Comparative Analysis of Aroma Emissions in ‘Gala’ Apples Stored in Ethanol- and Hexanal-Enriched Controlled Atmosphere

The objectives of this study were to investigate the effects of extended and constant ethanol and hexanal exposure on ‘Gala’ apples’ production of aroma compounds after long-term CA storage. ‘Gala’ apples were stored in a CA under 2 kPa O₂ and 98 kPa N2 at 1.0 ± 0.1 °C with a constant ethanol (CA-et) or hexanal (CA-he) concentration maintained at 50 µgL⁻¹ throughout a six-month storage period. A total of 25 volatile compounds (VOCs) were identified. The odor activity value (OAV) results show that nine VOCs were key aroma compounds. Among them, hexyl acetate, 2-methylbutyl acetate, and 1-butanol were the highest. Hexanal increased the production of hexyl acetate, while ethanol increased the production of 2-methylbutyl acetate and ethyl 2-methylbutanoate. Both precursors promoted the production of 1-butanol after two months of storage and 1 day of shelf life. Overall, the impact of the precursors on aroma production was more pronounced after two months than after six months of storage. Different storage atmospheres significantly influenced VOC correlations, suggesting that ethanol and hexanal addition altered aroma biosynthesis pathways in the ‘Gala’ apples. For varieties like ‘Gala’ that rapidly lose their aroma during CA storage, CA-et and CA-he treatments may be beneficial for short-term storage, enhancing key aroma compounds and improving sensory quality.