Optimizing process of brewing onion peel tea using a response surface methodology

Abstract

The effects of boiling time and water volume on brewing onion peel tea were investigated using a response surface methodology. Two responses, total phenolic content (TPC) and total antioxidant capacity (TAC) were measured after brewing 0.5 g of onion peel at a constant brewing temperature (100 °C) for different lengths of time and in different water volumes. The TPC was influenced by both time and volume and was more strongly affected by volume. The TAC was slightly affected by volume, but not by time. Thus, TPC and water volume are critical factors for determining the brewing conditions of onion peel tea. The optimum brewing time and water volume were found to be 180 min and 160.82 mL, respectively. The OPT brewed under the optimized condition showed protocatechuic acid, isoquercetin, and quercetin as major bioactive compounds. In a scaled-up experiment to determine the effect of volume, the OPT brewed in proportionally increased volumes of water and amount of onion peel at the optimized time (180 min) and 100 °C exhibited similar TPC and TAC. This study will provide an applicable brewing condition for the domestic process of brewing onion peel, a byproduct of onion, to obtain beneficial dietary compounds.