The physico-chemical characterization of casein-modified surfaces and their influence on the adhesion of spores from a Geobacillus species

To gain a better understanding of the factors influencing spore adhesion in dairy manufacturing plants, casein-modified glass surfaces were prepared and characterized and their effect on the adhesion kinetics of spores from a Geobacillus sp., isolated from a dairy manufacturing plant (DMP) was assessed using a flow chamber. Surfaces were produced by initially silanizing glass using (3-glycidyloxypropyl) trimethoxysilane (GPS) or (3-aminopropyl) triethoxysilane to form epoxy-functionalized (G-GPS) or amino-functionalized glass (G-NH₂) substrata. Casein was grafted to the G-GPS directly by its primary amino groups (G-GPS-casein) or to G-NH₂ by employing glutaraldehyde as a linking agent (G-NH₂-glutar-casein). The surfaces were characterised using streaming potential measurements, contact angle goniometry, infrared spectroscopy and scanning electron microscopy. The attachment rate of spores suspended in 0.1 M KCl at pH 6.8, was highest on the positively charged (+14 mV) G-NH₂ surface (333 spores cm^?2 s^?1) compared to the negatively charged glass (?22 mV), G-GPS (?20 mV) or G-GPS-casein (?21 mV) surfaces (162, 17 or 6 spores cm^?2 s^?1 respectively). Whilst there was a clear decrease in attachment rate to negatively charged casein-modified surfaces compared to the positively charged amine surface, there was no clear relationship between surface hydrophobicity and spore attachment rate.