Dry matter content association with time of on-tree maturation, quality at harvest, and changes in quality after controlled atmosphere storage for ‘Royal Gala’ apples

Abstract

On-tree maturation was monitored in a commercial ‘Royal Gala’ apple orchard in two separate years (2016 and 2017) and was found to advance more quickly in 2017 as compared with 2016. Dry matter was predicted using a handheld infrared spectrometer and dry matter content (relative to fresh weight) was 18.2% in 2016 and 14.7% in 2017. The lower average dry matter content in 2017 was hypothesized to be associated with accelerated maturation on the tree. Apples were harvested for storage testing, in both years, at a target maturity at which internal ethylene levels had reached approximately 1 μL·L−1, starch clearing index was between 2 and 4 on the Cornell starch chart, and IAD value (measure of relative chlorophyll content in the peel) was approximately 0.5. Consequent, instrumentally measured flesh quality changes were monitored after ultra-low oxygen, controlled atmosphere (CA) storage (0.7 kPa O2 + 1.0 kPa CO2) at 0.5 °C for 3 and 6 mo. The firmness, soluble solids, and titratable acidity were much higher in the apples from the 2016 harvest. While these quality measures declined during 3 and 6 mo of storage, they were consistently higher in the apples from the 2016 season. These results show that when dry matter contents were higher for ‘Royal Gala’ apples from this orchard, harvest maturity was delayed and fruit were much firmer and had higher contents of soluble solids and somewhat higher titratable acidity at harvest and after ultra-low oxygen CA storage for up to 6 mo.