Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: By world standards South Africa’s contribution to fresh blueberry production is very
small, a mere 0.25 %. This seemingly insignificant and unimpressive statistic is,
however, by no means indicative of the impending impressive potential the South African
blueberry industry holds. South Africa is encountering a rapid growth phase off a very
small base and the current 100-150 ton export crop is expected to increase to a range of
500 to 600 tons or more in the next five years. Consequently, export by sea must be
considered as a logistic alternative. Seafreight success relies on controlled atmosphere
storage which in turn relies on berries of exceptional quality. To achieve this,
fundamental differences between blueberry cultivars must be examined and blueberry
handling and storage regimes must be assessed and optimised.
This study investigates the storage potential of certain rabbiteye blueberries relative to
controlled atmospheres and short pre-cooling delays. Quality assessments were based on
external colour, soluble solids, titratible acidity, firmness and decay development.
Furthermore, the respiration and ethylene production rates as well as moisture loss, of
various cultivars were determined to characterize fundamental differences amongst
cultivars and to gain insight into their postharvest behaviour. Lastly the effect of infection
on pigment levels of blueberry flesh and peel was examined for the purpose of laboratory
experience.
Controlled atmosphere storage had the greatest impact on berry firmness and percentage
decay. No off flavours were detected during sensory analysis at the CA levels tested. CAstored
berries were firmer and incidence of decay was reduced significantly. Significant
decay reduction was challenged by the market tolerance of no more than 2 %. Decay
suppression and storage extension was insufficient (for the set period), particularly after
the shelf life period. Cultivar and seasonal differences as well as picking maturity and
inoculum pressure determine blueberry CA storability. CA may be a valuable technology,
however advances must first be made in ensuring optimal blueberry quality to warrant
export by sea. Short pre-cooling delays (0, 2, 4, 6 h) at 20 ºC had no effect on colour (L, C, H), total
soluble solids, titratable acidity and firmness of blueberry cultivars, ‘Centurion’,
‘Premier’ and ‘Tifblue’. Results for percentage decay indicate that prompt cooling
becomes more critical as the duration of storage increases, particularly when market
specification of no more than 2 % decay must be met. Berries subjected to longer delays
appear to be more susceptible to decay. Differences exist among cultivars and knowledge
gained from this research can be used to adapt handling and cooling regimes. Information
generated will benefit cultivar selection for marketing (local vs. export), storage (short vs.
long term) and logistics (air vs. seafreight).
Rabbiteye blueberry cultivars differ considerably in terms of their respiration rate,
ethylene production and moisture loss. These quality parameters were evaluated for
various cultivars at 15 ºC. ‘Climax’ appears to have the highest respiration rate, ethylene
production and moisture loss, whilst ‘Premier’ has the lowest respiration rate and
ethylene production was too low to be detected by gas chromatography. The lowest
moisture loss proportionality constant was found for ‘Tifblue’ and ‘Centurion’.
A change in blueberry flesh colour from white to dark red was noted in infected berries.
Artificial inoculation with Botrytis cinerea showed a similar result. The colour change
was evaluated by comparing anthocyanin pigment levels (determined by
spectrophotometry and HPLC) of the peel and flesh. Anthocyanin content of infected
flesh doubled, whilst that of infected peel was less than 50 % of the control. Pigment
leakage has been reported in blueberries. It would appear that cell disruption, induced by
infection may facilitate migration of anthocyanin from the peel to the flesh.
The storage potential of blueberries depends on cultivar, maturity at harvest, climatic
conditions as well as the inoculum pressure. Under favourable conditions storage life of
blueberries can be manipulated effectively. Further cultivar specific research that targets
relevant quality issues should be investigated. Reliable techniques should be developed to
quantify blueberry firmness changes. Research on inoculum levels may give insight into the reduction of decay pressure and decay suppressing alternatives such as antibacterial
pads can be examined. Peel integrity relative to decay susceptibility can also be
researched on a cellular level. / AFRIKAANSE OPSOMMING: Suid-Afrika se bydrae tot wêreld bloubessie produksie is baie klein, ‘n skrale 0.25 %.
Hierdie onindrukwekkende statistiek weerspieel egter glad nie die indrukwekkende
potensiaal van die Suid-Afrikaanse bloubessie bedryf nie. Die bedryf ondervind tans ‘n
dramatiese groei met ‘n klein begin vanaf die huidige 100-150 ton opbrengs tot wat
volgens verwagting binne die volgende vyf jaar sal styg tot in die orde van 500-600 ton.
Na aanleiding van die verwagte toename in produksie, sal seevrag verskeping oorweeg
moet word as alternatief vir uitvoer eerder as lugvrag. Die sukses van seevrag lê in die
gebruik van beheerde atmosfeer opberging (BA), waarvan die sukses op sy beurt bepaal
word deur bessies van hoogstaande kwaliteit. Om steeds aan die verwagtings van die
oorsese mark te voldoen moet grondliggende verskille tussen bloubessie kultivars
ondersoek word en daaropvolgend moet hantering en opbergingstelsels aangepas en
geoptimeer word.
