Bioaccessibility of total phenolic concentration and antioxidant capacity of pomegranate fruit juice and marc after in vitro digestion

Processing of pomegranate fruit yields the juice during extraction but also generates pomegranate marc, a by-product made of seeds and peels which are usually used as cattle or pig feed or directly disposed as waste. The objective of this study was to investigate the effect of digestion on total phenolic concentration and antioxidant capacity of pomegranate juice and by-products. Pomegranate juice, peel and marc were extracted in water, 50% ethanol (50%EtOH) and absolute ethanol (100% EtOH) and analysed for total phenolic concentration (TPC) and total antioxidant capacity (via Ferric Reducing Antioxidant Power (FRAP), 2,2-diphenyl-1-picrylhydrazyl (DPPH.) before and after in vitro digestion. Peel contained the highest TPC, between 91.85 and 97.81% of the TPC found in all fruit parts, with TPC order being peel > marc > juice. However, there was a significant (p<0.05) increase in TPC in most of the extracts at gastric phase of in vitro digestion. The most notable increase was in marc extracts with between 1.5- to 4.3-folds increase in gastric phase. In contrast, after the duodenal, TPC decreased significantly compared to gastric phase. Overall, higher total antioxidant capacity was exhibited by 50% ethanol for juice and marc in all the antioxidant assays. Radical scavenging activity (RSA) decreased significantly in gastric phase, with peel extracts having between 7-10% decreases. However, in duodenal phase RSA increased significantly in all the extracts compared to gastric phase, ranging between 5-18%. Peel extracts showed between 5- to 30-fold ferric reducing powers (FRAP). FRAP increased significantly in gastric phase of digestion, however, it decreased significantly (p<0.05) by 10 to 26% in duodenal phase of in vitro digestion. Radical cation scavenging activity (RCSA) in peel was between 6- to 10-fold and 2.5- to 20-fold for juice and marc, respectively. As observed in DPPH assay, RCSA decreased significantly in gastric phase of digestion. However, in duodenal phase RCSA increased in all the extracts compared to the previous phases. Pomegranate fruit waste products (peel and marc) showed great nutraceutical value addition potentials to pomegranate fruit. However, changes in total phenolic concentrations in fruit parts during in vitro digestion phases influenced the antioxidant capacities.