Adhesion of Megasphaera cerevisiae onto solid surfaces mimicking materials used in breweries

摘要

Developments in filling technologies have led to a reduction in oxygen content in beer, thus producing an anaerobic environment suitable for the growth of anaerobic beer-spoiling microorganisms. Anaerobic bacteria survive well in a biofilm that provides protection against environmental stress factors. The initial step in biofilm formation is adhesion of cells to a solid surface. Therefore the purpose of this research was to study theoretically and experimentally adhesion of strains of Megasphaera cerevisiae to different solid surfaces with properties covering a wide range of materials used in breweries. Experimental characterization of surface properties was used to model surface interactions, resulting in a quantitative prediction of cell adhesion. The colloidal model predictions were then compared with adhesion tests. As revealed experimentally, the most significant adhesion occurred to 3-aminopropyltriethoxysilane-modified glass (substitute for stainless steel) at pH 3-7. According to physicochemical interaction models, under these conditions interactions were influenced mostly by electrostatic attractions between surfaces. At pH 3, experimental data, supported by theoretical predictions, showed significant bacterial adhesion to borosilicate glass (a hydrophilic surface) and propyltriethoxysilane-modified glass (a hydrophobic surface). Conversely, the least adhesion of M. cerevisiae was both predicted and observed at pH 10, since at an alkaline pH, electrostatic repulsion between surfaces predominates. Since adhesion can be expected mainly at an acidic pH, prevention should be based on the use of alkaline cleaning agents and/or alkaline rinse water at the end of the cleaning procedure. An elevated risk of adhesion to stainless steel was also identified, allowing appropriate measures to be taken. (C) 2017 The Institute of Brewing & Distilling