Modeling the pressure inactivation of Escherichia coli and Salmonella typhimurium in sapote mamey ( Pouteria sapota (Jacq.) H.E. Moore & Stearn) pulp.

High hydrostatic pressure inactivation kinetics of Escherichia coli ATCC 25922 and Salmonella enterica subsp. enterica serovar Typhimurium ATCC 14028 ( S. typhimurium) in a low acid mamey pulp at four pressure levels (300, 350, 400, and 450 MPa), different exposure times (0-8 min), and temperature of 25 ± 2℃ were obtained. Survival curves showed deviations from linearity in the form of a tail (upward concavity). The primary models tested were the Weibull model, the modified Gompertz equation, and the biphasic model. The Weibull model gave the best goodness of fit ( R2adj > 0.956, root mean square error < 0.290) in the modeling and the lowest Akaike information criterion value. Exponential-logistic and exponential decay models, and Bigelow-type and an empirical models for b'( P) and n( P) parameters, respectively, were tested as alternative secondary models. The process validation considered the two- and one-step nonlinear regressions for making predictions of the survival fraction; both regression types provided an adequate goodness of fit and the one-step nonlinear regression clearly reduced fitting errors. The best candidate model according to the Akaike theory information, with better accuracy and more reliable predictions was the Weibull model integrated by the exponential-logistic and exponential decay secondary models as a function of time and pressure (two-step procedure) or incorporated as one equation (one-step procedure). Both mathematical expressions were used to determine the td parameter, where the desired reductions ( 5D) (considering d = 5 ( t5) as the criterion of 5 Log10 reduction (5 D)) in both microorganisms are attainable at 400 MPa for 5.487 ± 0.488 or 5.950 ± 0.329 min, respectively, for the one- or two-step nonlinear procedure.

Prediction of Mechanical Properties and Subjective Consistency of Meningiomas Using T1-T2 Assessment Versus Fractional Anisotropy.

OBJECTIVE: This study aims to evaluate quantitatively the mechanical properties of meningiomas and their correlation with the qualitative surgeon's assessment of consistency, as well as comparing the capability to predict tumor consistency of fractional anisotropy values calculated from the diffusion tensor imaging and T1/T2 signal intensities. METHODS: Sixteen patients with the diagnosis of intracranial meningioma were included. Fractional anisotropy values were calculated and T1/T2 assessment was performed. The qualitative assessment of the tumor consistency intraoperatively was determined by a neurosurgeon and quantitative assessment was obtained with the Warner-Bratzler mechanical test. RESULTS: Surgeon's qualitative assessment was concordant with the cutting force obtained from the mechanical tests (P = 0.046). There was a high correlation between tumor consistency reported by the surgeon and T1/T2 assessment (0.622/P = 0.01) and a moderate correlation with cutting force (0.532/P = 0.034) and elasticity (0.49/P = 0.05). Fractional anisotropy values for hard tumors were not significantly higher than for soft tumors (P = 0.115). There was no significant correlation between the fractional anisotropy and mechanical measurements (0.192/P = 0.3). Predictions of hard consistency in meningiomas were obtained with a sensitivity of 25% and a specificity of 100% when using the T1/T2 assessment and a sensitivity of 87.5% and a specificity of 50% when using the fractional anisotropy value. CONCLUSIONS: Qualitative surgeon's assessment was in accordance with measured mechanical properties. Fractional anisotropy value was not an independent predictor for tumor consistency and was not correlated with the mechanical tests results. T1/T2 assessment was correlated with mechanical properties and it can be used to discriminate very hard or soft tumors.

Enzymatic synthesis of poly-L-lactide and poly-L-lactide-co-glycolide in an ionic liquid.

The syntheses of poly-L-lactide (PLLA) and poly-L-lactide-co-glycolide (PLLGA) is reported in the ionic liquid 1-hexyl-3-methylimidazolium hexafluorophosphate [HMIM][PF(6)] mediated by the enzyme lipase B from Candida antarctica (Novozyme 435). The highest PLLA yield (63%) was attained at 90 degrees C with a molecular weight (M(n)) of 37.8 x 10(3) g/mol determined by size exclusion chromatography. This procedure produced relatively high crystalline polymers (up to 85% PLLA) as determined by DSC. In experiments at 90 degrees C product synthesis also occurred without biocatalyst, however, PLLA synthesis in [HMIM][PF(6)] at 65 degrees C followed only the enzymatic mechanism as ring opening was not observed without the enzyme. In addition, the enzymatic synthesis of PLLGA is first reported here using Novozyme 435 biocatalyst with up to 19% of lactyl units in the resulting copolymer as determined by NMR. Materials were also characterized by TGA, MALDI-TOF-MS, X-ray diffraction, polarimetry and rheology.