Postharvest moisture loss in Japanese plums

[摘要] ENGLISH ABSTRACT: Plums exported from South Africa reach overseas markets after a long sea freightperiod. Yet consumers still expect fruit to be in perfect condition upon arrival at thesupermarket. While care is taken to limit moisture loss throughout the handling chain,fruit still show the negative effects thereof. Reduced fruit quality due to moisture lossmay lead to rejection of export consignments at overseas markets, causing majorfinancial losses for South African producers.The aim of this study was to investigate the role of the fruit cuticle in determiningmoisture loss and susceptibility to shrivel development in Japanese plum cultivars.Peel permeability differed between farms, seasons, cultivars, orchards anddevelopmental stage. In general, the water vapour permeance of the peel was higherin cultivars that are susceptible to moisture loss and shrivelling. However, this was nottrue in all cases and measuring pre-harvest water vapour permeance of the peel topredict shrivel susceptibility was only successful in some cultivars.Lenticel numbers differed between seasons and cultivars and clearly contribute tomoisture loss, but this contribution differs between cultivars. As the number of openlenticels could not explain all the variation in peel permeability between cultivars,cuticle composition must play an important role in determining peel permeability.Cuticular composition differed significantly between cultivars and seasons. Thecompound 2,4-bis (dimethyl benzyl) phenol was present in high concentration in bothcultivars. We propose that the combination of a rigid cuticle, due to high phenolcontent, fewer tri-hydroxy acids, and high primary alcohol content, and its smallerintercellular spaces, reduces 'Songold' cuticle deformation due to excessivepostharvest moisture loss. Since the hypodermal cells of 'Songold' are closer together,their dehydration and collapse might not lead to significant shrinkage compared to theother cultivars. The cuticle is rigid, which means that it is less likely to collapse whenthe supporting cells underneath it shrink and collapse due to moisture loss.Packaging solutions to reduce moisture loss need to be optimized for individualcultivars since they vary so much in terms of susceptibility to moisture loss and shrivel.Using Low-Density Poly-Ethylene packaging with 92 or 72 micro-perforations mightbe a viable option to reduce moisture loss, while still preventing excessive in-packagehumidity, decay and chilling injury. In seasons when high rates of moisture loss areexperienced, the use of these bags might reduce the number of consignments rejectedat overseas markets.This study showed the complex interplay of different cuticle characteristics in responseto or as a result of, moisture loss. It would be interesting to investigate howenvironmental signals lead to a certain cuticular response – which genes are involved,how these genes activated and so forth. Elucidating some of the mechanisms involvedin the functioning and response of this complex biopolymer might enable manipulationof the cuticle to improve fruit quality and extend shelf life or to select and breedcultivars that are not prone to cuticular defects.

[发布机构] Stellenbosch University