Real Time-based Targeted Metabolomic Approach as Risk Assessment Tools for Controlling Superficial Scald in 'Granny Smith' Apples during Storage

The risk of superficial scald incidence in ‘Granny Smith’ apple [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] fruit during cold or controlled atmosphere (CA) storage increases with increased storage duration and oxygen level during CA storage.  The objective of this study was to investigate risk assessment of superficial scald using biomarkers. ‘Granny Smith’ apples were harvested from 4 orchards in Prosser, WA and held for up to 9 months at 0.5 ^oC in either air or CA at 0.5 kPa O₂ and 1 kPa CO₂, or 2 kPa O₂ and 1 kPa CO₂.  Superficial scald began to develop at 3 months in air storage with severity and incidence increasing gradually thereafter.  Scald was not detected on fruit stored in 0.5 kPa O₂ and 1 kPa CO₂ CA.  When scald risk was detected at 3 months in both 2 kPa O₂ and 1 kPa CO₂ chambers, O₂ levels were reduced to 0.5 kPa in one of the rooms, reducing final scald incidence at 9 months + 7 days shelf life.  Scald first appeared on fruit stored at 2 kPa O₂ and 1 kPa CO₂ at 6 months storage and increased during 7 days post-storage ripening.  α-Farnesene and conjugated trienol levels measured using a spectrophotometer correlated with levels of 2,6,10-trimethyldodeca-2,7(E),9(E),11-tetraen-6-ol (CTol) and a number of unknown non-polar compounds measured using LC-MS.  These compounds are tentatively identified as acyl conjugates of CTol.  The identification process is ongoing. We hypothesize that the genesis of these putative conjugates results from further metabolism of CTol once it forms.   Results show that risk assessment biomarkers indicate when scald risk is elevated and which storage conditions have the highest risk.