Stability and preservation of phenolic compounds and related antioxidant capacity from agro-food matrix: Effect of pH and atmosphere

Phenolic compounds are major bioactive chemicals in plant-based food products with proven health benefits. However, alkaline pH processing promotes phenolic compounds auto-oxidation, leading to a loss in food products and by-products. A phenolic-rich brewery effluent, representative of plant-based food matrices, was subdued to aging tests to investigate phenolic compounds stability in different conditions. Three conditions were tested: pH 2 in atmospheric air, pH 13.5 in atmospheric air and under N2 flow. Studied phenolic compounds remained stable in acid pH and alkaline pH under N2 but decreased sharply in alkaline pH. Interestingly, global antioxidant capacity was either stable or degraded according to antioxidant assay performed. Phenolic compounds and their corresponding antioxidant capacity study with coupled HPLC-antioxidant capacity showed that their chemical structure drove their stability. Flavan-3-ols were the main compounds prone to auto-oxidation, followed by catechol acids. Monohydroxy phenolic acids were resistant to major auto-oxidation. This study highlights food phenolic compounds behavior with consequences on antioxidant capacity in a real agro-food system in extreme alkaline condition.