Influence of branch bending on sugar, organic acid and phenolic content in fruits of 'Williams' pears (Pyrus communis L.)

Selected sugars, organic acids and phenolic compounds were analysed in mature fruits of 'Williams' pears using high-performance liquid chromatography. Fruits were harvested from the branches of trees tested in three treatments: branches were bent in summer 2003 (1 September), in spring 2004 (15 May) and control (branches were not bent). Pears contained up to 73.54 g kg⁻¹ fresh weight (FW) of fructose, 9.42 g kg⁻¹ FW of glucose, 7.94 g kg⁻¹ FW of sucrose and 24.59 g kg⁻¹ FW of sorbitol. Major organic acids were (in order of descending quantity) citric, malic, shikimic and fumaric acid (up to 3.05 g kg⁻¹ FW, 2.24 g kg⁻¹ FW, 71.79 mg kg⁻¹ FW and 0.49 mg kg⁻¹ FW, respectively). Chlorogenic acid (280.86-357.34 mg kg⁻¹ FW) was the predominant phenolic acid, followed in concentration (mg kg⁻¹ FW) by syringic acid (95.46-131.32), epicatechin (46.55-83.09), catechin (25.67-44.81), vanillic acid (1.87-3.48), sinapic acid (0.83-1.72) and caffeic acid (0.72-1.04). Significant differences in content of fructose, sorbitol, total sugars, catechin, epicatechin, sinapic acid, syringic acid, and a sum of determined phenolic compounds were observed among the treatments. Fruits from summer bending branches had the lowest content of individual sugars, citric acid and phenolic compounds and the highest content of malic, shikimic and fumaric acid. The highest content of fructose, sorbitol, sucrose, total sugars, caffeic acid, catechin, epicatechin and syringic acid were determined in the fruits from the spring treatment. In the control treatment the highest content of glucose, citric acid, chlorogenic acid, sinapic acid, vanillic acid, as well a sum of determined phenolics, were observed. The lowest content of fumaric acid was in the spring treatment and of malic and shikimic acid in the control.