Studies to reduce the incidence of chilling injury in navel orange fruit

Hordijk, Jeanine (2013-03)

Thesis (MScAgric)--Stellenbosch University, 2013.


ENGLISH ABSTRACT: Citrus fruit exported from South Africa to markets such as the USA and China undergo a mandatory 24 day exposure of -0.6°C during shipment to kill any insect larvae in the fruit, however, this protocol causes chilling injury (CI). The aim of this study was firstly to determine the influence of various preharvest factors on chilling sensitivity. In addition, Near-Infrared (NIR) spectroscopy was tested as a potential management tool to identify variation in CI susceptibility of fruit and lastly the efficacy of thiabendazole (TBZ) applied in the packline to reduce CI was determined. Various factors influence the susceptibility of a navel orange fruit to CI including cultivar, micro-climate, harvest date, fruit size and rind colour. In this study it was found that ‘Washington’ was more susceptible to CI compared to ‘Navelina’ navel orange. Fruit from the coldest part of Citrusdal (Tharakama) had the highest incidence of CI, which concurred with literature. The incidence of CI was overall less when fruit were harvested in the middle of the commercial harvest window; however, the internal maturity at harvest does not appear to be related to the sensitivity of orange fruit to CI. Near infrared (NIR) spectroscopy was tested as a potential tool to predict fruit quality parameters in relation to CI. Analysing the NIR data with principal components analysis (PCA), score plots were obtained that separate fruit in clusters from the inside and outside of the canopy positions as well as different sizes and rind colours (green vs. orange). However, analysing data with partial least square regression (PLS) using fruit quality parameters (firmness, rind colour and mass), the NIR spectra obtained with the integrated sphere did not provide a good prediction model for CI index. Thiabendazole (TBZ) is reported to reduce the incidence of CI of citrus fruit and this fungicide was applied in a semi-commercial packline in the wax as well as the drench. The results of the application of different fungicides from the TBZ chemical group indicated that the TBZ dip treatments had the highest efficacy in reducing both the incidence and severity of CI and in addition were more effective when applied in warm (40°C) than cold water (10°C). Applications at the commercial recommended rate (20mL.L-1 and half of the commercial recommended rate were both effective in reducing the incidence of CI. Wax application was effective in reducing the incidence of CI however, the application of TBZ in the wax reduced the incidence of CI even more. For the successful reduction of CI incidence in commercial shipments of citrus fruit the focus should not be on a single factor but rather a strategy that encompasses pre-harvest factors that would influence rind quality as well as specific postharvest technologies know to decrease the impact of CI.

AFRIKAANSE OPSOMMING: Sitrus vrugte ondergaan 'n verpligte 24 dae blootstelling aan -0,6°C om moontlike insek-larwes te dood gedurende die uitvoer na markte soos die VSA en China, maar hierdie protokol veroorsaak koueskade. Die doel van hierdie studie was eerstens om die invloed van verskillende voor-oes faktore op koueskade-sensitiwiteit van nawel lemoene te bepaal. Daarbenewens is naby-infrarooi (NIR) spektroskopie as 'n potensiële tegniek getoets om variasie in koueskade-sensitiwiteit van nawel lemoene te identifiseer, en laastens is die effektiwiteit van thiabendazole (TBZ) toediening in die verpakkings lyn, om koueskade te verminder, ondersoek. Verskillende faktore soos kultivar, mikroklimaat, oesdatum, vruggrootte en skilkleur beïnvloed die koueskade-sensitiwiteit van sitrus. Hierdie studie het bevind dat die ‘Washington’ meer sensitief is vir koueskade as die ‘Navelina’ nawels. Vrugte afkomstig uit die koudste deel van Citrusdal (Tharakama) het die hoogste voorkoms van koueskade. In die algemeen was vrugte ge-oes in die middel van die kommersiële-venster die minste koueskade-sensitief, maar interne rypheid hou nie verband met koueskadesensitiwiteit nie. Naby-Infrarooi (NIR) spektroskopie is getoets as 'n potensiële instrument om vrugkwaliteit parameters te voorspel met betrekking tot koueskade. Deur ontleding van die NIR data met behulp van ‘Principal Components Analysis’ kon vrugte groepeer word volgens posisie (binne vs. buite blaredak), groottes en skilkleur. Deur ‘Partial Least Square Regression’ verdere data ontleding en met inagneming van vrugkwaliteit parameters (fermheid, skil kleur en massa), kon die NIR spektra wat verkry was egter nie 'n goeie voorspelling model vir koueskade verskaf nie. TBZ verminder die voorkoms van koueskade van sitrusvrugte na dit toegedien was in 'n semi-kommersiële verpakkingslyn in die waks, ‘drench’ of baddens. Die toediening van verskillende swamdoders van die TBZ chemiese groep in baddens, het aangedui dat die TBZ doop behandeling effektief was om die voorkoms van koueskade te verminder. Daarbenewens was TBZ meer effektief in verlaging van koueskade as dit toegedien word in warm (40°C) as koue (10°C) water, asook teen die volle (20mL.L-1) en die helfte van die aanbevole kommersiële dosis. Wakstoediening was effektief in die vermindering van die voorkoms van koueskade en byvoeging van TBZ in die waks het die effektiwiteit verhoog. Die suksesvolle vermindering van koueskade tydens kommersiële verskeping van sitrusvrugte moet egter nie fokus op 'n enkele faktor nie, maar op 'n strategie wat bestaan uit voor-oes faktore wat die vrugskil kwaliteit beïnvloed, sowel as spesifieke na-oes tegnologieë en hanteringsprotokolle wat bekend is vir die vermindering van koueskade.

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