Valorization of pomegranate husk – Integration of extraction with nanofiltration for concentrated polyphenols recovery
A process development study is reported, involving water-based extraction of polyphenols from pomegranate husk and their subsequent membrane concentration. Aiming to optimize extraction, various experimental conditions were investigated, including extraction duration, solid to liquid ratio (2-14 % w/v dry weight), extraction temperature, number of sequential extraction stages (single, double and triple) and type of solvent. It was found that two extraction stages (90 min each) under a solid to water ratio of 3% w/v at 30 °C, were sufficient for obtaining a yield of 85% of total polyphenols from the husk. Subsequently, nanofiltration (NF) was used to concentrate the polyphenols extracts by a volume concentration factor (VCF) of three. Two main process parameters, namely pressure (4-14 bar) and pH (4-8), were examined at constant temperature 30◦C, in batch concentration mode. Results show near optimum NF-membrane performance, with high total polyphenols retention (≥ 98%) at 10 bar pressure and pH 6. Interestingly, the NF-membrane, used for up to 10 filtration batches, exhibited satisfactory flux without intermediate cleaning, suggesting that it could be employed for an extended period. Prospects and challenges are discussed for further process development and practical application.