Effect of in vitro simulated gastro-duodenal digestion on the antioxidant and anti-inflammatory activity of South Africa Fynbos honey

Abstract

Honey has been shown to have bioactivity. Fynbos (FB) honey was investigated for its bioactivity as this vegetation type is from a unique bio diverse region in the Cape Floristic Kingdom. Six FB and one medical grade Manuka (MAN) UMF 15+ honeys that were of quality grade (Codex Alimentarius) were used. Each honey sample was subjected to in vitro simulated gastro-duodenal digestion and the antioxidant and anti-inflammatory activity of each fraction was determined. These fractions were undigested/raw honey (UD), gastric digest (GD) and gastro-duodenal digest (GDD). Included were pH and digestive enzyme controls. The total polyphenol and the flavonoid content (TPC and TFC) were determined with the Folin-Ciocalteu (F-C) and aluminium chloride methods respectively. Antioxidant activity was measured with the trolox equivalent antioxidant capacity (TEAC) and oxygen radical absorbance capacity (ORAC) assays. Cellular antioxidant activity (CAA) in the Caco-2 and SC-1 cell lines using the dichloroflourescein diacetate (DCFH DA) assay was investigated. Nitric oxide (NO) scavenging activity was determined with the sodium nitroprusside (SNP) assay. Pro-inflammatory and anti-inflammatory effects of honey were evaluated in non-stimulated and stimulated with LPS/IFN γ murine macrophage RAW 264.7 cells, respectively. Cell viability using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was done. TPC and TFC of MAN were higher than that of FB honeys. With GD, TPC and TFC of MAN increased and following GDD, TPC decreased and TFC remained unchanged. In contrast TPC and TFC of FB honey were maintained with GD and GDD. TEAC assay revealed activity by MAN being higher than that of FB honeys. With GD digestion, the antioxidant activity of MAN was unchanged but following GDD, activity was reduced. For FB honeys, TEAC was maintained with GD and GDD. ORAC assay revealed that the activity of MAN was similar to that of FB. Digestion had no effect on activity of both MAN and FB honeys. CAA in the Caco-2 and SC-1 cell line was higher for MAN compared to FB honey. In both cell lines a similar trend was observed where with GD, CAA was unchanged while with GDD, CAA was reduced. This loss of CAA following GDD was found to be due to H2O2 formation as a result of polyphenol degradation in an alkaline environment containing sodium bicarbonate and pancreatin. NO scavenging activity of MAN was greater than FB. For both types of honey with GD, NO scavenging activity was unchanged and with GDD for MAN was reduced and for FB unchanged. Digestion showed an increased pro-inflammatory effect for MAN, FB1, FB2 and FB3. The UD fractions of MAN, FB1 and FB6 had anti-inflammatory effects. FB5 and FB6 honeys showed increased anti-inflammatory activity after GD and GDD. All honey fractions did not show any cytotoxicity. In conclusion, FB honey has antioxidant, pro- and anti-inflammatory properties. With digestion, GD activity was either increased or unchanged while with GDD activity was reduced, lost or unchanged. Observed effects were either due to pH and/or digestive enzyme activity. FB honey with its shown bioactivity could be an important local nutraceutical product.