Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/4/2021
Publication Date: 11/17/2021
Citation: Mattheis, J.P., Felicetti, D., Rudell Jr, D.R. 2021. ‘d’Anjou’ pear metabolism during ultra-low O2, low CO2 controlled atmosphere storage reflects disorder outcome. Postharvest Biology and Technology. 185. Article 111781. https://doi.org/10.1016/j.postharvbio.2021.111781.
Interpretive Summary: Controlled atmosphere (CA) storage reduces European pear fruit ripening and incidence of some disorders, such as superficial scald, that significantly contribute to postharvest losses. However, controlled atmosphere conditions may also contribute to the development of other costly internal disorders in pears, most prominently internal browning and pithy brown core. Which storage conditions contribute to internal disorders and whether atmospheric setpoints are exacerbating symptom development is not clear. Our results confirm that low O2 conditions alone can control superficial scald but lead to pithy brown core development in ‘d’Anjou pear. Expanding on this, we found natural peel chemical levels that are indicative of the effectiveness of the CA atmosphere for controlling scald and, also, the risk for developing pithy brown core. Monitoring these metabolites may help development of storage regimes for scald susceptible cultivars by indicating whether storage conditions are controlling scald without provoking pithy brown core before the disorders develop.
Technical Abstract: With increasingly restrictive regulation of postharvest crop protectants and expected year-round availability, pear (Pyrus communis L.) production is ever more reliant on precise controlled atmosphere (CA) storage technologies to provide both ripening and disorder control for long term storage. Ultra-low oxygen (ULO; <1 kPa O2) CA storage meets many of these criteria affording control of ripening and superficial scald. However, internal browning often is an unintended outcome caused by atmospheric conditions and other events that occur, similarly to superficial scald, prior to symptom development. While this is often associated with elevated CO2, it also can occur at lower partial pressures (<0.5 kPa CO2) reducing its widespread use for storing pears. We expected levels of specific metabolites in ‘d’Anjou’, a cultivar susceptible to both disorders, would reflect specific disorder risk under ULO and low CO2. The metabolic profile of pear peel stored at 0.5°C in air, CA (1.5 kPa O2; 0.5 kPa CO2), or ULO (determined in the first week of storage by monitoring chlorophyll fluorescence; 0.5 kPa O2; 0.5 kPa CO2) was compared at multiple time points during 0-16 weeks storage. Final fruit quality and relative ripeness were assessed at 16 weeks plus 7 d at 20°C. Quality and ripeness differences and related metabolism followed that established in existing literature regarding peel color, titratable acidity, ethylene evolution, respiration, and sucrose metabolism. Superficial scald developed on air stored fruit and core browning incidence most in pears stored in 0.4 kPa O2. ''-Farnesene oxidation increased most in air followed by 1.5 kPa O2 storage indicating risk of this disorder on fruit from those storage conditions. As in other studies, ''-aminobutyric acid (GABA) was elevated most where internal browning had occurred, although levels were also elevated in the peel. Levels of glutamic acid, alanine, and, unique to this study, proline were also most elevated in peel from pears stored in 0.5k Pa O2 indicating their association with conditions that lead to core browning. Monitoring ''-farnesene oxidation coupled with GABA, glutamic acid, alanine, and proline levels in peel may be a means to indicate whether ULO CA atmospheres with reduced CO2 levels are accomplishing the critical task of controlling pear superficial scald without causing internal browning before injury occurs.