Advances in the research into physiological and biochemical characteristics and chilling injury of peach fruits after harvest

Abstract: The peach belongs to the Rosaceae family, subfamily Prunoideae, genus Prunus, subgenus Amygdalus L. which has a history of more than 4 000 years and is the main fruits produced in china. It was renowned for its rich nutrition, excellent quality and fresh flavour. Because of the biological and physiological characteristics of peach fruit such as soften, thin skin and juicy, as well as the high temperature and humidity, which reduce peach to decay and go bad quickly. Peach can be divided into four types (stiff solute, soft solute, solute and stony hard) according to their flesh texture. The sensitivity to low-temperature as well as comprehensive characteristics of peach fruits subjected to chilling injury are different. At present, more than 1 000 peach varieties are cultivated in the world. Most of soft solute peaches can be stored under room-temperature only for 3-5 d, the following is hard solute peach (5-7 d) , and for stony hard peach is 10-14 d. It is crucial for classification of different kinds of solute peach according to postharvest quality, physiological and biochemical characteristics. As is known to all, there are double respiratory peak and ethylene releasing peak in peach fruits after harvest. The softening of fruit suture is related to the ethylene release rate and the appearance time of respiratory peak, however, it is different among various varieties. Once the autocatalytic ethylene synthesis pathway is activated during the development of the fruit, it will accelerate to soften process and then loss commodity value soon. The enzymes that related to fruit softening are pectinase, lipoxygenase and galacturonic acid polymer enzyme. It was reported thatpectinase activities were closely related to the softening rate. What's more, the salt soluble pectin content had high correlation with firmness, water soluble pectin, chelating pectin and salt soluble pectin. It was also reported that the browning of peach was related to the total phenol and chlorogenic acid content. Treatment with 1.25, 2.5 and 5 mmol·L^-1 SA could inhibit the activities of polyphenol oxidase and lipoxygenase, and decrease the content of O2-and malondialdehyde. It could also inhibit the browning of the flesh during low-temperature storage. The change of aromatic compound also should be concerned. More than200 compounds have been identified from peach fruits till now. However, only a few ingredients or representative compounds which were named characteristic decision compounds could determine fruit aroma feature. Changes of aromatic compounds during peach fruit development and postharvest period have been reported. The accumulation of volatile substances is associated with peach maturity, and hexanal, benzaldehyde, linalool, γ-decalactone and δ-decalactone were the major aroma compounds. Long-time storage under low-temperature could reduce the fruit aroma and then chilling injury symptom appeared, however, 1-MCP and jasmonic acid methyl ester could inhibit this phenomenon. With the extension of storage time and the aging of yellow-peach, the cell wall of pericarp deformed, the structure became loose, intercellular space increased. The number of osmiophilic globules increased first and then decreased, and the volume presented increasing tendency. The mitochondria structure became blurred, mitochondria was deformed and stretched, the number of gorgias reduced and the structure collapsed. The aging process of mitochondria is later than chromoplast. Molecular biological tools have been used to identify increasing numbers of genes involved in fruit ripening and senescence. Other studies were carried out on peach ripening, stress response and defense. Some functional proteins of peach fruit are differentially regulated during the course of maturity. The last important symptom of peach after harvest is chilling injury. Low-temperature could prolong the storage time, however, that could also lead to chilling injury such as lignifications, woolliness, flesh browning, flesh red, sugar acid ratio imbalance, aromatic compounds loss, formation of harmful volatile substance and so on. Although, enzymology, molecular biology and proteomics have been employed to study the symptoms of fruit quality deterioration, the effective control of chilling injury through the quality control technology and biological engineering technology has not been successfully done yet.We should formulate fresh-keeping technology according to the physiology and storage characteristic of peach with different flesh texture.