RESUMEN
The aim of this study was to investigate the combined effect of carvacrol, thymol and nisin against Staphylococcus aureus and the combined effect of carvacrol and thymol against Salmonella Enteritidis. Minimum inhibitory concentrations (MIC) of carvacrol, thymol, and nisin for S. aureus were 200, 150 and 30 µg/mL, respectively. MIC of carvacrol and thymol for Salmonella Enteritidis was 200 µg/mL. A factorial method of independent variables was then used to study the combined effect of antimicrobials. Results showed that combinations of carvacrol-thymol-nisin (reduction of 1.2 log CFU/mL for MIC and 4.98 log CFU/mL for 2MIC), carvacrol-thymol (reduction of 1.33 log CFU/mL for 2MIC), nisin-thymol (reduction of 3.52 log CFU/mL for 2MIC) and nisin-carvacrol (reduction of 3.41 log CFU/mL for 2MIC) attained a significant inhibition of S. aureus. Similarly, there was significant reduction of Salmonella Enteritidis due to combined effect of thymol-carvacrol (reduction of 4.5 log CFU/mL for MIC and inhibition below detection limit for 2MIC). Therefore, the combinations of natural antimicrobials described in this work showed potential to be used as an additional barrier for food safety.
Asunto(s)
Nisina , Timol , Antibacterianos/farmacología , Cimenos , Pruebas de Sensibilidad Microbiana , Monoterpenos/farmacología , Nisina/farmacología , Salmonella enteritidis , Staphylococcus aureus , Timol/farmacologíaRESUMEN
INTRODUCTION: The number of registered foodborne diseases involving fresh produce is a preoccupation in many countries. For this reason, the aim of this study was to better understand the growth of Staphylococcus aureus and Escherichia coli, two indicators of hygienic and sanitary conditions, on fruits and vegetables that were exposed at different temperatures. METHODOLOGY: The main salads served at the buffets of commercial restaurants were artificially contaminated with separate pools of both pathogens and subsequently exposed at 10, 20 and 30 °C and at different time intervals. Then, the growth potential of S. aureus and E. coli on each fruit and vegetable was determined. RESULTS: There was no significant S. aureus and E. coli growth on all evaluated foods exposed at 10 °C until 6 hours. When comparing both microorganisms, E. coli demonstrated higher growth potential than S. aureus on all analysed salads. Peculiarly, E. coli had the highest growth rate for the tomato (α = 6.43 at 30 °C), a fruit with low pH. CONCLUSION: We suggest that fruits and vegetables should be distributed at temperatures equal to or lower than 10 °C and should not be kept for more than 2 hours at room temperature.
Asunto(s)
Escherichia coli/crecimiento & desarrollo , Frutas/microbiología , Staphylococcus aureus/crecimiento & desarrollo , Verduras/microbiología , TemperaturaRESUMEN
Lactobacillus sakei subsp. sakei 2a is a bacteriocinogenic lactic acid bacterium isolated from Brazilian pork sausage, capable of inhibiting the growth of microbial pathogens, mainly Listeria monocytogenes. In order to optimize bacteriocin production for industrial applications, this study evaluated the effect of supplementation of MRS broth with glucose, Tween 20, Tween 80, sodium citrate, potassium chloride and cysteine, and effect of the initial pH and temperature of incubation of the medium on production of bacteriocins by L. sakei 2a. Adding glucose and Tween 20 to the medium, an initial pH of 5.0 or 5.5, and incubation temperatures of 25 °C or 30 °C resulted to the highest bacteriocin yields. Thus, a 2(4) factorial design with the four variables was performed, and statistical analysis showed that it was an adequate model (R (2) = 0.8296). In the studied range, the four parameters significantly influenced bacteriocin production, with the maximum yield produced at an initial pH between 5.5 and 7.0, a temperature between 25 and 30 °C and supplementation of the MRS broth with glucose from 3.25 to 6.0 g L(-1) and Tween 20 from 0.575 to 1.15% (v/v). Response Surface Methodology analysis indicated that the highest bacteriocin production (12800 AU mL(-1)) occurred in the MRS broth supplemented with 5.5 g L(-1) glucose and 1.05% Tween 20 at an initial pH of 6.28 and an incubation temperature of 25 °C. The amount of bacteriocin produced in commercial MRS broths under the same conditions was only 5600AU mL(-1).