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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

Butler, Leana (2015-03)

Thesis (MSc)--Stellenbosch University, 2015.

Thesis

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.

AFRIKAANSE OPSOMMING: Die suksesvolle bemarking van ‘Pink Lady’™ appels in Suid-Afrika word benadeel deur interne verbruining. Verlenge opbergingsperiodes by lae temperature (<0 °C) onder beheerde atmosfeer (BA) toestande, asook oorrypheid tydens oes verhoog die insidensie van verbruining. Australiese navorsing het vooroes faktore geïdentifiseer wat verbruining beïnvloed. Die doel van hierdie studie was om die invloed van temperatuur, grondtipe, boomouderdom en die minerale samestelling van die vrug op die insidensie van verbruining te ondersoek onder Suid-Afrikaanse produksietoestande. Die tweede doel was om die gebruik van naby-infrarooirefleksie spektroskopie (NIRs) te ondersoek as ‘n moontlike tegniek vir die nie-destruktiewe identifisering van vrugte geaffekteer deur interne verbruining. Die eerste proef het die invloed van temperatuur gedurende verskillende ontwikkelingsstadia van die vrug op die insidensie van verbruiningstipes ondersoek in Elgin en die Koue Bokkeveld. Diffuse-verbruining het in albei seisoene voorgekom terwyl radiale-verbruining net in 2011/2012 voorgekom het. Diffuse-verbruining het ‘n verband getoon met die verskil tussen maksimum en minimum temperature gedurende die selverdelingsfase (0 – 50 DNVB) en hoë temperature gedurende rypwording (60 dae voor rypwording). Hoë temperature gedurende die selvergrotingsfase (50 – 100 DNVB) het die insidensie van radialeverbruining beïnvloed. ‘n Derde tipe verbruining wat patrone van beide verbruiningstipes besit is geïdentifiseer en “kombinasie-verbruining” genoem. “Kombinasie-verbruining” was positief gekorreleer met vruggrootte maar nie met voor-oes temperatuur nie. Die tweede proef het die invloed van grondtipe, boomouderdom en die minerale samestelling van die vrug op insidensie van verbruining ondersoek. Vrugte vanuit boorde met jong bome of sanderige grond was ryper en meer vatbaar vir diffuse-verbruining. Die insidensie van radiale-verbruining het nie verskil tussen boorde met verskillende grondtipes of boomouderdomme nie. ‘n Hoër kalium (K) inhoud en ‘n K:Magnesium (Mg) verhouding was waargeneem in nie-bruin vrugte en die K:Mg verhouding het ‘n sterk negatiewe korrelasie met die insidensie van verbruining getoon. NIR spektra is versamel vanaf vrugte na 7 maande BA opberging (7M) by -0.5 °C en na 7 maande BA + 4 weke in gewone atmosfeer (GA) by -0.5 °C + 1 week raklewe by 20 °C (7M4D7D) om die tweede doel van hierdie studie aan te spreek. Die insidensie van diffuseen “kombinasie-verbruining” het vermeerder vanaf die 7M na die 7M4W7D tydperk, maar nie die insidensie van radiale-verbruining nie. Spektra van bruin en nie-bruin vrugte is suksesvol geïdentifiseer na die 7M en die 7M4W7D tydperk met behulp van PLS-DA. NIR kalibrasie en validasie modelle het aangedui dat totale oplosbare vastestowwe (TOVS) suksesvol voorspel kan word deur NIRs. Weefsel van verbruiningstipes is ondersoek met behulp van skanderings-elektron mikroskopie om te bevestig of “kombinase-verbruining” deur beide verbruiningstipes beïnvloed word op anatomiese vlak. Ineengestorte korteks selle en groot intersellulêre ruimtes onder die skil is gevind in weefsel geaffekteer deur diffuse-verbruining. Selkrake en ineengestorte korteksselle langs die vaskulêre bondels is gevind in weefsel geaffekteer deur radiale-verbruining. Kenmerke van beide verbruiningstipes is gevind in weefsel geaffekteer deur “kombinasie-verbruining”. Dit bevestig dat vrugte wat geaffekteer is deur “kombinasieverbruining” wel vatbaar was vir radiale- en diffuse-verbruining.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96725
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