| Peach[Prunus persica(L.)Batsch]belongs to respiratory climacteric fruit.It is easy to soften quickly after harvesting,and has short shelf life,poor storage and transportation performance.To some extent,it has adversely affected the development of the peach industry.There are obvious differences in the storage performance of different varieties of peaches with different maturity degrees.Judging the maturity degrees in the production process and choosing the maturity degrees of timely storage are of great significance to improve the fruit’s storability and maintain the commodity value after storage.In this study,four fleshy types(soft-melting,hard-melting,stongyhard and non-melting)of peaches were used as test materials,and the maturity degrees was judged by observing the appearance and color dynamics and the changes in index of absorbance difference(IAD)of the peel of different development stages of the peach(young fruit stage,expanding stage,70%,80%and 90%maturity stage).The freezing-point temperature,fruit density,soluble solids content(SSC),soluble sugar and organic acid components of fruits in different development stages were measured and analyzed.The main factors affecting the freezing point of peach fruits were analyzed by grey correlation analysis.Secondly,at this freezing point,peach fruits of different maturity levels were stored at near freezing-point temperature,and the changes in the appearance and intrinsic quality of the fruit were analyzed,discussing the differences in storability of the fruits.In addition,ethylene release during ripening of peach fruits with different fleshy types was studied by gas chromatography.Combining firmness,respiration rate,and expression differences of genes related to ethylene biosynthesis,the mechanism of fruit softening was explored,and further providing theoretical basis for accurate judgment of fruit maturity.The main research results are as follows:(1)By observing the dynamic changes in appearance and color of peach fruits at different growth and development stages,and analyzing the changes in index of absorbance difference,color difference indicators,and chlorophyll and anthocyanin content of peel,it was found that the red color of the fruit surface gradually deepened as the fruit matured.The content of chlorophyll continued to decline,with the fastest decline from the young fruit stage to the expanding stage,and slowly decreased during the maturing stage.The ratio of anthocyanin content to chlorophyll content was increasing continuously,and the fastest increasing speed was from the expanding stage to the maturing stage,that was to say,the red color of the fruit started mainly from the expanding stage to the maturing stage.The change of the content of anthocyanin and chlorophyll determined the appearance and color of the fruit,and the dynamic change of the color was reflected by the color difference index of the peel(value of a*、a*/b*、h).(2)There was significant difference in freezing-point temperature of fruits in different development stages of different fleshy peach.The average freezing point temperature of fruit in maturing stage was higher than that in young stage and expanding stage,among which the lowest was in young stage.The average freezing-point temperature of fruit in maturing stage ranged from-1.62℃ to 0.14℃.The highest average freezing point temperature of peach fruit at the same development stage was soft-melting peach(’Xiahui 5’),and the lowest was non-melting peach(‘Babygold 8’).The results of grey correlation analysis showed that the content of soluble solids had the greatest influence on the freezing point temperature of peach fruit,which was closely related to the content of total acid,followed by the density of fruit,and the single fruit quality had less influence.(3)The freezing point temperature of peach fruits tested(’Shangshandayulu’ with soft-melting,‘Xiahui 8’with hard-melting,‘Huayu’with Stonyhard,‘Babygold 8’with non-melting)were below 0℃.The higher the maturity of peach fruits with the same maturity,the higher the freezing point temperature.Under the same maturity,the freezing point temperature of different cultivars of peach fruits was significantly different.The highest freezing point temperature was‘Shangshandayulu’.Compared with ambient temperature storage,near-freezing temperature storage can effectively alleviate fruit weight-lossing,delay the decline of firmness,better maintain the color of the peel,and delay the time when the anthocyanin and total sugar content,ratio of anthocyanin content to chlorophyll content(Ant/Chl),and sugar-acid ratio of the fruit reach the peak during storage,delayed the senescence and prolonged the storage time of fruits.During the storage period near-freezing temperature,the fruits of three maturity levels could maintain high firmness,and the fruit weight-lossing and SSC did not change significantly.The eight mature fruits at the end of storage showed high Ant/Chl and sugar-acid ratio.Comprehensively judged that 80%maturity stage of peach fruit was suitable harvest maturity for near-freezing temperature storage.(4)Eight peach varieties of four fleshy types were used as test materials to study the storage tolerance of fruit near-freezing point temperature.It was found that the fruit quality indexes of peach with different maturity and fleshy types had little change during the storage.The contents of total sugar and SSC of peach fruits of hard-melting and stonyhard were higher than those of other fleshy types during storage near-freezing point temperature.The fruits could maintain higher firmness at the end of storage,and there was not much difference between respiratory intensity and ethylene release.However,in terms of fruit coloring,hard-melting performed better than peach of stonyhard.It could keep better commercial value and storage characteristics under near-freezing point temperature storage.Compared with 90%maturity,80%maturity could better maintain the moisture of the fruit,alleviate weight loss and maintain edible firmness.It could effectively slow down the aging process of the fruit,and was the most suitable maturity for near-freezing point temperature storage.(5)In the process of peach fruit ripening,the firmness gradually decreased.The respiration rate of 70%,80%and 90%maturity fruits was always maintained at a high level,and the respiration rate of 90%maturity fruits was higher than that of 70%and 80%maturity fruits.In the process of maturation,peach fruit with soft-melting,hard-melting and non-melting mainly regulated the expression levels of PpACS1,PpACS4 and PpACO1 genes related to ethylene biosynthesis,thereby controlling the ripening and softening of peach fruit.PpACS2,PpACS3 and PpACS5 genes were hardly expressed during the ripening of peach fruit.PpACS1 gene expression maintained a high degree of coordination with the ethylene production in soft-melting,hard-melting and non-melting with the increase of maturity.And the PpACS1 gene of 90%maturity fruits had high expression abundance,the PpACS1 gene expression level in Stonyhard was extremely low.The PpaACS4 gene was up-regulated with increasing maturity in different fleshy peach fruits,and the gene expression levels of peach fruit with soft-melting,hard-melting and non-melting was significantly higher than that of with Stonyhard.PpACO1 gene was expressed in different fleshy peach fruits.Its expression level varied with fruit maturity,and the fruit gene expression abundance was mainly concentrated in 80%maturity fruits.Due to the suppression of gene expression levels,the fruit hardness of peaches with stonyhard remained high during the ripening process and the fruit could not normally soften. |
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