No abstract

No abstract

In addition to direct antioxidative effects, Maillard reaction products (MRPs) could increase the antioxidative capacity of cells through the induction of cytoprotective enzymes. Since many of those enzymes are regulated by the transcription factor Nrf2, the effect of MRPs on nuclear translocation of Nrf2 in macrophages and Caco-2 cells was investigated. Stimulation of both cell types by MRPs showed a concentration-dependent significant increase in nuclear translocation of Nrf2 up to fivefold after short-term (2 h) and up to 50-fold after long-term treatment (24 h). In intact human gut tissue, nuclear translocation of Nrf2 was significantly twofold increased after short-term incubation. To study the activation mechanisms, macrophages and Caco-2 cells were stimulated with MRPs in the presence of catalase, which significantly suppressed Nrf2 activation. Thus, activation was related to extracellular H2O2 continuously formed from MRPs. Short-term incubation with coffee, a MRP-rich beverage, led to a trend towards Nrf2 activation in macrophages, but not in Caco-2 cells or intact human gut tissue. Long-term incubation with coffee (1-4 mg/mL) significantly increased nuclear Nrf2 up to 17-fold. Since raw coffee was inactive under the tested conditions, the effect was related to roasting products. Coffee-induced Nrf2 translocation was, however, only slightly reversed by catalase. Therefore, the Nrf2 activity of coffee can only partially be explained by MRP-induced, H2O2-dependent mechanisms. Thus, it can be concluded that MRPs may increase the antioxidative capacity inside the cell by inducing Nrf2-regulated signalling pathways not only in different cell types, but also in intact gut tissue.

Coffee shows distinct antimicrobial activity against several bacterial genera. The present study investigated molecular mechanisms and active ingredients mediating the antimicrobial effect of coffee. Depending on concentration, roasted, but not raw coffee brew inhibited the growth of Escherichia coli and Listeria innocua. Several coffee ingredients with known antibacterial properties were tested for their contribution to the observed effect. In natural concentration, caffeine, ferulic acid and a mixture of all test compounds showed very weak, but significant activity, whereas trigonelline, 5-(hydroxymethyl)furfural, chlorogenic acid, nicotinic acid, caffeic acid, and methylglyoxal were not active. Antimicrobial activity, however, was completely abolished by addition of catalase indicating that H(2)O(2) is a major antimicrobial coffee component. In accordance with this assumption, bacterial counts during 16 h of incubation were inversely related to the H(2)O(2) concentration in the incubation solution. Pure H(2)O(2) showed slightly weaker activity. The H(2)O(2) dependent antimicrobial activity of coffee could be mimicked by a reaction mixture of d-ribose and l-lysine (30 min 120 °C) indicating that H(2)O(2) is generated in the coffee brew by Maillard reaction products. Identification of H(2)O(2) as major antimicrobial coffee component is important to evaluate the application of coffee or coffee extracts as natural preservatives.