Internal flesh browning of 'Cripps' Pink' apple(Malus domestica Borkh.) as influenced by pre-harvest factorsand the evaluation of near infrared reflectance spectroscopyas a non-destructive method for detecting browning

[摘要] ENGLISH ABSTRACT: The successful marketing of 'Pink Lady'™ apples produced in South Africa is under pressuredue to internal flesh browning (IFB) development. IFB incidence is increased by long termcontrolled atmosphere (CA) storage at low temperatures and overmaturity of fruit. Australianresearch has identified pre-harvest factors which influence the susceptibility of fruit towardsinternal browning. The first aim of this study was to investigate temperature, mineralconcentration, soil type and tree age as factors which influence incidence of browning underSouth African growing conditions. The second aim of this study was to evaluate NIRspectroscopy (NIRs) as a non-destructive tool for sorting out internally brown fruit beforeshipment.The first trial investigated the effect of temperature during different growth stages on theincidence of browning types for Elgin and the Koue Bokkeveld. Diffuse browning was foundin both seasons while radial browning was only found for the 2011/2012 season. Incidenceof diffuse browning related to the difference between the maximum and minimumtemperature during the cell division phase (0-50 DAFB) and high temperatures during thematuration phase (last 60 days before harvest). Radial browning related to maximumtemperatures during the early cell expansion phase (100-150 DAFB). A third type ofbrowning which exhibited browning patterns of both browning types was identified andnamed '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 offruit on the incidence of browning. Soil type and tree age affected incidence of diffusebrowning but not that of radial browning. Fruit harvested from orchards with sandy soil andyoung trees were more mature and were prone to develop diffuse browning. Higherpotassium (K) concentration and K:Magnesium (Mg) ratios were related to non-brown fruitand 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 7months CA at -0.5 °C + 4 weeks regular atmosphere (RA) 0.5 °C + one week shelf-life at20 °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 browningdid not. Brown and non-brown fruit were successfully identified by means of PLS-DA at bothstorage stages. NIRs calibration and validation models showed that NIRs can predict totalsoluble solids concentration (TSS) concentration of 'Cripps' Pink' apples at 7M.Anatomical investigation of tissue affected by 'combination browning with scanning electronmicroscopy (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 thevascular 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 browningtypes during long term storage.

[发布机构] Stellenbosch University