Doctoral Degrees (Food Science)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/537

Browse

Browsing Doctoral Degrees (Food Science) by browse.metadata.advisor "Gelderblom, W. C. A."

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    Exposure to polyphenol-enriched rooibos (Aspalathus linearis) and honeybush (Cyclopia spp.) extracts : implications of metabolism for the oxidative status in rat liver
    (Stellenbosch : Stellenbosch University, 2012-12) Van der Merwe, J. Debora; Gelderblom, W. C. A.; Joubert, E.; Manley, M.; Stellenbosch University. Faculty of AgriSciences. Dept. of Food Science.
    ENGLISH ABSTRACT: Potential beneficial and/or adverse modulatory effects of polyphenol-enriched extracts of rooibos (Aspalathus linearis) and honeybush (Cyclopia spp.) on the antioxidant homeostasis in the liver were investigated. Phase II metabolism of aspalathin and mangiferin, the major polyphenols of rooibos and honeybush respectively, was assessed for potential glucuronidation and sulphation. Glucuronidation resulted in a loss of antioxidant activity for aspalathin and mangiferin in post-column HPLC-DAD-DPPH• and HPLC-DAD-ABTS•+ assays and also a decreased activity of iron chelating properties of mangiferin in the FRAP assay. Two independent studies for 28 and 90 days with polyphenol-enriched extracts (PEEs) of unfermented rooibos [Aspalathus linearis (PER)] and honeybush [Cyclopia. subternata (PECsub) and C. genistoides (PECgen)] in male Fischer rats were conducted to assess possible beneficial and/or adverse biological effects. PECgen was only included in the 28 day study. PEEs were characterised by in vitro antioxidant assays and HPLC analysis. The importance of detailed chemical characterization of rooibos and honeybush when investigating biological effects in vivo is clear as distinctive biological effects and major differences in compositions were evident. Biological parameters included were serum chemical parameters, activities of selected antioxidant enzymes, levels of glutathione and the modulation of expression of oxidative stress and antioxidant defense related genes in the liver. Sub-chronic (90 days) exposure of rats to PER and PECsub both adversely affected iron absorption significantly (P<0.05) and significantly (P<0.05) and markedly lowered levels of reduced glutathione (GSH) in the liver. The high levels of polyphenol intake were implicated and interaction with glutathione was postulated to occur via catechol o-quinone conjugations with GSH. This was also implicated in the significantly (P<0.05) increased activity of glutathione reductase (GR) following 28 days. These findings suggest that PEEs from rooibos and honeybush have the potential to alter the glutathione homeostasis, which could contribute to oxidative status in the liver. PECsub resulted in alterations in the liver biliary system which was manifested as significantly (P<0.05) increased serum total bilirubin (Tbili) and alkaline phosphatase (ALP), depending on the age of the rats, level of total polyphenols and duration of exposure. The expression of a number of oxidative stress and antioxidant defense related genes were differentially altered by the PEEs of rooibos and honeybush in rat liver and further indicated potential oxidative stress. Modulatory effects of PEEs on expression of 84 of these genes in rat liver were assessed with a quantitative real-time reverse transcription polymerase chain reaction (RT-PCR) array and provided additional insights into the possible adverse and protective effects of rooibos and honeybush. Further investigation on total polyphenol dose levels and time of exposure in the application of PEEs of rooibos and honeybush as dietary supplements and functional foods is recommended and will also be of value in anticipated regulatory requirements for future substantiation of safety and efficacy.