Antioxidant Extraction and Biogas Production from Pomegranate Marc

Abstract

The pomegranate marc (PM), by-product from pomegranate juice processing, has not been effectively utilized. The objectives of this study were to (1) determine the yields and properties of antioxidants (total phenolics) extracted from peels and seeds of pomegranate marc in wet and dry forms, and (2) evaluate the anaerobic digestibility and biogas production potential of PM peels and seeds after antioxidant extraction (AE). Antioxidants from the ground PM peels and seeds were extracted with water at 25± 2 oC and their activities were evaluated by the DPPH radical scavenging potential based on antioxidant mass. The anaerobic digestion tests were conducted at 35 ± 2 oC with initial organic loading of 5.0 g VS/L and food to microorganism ratio of 0.5 on VS basis. The results showed that antioxidants from PM peels had higher yields (102-106 kg/ton d.b.) and purities (20.1-23.0 %) than those from PM seeds with yields and purities (11-14 kg/ton d.b. and 5.1-5.2 %), but antioxidants from PM peels and seeds gave similar DPPH scavenging activities (6.1-6.8 g/g). After nutraceuticals extraction, the AE treated PM peels and seeds had high biogas yields of 129.1-145.4 and 230-243.9 m3/ton (d.b.) and methane yields of 67.6-77.7 and 140.7-156.2 m3/ton (d.b.), respectively. Kinetics parameters estimated from model further revealed that AE treated PM peels and seeds had high biogas production potential (255-264 and 290-332 mL/g VS, respectively) and maximum biogas production rates (59-60 and 33-48 mL/g VS.d, respectively). Thus, the integrated processing of antioxidant extraction followed by biogas production via anaerobic digestion can be an effective system to utilize pomegranate marc for production of high value antioxidants as nutraceuticals and biogas as renewable energy.