Integrated Extraction and Anaerobic Digestion Process for Recovery of Nutraceuticals and Biogas from Pomegranate Marc

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Pomegranate marc (PM), a by-product of pomegranate juice processing, has not been effectively utilized. The objectives of this study were: (1) to determine the yields and properties of antioxidants (henceforth referring to total phenolics in terms of tannic acid equivalent) and oil extracted from various dry and wet constituents of PM, including peel, seeds, and mixture; and (2) to evaluate the anaerobic digestibility and biogas production potential of PM before and after antioxidant extraction (AE) and oil extraction (OE). Water and petroleum ether were used as solvents in the extraction of antioxidants and oil, respectively. The anaerobic digestion tests were conducted at 35C 2C with a feedstock to microorganism ratio of 0.5 on volatile solid (VS) basis under two initial organic loadings of 3.0 and 5.0 g VS L-1. According to the results, both dry and wet PM extracts had similar extraction efficiency and functionality. The wet PM extract had an antioxidant content of 23.0%, which corresponded to an antioxidant yield of 106 kg per ton of PM peel on dry basis (d.b.). The DPPH scavenging activities of antioxidants were 6.5 to 6.6 g g-1 (d.b.). The oil yield from the dry PM seeds was 138 kg ton-1 (d.b.). Compared to the low initial organic loading, the high initial organic loading improved methane content (55.1% to 67.5%) but not biogas yield. The extracted residuals of peel, seeds, and mixture had methane yields of 148, 183, and 161 mL g-1 VS, respectively, which were lower than that from raw PM. Because the integrated process of extraction followed by anaerobic digestion can produce high functional antioxidants and high-quality biogas and oil from the PM, it is recommended as a value-added utilization method for the by-product.