Effects of dynamic controlled atmosphere and initial low oxygen stress on superficial scald of 'Granny Smith' apples and 'Packham's Triumph' pears

Ramokonyane, Tlou Melrose (2016-03)

Thesis (MSc)--Stellenbosch University, 2016.

Thesis

ENGLISH ABSTRACT: ‘Granny Smith’ apples and ‘Packham’s Triumph’ pears are the main export pome fruit in South Africa. The fruit are stored for extended period to take advantage of main export markets such as the European Union (EU), and are susceptible to the storage physiological disorder superficial scald. Superficial scald is the main storage disorder in pome fruit, appearing as light brown to black blemishes on fruit peel, rendering affected fruit unmarketable. Current commercial practice to control superficial scald has been to drench susceptible fruit in diphenylamine (DPA), a synthetic antioxidant. The EU recently reduced the maximum allowable residue limit (MRL) of DPA from 5 ppm for apples and 10 ppm for pears to only 0.1 ppm as effective from April 2014. This has made it necessary to urgently investigate alternative non-chemical storage protocols to control the incidence of the disorder. DPA was not used in this study to avoid cross contamination in the treatment rooms. The aim of this study was to investigate the efficacy of controlled atmosphere and low oxygen stress technologies in inhibiting superficial scald in ‘Packham’s Triumph’ pears and ‘Granny Smith’ apples. Dynamic controlled atmosphere (DCA) protocol was effective as a scald control treatment on ‘Packham’s Triumph’ pears stored up to 7 months at -0.5 °C. Controlled atmosphere (CA) preceded by initial low oxygen stress (ILOS) was effective as a scald treatment on ‘Packham’s Triumph’ pears when fruit were cold stored for up to 5 months. Similarly, DCA storage was effective as a scald control treatment for up to 7 months at 0 °C on ‘Granny Smith’ apples harvested at pre-optimal and optimal maturity stages. Storing fruit under CA preceded by ILOS was not effective in controlling scald on ‘Granny Smith’ apples. Metabolomic studies showed that storing fruit under DCA and/or ILOS suppressed superficial scald development on ‘Packham’s Triumph’ pears by probably inhibiting the auto-oxidation of α-farnesene to its by-product, 6-methyl-5-hepten-2-one (MHO), in the fruit peel. There was a strong negative correlation between the α-farnesene concentration in the fruit peel and the superficial scald severity index of ‘Packham’s Triumph’ pears (R2 = -0.90). In ‘Granny Smith’ apples harvested at optimal maturity there was a strong negative correlation between the α-farnesene concentration and superficial scald severity index (R2 = -0.85). The correlations between MHO and the superficial scald severity index were 0.90, 0.85 and 0.57 for ‘Packham’s Triumph’ pears, for pre-optimally and optimally harvested ‘Granny Smith’ apples, respectively. Storing fruit in ILOS for 10 days followed by CA effectively controlled superficial scald on ‘Packham’s Triumph’ pears for up to 5 months, but for only 3 months on ‘Granny Smith’ apples. Storing fruit in ILOS for 10 days followed by long term CA storage inhibited superficial scald by suppressing the auto-oxidation of α-farnesene to MHO. In summary, this study showed that CA storage technology (DCA and ILOS followed by CA) are alternative options to control ripening, delay senescence and maintain quality of pome fruit for much longer than regular air (RA) in addition to controlling superficial scald and shrivelling in ‘Packham’s Triumph’ pears. Given the possibility of shrivelling due to weight loss and decay incidence on ‘Packham’s Triumph’ pears during long term storage, correct fruit handling and sanitation practices should be adhered to at optimal storage temperatures and relative humidity. Results obtained in this study suggest that DCA is the non-chemical alternative treatment for control of superficial scald for long term storage of ‘Granny Smith’ apples and ‘Packham’s Triumph’ pears.

