title: Influence of different extraction conditions on antioxidant properties of soursop peel.
abstract: BACKGROUND
  Soursop is a healthy fruit. Peels form about 20% of the soursop fruit and are usually discarded as waste product. With a view to utilizing soursop peel as a source of valuable compounds, this study aimed to investigate the influence of different extraction conditions on total phenolic content (TPC) and antioxidant capacity (AC) of soursop (Annona muricata L.) peel.
  
  
  METHODS
  Different ethanol concentrations (20-100%, v/v), extraction temperatures (25- 60°C), and extraction time (1-5 h) were tested. Extracts were prepared on the basis of the best optimal extraction conditions (20% ethanol, 40°C the extraction temperature, and 4 h of extraction time), an optimal TPC and AC was determined for the soursop peel using DPPH, ABTS, FRAP and β-carotene bleaching (BCB) assays. The different extraction conditions tested at best optimum conditions have significantly affected the TPC and AC of the soursop peel.
  
  
  RESULTS
  Soursop peel extract extracted in the best optimal extraction conditions had moderate levels of TPC (52.2 μg GAE/ml), and FRAP value (58.9 μg TE/ml extract). The extract demonstrated high BCB inhibitory activity (80.08%). The EC50 values of the extract were high, 1179.96 and 145.12 μg/ml, as assessed using DPPH and ABTS assays, respectively. The TPC was positively and highly correlated with the AC of soursop peel assessed by ABTS, FRAP, and BCB assay, but it was moderately correlated with DPPH radical scavenging activity. A moderate correlation of TPC with DPPH suggested that polyphenols in the extracts were partially responsible for the AC.
  
  
  CONCLUSIONS
  By-products of soursop such as its peel could be an inexpensive source of good natural antioxidants with nutraceutical potential in the functional food industry.
authors.affiliation: Department of Food Science and Nutrition, UCSI University,Kuala Lumpur, Malaysia.
authors.forename: Wei Zin
authors.initials: WZ
authors.lastname: Lee
authors.affiliation: Department of Nutrition and Dietetics, School of Health Sciences, International Medical University,Kuala Lumpur, Malaysia.
authors.forename: Sui Kiat
authors.initials: SK
authors.lastname: Chang
authors.affiliation: Department of Nutrition and Dietetics, Universiti Putra Malaysi, Selangor, Malaysia.
authors.forename: Hock Eng
authors.initials: HE
authors.lastname: Khoo
authors.affiliation: Department of Food Science and Nutrition, UCSI University,Kuala Lumpur, Malaysia.
authors.forename: Chiaw Mei
authors.initials: CM
authors.lastname: Sia
authors.affiliation: Department of Food Science and Nutrition, UCSI University,Kuala Lumpur, Malaysia.
authors.forename: Hip Seng
authors.initials: HS
authors.lastname: Yim
mesh_terms: D031041:Annona / Q000737:chemistry*; D000975:Antioxidants / Q000032:analysis*; D000431:Ethanol / Q000737:chemistry; D005638:Fruit / Q000737:chemistry*; D010936:Plant Extracts / Q000032:analysis*; D059808:Polyphenols / Q000032:analysis; D019207:beta Carotene / Q000032:analysis
chemical_list: D000975:Antioxidants; D010936:Plant Extracts; D059808:Polyphenols; D019207:beta Carotene; D000431:Ethanol
keywords: Annona muricata; antioxidant capacity; extraction parameters; soursop peel; total phenolic content; waste products