Food Funct. 2016 Mar 16;7(3):1664-70. doi: 10.1039/c5fo01409c.

Antistaphylococcal activity and metabolite profiling of manuka honey (Leptospermum scoparium L.) after in vitro simulated digestion.

Mannina L1, Sobolev AP2, Coppo E3, Di Lorenzo A4, Nabavi SM5, Marchese A3, Daglia M4.

• 1Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Università di Roma, Italy and Istituto di Metodologie Chimiche, Laboratorio di Risonanza Magnetica "Annalaura Segre", CNR, Rome, Italy.
• 2Istituto di Metodologie Chimiche, Laboratorio di Risonanza Magnetica "Annalaura Segre", CNR, Rome, Italy.
• 3Microbiology Unit, DISC, University of Genoa and IRCSS San Martino - IST, Italy.
• 4Department of Drug Sciences, Medicinal Chemistry and Pharmaceutical Technology Section, University of Pavia, Italy. maria.daglia@unipv.it.
• 5Applied Biotechnology Research Center, Baqiyatallah University of Medical Sciences, PO Box 19395 5487, Tehran, Iran.

Abstract

The antistaphylococcal activity against methicillin-susceptible and -resistant Staphylococcus aureus and the metabolite profiling of manuka honey (MH) were investigated before and after in vitro simulated gastric (GD) and gastroduodenal (GDD) digestions.

Undigested manuka honey showed antibacterial activity against all the tested strains, the GD sample showed no activity against S. aureus, and the GDD honey showed an antistaphylococcal activity, which was slightly reduced in comparison with the undigested sample.

To explain these results, methylglyoxal (MGO), to which most of the antibacterial activity of MH is ascribed, was subjected to in vitro simulated GD and GDD. After digestion, MGO showed antibacterial activity at concentrations definitively higher than those registered in digested MH samples. These results showed that the antistaphylococcal activity registered after digestion cannot be ascribed to MGO.

Thus 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 used to highlight the chemical modifications occurring from digestion. The results showed that
(1) the level of MGO decreases and
(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 in particular after gastroduodenal digestion, being 1.5 and 2.8 times higher in GDD-MH than in UND-MH, respectively.

Overall, the results obtained from chemical analysis provide at least a partial explanation of the registered antibacterial activity observed after gastroduodenal digestion.

PMID:  26948514