ENGLISH ABSTRACT: The export of Japanese plums from South Africa is challenging, since most cultivars are prone to
develop chilling injury (CI) when stored at low temperatures. This injury manifests as gel
breakdown or internal browning in the mesocarp tissue of the fruit on removal from low storage
temperature conditions, i.e. in the consumer’s fruit basket, who subsequently does not buy plums
again.
Loss of cell membrane integrity and oxidative stress are, respectively, the primary and secondary
physiological responses to CI. The main aim of this study was to investigate changes in cell
membrane composition and levels of antioxidants in plums throughout fruit development and
maturation, during forced air cooling (FAC) and storage under different temperature regimes.
‘Sapphire’ (a chilling susceptible cultivar) accumulated high levels of glutathione and
polyunsaturated fatty acids (PUFAs) during fruit development. Therefore, the cultivar is protected
against lipid peroxidation while developing on the tree, but the high levels of PUFAs, which are
easily oxidised, may cause this cultivar to be chilling susceptible when stored at low temperatures.
It is suggested that the high levels of monounsaturated fatty acids (MUFAs), which are not easily
oxidised, and ascorbic acid that accumulated in ‘Angeleno’ (a chilling resistant cultivar) during fruit
development, render this cultivar CI resistant during long-term cold-storage.
When stored at -0.5 °C, CI development increased at a higher rate, ethylene evolution rates were
higher and water soluble antioxidant activity (HAA), ascorbic acid and glutathione levels, and the
MUFA:PUFA ratio were lower in H2 (more mature) ‘Sapphire’ plums than H1 fruit (less mature).
Therefore, concurrent with H2 fruit having lower levels of antioxidants to quench free radicals
caused by chilling stress, their cell membranes were more vulnerable to oxidation due to their
phospholipid fatty acid composition. H2 fruit also had higher levels of saturated fatty acids, and
hence less fluid cell membranes than H1 fruit when stored at -0.5 °C.
An intermittent warming (IW) regime delayed symptom appearance and reduced CI severity in
plums significantly compared to storage at -0.5 °C. Fruit stored under the IW regime had a more optimal phospholipid fatty acid composition and lower membrane sterol levels under shelf-life
conditions to keep the membranes fluid. It also had higher levels of HAA and lipid soluble
antioxidant activity, ascorbic acid and glutathione, which rendered fruit better protected against
oxidation.
Elevated storage temperatures (2.5 °C to 7.5 °C) caused higher levels of lipid peroxidation or low
ascorbic acid levels and poor fruit quality compared to the IW regime in ‘Sapphire’ plums. ‘Laetitia’
plums stored at 5 °C and 7.5 °C had significantly less CI than under the IW regime, but softened
quicker due to higher ethylene evolution rates.
‘Sapphire’ tolerated both long and short FAC durations, but a slower initial FAC rate prevented CI
manifestation and caused a higher HAA after cold-storage in this fruit. ‘Laetitia’ cooled with a
slower initial FAC rate and for a longer duration resulted in the best fruit quality and had higher
HAA, total phenolic, phospholipid and saturated phospholipid fatty acid concentrations during
storage. / AFRIKAANSE OPSOMMING: Die uitvoer van Japanese pruime vanaf Suid-Afrika hou talle uitdagings in, want die meeste van die
kultivars ontwikkel koueskade wanneer hulle by lae temperature opgeberg word. Koueskade
manifesteer as gelverval of interne verbruining in die mesokarpweefsel van die vrugte wanneer die
vrugte verwyder word uit die lae opbergingstemperatuuromstandighede, m.a.w. in die verbruiker se
vrugtemandjie, wat nie weer pruime koop nie.
Verlies aan selmembraanintegriteit en oksidatiewe druk is, respektiewelik, die primêre and
sekondêre fisiologiese reaksies op koueskade. Die hoofdoel van hierdie studie was om die
veranderinge in selmembraansamestelling en antioksidantkonsentrasie in pruime te ondersoek
tydens vrugontwikkeling en volwassewording, tydens geforseerde lugverkoeling (GLV) en tydens
opberging onder verskillende temperatuurregimes.
