stage of fruits, that would present the optimum values of harvesting properties desirable in the investigated cultivar. It could contribute to assist growers in assessing fruit readiness for harvest.