Effects of relative air humidity on the phenolic compounds contents and coloration in the 'Fuji' apple (Malus domestica Borkh.) peel

- Our objective is to investigate the effect of air humidity (AH) on apple peel coloration.
- The high AH and low AH treatments were compared to investigate this effect using detachedly bagged 'Fuji' apples.
- Cyanidin-3-galactoside and 17 other types of phenolic compounds were detected using HPLC method.
- High AH samples had higher concentrations of chlorogenic acid, ferulic acid, epicatechin, quercetin-3-rutinoside, and cyanidin-3-galactoside than low AH samples.
- The results suggested that high AH conditions could significantly improve coloration and the eating quality of fruits.

To investigate the effects of relative air humidity (AH) on 'Fuji' apple (Malus domestica Borkh.) peel phenolic compounds and pigment coloration, the bagged fruits were bags moved and then exposed to high AH and low AH conditions, respectively. Cyanidin-3-galactoside, the main anthocyanin compound in apple, and 17 other types of phenolic compounds were detected and their concentrations were also compared between high and low AH treated apple peels. We observed that the removal of bags and subsequent re-exposure to sunlight could significantly decrease the concentrations of syringic acid, caffeic acid, ρ-coumaric acid, and quercetin-3-rhamnoside, but increase the concentrations of ferulic acid, quercetin-3-galactoside, quercetin-3-glucoside, quercetin-3-rutinoside, and cyanidin-3-galactoside. Furthermore, high AH samples had higher concentrations of chlorogenic acid, ferulic acid, epicatechin, quercetin-3-rutinoside, and cyanidin-3-galactoside than low AH samples as they were in the similar temperature conditions. These results suggested that high AH conditions could significantly improve coloration and the eating quality of fruits.