Abstract
Dairy products are a sector heavily impacted by food loss, often due to bacterial contaminations. A major source of contamination is associated with the formation of biofilms by bacterial species adopted to proliferate in milk production environment and onto the surfaces of milk processing equipment. Bacterial cells within the biofilm are characterized by increased resistance to unfavorable environmental conditions and antimicrobial agents. Members of the Bacillus genus are the most commonly found spoilage microorganisms in the dairy environment. It appears that physiological behavior of these species is somehow depended on the availability of bivalent cations in the environment. One of the important cations that may affect the bacterial physiology as well as survivability are Zn2+ ions. Thus, the aim of this study was to examine the antimicrobial effect of Zn2+ ions, intending to elucidate the potential of a zinc-based antibacterial treatment suitable for the dairy industry. The antimicrobial effect of different doses of ZnCl2 was assessed microscopically. In addition, expression of biofilm related genes was evaluated using RT-PCR. Analysis of survival rates following heat treatment was conducted in order to exemplify a possible applicative use of Zn2+ ions. Addition of zinc efficiently inhibited biofilm formation by B. subtilis and further disrupted the biofilm bundles. Expression of matrix related genes was found to be notably downregulated. Microscopic evaluation showed that cell elongation was withheld when cells were grown in the presence of zinc. Finally, B. cereus and B. subtilis cells were more susceptible to heat treatment after being exposed to Zn2+ ions. It is believed that an anti-biofilm activity, expressed in downregulation of genes involved in construction of the extracellular matrix, would account for the higher sensitivity of bacteria during heat pasteurization. Consequently, we suggest that Zn2+ ions can be of used as an effective antimicrobial treatment in various applications in the dairy industry, targeting both biofilms and vegetative bacterial cells.
Highlights
Dairy products constitute one of the leading sectors impacted by food loss [1,2]
This studythat wasfrequently designed to test in whether zinc as an antimicrobial can provide a solution to contaminations occur the dairy industry, regarding contaminations microbial from contaminations that frequently the dairy industry, regarding emerging bacterial presence of membersoccur of theinBacillus spp [14,39]
Since concern in various food sectors, many studies have been done in order to gain a better understanding biofilms are a great concern in various food sectors, many studies have been done in order to gain a of their development, subsequently coming up with fitting countermeasures [3]
Summary
Bacterial contamination can adversely affect the quality, functionality and safety of milk and its derivatives. It appears that one major source of contaminations of dairy products is often associated with the formation of biofilms on the surfaces of milk processing equipment [3]. After the establishment of the surface-attached biofilms, their removal can be extremely challenging. Their extraordinary resistance to antibacterial treatments is attributed to several factors, including inability of the antimicrobial agent to fully penetrate the biofilm through the matrix [8,9,10]
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