## 3 Results and Discussion
Moreover, other researchers [5] applied high-pressure treatment at 600 MPa/45 \({}^{\circ}\)C for 10 min using a 10 \({}^{\circ}\)Brix broth medium (close to 11.45 \({}^{\circ}\)Brix of the orange juice employed in this study) and reported 1.2 log-cycles reduction of _A. acidoterrestris_ spores. Complete spore inactivation was achieved at 600 MPa/70 \({}^{\circ}\)C and 500 MPa/70 \({}^{\circ}\)C after 20 and 30 min, respectively (Figures 1 and 2). Comparing the two strains, it can be underlined that the wild-type strain A was less resistant to high-pressure treatment compared to the reference strain B at all temperatures assayed (45 and 60 \({}^{\circ}\)C) with the exception of 70 \({}^{\circ}\)C where stain A was proved more resistant (Figures 1 and 2). Specifically, strain A presented 5 log-cycles' reduction when treated at 500 MPa/60 \({}^{\circ}\)C and 600 MPa/60 \({}^{\circ}\)C for 15 min, whereas the respective reduction for strain B under the same conditions was 3 log-cycles. For complete spore inactivation, a treatment at 600 MPa/70 \({}^{\circ}\)C for 15 and 20 min was necessary for strains B and A, respectively (Figures 1 and 2). This difference in high-pressure  
Figure 1: Inactivation curves of _A. acidoterrestris_ spores at 500 MPa and 45 \({}^{\circ}\)C (\(\blacklozenge\)), 60 \({}^{\circ}\)C (\(\blacklozenge\)) and 70 \({}^{\circ}\)C (\(\bullet\)). Solid lines represent data fitting with the Weibull model. Data are mean values of two replications \(\pm\) standard deviation. Figure 2: Inactivation curves of _A. acidoterrestris_ spores at 600 MPa and 45 \({}^{\circ}\)C (\(\blacklozenge\)), 60 \({}^{\circ}\)C (\(\blacklozenge\)) and 70 \({}^{\circ}\)C (\(\bullet\)). Solid lines represent data fitting with the Weibull model. Data are mean values of two replications \(\pm\) standard deviation. tolerance could be attributed to the fact that the effectiveness of HHP against _A. acidoterrestris_ spores is strain-dependent [9; 41], possibly due to the different distribution of fatty acids in the cytoplasmatic membrane of the bacterium [9; 42]. Furthermore, other factors that may affect HPP thermal resistance include the number and age of spores, protoplast dehydration and sporulation temperature [43]. The inactivation curves of both strains A and B of _A. acidoterrestris_ spores fitted with the Weibull model are also depicted in Figures 1 and 2, respectively. The model provided a good fit enabling the study of inactivation of _A. acidoterrestris_ spores through the variation of \(\delta\) and \(p\) parameters (Table 1). Concave upward (\(p<1\)) inactivation curves were observed at all temperature/high-pressure combinations tested (Table 1). From this type of concavity we can assume that spores presented a mixed resistance to inactivation treatment [38; 39] and the remaining spores were more resistant or maybe they could adapt better to stressful conditions and therefore have higher possibility to survive. The fitting capacity of the model was evaluated by estimating the RMSE and the R\({}^{2}\) values. The mean values of RMSE were 0.421 log CFU/mL and 0.281 log CFU/mL for strain A at 500 and 600 MPa, respectively, whereas for strain B the RMSE mean values were 0.281 log CFU/mL and 0.418 log CFU/mL at the same high-pressure levels. In addition, the R\({}^{2}\) values for most curves were higher than 0.940 indicating that the Weibull model fitted the experimental data closely, justifying thus its use to describe the inactivation kinetics of _A. acidoterrestris_ (Table 1). The Weibull model has been extensively used in previous works to model the inactivation of _A. acidoterrestris_ due to its simplicity and flexibility. Specifically, [PERSON] and [PERSON] [5] reported the successful use of the Weibull model during HHP treatment at 600 MPa combined with different temperatures (35, 45, 55, and 65 \({}^{\circ}\)C) in malt extract broth adjusted to 10, 20 and 30 \({}^{\circ}\)Brix for the inactivation of _A. acidoterrestris_ spores. In addition, it has been successfully employed to model the inactivation kinetics of _A.