Food Funct., 2016, Accepted Manuscript
First published online 18 Feb 2016
The antistaphylococcal activity against methicillin-susceptible and -resistant Staphylococcus aureus as well as metabolite profiling of manuka honey, before and after in vitro simulated gastric (GD), and gastroduodenal digestion (GDD) were investigated.
Undigested manuka honey showed antibacterial activity against all the tested strains. GD sample showed no activity against S. aureus, while GDD honey showed an antistaphyloccoccal activity which was slightly reduced in comparison with undigested sample. To explain these results, methylglyoxal (MGO), to which is ascribed most of the antibacterial activity of MH, was submitted to in vitro simulated GD and GDD.
After digestion, MGO showed antibacterial activity at concentrations definitively higher than those registered in digested MH samples. This results showed that the antistaphylococcal activity registered after digestion cannot be ascribed to MGO. Thus, the metabolite analysis, carried out using an explorative untargeted NMR-based approach and a targeted RP-HPLC-PAD-ESI-MSn analysis focused on bio-active substances, was use to highlight the chemical modifications occurring after digestion.
The results showed that 1) the level of MGO decreases, 2) the content of aromatic compounds, such as leptosin and methyl syringate, markers of manuka honey, was stable under gastric and gastroduodenal conditions, whereas 3) the levels of acetic and lactic acids increase especially after gastroduodenal digestion.
Overall, the results obtained from chemical analysis provide the explanation of the registered antibacterial activity observed after gastroduodenal digestion.