| Papaya fruit(Carica papaya L.)is rich in nutrition,which is sensitive to the temperature.Papaya is prone to chilling injury in low temperature environment and rapid ripening and softening under higher temperature storage,so it is difficult to keep fresh and long-distant transport.In this article,a major Taiwan papaya cultivar "Taiwan farmerⅡ" was used to establish the mathematical models of color,firmness and sugar-acid ratio with different maturity,revealing some mechanisms of papaya chilling injury and chilling tolerance through the correlation analysis between different pre-treatment conditions,different storage temperatures,with different factors such as maturity and the indicators of papaya chilling injury.The details are specified as follows:1.Using color,firmness,total sugar and total acid of papaya fruits as reference indicators,the relationship between maturities and indicators were studied.The results show that with the increase of papaya maturity,L value reduced,and a,b value increased gradually,and there exists a certain linear relationship between maturity and the value of L,a,b.At the same time,total sugar accumulates with the maturity increasing,but the acid were reduced thus sugar-acid ratio increases dramatically.In addition,the relationship between maturity and firmness is y=1991.7403x-3.0754.2.Storing 70%ripening papayas at(6±0.5)℃,(9±0.5)℃,(12±0.5)℃, (15±0.5)℃,(18±0.5)℃,(21±0.5)℃and(24±0.5)℃separately,the effects of storage temperature on papaya quality and chilling injury were studied.Results indicated that chilling injury index rapidly increased when the temperature was below 12℃,but appearance quality index showed a decreased trend during anaphase storage when the temperature was higher than 15℃.Therefore,the critical temperature of papaya chilling injury is 12℃.3.Storing 70%ripening,80%ripening and 90%ripening papaya fruits at 12℃, effects of different maturities on papaya quality and chilling injury were studied.It was found that there was close relationship between maturity and papaya chilling injury.Chilling injury has less influence on papaya qualities at higher maturity.The activities of antioxidant enzymes in low maturity papaya fruits were low and poorly resistant to cold.Therefore,low maturity papaya fruits were prone to chilling injury during lower temperature storage.4.Comparing with the control group without cold shocking,pre-treating by two kinds of cold shock,the optimal cold shock was selected by observing the quality index of papaya pericarp and chilling injury index regularly.Physiological changes of papaya during storing at(12±0.5)℃after cold shocking treatment were studied. Effects of cold shock on papaya quality and chilling resistance were also examined. The results showed that the treatment of 0℃cold air for 3.5h was the best for papaya fruits,which decreased the respiration rate of papaya effectively,but had little impact on the peak respiration time.Meanwhile,cold shock not only inhibited the decline of firmness,delayed the decline of SOD and AsA-POD,but also enhanced the activity of CAT.To certain degree,cold shock can reduce the occurrence of chilling injury of papaya during cold storage.5.Using different heat treatment and different processing times before cold storage and post-ripening,effects of heat treatment on storage property and chilling resistance of papaya fruits were studied.Results explained that the activities of CAT, SOD,AsA-POD during cold storage after heat treatment were higher than the control group.Heat treatment improved chilling resistance of papaya fruits and the resistance of diseases,however,reduced the incidence of decay.6.The combined trails between hot-air treating time,storage temperature, storage time and maturity on papaya chilling injury and chilling resistance were studied by U12(43×3)uniform design experiment.The primary-secondary roles of factors on papaya chilling injury were obtained.The result showed that maturity was the most significant effect on papaya appearance quality index,but chilling injury index and activities of CAT,POD were determined by storage temperature, meanwhile,the activity of SOD increased by heat treatment.Activities of CAT and POD increased with the rise of storage temperature.
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