Phytochemical and antioxidant comparison of Quercus ilex and Quercus robur acorn extracts obtained by matrix solid-phase dispersion

Abstract

Oak (Quercus spp.) acorns are used in animal feed and in the treatment of specific diseases due to their nutritional value and high content of bioactive compounds. The aim of the present work is to investigate and compare polyphenolic compounds and the antioxidant activity of Quercus ilex and Quercus robur acorn extracts. This is performed using the matrix solid-phase dispersion (MSPD) extraction process, in an environmentally friendly way with different generally recognised as safe (GRAS) solvents. The GRAS solvents considered were an alcohol, a ketone, an ester and a glycol. Total polyphenolic content (TPC) and antioxidant activity (DPPH and ABTS scavenging test) were determined spectrophotometrically. The different antioxidant data obtained by two approaches are discussed. All Quercus robur extracts show better results than Quercus ilex in both total polyphenolic content and antioxidant activity, the highest results being obtained with ethyl lactate, 76 mgGAE g⁻¹ DW and 2636 μmolTE g⁻¹ DW, respectively. These results demonstrate the correlation between total polyphenolic content and antioxidant activity, and that free radical scavenging is concentration dependent. Individual quantification of the polyphenols was performed by liquid chromatography-tandem mass spectrometry (LC-MS/MS), with the major compounds being gallic acid, ellagic acid, catechin, quercetin and gallotannins in all extracts. MSPD, for the first time applied to acorns, has proven to be a good alternative to conventional processes for obtaining antioxidant extracts rich in bioactive compounds.