Graduation date: 2002

Graduation date: 1962

Modified atmosphere packaging storage combines an atmosphere of higher carbon dioxide and lower oxygen levels than air, with chilling temperatures to extend shelf-life of fresh fruits. In three modified atmosphere packaging storage trials, blueberries were packaged in film bags with different gas permeabilities, and stored at about 4°C. Storage of blueberries in packages of a film with intermediate gas permeability produced an aerobic atmosphere and a relatively low carbon dioxide level, resulting in rapid growth of yeast and molds on blueberries. Packaging blueberries in a film with very low gas permeability created a high carbon dioxide almost anaerobic atmosphere, which successfully inhibited yeast and mold growth on blueberries for up to eight weeks. The possibility of yeast inhibition by antifungal compounds accumulated in blueberries stored under modified atmosphere packaging conditions was investigated by using the disk diffusion assay. The results of these assays showed the absence of antifungal activity against two Rhodotorula species, a Zygosaccharomyces species, a Cryptococcus species, a Debaryomyces species, and indicated that the inhibition of yeast growth was due to low temperature, high carbon dioxide level and anaerobic conditions. The effects of temperature and atmosphere composition were investigated by using natural flora of blueberry juice and two yeast isolates grown in sterilized juice. At 21°C, yeast growth was slow in the presence of carbon dioxide and absence of oxygen. At low temperature, yeast growth was slow in the presence of oxygen, but was inhibited in the anaerobic, high carbon dioxide environment. It is proposed that the micro-aerobic environment of modified atmosphere packaging storage might have allowed slow desaturation of yeast membrane fatty acids which enabled yeasts to maintain membrane fluidity and function at low .temperature. Furthermore, yeast growth during storage of modified atmosphere packaged blueberries may be affected by low temperature and high carbon dioxide conditions. / Land and Food Systems, Faculty of / Graduate

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.