Quality variations of peach fruit from different tree canopy positions during cold storage

Abstract: 【Objective】Peach [Prunus persica(L.) Batsch] is one of the typical climacteric fruits and has a short shelf life. The rapid loss of fruit quality after harvest has seriously restricted long-distance transportation of the fruit. There is obvious quality difference at harvest among fruit from different canopy positions with different canopy micro-environmental conditions. Fruit quality at harvest may affect its storage characteristics. In this study, quality variations of peach fruit harvested from different positions of tree canopy during cold storage were examined.【Methods】Mature(85% full maturity) fruits of mid-season cultivar'Xiahui 6'and late-season cultivar'Xiahui 8'were collected from different positions of the canopy(upper, outer middle, inner middle and lower canopy). The fruit were stored in an experimental cold chamber kept at(4±0.5) ℃, 75%-85% relative humidity. According to a pre-experiment conducted in the previous year, the storage time was set separately for two cultivars, 12 d for'Xiahui6'and 20 d for'Xiahui 8'. Fruit samples were taken every 3 d for'Xiahui 6'and 5 d for'Xiahui 8'during storage. Fruit firmness, values of red saturation scale(a*), yellow saturation scale(b*), ratio of a*and b*and hue angle(h), contents of sucrose, glucose, fructose, sorbitol, quinic acid, malic acid, citric acid, total sugars, total aci and soluble solids, and sugar/acid ratio were measured five times during storage to quantify changes in fruit quality. Three biological replicates were performed each with 10 fruit.The differences in storage characteristics was compared by analyzing the variations in appearance quality, flavor quality, as well as textural attributes among fruit from different canopy positions.【Results】At the end of storage, the softening rates in fruit from the upper and outer-middle canopy was higher than in those from the inner-middle and lower canopy, and was the lowest(p<0.05) in the lower canopy fruit. The red color of pericarp of the upper-and the outer-middle canopy fruit of'Xiahui 6'gradually became lighter after the 3 rdday during storage; that of the inner-middle and the lower canopy fruit became darker; that of the lower canopy fruit of'Xiahui 8'became lighter earlier compared with the fruit from the other canopy positions. The contents of sucrose and total sugars in both cultivars increased initially and then decreased during cold storage. The decline in contents of sucrose and total sugars in fruit from the lower canopy in'Xiahui 6'and from upper canopy in'Xiahui 8'was relatively faster than those from the other positions. The glucose content in'Xiahui 6'peach fruit from the four canopy positions did not change significantly during cold storage, while fructose content showed a fluctuating increase trend. The contents of glucose and fructose in'Xiahui 8'fruit from all the positions increased rapidly during the late storage period. Sorbitol content in the flesh of the two peach cultivars decreased slowly initially and then rapidly during cold storage. The quinic acid content in the two cultivars increased significantly during cold storage, while the contents of malic acid and citric acid initially increased and then decreased. The increase in the contents of quinic acid, malic acid, as well as total organic acids in fruit from the upper canopy were relatively higher than fruit from the other positions in both cultivars. The variation trend of soluble solid content(SSC) in the flesh was quite similar to that of total sugar content and the sugar/acid ratio. The SSC in the upper canopy fruit of'Xiahui 6'was relatively stable during storage, but decreased in fruit from the other positions. The decline in the inner middle and the lower canopy fruit was relatively faster. The SSC in lower canopy fruit of'Xiahui 8'increased, while in fruit from the other positions decreased with a similar pattern.【Conclusion】Good quality at harvest was valuable to the overall quality of fruit during cold storage. For the mid-season cultivar of'Xiahui 6', the red color and flavor in the upper and the outer-middle canopy fruits were the best at harvest. Although the red color of the pericarp became lighter during the late storage period, relatively ideal pericarp coloration was maintained during storage, and fruit flavor quality was always well maintained. For late-season cultivar'Xiahui 8', pericarp coloration and flavor of the fruit from the upper,the outer-middle and the inner-middle canopy were relatively better at harvest, and the overall quality of these fruit was well maintained.'Xiahui 6'and'Xiahui 8'peach fruits softened rapidly from the 6 th and 10 thday of the storage period, respectively. The fruit softening rate in fruit with better overall quality at harvest was generally higher.