The interaction between the surface of stainless steel and Bacillus cereus was studied in terms of the characteristics of interfacial interaction determined from the measurement of the contact angle of the surface of B. cereus and stainless steel in the presence or absence of B. cereus adherence. The microtopographies and the roughness of the surface of stainless steel and stainless steel adhered by B.cereus were evaluated with the help of atomic force microscopy and perfilometry. The strain of B. cereus studied was considered hydrophilic, whereas the stainless steel was considered hydrophobic. The adhesion was not thermodynamically favorable ( G adhesion > 0) between the stainless steel and the strain of B. cereus studied. Thus, the interaction between them was not favored by the thermodynamic aspect of adhesion.There was no difference (p > 0.05) in the roughness of the surfaces of stainless steel adhered by B. cereus when analyzed by atomic force microscope and perfilometry.

Given the increasing number of antibiotic-resistant bacteria and the need to synthesize new antimicrobials, silver has attracted interest in the scientific community because of its recognized antimicrobial activity. This study aimed to evaluate the antimicrobial effects of silver nanoparticles (NP) obtained by a new method and tested at concentrations of 6 μg/ml and 60 μg/ml against the species Staphylococcus aureus, Listeria innocua, Salmonella Choleraesuis, Pseudomonas aeruginosa, Escherichia coli, and Bacillus cereus. The ability of these nanoparticles to remove or kill vegetative cells adhered to stainless steel surfaces was also evaluated. We observed that the NP obtained with the new method, concentrated silver nanoparticles (CNP), and silver nanoparticles with added sodium chloride (NPNaCl) had high antimicrobial activities (P < 0.05). We also verified that the most effective condition for the removal of P. aeruginosa cells on stainless steel coupons (10 by 10 mm) was immersion of the surfaces in CNP. The CNP treatment produced a 5-log reduction of the microbial population after 30 to 60 min of immersion. The CNP treatment also performed better than water and sodium carbonate, a compound commonly applied in clean-in-place procedures in the food industry, in removing adherent B. cereus cells from stainless steel cylinders. Therefore, these results suggest that NP synthesized by a new procedure may be used as antimicrobials in the food industry, for example, for the sanitization of utensils that come into contact with foods.

Adhesion of Bacillus cereus A6 and L1, isolated from dairy plants, to stainless steel, granite, and glass surfaces was evaluated. Adhesion of B. cereus to all surfaces was affected by hydrophobicity. Adhesion to the hydrophobic surfaces (DG sws TOT < 0) of granite and stainless steel was greater than adhesion to glass, which was classified as a hydrophilic surface (DG sws TOT > 0). Bacillus cereus A6 adhered in higher numbers to all three surfaces evaluated and was less hydrophilic (DG bwb TOT = 19.83) than B. cereus L1 (DG bwb TOT = 23.50). For instance, in stainless steel the number of adhered cells of B.cereus A6 was 2.42 log CFU cm )2 while to B. cereus L1 was 1.96 log CFU cm )2 . The adhesion of B. cereus was thermodynamically favourable in granite and stainless steel surface (DG adhesion < 0). Therefore, the adherence process was affected by the strain of B. cereus and by the hydrophobicity of stainless steel, granite, glass and microorganisms surfaces.

Adhesion of Bacillus cereus to stainless steel 304 #4 was evaluated after different times and temperatures of contact. Mathematical model was obtained, which was capable of predicting the adhesion of B. cereus to stainless steel as a function of temperature (4-35C) and time (1-10 days). The increase in temperature from 4 to 35C resulted in an increased number of B. cereus cells attached more than 3 log cycles for an adhesion time of 1 day and more than 4 log cycles for an adhesion time of 10 days, indicating the importance of temperature in adhesion. The maximum number of cells attached to coupons incubated at 35C for 10 days (4.43 log cfu/cm 2 ) was close to the number of cells attached to coupons incubated at 35C for 1 day (4.01 log cfu/cm 2 ). The model obtained represents well the relationship between temperature and rate of adhesion, which is indicated by the statistical indices calculated. PRACTICAL APPLICATIONSThis research shows important information for people dealing with food quality control, quality management, risk assessment, risk management hazard analysis by critical point control and good manufacturing practices, which are well-recognized food safety tools. The number of manufactured foods has widely increased to meet the increasing number of consumers and, sometimes, the hygiene procedures in the food industry are poor or overlooked. It is essential that those responsible for producing food be knowledgeable about the characteristics of the material surfaces used to make the equipment, utensils and conveyors to help in the control of foodborne diseases. The viable alternatives to avoid or minimize food contamination are (1) improving surface quality related to microtopography by improving surface production process; (2) choosing surfaces with better characteristics concerning microtopography to control the adherence process and biofilm formation; and (3) implementing effective controls of cleaning and sanitizing procedures. bs_bs_banner Journal of Food Process Engineering

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