Changes in phenolic compounds and antioxidant capacity of Andean raspberries in response to Peronospora sparsa

Abstract

In Colombia, the Andean raspberry (Rubus glaucus Benth) is of large economic significance because of its use in industry and widespread consumption as a fresh fruit. However, this crop is highly susceptible to disease by Peronospora sparsa, a fungus that causes between 50 % and 70 % production loss. Plants respond to pathogen-induced damage by increasing the production of specific secondary metabolites, such as phenolic compounds, which have broad industrial applications. This work estimated the antioxidant capacity and phenolic content of healthy and Peronospora sparsa-infected Andean raspberry fruits. Antioxidant capacity was analyzed by DPPH and FRAP methods, while phenolic compounds were analyzed by high performance liquid chromatography coupled to diode array detection (HPLC-DAD). According to the DPPH method, antioxidant capacity increased from 45.9 ± 1.61 µmol TE g−1 fresh sample in healthy fruits to 67.02 ± 0.58 µmol TE g−1 fresh sample in affected fruits. The FRAP method revealed an antioxidant response difference from 5.19 ± 0.8 mmol TE 100 g−1 fresh sample in healthy fruits vs. 10.97 ± 0.27 mmol TE 100 g−1 fresh sample in affected fruits. The phenolic compound content was observed in a range of 4.14 ± 1.16 to 72.03 ± 26.68 mg GAE L−1 for healthy fruits and from 4.48 ± 1.76 to 221.89 ± 1.18 mg GAE L−1 for affected fruits. Phenolic acids were the main phenols detected, encompassing derivatives of gallic acid, chlorogenic acid, ferulic acid, ellagic acid, and p-coumaric acid. This work confirmed that the Peronospora sparsa-infected berries contained relatively more antioxidants and phenolic acid compounds than their healthy counterparts, and that this difference was likely due to a defense mechanism to cope with pathogen-induced damage.