Impact of Fruit Maturity and Growing Season on Phenolic Phytochemicals and Antioxidant Activity Among Four Asian Plum Cultivars

Abstract

Various factors, including environment, maturity, weather, and cultivars are known to impact the profile and concentration of phenolic phytochemicals in plums. Major anthocyanins and neochlorogenic acids were quantified in fruit among four cultivars (Methley, Obilnya, Shiro and Vanier) of Asian plum, Prunus salicina, at the partial-ripe and tree-ripe stages of maturity in 2014 and 2015. Anthocyanin concentration was greater with the later stage of maturity in every cultivar except ‘Shiro’ which did not have detectable anthocyanins. ‘Obilnya’ had the greatest anthocyanin concentration, followed by ‘Methley’ and ‘Vanier’. Anthocyanin concentration was greater in 2015 than in 2014 in ‘Methley’ and ‘Obilnya’, but in ‘Vanier’, it was greater in 2014 in tree-ripe fruit. Cyanidin 3− O−glucoside and cyanidin 3− O−rutinoside were detected in three cultivars, but their relative concentrations varied. Cyanidin 3− O−glucoside was predominant in ‘Methley’ in both years and in ‘Vanier’ partial-ripe fruit in both years, but cyanidin 3− O−rutinoside was the predominant anthocyanin in ‘Obilnya’ in both years and in ‘Vanier’ tree-ripe fruit only in 2014. Cyanidin 3− O−galactoside occurred in only ‘Methley’ and ‘Obilnya’ and was generally less than 25% of the total concentration. Large year-to-year variation in neochlorogenic acid, the predominant hydroxycinnamic acid (HCA), occurred in ‘Shiro’ and ‘Vanier’ fruit, but variation due to maturity was small in all four cultivars. Total phenolic concentration (TPC) was measured by the Folin−Ciocalteu method and antioxidant activity (AOA) by DPPH assay in only 2015. TPC was greater in tree-ripe than in partial-ripe plums of every cutlivar. The relationship between TPC and AOA was curvilinear indicating a reduction in slope as TPC increased.