Study On Effect And Mechanisms Of Hot Air Combined With MeJA On Quality Maintenance In Loquat Fruit

Loquat fruit (Eriobotrya japonica Lindl.), a special local fruit in south China, is famous for its softness, juicy taste and nutritional value and is highly popular with consumers worldwide. Since loquat fruit mature in hot and raining season, the fruit have a short postharvest life at ambient temperature because they are susceptible to microbial decay, mechanical damage, moisture and nutritional losses. Colletotrichum acutatum is the major pathogen that causes postharvest loquat anthracnose and soft rot. Low temperature storage is commonly used to inhibit decay incidence and extend loquat storage periods. However, Chilling injury, such as increase in fruit firmness, juiceless pulp and adhesion of peel to the flesh, is uaually found in loquat fruit stored at low temperature for long time, which finally causes the loss of commodity value. Therefor, it is crucial to study the regulation and mechanism of decay and flesh leatheriness of loquat fruit after harvest for transportation and storage. In this paper, the effect of hot air treatment (HAT) combined with methyl jasmonate (MeJA) treatment on decay and flesh leatheriness of loquat fruit and the possible mechanisms involved were investigated. The results were as follows:(1) The effects of different combined treatment conditions of hot air and MeJA on quality of loquat fruit were investigated and optimized by using the response surface methodology (RSM). Freshly harvested loquat fruit were treated with different temperature (35-45℃)-time (3-7h)-concentrate (10-30μmol/L) combinations, and then stored at 1℃for 35 days. Fruit internal browning, firmness and extractable juice were measured after the storage. Three second order quadratic equations of fruit internal browning, firmness and extractable juice were established, and the fitting degree were analyzed through RSM. The results indicated that the response and variables were fitted well to each other by multiple regressions, and the optimum conditions for combined treatment of hot air and MeJA were: temperature 38℃, time 6 h, MeJA concentration 16μmol/L(2) The combined treatment of HAT and MeJA inhibited the increase in firmness, the decrease in juice percentage and internal browning, and had the positive effects on maintaining TSS, TA, sobluble protein and heat-stable protein contents, thereby reducing the development of flesh leatheriness and maintaining quality of cold-stored loquat fruit. In addition, the combined treatmet effectively maintained the activities of SOD, CAT and APX, and reduce the accumulation of O2- and H2O2 and MDA in loquat fruit. Meanwhile, The combined treatmet inhibited the increase in PAL, PPO and POD activities and the decrease in PG activity, and reduced the content of lignin and protopectin and maintained higher accumulation of water soluble pectin and TP. These results suggest that the combination of HAT and MeJA could significantly reduce the chilling symptoms of flesh leatheriness of loquat fruit due to maintain the balance between the formation and detoxification of activity oxygen species, delay the lipid peroxidation process, and inhibit the activities of enzymes involved lignin biosynthesis.(3) The combined treatment of HAT and MeJA resulted in significantly lower disease incidence rate and smaller lesion diameter compared with HAT or MeJA alone. The combined treatment induced higher activities of the defense-related enzymes including chitinase,β-1,3-glucanase, and maintained higher content of TP. Meanwhile, the combined treatment maintained lower activities of CAT,SOD and APX in early storage, thus resulting in a higher level of H2O2. The enhanced H2O2 generation by the combined treatment might serve as a signal to induce resistance against C. acutatum infection. In addition, the combined treatment decreased the activities of PAL, PPO and POD enzymes and inhibited the accumulation of lignin in loquat fruit during cold storage. The in vitro experiment showed that HAT in combination with MeJA inhibited mycelial growth, spore germination and germ tube length of C. acutatum. These results indicated that the control of the disease is directly because of the inhibitory effect of the combination of HAT and MeJA on pathogen growth, and indirectly because of the induced disease resistance triggered by enhanced TP level and activities of chitinase andβ-1,3-glucanase.