Thesis (MSc Food Sc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: The South African avocado fruit industry is export driven and the successful
storage of fruits for extended periods is, therefore, essential. It was recorded
that 7.7 million cartons were exported during the 1995 season. The shipping
of the avocados takes approximately 15 days and the fruits are being stored
at low temperatures to minimise the possibility of fruits softening.
Unfortunately low temperature storage results in chilling injury. A possible
method to increase avocado resistance to chilling injury is to administer a heat
shock treatment. In this way the fruits are protected from chilling injury by
inducing the formation of so-called heat-shock proteins which render the cell
membranes more resistant to chilling injury.
The objective of this study was to evaluate different heat shock
treatment protocols as a method of preventing or minimising chilling injury and
to extend the shelf-life of avocado fruits while exporting at the lowest possible
temperature. Examining the effect of different temperatures and exposure
times on the quality of the different avocado cultivars pursued this. The
exterior chilling injury on each fruit was quantified and the firmness and
internal quality parameters evaluated.
A total of 32 Experimental Studies were conducted. The results
showed that the Hot Water Heat shock Treatment (HWHST) worked
effectively for the South African 'Fuerte' cultivar between 40° and 42°C for
exposure times of between 20 and 30 min. The 'Edranol' cultivar also showed
promising results between 40° and 42°C for exposure time of between 8 and
22 min. The HWHST was not effective on the South African 'Hass' cultivar.
The 'Ryan' cultivar with its thick skin made this cultivar less susceptible to
chilling injury and therefore HWHST would be unnecessary. The 'Pinkerton'
cultivar had a lot of factors that influenced the results. Therefore, more
research needed to be done on the 'Pinkerton' cultivar, before any
conclusions could be obtained from this cultivar, although it showed potential.
Hot air treatment worked fairly well, but unfortunately the long exposure time
needed made this treatment unpractical. Throughout the whole study the
importance of maturity surfaced as a major role in all the aspects of post
harvest quality. / AFRIKAANSE OPSOMMING: Die Suid-Afrikaanse avokado vrugtebedryf is hoofsaaklik gerig op die
uitvoermark en daarom is dit belangrik dat die vrugte vir 'n bepaalde tyd
suksesvolopgeberg kan word. Die sensus opname gedurende die 1995
seisoen het getoon dat 7.7 miljoen bokse avokados uitgevoer is. Die
avokados word vir ongeveer 15 dae per boot vervoer, wat kan lei tot vrugte
wat sag word. Om dit te verhoed, word die vrugte by lae temperature
opgeberg. Ongelukkig veroorsaak lae opbergingstemperature koueskade. 'n
Moontlike metode om avokados te beskerm teen lae temperature en
koueskade te verminder, is om 'n hitteskok behandeling toe te pas. Op
hierdie manier word die vrugte beskerm teen koueskade deur die vorming van
sogenaamde hitteskok proteïene wat die selwande meer bestand maak teen
koueskade.
Die doel van hierdie studie was om die verskillende hitteskok
behandelings protokols te evalueer as 'n metode van beskerming of
vermindering van koueskade en om sodoende die rakleeftyd van avocados te
verleng as die vrugte by lae temperature uitgevoer word. Eksperimente is
uitgevoer om die effek van verskillende temperature en blootstellingstye op
die kwaliteit van die verskillende avokado kultivars te bepaal. Die koueskade
op die oppervlakte van elke vrug is bepaal en die fermheid en interne kwaliteit
parameters is geëvalueer.
In totaal is daar altesaam 32 Eksperimentele Studies gedoen. Die
resultate het gewys dat die Warm Water Hitteskok Behandeling (WWHB)
effektief was op die Suid-Afrikaanse 'Fuerte' kultivar by temperature tussen
40° en 42°C en by blootstellingstye van tussen 20 en 30 min. Belowende
resultate is ook met die 'Edranol' kultivar by temperature tussen 40° en 42°C
met blootstellingtye van tussen 8 en 22 min behaal. Die WWHB was
oneffektief vir die Suid-Afrikaanse 'Hass' kultivar. Die 'Ryan' kultivar se dik
skil het hierdie kultivar minder vatbaar gemaak vir koueskade en daarom was
'n WWHB onnodig gewees. By die 'Pinkerton' kultivar kon daar nog nie 'n
gevolgtrekking gemaak word nie, aangesien daar nog baie faktore is wat
ondersoek moet word, alhoewel die kultivar baie potentiaal getoon het. Warm
lug behandeling het potensiaal gehad, maar die lang blootstellingstye het hierdie behandeling onprakties gemaak. Gedurende die hele studie is daar
klem gelê op die rypheisgraad van die vrugte wat na vore gekom het as 'n
belangrike faktor wat 'n hoofrol speel in al die aspekte van die na-oes
kwaliteit.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/52835 |
| Date | 12 1900 |
| Creators | Kritzinger, Madeleine |
| Contributors | Britz, T. J., Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 122 pages : illustrations |
| Rights | Stellenbosch University |
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