Characterization of phenolic compounds and active anthocyanin degradation in crabapple (Malus orientalis) flowers

The red coloration of young crabapple (Malus orientalis) flowers results from their high cellular concentration of anthocyanins. As the petals grow larger, the color fades, which is commonly regarded as being caused by floral tissue expansion diluting the anthocyanin levels in larger cells. We hypothesized that the anthocyanins are degraded due to hydrogen peroxide (H2O2) and that the concentrations of each phenolic intermediate depends on the physiological growth of flower petals. A high-performance liquid chromatography (HPLC) analysis was performed to characterize the identities and concentrations of the diverse array of phenolics present during different growth stages in the crabapple flowers. The concentrations of gallic acid, caffeic acid, syringic acid, chlorogenic acid, phloridzin, procyanidin B1, procyanidin B2, and catechin significantly increased throughout development, while epicatechin and cyanidin-3-galactoside levels declined. Most flavonols (quercetin-3-xyloside, quercetin-3-rhaminose, quercetin-3-glucoside, and quercetin-3-arabinoside) increased until the fourth stage, after which they declined suddenly. Likewise, cyanidin-3-galactoside degraded sharply at stage III, exhibiting reciprocal relationship with H2O2 concentration. Our results suggest that the concentrations of phenolic compounds are congruent with their functional activities in floral tissues, and that their systematic fluctuation mainly depends on environmental cues and physiological imbalances, not merely petal expansion. The results of this study will be useful for better understanding the physiological changes in phenolic content and anthocyanin degradation that occur during flower development.