Optimization of the extraction of apple monomeric phenolics based on response surface methodology: Comparison of pressurized liquid–solid extraction and manual-liquid extraction

Response surface methodology (RSM) was performed in order to evaluate the optimal extraction conditions for flavan-3-ol monomers ((+)-catechin and (−)-epicatechin), phloridzin, chlorogenic acid, hyperoside, isoquercitrin, quercitrin, ideain and total phenolic content (TPC) from Braeburn freeze-dried apples, using a pressurized liquid solid (PLS) extractor. The aim of this study was to evaluate the effect of four independent extraction factors, including nature of extraction solvent (pure methanol, acetone–water (70:30, v/v)), sample mass (50–550 mg), extraction duration (1–15 min) and number of extraction cycles (1–3), on these polyphenol concentrations (HPLC–DAD analysis). Methanol was the most suitable extraction solvent for the studied phenolic compounds. Optimal conditions varied with phenolic compound and must be chosen as a compromise. For an extraction in favour of chlorogenic acid, hyperoside, quercitrin and ideain, we recommended the following experimental conditions using the pressurized liquid solid extraction (PLE) method: two successive extractions with pure methanol from 50 mg freeze-dried apple-samples for 15 min, using three extraction cycles. In comparison with manual methods, benefits from the increase of polyphenol concentrations, the reduction of extraction time and organic solvent amounts were observed with the PLE method.