Modelagem da adesão de Bacillus cereus ao aço inoxidável em função do tempo e da temperatura e influência da rugosidade e da hidrofobicidade sobre a adesão / Modeling of adhesion of Bacillus cereus to stainless steel as function of time and temperature and influence of roughness and hydrophobicity in the adhesion

Patrícia Campos Bernardes

Adhesion of Bacillus cereus to stainless steel 304 #4 was evaluated after different times and temperatures of contact. Mathematical models were obtained capable of predicting the adhesion of B. cereus in stainless steel, as a function of temperature (4 oC 35 oC) and time (1d - 10 d). The interaction between the surface of stainless steel and B. cereus was studied by the characteristics of interfacial interaction, determined from the measurement of contact angle of the surface of B. cereus, stainless steel and stainless steel attachment with B. cereus, in association with the extended DLVO theory and the thermodynamic theory of adhesion. It was evaluated the microtopographies and the roughness of the surface of stainless steel and stainless steel attachment with B. cereus with the help of atomic force microscopy and perfilometry. The increase in temperature of 4 oC to 35 oC increased the number of B. cereus attached more than 3 cycles log for the time of adhesion of 1 d and more than 4 cycles log for the time of adhesion of 10 d showing the importance of temperature in adhesion. The maximum number of attached cells, found in coupons incubated for 35 oC for 10 days (log 4.43 CFU/cm2) was close to that of cells attached when the coupons remained at the same temperature for 1 day (log 4.01 CFU/cm2) showing once again the importance of temperature in relation to time to adhesion of this bacteria. When the temperature rose from 7 oC to 15 oC the number of CFU/cm2 increased about 3 cycles log. Only in the region of high temperature was a good adjustment of the data obtained by the mathematical model. The strain of B. cereus study was considered hydrophilic while the stainless steel was considered hydrophobic. The adhesion was not thermodynamically favorable (ΔGadesão>0) between the stainless steel and strain of B. cereus studied. Thus, the interaction between them was not favoured by thermodynamic aspect of adhesion. There was no difference (p>0.05) in the roughness of the surfaces of stainless steel attachment with B. cereus when analyzed by atomic force microscope and for perfilometry. The effect of temperature was more important than the effect of time on the adhesion of B. cereus to stainless steel 304 #4. The strain of B. cereus study was able to adhere to the coupons of stainless steel 304 #4 at low temperatures (4 C, 7 C and 10 C). The results indicated that possible abuses in the temperature of storage under refrigeration decisively affect the number of attached bacteria, which may adversely affect the quality of milk.

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