Wilmer Edgard Luera Peña

Microbial modeling of Alicyclobacillus acidoterrestris CRA 7152 growth in orange juice with nisin added

The adaptation time of Alicyclobacillus acidoterrestris CRA 7152 in orange juice was determined as a response to pH (3 to 5.8), temperature (20 to 54 degrees C), soluble solids concentration ((o)Brix; 11 to 19 (o)Brix), and nisin concentration (0 to 70 IU/ ml) effects. A four-factor central composite rotational design was used. Viable microorganisms were enumerated by plating on K medium (pH 3.7). Two primary models were used to represent growth and adaptation time. A second-order polynomial model was applied to analyze the effects of factors. Results showed that the Baranyi and Roberts model was better than the modified Gompertz model, considering the determination coefficient (R2) for experimental data description. Inhibition of bacteria can be obtained through several studied combinations for at least 47 days of storage. The shortest period of adaptation was observed between 37 to 45 degrees C, with pHs between 4 and 5, yet the longest periods of adaptation could be obtained around 20 degrees C with pHs close to 3.0. Statistical analysis of the quadratic model showed that the adaptation time increased as temperature or pH decreased, and as nisin concentration or soluble solids increased. The model showed that adaptation time has a minimum value for juice without nisin added, with 13.5% soluble solids, pH 5.0, and incubated at 43.8 degrees C. The statistical parameters that validated this model were an R2 of 0.816, a bias factor of 0.96, and an accuracy factor of 1.14. Manipulation of more than one factor, as well as the use of an antimicrobial agent, can be an alternative to preventing the development of A. acidoterrestris in orange juice, thus contributing to increased orange juice shelf life.

Microbial modeling of thermal resistance of Alicyclobacillus acidoterrestris CRA7152 spores in concentrated orange juice with nisin addition

Estudou-se o efeito da nisina na inativacao termica dos esporos de Alicyclobacillus acidoterrestris CRA 7152 em suco de laranja concentrado (64 oBrix). Foram avaliadas as concentracoes de 0, 50, 75 e 100 UI de nisina/ml de suco nas temperaturas de 92, 95, 98 e 102 oC. Foi utilizado o modelo polinomial quadratico para analisar os efeitos dos fatores e suas interacoes. A contagem dos esporos sobreviventes foi feita atraves de plaqueamento em meio K (pH = 3,7). De acordo com os resultados obtidos encontrouse um valor de D sem adicao de nisina de 25,5; 12,9; 6,1 e 2,3 min para as temperaturas de 92, 95, 98 e 102 oC respectivamente. Quando a nisina foi adicionada ao suco observouse uma queda na resistencia termica em funcao do aumento da concentracao de nisina para os mesmos valores de temperatura. Ao utilizar as concentracoes de 30, 50, 75 e 150 IU/ml a 95 oC, o valor de D obtido foi de 12,34; 11,38; 10,49; 9,49; e 9,42 min respectivamente demonstrando que a adicao de nisina provoca um decrescimo de ate 27 % no valor de D. O modelo polinomial de segunda ordem ajustado com r2 = 0,995 mostrou que a resistencia do microorganismo foi afetada pela temperatura seguida da concentracao de nisina. A adicao de nisina e, portanto, uma alternativa para reduzir o rigor do tratamento termico em A. acidoterrestris CRA 7152.The nisin effect on thermal death of Alicyclobacillus acidoterrestris CRA 7152 spores in concentrated orange juice (64oBrix) was studied. Concentrations of 0, 50, 75 and 100 IU of nisin/ml juice, at temperatures of 92, 95, 98 and 102oC were evaluated. The quadratic polynomial model was used to analyze the effects of the factors and their interaction. Verification of surviving spores was carried out through plating in K medium (pH 3.7). The results showed that the D values without nisin addition were 25.5, 12.9, 6.1 and 2.3 min for 92, 95, 98 and 102oC respectively. With addition of nisin into the juice there was a drop of heat resistance as the concentration was increased at a same temperature. With 30, 50, 75, 100 and 150 IU/ml at 95oC, the D values were 12.34, 11.38, 10.49, 9.49 and 9.42 min respectively, showing that a decrease in the D value up to 27% can be obtained. The second order polynomial model established with r2 = 0.995 showed that the microorganism resistance was affected by the action of temperature followed by the nisin concentration. Nisin therefore is an alternative for reducing the rigor of the A. acidoterrestris CRA 7152 thermal treatment.

Predicting adhesion and biofilm formation boundaries on stainless steel surfaces by five Salmonella enterica strains belonging to different serovars as a function of pH, temperature and NaCl concentration

This study aimed to assess the capability of 97 epidemic S. enterica strains belonging to 18 serovars to form biofilm. Five strains characterized as strong biofilm-producers, belonging to distinct serovars (S. Enteritidis 132, S. Infantis 176, S. Typhimurium 177, S. Heidelberg 281 and S. Corvallis 297) were assayed for adhesion/biofilm formation on stainless steel surfaces. The experiments were conducted in different combinations of NaCl (0, 2, 4, 5, 6, 8 and 10% w/v), pH (4, 5, 6 and 7) and temperatures (8 °C, 12 °C, 20 °C and 35 °C). Only adhesion was assumed to occur when S. enterica counts were ≥3 and <5 log CFU/cm2, whereas biofilm formation was defined as when the counts were ≥5 log CFU/cm2. The binary responses were used to develop models to predict the probability of adhesion/biofilm formation on stainless steel surfaces by five strains belonging to different S. enterica serovars. A total of 99% (96/97) of the tested S. enterica strains were characterized as biofilm-producers in the microtiter plate assays. The ability to form biofilm varied (P < 0.05) within and among the different serovars. Among the biofilm-producers, 21% (20/96), 45% (43/96), and 35% (34/96) were weak, moderate and strong biofilm-producers, respectively. The capability for adhesion/biofilm formation on stainless steel surfaces under the experimental conditions studied varied among the strains studied, and distinct secondary models were obtained to describe the behavior of the five S. enterica tested. All strains showed adhesion at pH 4 up to 4% of NaCl and at 20 °C and 35 °C. The probability of adhesion decreased when NaCl concentrations were >8% and at 8 °C, as well as in pH values ≤ 5 and NaCl concentrations > 6%, for all tested strains. At pH 7 and 6, biofilm formation for S. Enteritidis, S. Infantis, S. Typhimurium, S. Heidelberg was observed up to 6% of NaCl at 35 °C and 20 °C. The predicted boundaries for adhesion were pH values < 5 and NaCl ≥ 4% and at temperatures <20 °C. For biofilm formation, the predicted boundaries were pH values < 5 and NaCl concentrations ≥ 2% and at temperatures <20 °C for all strains. The secondary models obtained describe the variability in boundaries of adhesion and biofilm formation on stainless steel by five strains belonging to different S. enterica serovars. The boundary models can be used to predict adhesion and biofilm formation ability on stainless steel by S. enterica as affected by pH, NaCl and temperature.