Industrial processing of raspberry juice and wine generates considerable byproducts of raspberry pomace. Ellagic acids/ellagitannins, being characterized by their antioxidant and antiproliferation properties, constitute the majority of polyphenolics in the pomace and are valuable for recovery. In the present study, we developed a novel procedure with sodium bicarbonate assisted extraction (SBAE) to recover ellagic acid from raspberry wine pomace. Key parameters in the procedure, i.e., sodium bicarbonate concentration, temperature, time and solid/liquid (S/L) ratio, were investigated by single factor analysis and optimized subsequently by Response Surface Methodology (RSM). Optimal parameters for the SBAE method here were found to be 1.2% (w/v) NaHCO3, 1:93 (w/v) S/L ratio, 22 min and 100 °C. Under these conditions, the ellagic acid yield was 6.30 ± 0.92 mg/g pomace with an antioxidant activity of 79.0 ± 0.96 μmol Trolox eq/g pomace (DPPH assay), which are 2.37 and 1.32 times the values obtained by extraction with methanol-acetone-water solvent, respectively. The considerable improvement in ellagic acid extraction efficiency could be highly attributed to the reactions of lipid saponification and ellagitannin hydrolysis resulted from sodium bicarbonates. The present study has established an organic solvent-free method for the extraction of ellagic acid from raspberry wine pomace, which is feasible and practical in nutraceutical applications.
Keywords: ellagic acid; extraction; raspberry; response surface methodology; sodium bicarbonate; wine pomace.