[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.
Lin
He-Tong
HT
College of Food Science and Technology, Fujian Agriculture and Forestry University, Fuzhou 350002, China. hetonglin@163.com
Xi
Yu-Fang
YF
Chen
Shao-Jun
SJ
D002374:Catalase / Q000378:metabolism; D003890:Desiccation; D005638:Fruit / Q000201:enzymology / Q000378:metabolism*; D005980:Glutathione Reductase / Q000378:metabolism; D010636:Phenols / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D029631:Sapindaceae / Q000201:enzymology / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000378:metabolism
D010636:Phenols; D010940:Plant Proteins; D017382:Reactive Oxygen Species; D002374:Catalase; D013482:Superoxide Dismutase; D005980:Glutathione Reductase