‘Sapphire’ (‘n koueskade sensitiewe kultivar) het hoër konsentrasies van glutatioon en polionversadigde
vetsure (POV) tydens vrugontwikkeling geakkumuleer. Dié kultivar is dus voldoende
beskerm teen lipiedperoksidasie tydens vrugontwikkeling aan die boom, maar die hoë
konsentrasies van POVs, wat maklik oksideer, mag veroorsaak dat hierdie kultivar meer
koueskadesensitief is wanneer dit by lae temperature opgeberg word. Die hoë konsentrasies van
mono-onversadigde vetsure (MOV), wat nie maklik oksideer nie, en askorbiensuur wat in
‘Angeleno’ (‘n koueskade weerstandbiedende kultivar) geakkumuleer het tydens vrugontwikkeling,
verleen moontlik weerstandbiedendheid teen koueskade aan hierdie kultivar tydens langtermyn
koelkopbering.
Tydens opberging by -0.5 °C het koueskade ontwikkeling vinniger toegeneem, was
etileenvrystellingstempos hoër en die wateroplosbare antioksidantaktiwiteit (HAA), askorbiensuuren
glutatioonkonsentrasies en die MOV:POV verhouding laer in H2 (meer volwasse) ‘Sapphire’
pruime as in die H1 vrugte (minder volwasse). Dus, tesame met die laer antioksidantkonsentrasies
in die H2 vrugte om die vry radikale veroorsaak deur koelopbering te verminder, was hul
selmembrane ook meer vatbaar vir oksidasie a.g.v. die vetsuursamestellling van hul
membraanfosfolipiede. Die H2 vrugte het ook ‘n hoër konsentrasie van versadigde vetsure, en dus
minder vloeibare membrane as die H1 vrugte gehad tydens opberging by -0.5 °C.
Die dubbeltemperatuurregime (DT) het simptoomontwikkeling vertraag en koueskade-intensiteit
betekenisvol verminder in vergelyking met pruime wat by -0.5 °C opgeberg is. Vrugte wat met die
DT regime opgeberg is, het ‘n meer optimale fosfolipiedvetsuursamestelling en laer konsentrasie
van membraansterole tydens gesimuleerde raklewe gehad wat meer vloeibare membrane
verseker het. Hierdie behandeling het ook hoër HAA en lipiedoplosbare antioksidantaktiwiteit
(LAA), askorbiensuur- en glutatioonkonsentrasies gehad wat die vrugte beskerm het teen
oksidatiewe druk.
Verhoogde opbergingstemperature het hoër vlakke van lipiedperoksidasie of lae
askorbiensuurkonsentrasies asook swak vrugkwaliteit in ‘Sapphire’ pruime veroorsaak in
vergelyking met die DT regime. ‘Laetitia’ pruime wat by 5 °C en 7.5 °C opgeberg is, het
betekenisvol minder koueskade gehad in vergelyking met die DT regime, maar het vinniger sag
geword a.g.v. hoër etileenvrystellingstempos.
‘Sapphire’ kon lang en kort GLV tye weerstaan, maar ‘n stadiger inisiële GLV spoed het die
manifestasie van koueskade voorkom en het ‘n hoër HAA in die vrugte tot gevolg gehad na
koelopberging. ‘Laetitia’ wat met ‘n stadiger inisiële GLV spoed en oor ‘n langer tyd verkoel is, het
die beste vrugkwaliteit, en hoër HAA, totale fenool-, fosfolipied- en versadigde
fosfolipiedvetsuurkonsentrasies as die ander behandelings tydens koelopberging gehad
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71607 |
| Date | 12 1900 |
| Creators | Jooste, Mariana |
| Contributors | Huysamer, Marius, Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | xxiii, 271 p. : ill. |
| Rights | Stellenbosch University |
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