Effect of quorum sensing molecules and natamycin on biofilms of Candida tropicalis and other yeasts isolated from industrial juice filtration membranes

Aims Cells limit the cell number of dense biofilms by releasing self-inhibitory molecules. Here, we aim to assess the effectiveness of yeast quorum sensing (QS) molecules and the antifungal agent natamycin against yeast biofilms of strains commonly isolated from fruit juice ultrafiltration membranes. Methods and Results Yeast QS molecules, such as tyrosol, 2-phenylethanol and farnesol, were detected by solvent extraction and HS-SPME GC-MS in Candida tropicalis cultures. The effect of QS molecules on mono- and multispecies biofilms formed by Rhodotorula mucilaginosa, C. tropicalis, Candida krusei and Candida kefyr was evaluated by plate count and epifluorescence microscopy. Farnesol caused a decrease in cell number and disrupted mono- and multispecies yeast biofilms during adhesion (0 center dot 6 mmol l(-1)). 2-phenyl ethanol 1 center dot 2 mmol l(-1) stimulated biofilm density and increased cell number in both mono- and multispecies biofilms, while tyrosol did not show effects when tested against C. tropicalis biofilms (0 center dot 05-1 center dot 2 mmol l(-1)). Natamycin caused a strong decrease in cell number and disruption of biofilm structure in C. tropicalis biofilms at high concentrations (0 center dot 3-1 center dot 2 mmol l(-1)). The combination of farnesol 0 center dot 6 mmol l(-1) and natamycin at 0 center dot 01 mmol l(-1), the maximum concentration of natamycin accepted for direct addition into fruit juices, effectively reduced cell counts and disrupted the structure of C. tropicalis biofilms. Conclusion Farnesol 0 center dot 6 mmol l(-1) significantly increased the inhibition exerted by natamycin 0 center dot 01 mmol l(-1) (similar to 5 ppm) reducing biofilm development from juice on stainless steel surfaces. Significance and Impact of the Study These results support the use of QS molecules as biofilm inhibitors in beverages and would certainly inspire the design of novel preservative and cleaning products for the food industry based on combinatory approaches.