Thesis (MScAgric) -- University of Stellenbosch, 2000. / ENGLISH ABSTRACT: Postharvest berry split and abscission are prevailing physiological disorders that negatively
impact on the quality of table grapes exported from South Africa. Inferior grape quality due to
these disorders results in a considerable decline in consumer confidence in the branded
product, which leads to a drop in demand, and consequently, lower prices. Since information
concerning postharvest factors influencing postharvest berry split and abscission is limited, the
search for reliable methods to adequately control these problems remains elusive. In an
attempt to obtain the required information, the influence of harvest temperature, harvest
maturity, perforated liners, field heat removal prior to packing, delay periods before and after
packing, storage duration and the elevation of storage temperature on the development of berry
split and abscission in 'Thompson Seedless' (Vitis vinifera Linnaeus) table grapes was
investigated. Changes in abscission related factors during berry development, and the influence
of pre-and postharvest ethylene inhibitors on the development of berry abscission in 'Waltham
Cross' table grapes, was also studied.
Berry split was aggravated by packing 'Thompson Seedless' grapes at high pulp temperatures
of approximately 30°C, especially if the grapes were packed in non-perforated bags. The
incidence of berry split could be reduced by between 80 and 90% by packing grapes in
perforated instead of non-perforated liners. Perforated bags also reduced levels of S02
damage. However, due to significantly more moisture loss from grapes in perforated bags,
compared to non-perforated bags, the risk of higher fruit and stem desiccation and softer berries
existed. Optimum size and density of perforations needs to be determined to reduce berry split
without excessive loss of moisture from the grapes, and S02gas from the air space surrounding
the product. The influence of harvest temperature and liner type on berry abscission was not
conclusive. Advanced maturity increased grape resistance to berry split. However, grapes
harvested too mature were prone to stem desiccation and the development of Botrytis decay.
The occurrence of berry abscission also appeared to increase with advanced harvest maturity.
Consequently, to ensure optimal post-storage quality, 'Thompson Seedless' grapes should be
harvested as soon as horticultural maturity has been reached, which appears to be at
approximately 18°Brix.
Field heat removal for 1.5 hours at 19°C prior to packing had no beneficial or adverse effect on
berry split and abscission. Delay periods prior to packing aggravated berry abscission, but did
not influence berry split significantly. Grapes delayed for 12 hours showed a significant increase
in berry abscission and Botrytis decay, compared to grapes delayed for only 3 or 8 hours. Considering that the absence of fungal decay is the most important quality prerequisite in table
grapes, it is of vital importance to pack grapes with as short a delay period as possible. Grapes
packed in non-perforated liners and delayed for different durations after packing, before the
onset of forced-air cooling (FAC), showed significant differences regarding the incidence of
berry split. Grapes delayed for 18 hours had significantly higher levels of berry split directly after
the delay period, compared to grapes delayed for 6 or 12 hours. No significant difference in
berry abscission occurred between grapes delayed for different periods. To minimise the
amount of berry split, FAC should be applied as rapidly as possible after the packing of grapes
in non-perforated liners.
Two storage related factors significantly influenced the incidence of berry split in 'Thompson
Seedless' grapes during cold storage significantly, viz. the duration of storage at -O.soC,and the
increase in temperature after low temperature storage. Berry split increased almost linearly with
prolonged storage at -O.soC. An elevation of storage temperature from -O.soC to 10°C any time
during the cold storage period, further aggravated the split problem. Consequently, the
reduction of berry split in 'Thompson Seedless' table grapes during cold storage requires (a) the
shortest possible cold storage period, and (b) good temperature management throughout
distribution, from initiation of cooling until the final point of sale.
