Post-harvest Quality-improving Treatment And Refrigerated Preservation Technology Of Passion Fruit

Passion fruit（Passiflora edulis Sims）is loved by consumers,since it has a bright color and a pleasant aroma with high nutritional and medicinal value after maturity.However,post-harvest passion fruit has a strong respiratory metabolism and it is easy to shrink due to dehydration at room temperature storage.Its appearance quality sharply decreases at room temperature for about one week,which severely limits the fruit marketability.Cold storage is a safe and effective physical preservation method,suitable for delaying the maturation and aging of various fresh fruits and vegetables,which could ensure post-harvest quality.But passion fruit shows high sensitivity to low temperature,it has poor tolerance at low temperature,So unsuitable low temperature is likely to cause chilling injury for passion fruit,resulting in the lost of its commercial value.Therefore,this study took’Fujian No.1’passion fruit as raw materials to investigate the effects of cold storage,post-harvest treatment and the combination of both treatment on the quality of passion fruit during cold storage.Also,the relationship between post-harvest treatment and chilling injury in terms of active oxygen metabolism was explored.The main research contents and results are as follows:1、Effects of cold storage on the quality of passion fruits.The fruit size and weight of the test materials were in accordance with the local standard of Fujian Province’DB35/T 1858-2019 Passion Fruit（Passiflora edulis Sims）Cultivation Technical Specifications’,which has reached the harvest maturity,but the aroma,flavor and color of the fruit have not yet been fully expressed the characteristics of the variety,and the edible maturity has not reached.Fresh passion fruits samples were individually packaged in polyethylene fresh-keeping bags and stored in the cold room at 0℃,3℃,6℃,9℃and 12℃,respectively.The appearance,nutritional composition and chilling injury of fruits were studied at different refrigerated temperatures.The results showed that chilling injury did not occur at the 9℃and 12℃,but the fruits in the groups of 0℃,3℃and 6℃appeared water-stained chilling injury spots after storage for 12d,15d and 20d,respectively.And the lower the temperature was,the more severe the chilling injury occurred.Cold storage significantly reduced the weight loss rate of the fruit during storage,with the maximum weight loss rate only being 0.86%,which effectively solved the post-harvest problem of water loss and shrinkage;Also,cold storage significantly reduced the respiration intensity of fruits,which was not conductive the turning-color of post-harvest fruits.The fruit has poor sensory quality when cold storage for 35 days,which was inedible and no longer had commercial value.2、Effects of post-harvest constant-temperature treatment on the quality of passion fruits.Passion fruit samples were divided into four groups and stored in a closed foam box,of which half the volume was occupied,at 18℃±2℃for 0,3,7 and 11 days,respectively.The differences of fruit appearance and nutritional composition in different treatment groups were compared.The results showed that constant-temperature treatment increased the respiratory intensity,edible rate and ascorbic acid content of post-harvest passion fruits,and reduced the contents of TSS,SS and TA;moreover,the sugar-acid ratio went up from 3.62 to 4.58,and the appearance and flavor quality of the fruits significantly improved.As a result,the overall sensory quality of passion fruits,with post-harvest constant-temperature treatment（18℃±2℃）for7 days,was found to be the best;at that time,passion fruits were dark red,with no shrinkage,pleasant aroma,suitable sweet and sour.3、Effects of post-harvest constant-temperature treatment combined with cold storage on the quality of passion fruits.Taking passion fruits treated with post-harvest constant-temperature treatment（18℃±2℃）for7 days as study objects.The changes in fruit appearance,nutritional composition,and chilling injury were studied at 6℃,8℃and 10℃.The cold storage group of passion fruits without post-harvest constant-temperature treatment was used as a reference group,and results showed that post-harvest constant-temperature treatment combined with cold storage significantly reduced the fruit’s respiration intensity and weight loss rate,which could effectively solved post-harvest problem of water loss and shrinkage.Also,there was more obvious effect on reducing the loss of fruit TSS,SS,TA and ascorbic acid contents,and decreasing the index and the incidence of chilling injury.Moreover,post-harvest constant-temperature treatment combined with cold storage better promoted turning-color and effectively improved the appearance and edible quality.As a result,the rate of good fruits could reach above90%when the fruits were stored at 6℃and 8℃for 28 days.4、Effects of post-harvest constant-temperature treatment on active oxygen metabolism in passion fruit during cold storage.Passion fruits with and without post-harvest constant-temperature treatment（18℃±2℃）for 7 days were used as study objects.The changes of free proline content,MDA content,O₂^-production rate,H₂O₂content and the activities of related active oxygen-scavenging enzymes of the fruits during cold storage were determined.The results showed that post-harvest constant-temperature treatment significantly increased free proline content,suppressed O₂^-production,reduced the levels of H₂O₂and MDA,and enhanced the activities of antioxidant enzymes such as CAT and APX,which then effectively mitigated the degree of chilling injury of passion fruits.