Postharvest moisture loss in Japanese plums

Kritzinger, Imke (2019-04)

Thesis (PhDAgric)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Plums exported from South Africa reach overseas markets after a long sea freight period. Yet consumers still expect fruit to be in perfect condition upon arrival at the supermarket. 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 loss may lead to rejection of export consignments at overseas markets, causing major financial losses for South African producers. The aim of this study was to investigate the role of the fruit cuticle in determining moisture loss and susceptibility to shrivel development in Japanese plum cultivars. Peel permeability differed between farms, seasons, cultivars, orchards and developmental stage. In general, the water vapour permeance of the peel was higher in cultivars that are susceptible to moisture loss and shrivelling. However, this was not true in all cases and measuring pre-harvest water vapour permeance of the peel to predict shrivel susceptibility was only successful in some cultivars. Lenticel numbers differed between seasons and cultivars and clearly contribute to moisture loss, but this contribution differs between cultivars. As the number of open lenticels 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. The compound 2,4-bis (dimethyl benzyl) phenol was present in high concentration in both cultivars. We propose that the combination of a rigid cuticle, due to high phenol content, fewer tri-hydroxy acids, and high primary alcohol content, and its smaller intercellular spaces, reduces ‘Songold’ cuticle deformation due to excessive postharvest moisture loss. Since the hypodermal cells of ‘Songold’ are closer together, their dehydration and collapse might not lead to significant shrinkage compared to the other cultivars. The cuticle is rigid, which means that it is less likely to collapse when the supporting cells underneath it shrink and collapse due to moisture loss. Packaging solutions to reduce moisture loss need to be optimized for individual cultivars 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 might be a viable option to reduce moisture loss, while still preventing excessive in-package humidity, decay and chilling injury. In seasons when high rates of moisture loss are experienced, the use of these bags might reduce the number of consignments rejected at overseas markets. This study showed the complex interplay of different cuticle characteristics in response to or as a result of, moisture loss. It would be interesting to investigate how environmental signals lead to a certain cuticular response – which genes are involved, how these genes activated and so forth. Elucidating some of the mechanisms involved in the functioning and response of this complex biopolymer might enable manipulation of the cuticle to improve fruit quality and extend shelf life or to select and breed cultivars that are not prone to cuticular defects.

AFRIKAANSE OPSOMMING: Pruime wat vanaf Suid-Afrika na oorsese markte uitgevoer word, spandeer lang periodes in opberging.Verbruikers verwag egter dat vrugte in perfekte kondisie by supermarkte aanland. Alhoewel vogverlies so veel as moontlik beperk word in die koueketting, affekteer die negatiewe effek van vogverlies steeds vrugkwaliteit. Verlaagde kwaliteit van vrugte as gevolg van vogverlies lei tot afkeur van vrugte by aankoms in oorsese markte. Dit lei tot geweldige finansiële verliese vir Suid- Afrikaanse steenvrug-produsente. Die doel van hierdie studie was om die rol van die kutikula in vogerverlies en verrimpeling van Japanese pruim kultivars te ondersoek. Skildeurlaatbaarheid het beduidend verskil tussen seisoene en kultivars. Die skildeurlaatbaarheid van kultivars wat sensitief is ten opsigte van vogverlies en verrimpeling was beduidend hoër as die deurlaatbaarheid van nie-sensitiewe kultivars. Hierdie bevindinge was egter nie van toepassing op al die kultivars nie. Die bepaling van vooroes skildeurlaatbaarheid om na-oes verripeling te voorspel was dus net suksesvol in sekere kultivars. Die aantal lentiselle het beduidend verskil tussen seisoene en kultivars en het duidelik ‘n bydrae gelwer tot vogverlies. Hierdie bydrae het egter verskil tussen kultivars. Aangesien die hoeveelheid oop lentiselle nie al die variasie in skildeurlaatbaarheid tussen kultivars kon verklaar nie, speel die samestelling van die kutikula duidelik ‘n rol in die bepaling van skildeurlaatbaarheid. Die samestelling van die kutikula het ook beduidend verskil tussen kultivars en seisoene. ‘n Komponent, naamlik 2,4-bis(dimetiel benzyl) fenol, het in hoë konsentrasies voorgekom in albei kultivars. ‘n Kombinasie van ‘n rigiede kutikula, as gevolg van hoë fenol konsentrasies, tri-hidroksie sure, en primêre alkohole, saam met die kleiner intersellulêre ruimtes van ‘Songold’, verminder die kanse van misvorming as gevolg van oormatige vogverlies in hierdie kultivar. Aangesien die hipodermale selle van ‘Songold’ nader aan mekaar is, sal hul dehidrasie en ineenstorting moontlik nie lei tot soveel misvorming en verrimpeling as die ander kultivars nie. Die kutikula is meer rigied, wat beteken dat dit minder geneig sal wees om ineen te stort wanneer die ondersteunende selle onder die kutikula ineenstort as gevolg van vogverlies. Plastiek verpakking om vogverlies te verminder moet volgens individuele kultivars aangepas word, aangesien daar so baie variasie is tussen kultivars in terme van gevoeligheid tot vogverlies en verrimpeling. Die gebruik van Lae Digtheid Poli-Etileen sakke met 72 of 92 mikro-perforasies het vogvervlies verminder sonder om vrugkwaliteit negatief te beïnvloed. In seisoene wannneer vogverlies en verrimpeling hoog is, sal gebruik van hierdie sakke die aantal versendings wat by oorsese markte afgekeur word, kan verminder. Hierdie studie het bewys dat daar ‘n komplekse interaksie tussen die verskillende eienskappe van die kutikula is in reaksie op, of as gevolg van, vogverlies. Dit sal interessant wees om te die omgewings-seine wat tot verandering van die kutikula lei te ondersoek en te bepaal watter gene betrokke is, hoe hulle geaktiveer word, ensovoorts. Kennis van die meganismes betrokke by die funksionering en reaksies van hierdie komplekse polimeer kan die manipulasie van die kutikula om vrugkwaliteit en raklewe te verleng of kultivars te teel wat nie geneig is tot kutikula defekte nie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/105958
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