processing conditions or type of products. This could allow a deeper understanding of the adhesion process, resulting in better development and selection of the most effective sanitary treatments of dairy equipment.
Surface roughness The type of surface found in dairy equipment plays a big role in development of bacterial biofilms. Although non-corrosive steel is mainly used for the dairy equipment, differences in roughness are common at the microsopic level. The influence of surface roughness on the process of biofilm formation on non-corrosive steel used as dairy equipment was realised by studying Escherichia coli bacteria. The roughness of surfaces was measured in mcm (where 1mcm = 0.5mm2
). The re-
search ers evaluated three different surfaces with roughness values of 0.16mcm, 0.63mcm and 0.955mcm. For each of these roughness levels, a corresponding measurement of the density of E. coli was recorded. Observations were made dur- ing a 24-hour incubation period at 17°С. The results demonstrated that the less rough the surface, the slower the process of the initial adhesion to the surface for bio film formation. The roughness of surfaces influences the process of biofilm formation and density of E. coli; on the non-corrosive steel surface with the roughness of 0.16mcm, E. coli forms biofilms of lower density compared to on the sur- face with a roughness of 0.63mcm, while the densest biofilms were found on the highest roughness of 0.955mcm. Thus, the research indicated that dairy equipment in direct contact with the product must have a surface roughness that hinders both the process of initial bacteria adhesion and subsequent
biofilm formation. Additionally, the density of biofilms would be expected to influence the effectiveness of sanitary pro- cessing by disinfectants – this is confirmed in the section be- low describing the effectiveness of disinfectants. It would be interesting to determine how different microbes respond to differences in surface roughness.
Prevalence of microbes Research findings show that the most prevalent bacteria in contamination of dairy equipment are the Bacillus cereus and the Enterococcus faecalis. Micro-organisms of Staphylo- coccus, Streptococcus and Pseudomonas genera were less prevalent when extracts were collected from the equipment. Following the analysis of these collected samples, it was clear that even with standard sanitary processing, dairy equipment is not sterile since micro-organisms that form microflora of final products were extracted from its surface. To study the possibility of resistance, the density of common bacterial biofilms in dairy equipment was determined. The density of created biofilms was considered low when the density was less than 0.5, medium when the density was in the range 0.5–1.0 and high when density was higher than 1.0. A denser biofilm formation testifies to the fact that bacte- ria in a formed biofilm can remain on internal surfaces of dairy equipment for a long time and play a key role in the contamination of products. The densest biofilms (density 1.75–1.77) were formed by bacteria of B. cereus and E. faeca- lis genera in 100% of cases. The medium-dense biofilms were observed with the Pseudomonas aeruginosa, E. coli and En- terococcus fаecium. The least dense biofilms (1.13–1.21)
▶DAIRY GLOBAL | Volume 7, No. 4, 2020 23
Enterococcus faecalis is one of the most prevalent bacte- ria in contami- nation of dairy equipment.
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