Analysis of physicochemical and antioxidant properties of Malus spp. petals reveals factors involved in flower color change and market value

Abstract

Flower color is the most important ornamental character trait of Malus species. The study aimed to clarify the roles of phenolic compounds and compositions in the petal color change of Malus spp. cultivars at various flowering stages. Meanwhile, the antioxidant activity in the petals of Malus spp. was detected to estimate the potential of market application. Eight Malus spp. cultivars were divided into four systems according to the flower color, namely dark-red (‘Royalty’ and ‘Perfect Purple’), rose-red (‘Kelsey’ and ‘Sparkler’), pink-red (‘Strawberry Parfait’ and ‘Pink Spires’), and white (‘Jewelberry’ and ‘Snow Drift’). Total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), and antioxidant activity of the petals were measured. The results revealed that high levels of TPC, TFC, TAC, and antioxidant activity in petals significantly decreased during flower development. These indicators were significantly and positively related to each other. Abundant phenolic metabolites in petals were determined by HPLC-DAD, and these compounds included anthocyanins, flavonols, flavanols, flavonones, phenolic acids, and dihydrochalcones. Anthocyanin concentrations and ratios in petals were notably different among the four color systems, with the highest levels noted in dark-red colored flowers, followed by rose-red, pink-red, and white flowers. Cyanidin-3-O-galactoside was the major anthocyanin noted. Its concentration reduced significantly with flower development, which is described as the primary cause of petal color fading. In addition, the petals contained abundance quercetin-3-O-glucuronide, hyperoside, taxifolin, chlorogenic acid, ferulic acid, phloridzin and other substances known for their antioxidant activities. Given these findings, we propose that the flowers of Malus spp. hold good utilization value as new sources of bioaccessible polyphenols and strong potential for development. Especially, the flowers at early stages will be supplements to the natural colorant market.