Control Of Postharvest Chilling Injury Of 'Xiao Bai' Apricot Fruits By Storage At Near-freezing Point

'Xiao bai' apricot is a typical respiratory transition type fruit.The harvest season is relatively concentrated.Postharvest uncomfortable storage at low temperatures can easily lead to chilling injury symptoms,and chilling injury symptoms are generally found from low temperature environment to warm environment.After chilling injury,the fruit is easily infected by pathogenic microorganisms,and its storage quality and commercial value will be seriously affected.In this study,Xinjiang 'Xiao bai' apricot was used as a test material to explore the control of post-harvest chilling injury of apricot fruits during near-freezing temperature storage,and analyzes the physiological mechanism of controlling chilling injury from near-freezing temperature storage from the perspective of storage quality,active oxygen metabolism and cell wall metabolism.Transmission electron microscopy was used to observe changes in cell tissue ultrastructure at different periods during storage.At the end of storage,the shelf-life quality was determined by different out-store modes to find the best delivery method to extend its shelf life.It provides the corresponding theoretical basis for storing near-freezing temperature to reduce the chilling injury of apricot fruits.(1)Take ordinary cold storage(1?2 and 4?6)? as the control group,the apricot fruits were stored in near-freezing temperature(-1.5?-1)? for 49 d.The apricot fruit chilling injury index and chilling injury incidence rate were regularly measured,and the fruits changes in respiratory intensity,hardness,soluble solids content(SSC),titratable Acidity(TA),ascorbic acid(Vc),chromaticity parameters(L*,a*),cell membrane permeability and malondialdehyde(MDA)content.The results showed that near-freezing temperature can effectively delay the time of chilling injury and reduce the incidence of chilling injury,delay the decrease of fruit hardness,SSC,TA,Vc content and surface color change,reduce MDA accumulation and increase of cell membrane permeability.It could be obtained that near-freezing temperature can better maintained the quality of apricot fruits during storage,thereby improving the cold resistance of apricot fruits.(2)To study the effects of chilling injury and active oxygen metabolism of apricot fruits at different temperatures,regularly determined catalase(CAT),superoxide dismutase(SOD),peroxidase(POD),ascorbic acid changes in the activities of ascorbate peroxidase(APX),the production rate of superoxide anion(O2-·),and the content of hydrogen peroxide(H2O2).The results showed that compared with ordinary cold storage(1?2 and 4?6)?,near-freezing temperature could significantly increased the SOD activity of apricot fruits,delayed the decline of POD,CAT and APX activities during storage,and effectively inhibit the H2O2 content and O2-· the production rate of indicates that the occurrence of fruit chilling injury is closely related to active oxygen metabolism.Near freezing temperature can maintain high antioxidant enzyme activities and inhibit the production of active oxygen,thereby reducing the damage caused by oxidation.(3)To study the effects of near-freezing temperature on cell wall metabolism and ultrastructure of postharvest apricot fruits.The cell wall polysaccharide content and cell wall metabolism-related enzyme activities are measured regularly.Transmission electron microscope is used to further observe the ultrastructure of apricot fruit cells under near-freezing temperature.The results show that near-freezing temperature storage can maintain low pectin methylesterase(PME)and polygalacturonase(PG)activities and their metabolic balance,effectively inhibiting cellulase(CEL),?-galactosidase(?-GAL)activity.Delayed the degradation of Na2CO3-soluble pectin(NSP)and cellulose content,Slowed the increase of water-soluble pectin(WSP)and CDTA-soluble pectin(CSP).Transmission electron microscopy observed that the cell wall of apricot fruit after storage at near-freezing temperature for 49 days showed only slight deformation,uneven thickness,and no plasmolysis or flocculent structure,and the mesial layer was still clearly visible.Reduces the damage to chloroplasts,mitochondria,starch granules and other organelles,and protects the structure of plant cell walls to the greatest extent,Thereby delaying the appearance of chilling injury symptoms.(4)The effects of different out-store modes on the shelf-life quality of apricot fruits after 49 days of near-freezing temperature storage were studied.Physiological indexes and sensory qualities of fruit were measured daily during shelf-life.Results showed that:compared with direct out-store(CK),both low-temperature chain out-store(A)and slow-temperature out-store(B)could maintain high fruit firmness and SSC,and effectively delay the decrease of TA,Vc content and fruit color change(L*,a*,b*),besides,the fruit commodity rate and sensory evaluation also maintained a high level;Compared to the group CK and B,A had better parameters of experiment.Specifically,the shelf-life under the experiment of A could be extended longer than CK and B,and the sensory evaluation was significantly higher than group B.The results illustrated that the qualities during shelf-life of apricot fruits treated with low-temperature chain out-store(A)is the best among the three experimental groups.