Moisture loss studies in nectarine (Prunus persica var. necterina)

[摘要] ENGLISH ABSTRACT: Moisture loss studies in nectarines (Prunus persica var. nectarina)Moisture loss during long term storage is one of the main post-harvest problems in nectarines. The long handling chain to which fruit are exposed to, from harvest until the end of shelf-life, exposes fruit to moisture loss. Moisture loss occurs as a result of the vapour pressure deficit (VPD) between the fruit and surrounding atmosphere. In addition to causing loss of saleable weight, moisture loss also results in fruit having a shrivelled appearance. Moisture is lost from fruit through various openings in the fruit peel such as micro-cracks and lenticels.In this study we investigated the effect of fruit to fruit variation, harvest date, tree and orchard effects and cultivar differences on the variation in water vapour permeance (P'H2O) of three nectarine cultivars namely 'Alpine', 'Summer Bright' and 'August Red'. The study showed that large fruit to fruit differences were the main contributor (>45%) to the variation in P'H2O, followed by harvest date (>35%), cultivar differences (>7%) and orchard effects (>3%) whilst tree effects did not contribute to P'H2O. Generally, the P'H2O of all three cultivars increased steadily as the harvest date approached and continued to increase post-harvest, but P'H2O at optimum harvest was not closely correlated to their susceptibility to shrivel.In addition, 'August Red' nectarines were exposed to different handling chains from harvest until the end of shelf-life to determine the VPD at different stages in the handling chain in order to establish the point which is most effective in reducing moisture loss and shrivel. The results indicated that none of the proposed handling chains performed better than the current standard handling protocol in reducing moisture loss and shrivel. This protocol stipulates that nectarines should be harvested during the cooler time of the day and field heat should be removed as soon as possible after harvesting. Furthermore, the handling protocol requires that nectarines should be packed within 12 hours of arrival at the pack-house.Several researchers have reported that silicon containing fertilizers improve fruit quality and we therefore also investigated whether pre-harvest applications of potassium silicate (K2SiO3) can reduce post-harvest moisture loss, shrivel and split pit in 'Southern Glo' nectarines. The results showed that both soil and foliar K2SiO3 applications were not effective in reducing post-harvest moisture loss, shrivel or the incidence of split pit in 'Southern Glo' nectarines. For future studies, it is recommended to increase the frequency of K2SiO3 applications.The study also looked at the effectiveness of different packaging films in reducing moisture loss and shrivel in 'August Red' and 'Alpine' nectarines. Failure to package fruit optimally may result in weight loss, shrivel, decay and the incidence of internal defects such as woolliness, pulpiness and over-ripeness. The results showed that the use of Xtend® and high density poly-ethylene (HDPE) bags significantly reduced moisture loss and shrivel in nectarines in both pulp trays and plastic punnets. The standard nectarine HDPE wrappers resulted in significantly higher percentage mass loss as well as shrivel incidence in 'Alpine' nectarines.It is therefore important to reduce moisture loss at harvest by following the standard handling protocol and by packing fruit optimally.

[发布机构] Stellenbosch University