Faculty of AgriSciences

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The Faculty of AgriSciences at Stellenbosch University (SU) is held in high esteem at national and international levels for the quality of its training and research and also as consultant in the agricultural and forestry industry.

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Browsing Faculty of AgriSciences by Subject "'Cripps' Pink' apple (Malus domestica Borkh)"

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    Internal flesh browning of ‘Cripps’ Pink’ apple (Malus domestica Borkh.) as influenced by pre-harvest factors and the evaluation of near infrared reflectance spectroscopy as a non-destructive method for detecting browning
    (Stellenbosch : Stellenbosch University, 2015-03) Butler, Leana; Crouch, E. M.; Lotze, Elmi; Crouch, I. J.; Theron, K. I.; Stellenbosch University. Faculty of AgriSciences. Dept. of Horticulture.
    ENGLISH ABSTRACT: The successful marketing of ‘Pink Lady’™ apples produced in South Africa is under pressure due to internal flesh browning (IFB) development. IFB incidence is increased by long term controlled atmosphere (CA) storage at low temperatures and overmaturity of fruit. Australian research has identified pre-harvest factors which influence the susceptibility of fruit towards internal browning. The first aim of this study was to investigate temperature, mineral concentration, soil type and tree age as factors which influence incidence of browning under South African growing conditions. The second aim of this study was to evaluate NIR spectroscopy (NIRs) as a non-destructive tool for sorting out internally brown fruit before shipment. The first trial investigated the effect of temperature during different growth stages on the incidence of browning types for Elgin and the Koue Bokkeveld. Diffuse browning was found in both seasons while radial browning was only found for the 2011/2012 season. Incidence of diffuse browning related to the difference between the maximum and minimum temperature during the cell division phase (0-50 DAFB) and high temperatures during the maturation phase (last 60 days before harvest). Radial browning related to maximum temperatures during the early cell expansion phase (100-150 DAFB). A third type of browning which exhibited browning patterns of both browning types was identified and named “combination” browning and was related to fruit size but not pre-harvest temperature. The second trial investigated the influence of tree age, soil type and mineral concentration of fruit on the incidence of browning. Soil type and tree age affected incidence of diffuse browning but not that of radial browning. Fruit harvested from orchards with sandy soil and young trees were more mature and were prone to develop diffuse browning. Higher potassium (K) concentration and K:Magnesium (Mg) ratios were related to non-brown fruit and the K:Mg ratio had a strong negative correlation with browning incidence. NIR spectra were collected from fruit after 7 months CA storage (7M) at -0.5 °C and after 7 months CA at -0.5 °C + 4 weeks regular atmosphere (RA) 0.5 °C + one week shelf-life at 20 °C (7M4W7D) in pursuit of the second aim of this study. Incidence of diffuse- and “combination” browning increased from 7M to 7M4W7D while incidence of radial browning did not. Brown and non-brown fruit were successfully identified by means of PLS-DA at both storage stages. NIRs calibration and validation models showed that NIRs can predict total soluble solids concentration (TSS) concentration of ‘Cripps’ Pink’ apples at 7M. Anatomical investigation of tissue affected by “combination” browning with scanning electron microscopy (SEM) showed collapsed cells and large intercellular spaces below the fruit peel, as found for diffuse browning, and cell fracture and collapse of cortical tissue near the vascular bundles, as found for tissue affected by radial browning. Tissue of samples affected by “combination” browning showed symptoms of both diffuse and radial browning thus, confirming that fruit affected by “combination” browning were susceptible to both browning types during long term storage.