AFRIKAANSE OPSOMMING: ‘Granny Smith’ appels en ‘Packham’s Triumph’ pere is die hoof uitvoer kernvrugte in Suid-Afrika. Die vrugte word vir lang periodes opgeberg om die voordeel te kry van die belangrikste uitvoermarkte soos die Europese Unie (EU). ‘Granny Smith’ appels en ‘Packham’s Triumph’ pere is gevoelig vir die fisiologiese defek, oppervlakkige brandvlek. Oppervlakkige brandvlek is die vernaamste opbergingsdefek in kernvrugte. Dit verskyn in die vorm van ligbruin tot swart letsels op die skil van die vrug en maak die vrugte onbemarkbaar vir die varsproduktemark. Standaard kommersiële praktyke om oppervlakkige brandvlek te beheer was om sensitiewe vrugte met difenielamien (DFA), 'n sintetiese antioksidant, te behandel. Die EU het die maksimum toelaatbare residu limiet van DFA vanaf 5 dpm vir appels en 10 dpm vir pere na 0.1 dpm verlaag, geldig vanaf April 2014. Dit is dus nodig om dringend alternatiewe nie-chemiese opbergingsprotokolle te ondersoek om die voorkoms van die defek te beheer. DFA is nie in hierdie studie gebruik nie, om besmetting van die spesifieke behandelings kamers te voorkom. Die doel van hierdie studie was dus om die doeltreffendheid van beheerde atmosfeer en lae suurstof stres tegnologie te ondersoek wat ‘n inhiberende effek op oppervlakkige brandvlek van 'Packham's Triumph' pere en 'Granny Smith' appels kan hê. Resultate het getoon dat die dinamies beheerde atmosfeer (DBA) protokol effektief was om oppervlakkige brandvlek op 'Packham's Triumph' pere, gestoor vir solank as 7 maande by -0.5 °C te beheer. Die opberging van vrugte onder beheerde atmosfeer (BA), voorafgegaan deur aanvanklike lae suurstof stres (ALSS), was effektief as 'n oppervlakkige brandvlek behandeling op 'Packham's Triumph' pere tot en met 5 maande in koelopberging. Soortgelyk was die DBA opberging protokolle effektief as oppervlakkige brandvlek beheer behandeling vir pre-optimum en optimum geoeste 'Granny Smith' appels gestoor tot en met 7 maande by 0 °C. Die opberging van vrugte onder beheerde atmosfeer, voorafgegaan deur aanvanklike lae suurstof, was nie effektief om oppervlakkige brandvlek op 'Granny Smith' appels te beheer nie. Metabolomiese studies het getoon dat die opberging van vrugte onder DBA en / of ALSS, oppervlakkige brandvlek op 'Packham's Triumph' pere kon onderdruk deur waarskynlik die outo-oksidasie van α-farneseen na sy byproduk 6-metiel-5-hepten-2-een (MHE) in die skil van 'Packham's Triumph' pere te beperk. Daar was 'n sterk negatiewe korrelasie tussen α-farneseen vlakke in die skil en die graad van oppervlakkige brandvlek indeks (R2 = -0.90) in 'Packham's Triumph' pere. Daar was 'n sterk negatiewe korrelasie tussen α-farneseen vlakke en die graad van oppervlakkige brandvlek indeks (R2 = -0.85) in optimum geoeste ‘Granny Smith’ appels. Die korrelasies tussen MHE en die graad van oppervlakkige brandvlek indeks was R2 = 0.90, R2 = 0.85 en R2 = 0.57 vir 'Packham's Triumph' pere, optimum en pre-optimum geoeste ‘Granny Smith' appels, onderskeidelik. Die resultate in hierdie studie het getoon dat DBA effektief oppervlakkige brandvlek vir tot 7 maande op ‘Packham's Triumph' pere en ‘Granny Smith’ appels beheer, deur die outo-oksidasie van α-farneseen na MHE te onderdruk. BA voorafgegaan deur ALSS vir 10 dae het oppervlakkige brandvlek effektief beheer op ‘Packham's Triumph’ pere vir tot 5 maande, maar dit onderdruk oppervlakkige brandvlek vir slegs 3 maande op 'Granny Smith' appels. BA voorafgegaan deur ALLS vir 10 dae verhoed die ontwikkeling van oppervlakkige brandvlek deur die outo-oksidasie van α-farnesene na MHE te onderdruk. Opsommend het die studie getoon dat BA stoor protokolle, DBA en ALLS alternatiewe opsies is om rypwording te beheer, veroudering te vertraag en kwaliteit van kernvrugte te behou vir baie langer as onder gewone atmosfeer, bykomend beheer dit ook oppervlakkige brandvlek, bederf en verrimpeling op 'Packham's Triumph' pere. Gegewe die moontlikheid van verrimpeling weens gewigsverlies en die voorkoms van bederf op 'Packham's Triumph' pere gedurende lang termyn opberging, moet korrekte vrug hantering en sanitasie praktyke nagekom word teen optimum temperature en relatiewe humiditeit. Resultate van hierdie studie blyk dat DBA is tans die enigste nie-chemiese alternatiewe behandeling vir die beheer van oppervlakkige brandvlek vir langtermyn opberging van 'Granny Smith' appels en ‘Packham’s Triumph’ pere.

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