Optimisation of blueberry postharvest handling and storage

[摘要] ENGLISH ABSTRACT: By world standards South Africa's contribution to fresh blueberry production is verysmall, a mere 0.25 %. This seemingly insignificant and unimpressive statistic is,however, by no means indicative of the impending impressive potential the South Africanblueberry industry holds. South Africa is encountering a rapid growth phase off a verysmall base and the current 100-150 ton export crop is expected to increase to a range of500 to 600 tons or more in the next five years. Consequently, export by sea must beconsidered as a logistic alternative. Seafreight success relies on controlled atmospherestorage which in turn relies on berries of exceptional quality. To achieve this,fundamental differences between blueberry cultivars must be examined and blueberryhandling and storage regimes must be assessed and optimised.This study investigates the storage potential of certain rabbiteye blueberries relative tocontrolled atmospheres and short pre-cooling delays. Quality assessments were based onexternal colour, soluble solids, titratible acidity, firmness and decay development.Furthermore, the respiration and ethylene production rates as well as moisture loss, ofvarious cultivars were determined to characterize fundamental differences amongstcultivars and to gain insight into their postharvest behaviour. Lastly the effect of infectionon pigment levels of blueberry flesh and peel was examined for the purpose of laboratoryexperience.Controlled atmosphere storage had the greatest impact on berry firmness and percentagedecay. No off flavours were detected during sensory analysis at the CA levels tested. CAstoredberries were firmer and incidence of decay was reduced significantly. Significantdecay reduction was challenged by the market tolerance of no more than 2 %. Decaysuppression and storage extension was insufficient (for the set period), particularly afterthe shelf life period. Cultivar and seasonal differences as well as picking maturity andinoculum pressure determine blueberry CA storability. CA may be a valuable technology,however advances must first be made in ensuring optimal blueberry quality to warrantexport by sea. Short pre-cooling delays (0, 2, 4, 6 h) at 20 ºC had no effect on colour (L, C, H), totalsoluble solids, titratable acidity and firmness of blueberry cultivars, 'Centurion','Premier' and 'Tifblue'. Results for percentage decay indicate that prompt coolingbecomes more critical as the duration of storage increases, particularly when marketspecification of no more than 2 % decay must be met. Berries subjected to longer delaysappear to be more susceptible to decay. Differences exist among cultivars and knowledgegained from this research can be used to adapt handling and cooling regimes. Informationgenerated 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 forvarious cultivars at 15 ºC. 'Climax' appears to have the highest respiration rate, ethyleneproduction and moisture loss, whilst 'Premier' has the lowest respiration rate andethylene production was too low to be detected by gas chromatography. The lowestmoisture 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 changewas evaluated by comparing anthocyanin pigment levels (determined byspectrophotometry and HPLC) of the peel and flesh. Anthocyanin content of infectedflesh doubled, whilst that of infected peel was less than 50 % of the control. Pigmentleakage has been reported in blueberries. It would appear that cell disruption, induced byinfection may facilitate migration of anthocyanin from the peel to the flesh.The storage potential of blueberries depends on cultivar, maturity at harvest, climaticconditions as well as the inoculum pressure. Under favourable conditions storage life ofblueberries can be manipulated effectively. Further cultivar specific research that targetsrelevant quality issues should be investigated. Reliable techniques should be developed toquantify blueberry firmness changes. Research on inoculum levels may give insight into the reduction of decay pressure and decay suppressing alternatives such as antibacterialpads can be examined. Peel integrity relative to decay susceptibility can also beresearched on a cellular level.

[发布机构] Stellenbosch University