The grape berry abscission potential, as quantitatively indexed by the measurement of the fruit
removal force (FRF), showed significant changes during berry development of 'Waltham Cross'
table grapes, from 27 to 111 days after full bloom (OAFB). This showed that at certain stages of
fruit growth, 'Waltham Cross' grapes are more prone to berry abscission. At 27 OAFB, when the
berries had an average diameter of 6.6mm, the grape bunches showed a significantly higher
potential for berry abscission, compared to grapes sampled at a later stage. 'Waltham Cross'
has inherently straggly bunches with bare shoulders. Therefore, any abscission during berry
development will aggravate the problem. Consequently, it is of vital importance that any
adverse factors such as moisture stress be avoided, especially during the period when
'Waltham Cross' grapes appear to be very susceptible to berry abscission. Of all parameters
measured, moisture loss showed the best correlation with abscission. Grapes harvested with
total soluble solids (TSS) of 12.3°Brix, 83 OAFB, had a significantly higher abscission potential
than grapes harvested more mature. Therefore, by harvesting 'Waltham Cross' grapes at
optimum maturity, at a TSS of approximately 16.4°Brix, berry abscission can be reduced to a
great extent. It was evident that at veraison, the metabolism of grape berries changes
drastically, and additional to the rapid increase in sugars and the rapid decrease in acidity, a
decrease in FRF occurs. Preharvest sprays of ReTain™ (a derivative of aminoethoxyvinylglycine), which inhibits ethylene
synthesis, showed no promise as a means to reduce postharvest berry abscission. A
postharvest treatment with EthylBloc® (1-methylcyclopropene), which inhibits ethylene action,
only reduced berry abscission during one season. / AFRIKAANSE OPSOMMING: Die fisiologiese defekte korrelbars en los korrels wat algemeen voorkom tydens opberging van
sekere tafeldruif-kultivars, het 'n negatiewe invloed op tafeldruiwe wat uitgevoer word vanaf
Suid-Afrika. Minderwaardige kwaliteit as gevolg van hierdie defekte het 'n aansienlike afname
in verbruikers-vertroue tot gevolg wat aanleiding gee tot 'n ooreenkomstige afname in aanvraag
en prys van die produk. Inligting rakende na-oes faktore wat die voorkoms van korrelbars en los
korrels beïnvloed is beperk, en geen gewaarborgde metode bestaan om hierdie twee defekte
volkome te beheer nie. In 'n poging om dié gewenste inligting te bekom, is ondersoek ingestel
na die effek van oes-temperatuur, oes-rypheid, geperforeerde sakke, veldhitte verwydering voor
verpakking, vertragingsperiodes voor en na verpakking, tydsduur van opberging, en die
verhoging van die opbergingstemperatuur, op die voorkoms van korrelbars en los korrels by
'Thompson Seedless' (Vitis vinifera Linnaeus) druiwe. Daar is ook ondersoek ingestel na
veranderings in afsnoering verwante faktore tydens korrel-ontwikkeling, en die invloed van vooren
na-oes toedienings van etileen inhibeerders op die ontwikkeling van los korrels by 'Waltham
Cross'tafeldruiwe.
Korrelbars is vererger deur 'Thompson Seedless' met hoë pulptemperature van ongeveer
29.5°C te verpak, veral indien dit in 'n riie-geperforeerde sak verpak is. Die voorkoms van
korrelbars kon tussen 80 en 90% verminder word deur 'Thompson Seedless' druiwe in
geperforeerde sakke te verpak, in plaas van nie-geperforeerde sakke. Geperforeerde sakke het
ook S02 skade op die druiwe verminder. Tog, as gevolg van betekenisvol meer vogverlies
vanaf druiwe in geperforeerde sakke as vanaf druiwe in nie-geperforeerde sakke, bestaan die
risiko van meer stingel-uitdroging en minder ferm korrels indien druiwe in geperforeerde sakke
verpak word. Optimale grootte en digtheid van perforasies moet bepaal word om korrelbars te
verminder, maar sonder oormatige vogverlies vanaf die druiwe en oormatige verlies aan S02.
Die invloed van oes-temperatuur en sak-tipe op los korrels was nie oortuigend nie. Gevorderde
oes-rypheid het die druif se weerstand teen korrelbars verhoog. Daarteenoor was druiwe wat té
ryp geoes is, meer gevoelig vir stingel-uitdroging en Botrytis bederf. Dit wilook voorkom of die
voorkoms van los korrels toeneem met gevorderde rypheid. Dus, om optimum kwaliteit na
opberging te verseker, moet 'Thompson Seedless' geoes word sodra hortologiese rypheid
bereik word, wat blyk om by 'n totale opgeloste vaste stof-inhoud (TOVS) van ongeveer 18°Brix
te wees.
