Stability of total phenolic concentration and antioxidant capacity of extracts from pomegranate co-products subjected to in vitro digestion.
BACKGROUND
Co-products obtained from pomegranate juice processing contain high levels of polyphenols with potential high added values. From value-addition viewpoint, the aim of this study was to evaluate the stability of polyphenolic concentrations in pomegranate fruit co-products in different solvent extracts and assess the effect on the total antioxidant capacity using the FRAP, DPPH˙ and ABTS(+) assays during simulated in vitro digestion.


METHODS
Pomegranate juice, marc and peel were extracted in water, 50 % ethanol (50%EtOH) and absolute ethanol (100%EtOH) and analysed for total phenolic concentration (TPC), total flavonoids concentration (TFC) and total antioxidant capacity in DPPH˙, ABTS(+) and FRAP assays before and after in vitro digestion.


RESULTS
Total phenolic concentration (TPC) and total flavonoid concentration (TFC) were in the order of peel > marc > juice throughout the in vitro digestion irrespective of the extraction solvents used. However, 50 % ethanol extracted 1.1 to 12-fold more polyphenols than water and ethanol solvents depending on co-products. TPC and TFC increased significantly in gastric digests. In contrast, after the duodenal phase of in vitro digestion, polyphenolic concentrations decreased significantly (p < 0.05) compared to those obtained in gastric digests. Undigested samples and gastric digests showed strong and positive relationships between polyphenols and the antioxidant activities measured in DPPH, ABTS(+) and FRAP assays, with correlation coefficients (r (2)) ranging between 0.930-0.990. In addition, the relationships between polyphenols (TPC and TFC) and radical cation scavenging activity in ABTS(+) were moderately positive in duodenal digests.


CONCLUSIONS
Findings from this study showed that concentration of pomegranate polyphenols and the antioxidant capacity during in vitro gastro-intestinal digestion may not reflect the pre-digested phenolic concentration. Thus, this study highlights the need to provide biologically relevant information on antioxidants by providing data reflecting their stability and activity after in vitro digestion.
South African Research Chair in Postharvest Technology, Department of Horticultural Science, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa. olaniyi@sun.ac.za.
Olaniyi Amos
OA
Fawole
South African Research Chair in Postharvest Technology, Department of Horticultural Science, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa. opara@sun.ac.za.|South African Research Chair in Postharvest Technology, Department of Food Science, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa. opara@sun.ac.za.
Umezuruike Linus
UL
Opara
D000818:Animals; D001713:Biphenyl Compounds / Q000737:chemistry / Q000378:metabolism; D004063:Digestion / Q000502:physiology; D004355:Drug Stability; D016166:Free Radical Scavengers / Q000032:analysis / Q000737:chemistry*; D006801:Humans; D029561:Lythraceae / Q000737:chemistry*; D008954:Models, Biological; D010434:Pepsin A; D010636:Phenols / Q000737:chemistry*; D010851:Picrates / Q000737:chemistry / Q000378:metabolism; D010936:Plant Extracts / Q000032:analysis / Q000737:chemistry*; D013552:Swine
D001713:Biphenyl Compounds; D016166:Free Radical Scavengers; D010636:Phenols; D010851:Picrates; D010936:Plant Extracts; C004931:1,1-diphenyl-2-picrylhydrazyl; D010434:Pepsin A
By-product; DPPH; Pepsin; Polyphenols; Pomegranate; Value-addition