title: Effect of drying on the bioactive compounds, antioxidant, antibacterial and antityrosinase activities of pomegranate peel.
abstract: BACKGROUND
  The use of pomegranate peel is highly associated with its rich phenolic concentration. Series of drying methods are recommended since bioactive compounds are highly sensitive to thermal degradation. The study was conducted to evaluate the effects of drying on the bioactive compounds, antioxidant as well as antibacterial and antityrosinase activities of pomegranate peel.
  
  
  METHODS
  Dried pomegranate peels with the initial moisture content of 70.30 % wet basis were prepared by freeze and oven drying at 40, 50 and 60 °C. Difference in CIE-LAB, chroma (C*) and hue angle (h°) were determined using colorimeter. Individual polyphenol retention was determined using LC-MS and LC-MS(E) while total phenolics concentration (TPC), total flavonoid concentration (TFC), total tannins concentration (TTC) and vitamin C concentration were measured using colorimetric methods. The antioxidant activity was measured by radical scavenging activity (RSA) and ferric reducing antioxidant power (FRAP). Furthermore, the antibacterial activity of methanolic peel extracts were tested on Gram negative (Escherichia coli and Klebsiella pneumonia) and Gram positive bacteria (Staphylococcus aureus and Bacillus subtilis) using the in vitro microdilution assays. Tyrosinase enzyme inhibition was investigated against monophenolase (tyrosine) and diphenolase (DOPA), with arbutin as positive controls.
  
  
  RESULTS
  Oven drying at 60 °C resulted in high punicalin concentration (888.04 ± 141.03 mg CE/kg dried matter) along with poor red coloration (high hue angle). Freeze dried peel contained higher catechin concentration (674.51 mg/kg drying matter) + catechin and -epicatechin (70.56 mg/kg drying matter) compared to oven dried peel. Furthermore, freeze dried peel had the highest total phenolic, tannin and flavonoid concentrations compared to oven dried peel over the temperature range studied. High concentration of vitamin C (31.19 μg AAE/g dried matter) was observed in the oven dried (40 °C) pomegranate peel. Drying at 50 °C showed the highest inhibitory activity with the MIC values of 0.10 mg/ml against Gram positive (Staphylococcus aureus and Bacillus subtili. Likewise, the extracts dried at 50 °C showed potent inhibitory activity concentration (22.95 mg/ml) against monophenolase. Principal component analysis showed that the peel colour characteristics and bioactive compounds isolated the investigated drying method.
  
  
  CONCLUSIONS
  The freeze and oven dried peel extracts exhibited a significant antibacterial and antioxidant activities. The freeze drying method had higher total phenolic, tannin and flavonoid concentration therefore can be explored as a feasible method for processing pomegranate peel to ensure retention of the maximum amount of their naturally occurring bioactive compounds.
  
  
  BACKGROUND
  Not relevant for this study.
authors.affiliation: Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Sciences, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa.
authors.forename: Rebogile R
authors.initials: RR
authors.lastname: Mphahlele
authors.affiliation: Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Sciences, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa.|Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Food Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa.
authors.forename: Olaniyi A
authors.initials: OA
authors.lastname: Fawole
authors.affiliation: Department of Botany and Zoology, Faculty of Science, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa.
authors.forename: Nokwanda P
authors.initials: NP
authors.lastname: Makunga
authors.affiliation: Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Horticultural Sciences, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa. opara@sun.ac.za.|Postharvest Technology Research Laboratory, South African Research Chair in Postharvest Technology, Department of Food Science, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch, 7602, South Africa. opara@sun.ac.za.
authors.forename: Umezuruike L
authors.initials: UL
authors.lastname: Opara
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000975:Antioxidants / Q000737:chemistry / Q000494:pharmacology*; D001205:Ascorbic Acid / Q000032:analysis; D003890:Desiccation; D005290:Ferric Compounds / Q000378:metabolism; D005419:Flavonoids / Q000032:analysis; D016166:Free Radical Scavengers / Q000378:metabolism; D005612:Freeze Drying; D029561:Lythraceae / Q000737:chemistry*; D008826:Microbial Sensitivity Tests; D014442:Monophenol Monooxygenase / Q000037:antagonists & inhibitors; D010636:Phenols / Q000032:analysis; D010936:Plant Extracts / Q000737:chemistry / Q000494:pharmacology*; D013634:Tannins / Q000032:analysis
chemical_list: D000900:Anti-Bacterial Agents; D000975:Antioxidants; D005290:Ferric Compounds; D005419:Flavonoids; D016166:Free Radical Scavengers; D010636:Phenols; D010936:Plant Extracts; D013634:Tannins; D014442:Monophenol Monooxygenase; D001205:Ascorbic Acid
keywords: Freeze drying; Oven drying; Rutin; Total phenolics; Vitamin C