Browsing by Author "Marais, Evelyn"
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- ItemPostharvest manipulation of fruit colour in apples and pears(Stellenbosch : Stellenbosch University, 2000-04) Marais, Evelyn; Holcroft, D. M.; Jacobs, G.; Stellenbosch University. Faculty of Science. Dept. of Horticultural Sciences.ENGLISH ABSTRACT: Red colour development on bi-coloured apples and pears ensures better prices for producers. The use of postharvest irradiation to improve colour has been successful on apples, and the objectives of this thesis were to optimise conditions during irradiation for apples and to evaluate the effects of irradiation on pears. 'Cripp's Pink' apples responded to postharvest irradiation with high-pressure sodium (HPS) lights by developing a red blush, whereas the response to irradiation with UV 8 plus incandescent lights was less effective. '8raeburn' apples held at -0.5°C for 4 or 8 weeks prior to irradiation showed a decrease in hue angle and an increase in anthocyanin concentration after 72 hours of irradiation with HPS lamps. In 'Forelle' pears treated in the same way, neither colour development nor anthocyanin synthesis was affected by irradiation. '8raeburn' and 'Cripp's Pink' apples picked weekly for 5 weeks until the optimum harvest date were irradiated with HPS lights. A significant increase in fruit colour was only measured in mature fruit of both cultivars. 'Cripp's Pink' apples were harvested from two production areas with different microclimates, namely, Ceres and Grabouw, and stored for 0, 2 or 5 days at -0.5 °C before irradiation for 120 hours at either 6°C or 20°C. Fruit from Ceres that were irradiated immediately after harvest developed better colour at 6 °C than at 20°C. The differences between fruit irradiated at the two temperatures were no longer significant after 5 days of cold storage prior to irradiation. Fruit from Grabouw consistently developed better colour when irradiated at 6°C than at 20°C. Colour development slightly after 5 days of cold storage prior to irradiation. In another experiment, fruit from both areas were stored at -0.5°C for 20 days before irradiation at either 6°C or 6/20°C. The fluctuating temperature regime resulted in decreases in hue angle of 70° and 65° for the fruit from Grabouw and Ceres, respectively. The decreases were smaller (±200) when fruit were irradiated at 6°C. The hue angle value of well-coloured 'Cripp's Pink' apples held at 3rC under HPS lights for 144 hours increased from 29.3° to 48.3°, and anthocyanin concentration decreased from 739.9 IJg·g·1to 283.6 IJg·g·1. Control fruit held at the same temperature in the dark did not show any change in hue angle value or anthocyanin concentration. 'Bon Rouge' and 'Red d' Anjou', two full red pear cultivars, irradiated with HPS lights for 72 hours, showed no significant changes in hue angle. 'Forelle' pears, harvested with or without attached leaves, were irradiated with HPS at two temperature regimes, 20°C and 200/6°C. The resulting decreases in hue angle were attributed to yellowing and not red colour formation. In conclusion, the response of apples to postharvest irradiation was affected by maturity and temperature, while pears failed to respond at all.