cThis study investigated the effects of varied sodium, calcium, and magnesium concentrations in specialty milk formulations on biofilm formation by Geobacillus spp. and Anoxybacillus flavithermus. The numbers of attached viable cells (log CFU per square centimeter) after 6 to 18 h of biofilm formation by three dairy-derived strains of Geobacillus and three dairy-derived strains of A. flavithermus were compared in two commercial milk formulations. Milk formulation B had relatively high sodium and low calcium and magnesium concentrations compared with those of milk formulation A, but the two formulations had comparable fat, protein, and lactose concentrations. Biofilm formation by the three Geobacillus isolates was up to 4 log CFU cm ؊2 lower in milk formulation B than in milk formulation A after 6 to 18 h, and the difference was often significant (P < 0.05). However, no significant differences (P < 0.05) were found when biofilm formations by the three A. flavithermus isolates were compared in milk formulations A and B. Supplementation of milk formulation A with 100 mM NaCl significantly decreased (P < 0.05) Geobacillus biofilm formation after 6 to 10 h. Furthermore, supplementation of milk formulation B with 2 mM CaCl 2 or 2 mM MgCl 2 significantly increased (P < 0.05) Geobacillus biofilm formation after 10 to 18 h. It was concluded that relatively high free Na ؉ and low free Ca 2؉ and Mg 2؉ concentrations in milk formulations are collectively required to inhibit biofilm formation by Geobacillus spp., whereas biofilm formation by A. flavithermus is not impacted by typical cation concentration differences of milk formulations.T hermophilic bacilli belonging to the Geobacillus spp. and Anoxybacillus flavithermus groups are the predominant spoilage bacteria that may contaminate milk during its manufacture into milk powder (1, 2). The number of thermophilic bacilli in milk powder is of major importance because it is a measure of its quality and determines its market selling price (1, 2). Geobacillus spp. and A. flavithermus grow as biofilms on product contact surfaces in regions of milk powder manufacturing plants, such as in plate heat exchangers and evaporators, that are held at high temperatures (up to 70°C) (1, 2). It is postulated that these biofilms act as a reservoir of cells that slough off and disperse into milk as it transits through the plant (1, 2). The majority of thermophilic bacilli that appear in milk powder originate from biofilms on product contact surfaces (2).The concentrations and ratios of free cations in the aqueous phase that immerses a biofilm can influence biofilms in many ways. Electrostatic interactions of free cations with bacterial polymers in a biofilm matrix can influence the structural integrity and cohesion of a biofilm (3, 4). In addition, bacteria respond to fluctuations in free cation concentrations by adapting their physiology, which may influence biofilm formation. For example, Kara et al. (5) showed that increasing Na ϩ concentrations increased the proportion of negatively char...
cPreconditioning of Anoxybacillus flavithermus E16 and Geobacillus sp. strain F75 with cations prior to attachment often significantly increased (P < 0.05) the number of viable cells that attached to stainless steel (by up to 1.5 log CFU/cm 2 ) compared with unconditioned bacteria. It is proposed that the transition of A. flavithermus and Geobacillus spp. from milk formulations to stainless steel product contact surfaces in milk powder manufacturing plants is mediated predominantly by bacterial physiological factors (e.g., surface-exposed adhesins) rather than the concentrations of cations in milk formulations surrounding bacteria.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.