Pre-harvest spray application of phenylpropanoids influences accumulation of anthocyanin and flavonoids in 'Cripps Pink' apple skin

Poor colour development on 'Cripps Pink' apple fruit causes serious economic losses to the growers in the warmer regions of the world. Effects of pre-harvest spray application of different concentrations (0, 50, 100, or 200 mg L−1) of cinnamic acid, p-coumaric acid, d-phenylalanine, l-phenylalanine, and naringenin, on red blush development on the fruit surface and accumulation of anthocyanins, dihydrochalcones, hydroxycinnamic acid, flavanols, and flavonols, in the skin of 'Cripps Pink' apple at commercial fruit maturity were investigated. Skin of apple fruit harvested from the trees sprayed with l-phenylalanine or cinnamic acid contained significantly higher concentrations of total anthocyanins, cyanidin 3-galactoside, and flavonols, compared to control and to those treated with other phenylpropanoids, in a dose- independent pattern. Based on tristimulus system of colour perception {i.e. chromaticity values such as L*, a*, b*, chroma (C*), and hue angle (h°)}, a similar trend of red blush development was observed on fruit's exterior at commercial maturity, in response to pre-harvest spray application of phenylpropanoids. The apple fruit harvested from the trees sprayed with l-phenylalanine or cinnamic acid had the highest values of a* and the lowest values of h° for colour perception on the exposed side of apple fruit, irrespective of their doses applied, indicating a substantial trend of red blush intensification on the fruit surface. In conclusion, a single pre-harvest spray application of l-phenylalanine (100 mg L−1), applied 3-4 weeks prior to the anticipated commercial fruit maturity was most effective in improving red blush development, increased production of export-grade fruit, accumulation of total anthocyanins, cyanidin 3-galactoside, flavanols, chlorogenic acid and flavonols in the fruit skin, without adversely affecting the fruit quality.