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

[摘要] 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.

[发布机构] Stellenbosch University