Browsing by Author "Carmichael, Patricia Cassie"

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    Effect of fruit maturation and ripening potential for optimum eating quality of 'Forelle' pears
    (Stellenbosch : University of Stellenbosch, 2011-03) Carmichael, Patricia Cassie; Lotze, Elmi; Theron, K. I.; Crouch, E. M.; University of Stellenbosch. Faculty of AgriSciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: Climatic differences between production areas or seasons directly affect the rate of fruit maturation and the eating quality following storage and ripening. South African ‘Forelle’ pears are harvested at an optimum firmness of 6.4 kg and have mandatory cold storage duration of 12 weeks at -0.5°C to ensure even ripening. The firmness variable alone, however, is not a good indicator of ripening potential. Hence, various maturity variables (ethylene production, ground colour, firmness, total soluble solids (TSS) titratable acidity (TA), and starch breakdown) and their rates of change were evaluated to identify consistent maturity indices that can be reliably used in a prediction model to determine optimum harvest maturity (Chapter 2). This was then related to the ripening potential (Chapter 3) and eating quality (Chapter 4), defined by optimum ‘edible firmness’ (3.5 kg), presence or absence of astringency or mealiness. Fruit were harvested from three main producing areas: Warm Bokkeveld (WBV), Elgin and Koue Bokkeveld (KBV). Harvesting was done biweekly on five harvest dates over three successive seasons (2007-2009). At harvest, 20 of 240 fruit per block were used to determine maturity using all the mentioned parameters in order to understand their changes and behaviour pre-harvest. The remaining 220 fruit were stored at -0.5°C for three storage durations followed by ripening at 15°C. At harvest, the 2007 season’s fruit were more advanced in ground colour and were significantly softer (6.7 kg) than the 2008 (7.0 kg) and 2009 (7.1 kg) seasons. Firmness, ground colour, TSS and TA, all displayed a linear relationship with days after full bloom. For the firmness and ground colour, more than 90% and 73%, respectively, was explained by the variation in the linear model, while for the TSS and TA less than 70% could be accounted for by the model. Fruit harvested before commercial harvest (pre-optimum) in 2007 and 2009 failed to ripen to an ‘edible firmness’ when stored for eight weeks at -0.5oC plus 11 days at 15oC. In 2008, eight weeks storage was sufficient to induce ripening changes in pre-optimum harvested fruit. The development of ripening potential in the 2008 earlier harvested fruit, corresponded with a higher rate of change (3.15 µL.kg-1.h-1.day-1) in ethylene production at 15oC compared to the 2007 (1.98 µL.kg-1.h-1.day-1) and 2009 (1.87 µL.kg-1.h-1.day-1) seasons. The 2007 season fruit experienced maximum incidence of astringency (36.7%) on the first harvested fruit. In all three seasons, fruit harvested at commercial harvest time and later (optimum and post-optimum), required an eight week storage period to induce ripening. However, the eight weeks storage period developed highest mealiness. More than 40% of the last harvested fruit were mealy after eight weeks at -0.5°C plus seven days at 15°C. Mealiness significantly reduced with prolonged storage at -0.5°C. Fruit from the WBV and Elgin, warmer areas than the KBV, were more prone to mealiness. In conclusion, firmness was the most consistent variable at harvest and could be used in conjunction with ground colour to determine ‘Forelle’ harvest maturity. Furthermore, the study does not support shortening the current mandatory 12 weeks period at -0.5°C due to the higher incidence of astringency and mealiness.