Veldhitte verwydering voor verpakking, vir 1.5 uur by 19°C, het geen effek gehad op die
voorkoms van korrelbars en los korrels nie. 'n Vertragingsperiode voor verpakking het die los korrel-probleem vererger, alhoewel dit geen betekenisvolle invloed op die voorkoms van
korrelbars gehad het nie. Druiwe wat vir 12 uur voor verpakking vertraag is, het betekenisvol
meer los korrels en Botrytis bederf getoon, in vergelyking met druiwe wat slegs 'n
vertragingsperiode van 3 of 8 uur ondergaan het. Aangesien die afwesigheid van bederf die
belangrikste kwaliteits-vereiste vir tafeldruiwe is, is dit van kardinale belang om druiwe so gou as
moontlik na oes te verpak. Druiwe, verpak in nie-geperforeerde sakke, wat vir verskillende
periodes vertraag is voor geforseerde-lug verkoeling, het betekenisvolle verskille getoon
betreffende die voorkoms van korrelbars. Druiwe vertraag vir 18 ure voor verkoeling, het
betekenisvol meer korrelbars getoon, soos gemeet onmiddellik na die vertragingsperiode, in
vergelyking met druiwe wat slegs vir 6 of 12 ure vertraag was. Geen betekenisvolle verskille in
los korrels het voorgekom tussen druiwe wat verskillende vertragingsperiodes ondergaan het
nie. Om korrelbars te verminder, moet geforseerde-lug verkoeling so gou as moontlik na
verpakking van druiwe in nie-geperforeerde sakke toegepas word.
Twee opbergings-verwante faktore beïnvloed die voorkoms van korrelbars by 'Thompson
Seedless' druiwe tydens koelopberging, naamlik die tydsduur van opberging by -O.soC,asook 'n
styging in temperatuur vanaf -O.soC tot 1DoC. Korrelbars het feitlik liniêr toegeneem met
verlengde opberging by -O.soC. 'n Styging in temperatuur vanaf -O.SoCtot 1DoCop enige tydstip
gedurende die koelopbergingsperiode, het korrelbars verder vererger. Dus, om korrelbars by
'Thompson Seedless' tydens opberging tot die minimum te beperk, moet die tydsduur van
opberging so kort as moontlik wees, en moet die koue ketting regdeur die distribusie-proses
gehandhaaf word, vanaf inisiëring van verkoeling tot en met die uiteindelike verkoop van die
produk.
Die afsnoerings-potensiaal van druiwe, soos kwantitatief geïndekseer is deur meting van die
vrug-verwyderings-vermoë (VVV), het betekenisvol verander gedurende korrel-ontwikkeling van
'Waltham Cross' tafeldruiwe, vanaf 27 tot 111 dae na volblom (DNVB). Dit het getoon dat
'Waltham Cross' druiwe by sekere stadiums van vrug-groei meer gevoelig is vir korrel
afsnoering. By 27 DNVB, wanneer die korrels 'n gemiddelde deursnee van 6.6mm gehad het,
het die druiwe 'n betekenisvolle hoër potensiaal vir afsnoering getoon, in vergelyking met druiwe
wat op 'n latere stadium getoets is. 'Waltham Cross' is inherent geneig tot yl trosse met kaal
skouers, gevolglik sal enige afsnoering tydens korrel-ontwikkeling die probleem vererger. Dus
is dit van kardinale belang dat enige nadelige faktor, soos byvoorbeeld vogstres, vermy moet
word, veral gedurende periodes wanneer dit wil voorkom of 'Waltham Cross' baie vatbaar is vir
korrel afsnoering. Van al die parameters wat gemeet is, het vogverlies die beste korrelasie met
korrel afsnoering getoon. Druiwe wat 83 DNVB, by 'n TOVS van 12.3°Brix geoes is, het 'n betekenisvol hoër potensiaal vir korrel afsnoering getoon, in vergelyking met druiwe wat ryper
geoes is. Dus, deur 'Waltham Cross' druiwe by optimum rypheid te oes, by 'n TOVS van
ongeveer 16.4°Brix, kan korrelbars in 'n groot mate verminder word. Tydens verelson, wanneer
die metabolisme van die druiwe drasties verander, was daar gepaardgaande met die drastiese
toename in TOVS en die drastiese afname in totale titreerbare sure (TSS), ook 'n afname in
Voor-oes bespuitings met ReTain™, wat etileen sintese inhibeer, het geen potensiaal getoon
om los korrels by 'Waltham Cross' te verminder nie. 'n Na-oes behandeling met EthyIBloc®,
wat etileen werking inhibeer, het slegs korrel afsnoering in een van die seisoene effens
verminder.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/51877 |
| Date | 12 1900 |
| Creators | Burger, D. A. (Dirk Albert) |
| Contributors | Taylor, M. A., Jacobs, G., Huysamer, M., Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 182 p. |
| Rights | Stellenbosch University |
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