Die navorsing bestudeer die opbergingspotensiaal van verskeie rabbiteye bloubessies
relatief tot beheerde atmosfere en kort vertragings in verkoeling. Kwaliteit, gebasseer op
eksterne kleur, oplosbare deeltjies, titreerbare sure, fermheid en persentasie bederf, is
ondersoek. Die respirasie en etileenproduksie tempos sowel as vogverlies van verskeie
kultivars was verder bepaal om die fundamentele verskille tussen kultivars te bepaal,
sowel as insig te verwerf in na-oes gedrag. Die effek van infeksie op pigment vlakke van
bloubessie vlees en skil was ondersoek vir die doel van laboratorium ondervinding.
Beheerde atmosfeer opberging het die grootste effek getoon op bessie fermheid en
persentasie bederf. Na aanleiding van sensoriese toetse is daar geen wansmaake
aangeteken ten op sigte van die BA vlakke wat getoets is nie. Bessies onderworpe aan
beheerde atmosfeeriese toestande was fermer en bederfonderdrukking was beduidend.
Die markverdraagsaamheid ten opsigte van bessiebederf, is egter 2 %. Hiervolgens was
onderdrukking van verval asook opbergingsvermoë, onvoldoende (spesifiek na die rakleeftyd). Kultivar en seisoenale verskille asook plukrypheid en inokulum druk, bepaal
ook die sukses van BA opberging. BA word beskou as ‘n waardevolle tegnologie vir
verlenging van opberging. Dit blyk egter dat daar eers ‘n vooruitgang gemaak moet word
in die versekering van optimale bessie kwaliteit voordat verskeping oorweeg kan word.
Kort vertragings (0, 2, 4, 6 uur by 20 ºC) in verkoeling, het geen invloed gehad op kleur,
(L, C, H), totale oplosbare vastestowwe, titreerbare suur en fermheid van bloubessie
kultivars ‘Centurion’, ‘Premier’ en ‘Tifblue’ nie. Bederfresultate dui daarop dat
onmiddelike verkoeling krities is, veral by verlengde opberging, om aan die 2 % bederf
drempelwaarde te voldoen. Bessies onderhewig aan langer vertragings voor verkoeling,
blyk meer vatbaar te wees vir bederf. Verskille bestaan tussen kultivars en kennis
ingewin tydens hierdie navorsing kan toegepas word om hanteringsprosedures en
verkoeling aan te pas. Ingeligte besluitneming kan dus ten opsigte van kultivarspesifieke
bemarking (plaaslik en uitvoer), opberging (kort- en langtermyn) en vervoer (lug- en
seevrag) gemaak word.
Rabbiteye bloubessie kultivars verskil aansienlik ten opsigte van hul respirasietempo,
etileenproduksie en vogverlies. Laasgenoemde kwaliteitsbepalers is by verskillende
kultivars ondersoek by 15 ºC. ‘Climax’ het die hoogste respirasietempo, etileenproduksie
en vogverlies getoon, terwyl ‘Premier’ die laagste respirasietempo gehad het, en die
etileenproduksie te laag was om met die gaschromatograaf te bepaal. Die laagste
vogverlies proporsionaliteitskonstante is waargeneem tussen ‘Tifblue’ en ‘Centurion’.
‘n Verandering is waargeneem in bloubessie vrugvleeskleur van wit tot donkerrooi by
besmette bessies. ‘n Soortgelyke resultaat is verkry met kunsmatige inokulering met
Botrytis cinerea. Die kleurverskil is geëvalueer deur vergelyking te tref met die
antosianienpigment vlakke tussen die skil en die vlees (bepaal deur spektrofotometrie en
HPLC). Antosianieninhoud van besmette vrugvlees het verdubbel, terwyl die van
besmette vrugskil minder as 50 % van die kontrole groep was. Pigmentlekkasie is al
vermeld by bloubessies. Dit wil voorkom of selskade veroorsaak deur infeksie beweging
van antosianien vanaf die skil na die vlees kan aanhelp. Die opbergingspotensiaal van bloubessies hang af van kultivar, rypheid by oes,
omgewings toestande sowel as inokulum druk. Onder gunstige toestande kan bloubessies
se opbergingsvermoë effektief gemanipuleer word. Verder kultivar-spesifieke navorsing
wat relevante kwaliteits kwessies aanspreek, kan gedoen word. Verder kan betroubare
tegnieke in die meting van bloubessie fermheid veranderinge ondersoek word. Navorsing
ten opsigte van inokulum vlakke mag insig gee in terme van bederf-druk vermindering en
die gebruik van bederf-onderdrukking alternatiewe soos anti-bakteriese lappies. Skil
integriteit relatief tot bederf-vatbaarheid kan ook op sellulere vlak ondersoek word.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20906 |
| Date | 12 1900 |
| Creators | Van Hoorn, A. T. (Aaltje Trientje) |
| Contributors | Huysamer, M., Jacobs, G., 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 | x, 137 leaves : ill. (some col.) |
| Rights | Stellenbosch University |
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