D. Rodrigo

Study of Inactivation of Lactobacillus plantarum in Orange-Carrot Juice by Means of Pulsed Electric Fields: Comparison of Inactivation Kinetics Models

The inactivation kinetics of Lactobacillus plantarum was studied in orange-carrot juice using high intensity pulsed electric fields. The results indicated that under the treatment conditions applied, 28.6, 32.0, and 35.8 kV/cm and treatment times ranging from 10.2 to 46.3 micros, the inactivation of L. plantarum obtained was up to 2.5 decimal reductions. Experimental and literature data were fitted to Bigelow, Hülsheger et al. and Peleg models and to Weibull frequency distribution function. Weibull was the one that best interpreted the data with accuracy factor values closer to 1.

Kinetic model for the inactivation of Lactobacillus plantarum by pulsed electric fields

The kinetics of Lactobacillus plantarum inactivation by pulsed electric fields (PEF) was studied in two different growth stages (exponential and stationary), but in the same reference medium (0.6% peptone water). Electric field intensity and treatment time varied from 20 to 28 kV/cm and 30 to 240 micros, respectively. The experimental data showed that cells in the exponential growth stage were more sensitive to PEF treatment than those in the stationary stage. The inactivation data were adjusted to the Bigelow and Hülsheger models and the Weibull frequency distribution function, and constants were calculated for both growth stages in each model. The models were tested and their accuracy was assessed by using the Accuracy Factor. According to this parameter, the Weibull frequency distribution function gave better fittings for the inactivation by PEF than Bigelow or Hülsheger models. On the other hand, the Bigelow model gave a good accuracy factor and is simpler.

Pectin Methyl Esterase and Natural Microflora of Fresh Mixed Orange and Carrot Juice Treated with Pulsed Electric Fields

The effects of pulsed electric fields (PEFs) on pectin methyl esterase (PME), molds and yeast, and total flora in fresh (nonpasteurized) mixed orange and carrot juice were studied. The PEF effect was more extensive when juices with high levels of initial PME activity were subjected to treatment and when PEF treatment (at 25 kV/cm for 340 micros) was combined with a moderate temperature (63 degrees C), with the maximum level of PME inactivation being 81.4%. These conditions produced 3.7 decimal reductions in molds and yeast and 2.4 decimal reductions in total flora. Experimental inactivation data for PME, molds and yeast, and total flora were fitted to Bigelow, Hülsheger, and Weibull inactivation models by nonlinear regression. The best fit (lowest mean square error) was obtained with the Weibull model.

Quality and safety aspects of PEF application in milk and milk products.

Abstract The articles published to date on the possibilities of applying the new PEF technology to milk and milk products are summarized in a review that presents them in chronological order and grouped on the basis of the factor studied (microorganism, enzyme, quality parameter, or shelf-life). An accompanying table shows details of the equipment and process corresponding to each article in chronological order.

Weibull distribution function based on an empirical mathematical model for inactivation of Escherichia coli by pulsed electric fields.

The pulsed electric field inactivation kinetics of Escherichia coli suspended in orange juices with three different concentrations of carrot juice (0, 20, and 60%) was studied. Electric field strengths ranged from 25 to 40 kV/cm, and treatment times ranged from 40 to 340 micros. Experimental data were fitted to Bigelow, Hülsheger, and Weibull distribution functions, and the Weibull function provided the best fit (with the lowest mean square error). The dependency of each models kinetic constant on electric field strength and carrot juice concentration was studied. A secondary model was developed to describe the relationship of Weibull parameters a and n to electric field strength and carrot juice concentration. An empirical mathematical model based on the Weibull distribution function, relating the natural logarithm of the survival fraction to treatment time, electric field strength, and carrot juice concentration, was developed. Parameters were estimated by a nonlinear regression. The results of this study indicate that the error rate for the models predictions was 6.5% and that the model was suitable for describing E. coli inactivation.

Synergistic effect of pulsed electric fields and CocoanOX 12% on the inactivation kinetics of Bacillus cereus in a mixed beverage of liquid whole egg and skim milk.

With a view to extending the shelf-life and enhancing the safety of liquid whole egg/skim milk (LWE-SM) mixed beverages, a study was conducted with Bacillus cereus vegetative cells inoculated in skim milk (SM) and LWE-SM beverages, with or without antimicrobial cocoa powder. The beverages were treated with Pulsed Electric Field (PEF) technology and then stored at 5 degrees C for 15 days. The kinetic results were modeled with the Bigelow model, Weibull distribution function, modified Gompertz equation, and Log-logistic models. Maximum inactivation registered a reduction of around 3 log cycles at 40 kV/cm, 360 micros, 20 degrees C in both the SM and LWE-SM beverages. By contrast, in the beverages supplemented with the aforementioned antimicrobial compound, higher inactivation levels were obtained under the same treatment conditions, reaching a 3.30 log(10) cycle reduction. The model affording the best fit for all four beverages was the four-parameter Log-logistic model. After 15 days of storage, the antimicrobial compound lowered Bacillus cereus survival rates in the samples supplemented with CocoanOX 12% by a 4 log cycle reduction, as compared to the untreated samples without CocoanOX 12%. This could indicate that the PEF-antimicrobial combination has a synergistic effect on the bacterial cells under study, increasing their sensitivity to subsequent refrigerated storage.

