Studies On Formation Mechanism Of Fruit Peel Epidermis Rust On Korla Fragrant Pear During Storage

Korla fragrant pear is the famous special fruit in Xinjiang, it was favored with its uniquecolor, aroma, taste, quality. Korla fragrant pear peel epidermis rust in pre-harvest occurredrarely, however, it was easy to occur during postharvest storage, and its appearance wasseriously influenced, and the value of the goods were greatly reduced. At present, moreresearch on the rust formation reasons before pear harvest and prevention technologies. It hasnot been reported on rust occurrence reason and its mechanism during postharvest storage.The purpose of this work was to analyze factors causing fruit rust spot disease and researchedthe correlation between factors and formation of rust on the basis of extensive investigationand statistic analysis of discipline on pear fruit rust incidence in the main producing areas ofKorla fragrant pear. Then characteristic components of rust were analyzed and identified. TheKorla fragrant pear fruit rust generation mechanism during postharvest storage was alsopreliminarily explored. The main conclusions as follows;1. From2008to2010, the Korla Pear Rust incidence of sampling was surveyed on massstorage of Korla fragrant pear in enterprises. It was found that the Korla Fragrant Pear rustincidence in controlled atmosphere storage (0.23%) was higher than that of in the commoncold storage(1.32%) in Korla area. The incidence time was5days before the latter; In Akesuarea, the Korla Fragrant Pear rust incidence in controlled atmosphere storage (0.34%)washigher than that of in the common cold storage(1.55%) The incidence time was10daysbefore the latter. In common cold storage, pear rust incidence ratio of was0.13%to0.57%higher than that of in Korla area. In controlled atmosphere storage area, Akesu Korla PearRust incidence ratio of0.24%to1.11%higher that of in Korla area. In Akesu area, rustdisease incidence was ahead of5days earlier than in Korla area. In common clod storage andcontrolled atmosphere storage, the fruit rust incidence rate was not same with the differentposition. It was highest in humidifying mouth, then the central section of cold room, finallythe most distant from the humidifying export. The two storage conditions of Korla FragrantPear shows from rust incidence statistics analysis, it was shown Korla Fragrant Pear Rustincidence was significantly higher(p<0.01) in controlled atmosphere storage than that of incommon storage; Akesu area of Korla Fragrant Pear rust incidence rates were significantlyhigher(p<0.01) than that of Korla area. In common cold storage conditions, the rust diseasemust be prevented after storage for180d. In controlled atmosphere storage conditions, the rustdisease sharply raised after storage for174d. It was shown from the statistical survey, KorlaFragrant Pear rust disease first appeared in fruit calyx, then gradually extended to the carcassand the stem of the pear fruit. The laboratory studies showed that the fruit peel rust formationwas closely related to environment temperature, humidity, gas composition during storage.2. Korla fragrant pear rust and respiratory strength were gradually reduced with rust areaexpanding during the storage of Korla Fragrant Pear, and the former speed was lower than thelatter. Meanwhile, the ethylene release rate gradually increased, Rust spot range was higher,the sound parts was gentle rising; cell membrane permeability and MDA content increased,the elevated range of rust was lager than the sound parts parts; the content of phenolic substances content decrease gradually, rusty part decrease faster than the sound parts;Polyphenol oxidase activity strengthened gradually, rust site of the enzyme activity wasgreater than the sound parts. Under common cold storage, phenylalanine ammonia-lyaseactivity of Korla pear strengthened. In controlled atmosphere storage, phenylalanineammonia-lyase activity increased then decreased, the enzyme activity in rust site was greaterthan that of in the sound parts; Lignin content increased, it was higher in rust site than in thesound parts; cellulose content raised in rust spot, and dropped in the sound parts. Therefore,after postharvest, physiological and biochemical mechanism of Korla pear fruit rust formationmay be Korla fragrant pear were stimulated by adverse storage environment, and epicuticularwax and cuticle ruptured, and the epidermal cell structure damage, and intracellular phenolsand the polyphenol oxidase enzymatic browned, and at the same time, the cork layed, rustsubstances accumulated gradually, then led to the occurrence of fruit rust disease.3. It was also shown in Korla fragrant pear epidermal microstructure studies, rust spotlignin content was higher than the sound parts, and lignin directed along the cell wall, andthen was perpendicular to the cell wall extension. The higher the Cell lignification degree andthe larger rust area. Meanwhile rust site on the cell membrane and cell wall graduallydisappeared,,and the mitochondria, endoplasmic reticulum, golgi apparatus and otherorganelles disintegrated, deposition of black material increased, and until it filled the entirecell; the cell membrane and cell wall of intact part was completed, there was no material lossin intracellular. With the Korla fragrant pear epidermal structure damaged, the middle lamellalignin increased, the callus formation was promoted, callus further corky, finally the rust wasformed.4. Korla fragrant pear skin rust characteristic components were analysed by HPLC (Highpressure liquid chromatography), UV(Ultraviolet spectrophotometer), LC-MS(Liquidchromatography and mass spectrometry) methods. The results were rust material mainchemical compositions were Rhein, Aloe Emodin, Emodin, chrysophanol and anthraquinones.It was confirmed deeply that the enzymatic browning reaction occurred during the Korla pearrust formation.Through this research, Korla pear rust generation mechanism was put forward, KorlaFragrant Pear were influenced by storage temperature, humidity, concentration of CO2adverse stimulus during postharvest storage. It accelerated senescence of fruit, the fruitepidermis wax and cuticle of ruptured, vacuole membrane invaginated and degradated, roomfunction was lost, a series of hydrolase extravasated within vacuoles and dispersed throughoutthe cell. Cell autolysis developed, the cell was disintegration and death, Intracellular phenolicsand polyphenol oxidase interacted, enzymatic browning was produced, dark brownanthraquinones generated; at the same time, the Korla Pear were Storage stressed by thestorage environment, cell wall would produce a series of resistance, and the epidermis thincell wall of continuous was thickening, corky was happened after the formation of cork layer,and continued to produce large quantities of cork cell division, the gradual accumulation andprominent on the fruit epidermis, thus Korla fragrant pear rust was formed.