The procedure for thermal inactivation was identical to the thermochemical one except for oregano EO addition. For thermal inactivation, tested temperatures were 95, 97, 100 and 103 °C. In order to test EO emulsion efficiency, a thermochemical resistance with 500 μg/g of EO at 100 °C was performed with the non-emulsified EO. In the case of thermochemical Dabrafenib price treatment, the studied temperatures were 95 and 100 °C, and the EO concentrations were 250, 300, 350, 400, 500 and 1000 μg/g (stage I). Subsequently, the EO concentration was fixed at 400 μg/g and the tested temperatures were 90, 95, 97 and 100 °C (stage II and III). For primary modeling, the Weibull distribution function (Equation (1)) was adjusted
to the experimental data through the program Matlab® (The MathWorks Inc, Natick, USA). equation(1) logN(t)N0=−(tβ)αwhere N0 is the initial number of spores (CFU/mL) and N(t) is the number of spores after t(min) of heat treatment (CFU/mL); β is known as the location factor and α is the shape factor. A general secondary model was used to describe the influence of
temperature on inactivation parameters. The exponential (Equation (2)) was applied as secondary model through Excel software BMS-354825 chemical structure (Microsoft®). equation(2) y=a·exp(c·x)y=a·exp(c·x)where a and c are empirical parameters of the equation; x corresponds to values of temperature (°C); and y corresponds to values of β or α or the time to reach six decimal reductions (t6D). In order to check the quality of the Weibull distribution fit, the following statistical parameters were calculated: correlation coefficient (R2 ), root mean square error (MSE) and 3-oxoacyl-(acyl-carrier-protein) reductase standard deviation (SD). The correlation coefficient (R2 ) measures the fraction of variation over the mean that is explained by a model. The higher the value (0 < R2 < 1), the better the prediction by the model is ( Jin, Zhang, Hermawan, & Dantzer, 2009). The mean square error (Equation (3)) presents the modeling error for data, i.e. how close the predicted values are to observed values ( Zimmermann, Miorelli, Massaguer, & Aragao, 2011). The standard deviation (SD)
of the estimated parameters was calculated with Equation (4). equation(3) MSE=∑(vobserved−vpredicted)2n−p equation(4) SD=∑(vobserved−v¯)2n−1The value of experimental data is given by v observed; the value estimated by the model is given by v predicted; v¯ is the mean value; n is the number of experimental observations and p the number of parameters in the model. Table 1 shows the 21 identified components for oregano EO by GC-MS analyses. Carvacrol (59.44%) is the major component, followed by ρ-cymene (12.27%), γ-terpinene (8.63%), linalool (3.43%) and thymol (2.91%). These molecules represent 86.7% of the fraction of total area of the peaks. According to literature, EO can be composed of more than 60 individual components, where the major components represent around 85% of the EO, and other components exist only as a trace ( Burt, 2004).