Stevia rebaudiana Bertoni as a natural antioxidant/antimicrobial for high pressure processed fruit extract: Processing parameter optimization

Response surface methodology was used to evaluate the optimal high pressure processing treatment (300-500 MPa, 5-15 min) combined with Stevia rebaudiana (Stevia) addition (0-2.5% (w/v)) to guarantee food safety while maintaining maximum retention of nutritional properties. A fruit extract matrix was selected and Listeria monocytogenes inactivation was followed from the food safety point of view while polyphenoloxidase (PPO) and peroxidase (POD) activities, total phenolic content (TPC) and antioxidant capacity (TEAC and ORAC) were studied from the food quality point of view. A combination of treatments achieved higher levels of inactivation of L. monocytogenes and of the oxidative enzymes, succeeding in completely inactivating POD and also increasing the levels of TPC, TEAC and ORAC. A treatment of 453 MPa for 5 min with a 2.5% (w/v) of Stevia succeeded in inactivating over 5 log cycles of L. monocytogenes and maximizing inactivation of PPO and POD, with the greatest retention of bioactive components.

Inactivation of human and murine norovirus by high-pressure processing.

The effect of high hydrostatic pressure (HPP) was evaluated for inactivation of murine norovirus (MNV), a propagable norovirus (NoV), and human NoV genogroup II.4. Inactivation of MNV was assessed by viral culturing (50% tissue culture infectious dose [TCID(50)]) and real-time reverse-transcription-polymerase chain reaction (RT-qPCR), whereas NoV survival was determined only by RT-qPCR. A treatment of 450 MPa for 15 min at 45°C was sufficient to inactivate 6.5 log(10) of infectious MNV in culture medium as determined by TCID(50). Further, the inactivation of MNV was enhanced when pressure was applied at an initial temperature of 25°C. On the other hand, a baroprotective effect was observed when MNV suspensions were supplemented with 10 mM of CaCl(2). A 400 MPa treatment at 45°C inactivated >5 log(10) of infectious MNV, whereas the addition of CaCl(2) increased the pressure resistance of MNV, with <0.5 log(10) reduction observed. MNV decay as determined by TCID(50) was generally greater than that determined by RT-qPCR; for instance, MNV genomes were detected even after 15 min treatment at 450 MPa, with <0.5 log(10) reduction. Experiments with NoV suspensions showed that all tested HPP treatments reduced the numbers of NoV by <0.5 log(10) units as determined by RT-qPCR. Additionally, RNA of human NoV was more resistant to certain HPP treatments than the RNA of MNV.

Chlorophylls and carotenoids of kiwifruit puree are affected similarly or less by microwave than by conventional heat processing and storage.

The impact of microwave (1000 W - 340 s) and conventional heat (97 °C - 30s) pasteurisation and storage (4, 10, 22 °C for up to 63 d) on total and individual carotenoids and chlorophylls in kiwifruit puree was evaluated. Bioaccessibility of carotenoids, before and after pasteurisation and storage, was also studied. Microwaves and conventional heating led to marked changes in the chlorophyll (42-100% losses) and carotenoid (62-91% losses) content. First- and second-order kinetics appropriately explained the degradation of total carotenoids and chlorophylls over time, respectively. Pasteurised samples showed significantly (p < 0.05) enhanced stability of these pigments, with microwaves (k = 0.007-0.031100 g mg(-1) day(-1) at 4-22 °C) promoting chlorophyll stability to a greater extent than conventional heating (k = 0.0015-0.034100 g mg(-1) day(-1) at 4-22 °C). Bioaccessibility of carotenoids remained (p < 0.05) unaffected by processing and storage. These results highlighted that the pigment composition of microwaved kiwifruit was more similar to that of the fresh fruit and better preserved during storage.

Review: Application of Pulsed Electric Fields in Egg and Egg Derivatives

This work overviews works published on the application of pulsed electric fields (PEF) in egg and egg derivatives, grouped by subject, and arranged chronologically in terms of the factor studied (microorganisms, quality aspects, shelf life and structural changes in gel formation properties). The inactivation of microorganisms by PEF in egg is very considerable, 3.5 decimal reductions in egg white were achieved by PEF in Salmonella enteritidis, 5.5 log reductions of Listeria innocua by means of a synergistic effect of PEF and nisin in liquid whole egg, and 5.6 log reductions of Escherichia coli in beaten fresh liquid egg by PEF treatment applied continuously or discontinuously in five steps. The shelf life of PEF-treated fresh liquid egg was extended to 4 weeks in refrigeration, and quality (colour, viscosity and sensory attributes) was not affected by PEF treatment. PEF treatment did not cause notable changes in proteins in a solution of ovalbumin and dialysed fresh egg white. However, some structural changes and functional modifications were observed in fresh egg white as a result of PEF treatment. The texture and microstructure of gels were affected by the application of PEF, and therefore PEF treatment conditions in egg white must be optimised to minimise possible modifications.