[Changes in cell wall components and cell wall-degrading enzyme activities of postharvest longan fruit during aril breakdown].

Longan (Dimocarpus longan Lour.) fruits are very susceptible to pericarp browning and aril breakdown, and postharvest aril breakdown is one of the most important factors degrading the quality and shorting storage life of longan fruit. Changes in aril breakdown index, cell wall components and cell wall-degrading enzyme activities in aril of longan cv. Fuyan fruits using sealed polyethylene film bags (0.015 mm thick) at (10+/-1) degrees C were investigated. The main results were as follows. Development of aril breakdown was higher with storage time (from day 0 to day 36). Aril breakdown index was positively and significantly correlated with storage time (P<0.01). During development of aril breakdown, the total dry weight of the cell wall materials, protopectin, cellulose, semicellulose and cell wall protein contents of aril decreased progressively. The total dry weight of the cell wall materials, contents of protopectin, cellulose, semicellulose and cell wall protein of aril were all negatively correlated with aril breakdown index. There were low beta-galactosidase activity, and high activities of pectinesterase (PE), polygalacturonase (PG) and cellulase in aril of harvested fruit. PE activity in aril gradually decreased during development of aril breakdown. The activities of PG and cellulase in aril increased significantly during storage from day 6 to day 12 and from day 0 to day 12, respectively. The peaks enzyme activities of both PG and cellulase appeared on the 12th day after harvest, then the enzyme activity decreased; whereas, the activities of PE, PG and cellulase changed little from day 0 to day 24, and then rapidly decreased. The beta-galactosidase activity in aril decreased slightly during storage from day 0 to day 24. However, the beta-galactosidase activity increased significantly after day 24. Especially, the beta-galactosidase activity increased rapidly after 30 d of storage, in the meantime, the activities of PE, PG and cellulase almost disappeared. From the results it can be seen that the development of aril breakdown was due to the degradation of cell wall components such as protopectin, cellulose, semicellulose and cell wall protein. The early and middle phases of development of aril breakdown were mainly brought about by the action of PE, PG and cellulase, whereas, beta-galactosidase played the key role at the late phase of aril breakdown.

[The relationship between the desiccation-induced browning and the metabolism of active oxygen and phenolics in pericarp of postharvest longan fruit].

Longan (Dimocarpus longan Lour.) fruits are very susceptible to water loss and pericarp browning, and postharvest pericarp browning is the most important factors degrading the quality of longan fruit and shorting storage life. Pericarp browning has been attributed to desiccation, chilling, heat stress, senescence and pest or pathogen attack. Desiccation is the most main factor of induced-pericarp browning in longan. The relationship between water loss from pericarp and pericarp browning in longan cv. Fuyan fruits using open plastic punnets and sealed polyethylene bags at 10 degrees C +/-1 degrees C and 50% relative humidity, and the effect of pericarp water loss of the fruit on active oxygen metabolism and phenolics metabolism were investigated. Water loss resulted in rapid pericarp browning. Development of pericarp browning was higher with higher rate of water loss from pericarp and storage time (from 0 to 6 days). Water loss from pericarp was positively correlated with pericarp browning index significantly (P<0.01). Water loss from pericarp resulted in reduced activities of reactive-oxygen-scavenging enzymes (SOD, CAT, APX and GR), decreased amounts of endogenous antioxidant substances (AsA and GSH), and increased rates of O(-.)(2) production, MDA content and relative leakage rate, which showed that membrane structure was broken. Water loss from pericarp resulted in an increase in activity of PPO, and obvious reductions in total phenolic and flavonoid contents, whereas there was not obvious change in anthocyanin content. These results show that phenolics and flavonoids are the main substrates for PPO during desiccation-induced browning. Water loss from pericarp caused a significant increase in activity of POD, which also plays an important role in desiccation-induced browning in pericarp of longan fruit. Water loss from pericarp caused an increase in pH value, which resulted in changes in anthocyanin structure and color, the degradation of anthocyanin became easier. The results suggest that desiccation-induced browning of longan pericarp may be due to a decrease in activities of reactive-oxygen-scavenging enzymes and amounts of endogenous antioxidant substances, an accumulation of active oxygen, an increase in membrane lipid peroxidation, an injury of the integrity of cellular membrane structure, which, in turn, may cause cellular decompartmentation, resulted in PPO and POD, located in plastid and other organelle, to come into contact with phenolic and flavonoid substrates, located in vacuole, to form brown polymers.

[Studies on chemical constituents in the peels of Citrus changshan-huyou (I)].

OBJECTIVE: To reveal the pharmacological activities of the components for their further utilization and development by studying the chemical constituents of Citrus changshan-huyou. METHOD: The structures were determined by repeated silica gel chromatographic separation and spectral analysis. RESULT: Five compounds were obtained, and identified as 3-oxo friedelin (I), limonin (II), beta-sitosterol (III), 8-(2',3'-dihydroxy-4'-methylbutane)-7-methoxycoumarin (IV), sucrose (V). CONCLUSION: The five compounds were obtained from this plant for the first time.