Rapid, enhanced and eco-friendly recovery of punicalagin from fresh waste pomegranate peels via aqueous ball milling

Although the waste pomegranate peel (WPP) is a popular antioxidant source, pomegranate antioxidant extracts available in the market lack key antioxidant “punicalagin”. Commercial production of pomegranate antioxidant extracts employ energy demanding drying of WPP followed by long hour extraction (detrimental to punicalagin) with organic solvents hazardous to the environment and human health that require stringent solvent recovery and disposal. Therefore, a fast and eco-friendly method based on aqueous ball milling (at pH 7 and 40 °C) without using hazardous reagent was developed to extract punicalagin enriched phenolics directly from fresh WPP. The systematic study of the combinations of ball milling time and liquid: solid ratio led to the highest recovery of phenolics (11–11.7 g 100 g−1 DW of WPP of wonderful and Ruby cultivar) containing 8.6–9.5 g punicalagin with highest antioxidant activity after 10 min ball milling with aqueous buffer at 15 mL g−1 liquid:solid ratio. The ball milling at these conditions using conventional organic solvents (methanol, ethanol, acetone, and ethyl acetate) yielded lower recoveries of total phenolics (4–11 g 100 g−1 DW of WPP) containing only 0.6–2.6 g punicalagin. The aqueous ball milling was also more rapid and efficient for the extraction of total phenolics and punicalagin than the ultrasound-assisted and Soxhlet extraction with methanol and aqueous buffer. Remarkably, the punicalagin content of the phenolic extract (70% w/w) obtained by aqueous ball milling is significantly higher compared to the punicalagin content (10–30% w/w) of commercially available pomegranate phenolic extracts. This extract also showed excellent storage stability as evident from no change in its punicalagin content even after 36 days of storage at 20 °C.