Study of inactivation of Lactobacillus plantarum in orange-carrot juice by means of pulsed electric fields: comparison of inactivation kinetics models

Recent developments in minimal processing: a tool to retain nutritional quality of food

The modernization during the last century resulted in urbanization coupled with modifications in lifestyles and dietary habits. In the same era, industrial developments made it easier to meet the requirements for processed foods. However, consumers are now interested in minimally processed foods owing to increase in their awareness to have fruits and vegetables with superior quality, and natural integrity with fewer additives. The food products deteriorate as a consequence of physiological aging, biochemical changes, high respiration rat,e and high ethylene production. These factors contribute substantially to discoloration, loss of firmness, development of off-flavors, acidification, and microbial spoilage. Simultaneously, food processors are using emerging approaches to process perishable commodities, along with enhanced nutritional and sensorial quality. The present review article is an effort to utilize the modern approaches to minimize the processing and deterioration. The techniques discussed in this paper include chlorination, ozonation, irradiation, photosensitization, edible coating, natural preservative use, high-pressure processing, microwave heating, ohmic heating, and hurdle technology. The consequences of these techniques on shelf-life stability, microbial safety, preservation of organoleptic and nutritional quality, and residue avoidance are the limelight of the paper. Moreover, the discussion has been made on the feasibility and operability of these techniques in modern-day processing.

A statistical model for multidimensional irreversible electroporation cell death in tissue

Background

Irreversible electroporation (IRE) is a minimally invasive tissue ablation technique which utilizes electric pulses delivered by electrodes to a targeted area of tissue to produce high amplitude electric fields, thus inducing irreversible damage to the cell membrane lipid bilayer. An important application of this technique is for cancer tissue ablation. Mathematical modelling is considered important in IRE treatment planning. In the past, IRE mathematical modelling used a deterministic single value for the amplitude of the electric field required for causing cell death. However, tissue, particularly cancerous tissue, is comprised of a population of different cells of different sizes and orientations, which in conventional IRE are exposed to complex electric fields; therefore, using a deterministic single value is overly simplistic.

Methods

We introduce and describe a new methodology for evaluating IRE induced cell death in tissue. Our approach employs a statistical Peleg-Fermi model to correlate probability of cell death in heterogeneous tissue to the parameters of electroporation pulses such as the number of pulses, electric field amplitude and pulse length. For treatment planning, the Peleg-Fermi model is combined with a numerical solution of the multidimensional electric field equation cast in a dimensionless form. This is the first time in which this concept is used for evaluating IRE cell death in multidimensional situations.

Results

We illustrate the methodology using data reported in literature for prostate cancer cell death by IRE. We show how to fit this data to a Fermi function in order to calculate the critical statistic parameters. To illustrate the use of the methodology, we simulated 2-D irreversible electroporation protocols and produced 2-D maps of the statistical distribution of cell death in the treated region. These plots were compared to plots produced using a deterministic model of cell death by IRE and the differences were noted.

Conclusions

In this work we introduce a new methodology for evaluation of tissue ablation by IRE using statistical models of cell death. We believe that the use of a statistical model rather than a deterministic model for IRE cell death will improve the accuracy of treatment planning for cancer treatment with IRE.

Kinetic study of anthocyanins, vitamin C, and antioxidant capacity in strawberry juices treated by high-intensity pulsed electric fields

A kinetic study of anthocyanins, vitamin C, and antioxidant capacity was carried out in strawberry juice treated with high-intensity pulsed electric fields. Samples were subjected to electric field strengths from 20 to 35 kV/cm for up to 2000 mus applying 1 mus bipolar pulses at 232 Hz. The suitability of simple first-order kinetics and an empirical model based on Weibull distribution function to describe changes in experimental data are discussed. In addition, different secondary models relating the antioxidant property retention to the electric field strength and treatment time are given. The Weibull kinetic model was the most accurate ( R (2) adj >or= 0.727) to predict anthocyanins, vitamin C, and antioxidant capacity changes in strawberry juice through the HIPEF treatment time. The combined effect of treatment time and electric field strength on health-related compounds of strawberry juice was successfully predicted (R(2) adj >or= 0.874) through secondary expressions. The proposed models are useful to predict the variation of the antioxidant potential of strawberry juice with the key parameters involved in HIPEF treatments.

Effects of sonication on the kinetics of orange juice quality parameters

The effects of sonication on pH, degrees Brix, titratable acidity (TA), cloud, browning index, and color parameters ( L*, a*, and b*) of freshly squeezed orange juice samples were studied. Ultrasonic intensity (UI) levels of 8.61, 9.24, 10.16, 17.17, and 22.79 W/cm2 and treatment times of 0 (control), 2, 4, 6, 8, and 10 min were investigated. No significant changes in pH, degrees Brix, and TA ( p < 0.05) were found. Cloud value, browning index, and color parameters were significantly affected by ultrasonic intensity and treatment time. Changes in cloud value followed first-order kinetics, whereas browning index, L*, a*, and b* values followed zero-order kinetics. Reaction rate constants were linearly correlated ( R2 > 0.90) to ultrasonic intensity.

Refrigerated fruit juices: quality and safety issues

Fruit juices are an important source of bioactive compounds, but techniques used for their processing and subsequent storage may cause alterations in their contents so they do not provide the benefits expected by the consumer. In recent years consumers have increasingly sought so-called "fresh" products (like fresh products), stored in refrigeration. This has led the food industry to develop alternative processing technologies to produce foods with a minimum of nutritional, physicochemical, or organoleptic changes induced by the technologies themselves. Attention has also focused on evaluating the microbiological or toxicological risks that may be involved in applying these processes, and their effect on food safety, in order to obtain safe products that do not present health risks. This concept of minimal processing is currently becoming a reality with conventional technologies (mild pasteurization) and nonthermal technologies, some recently introduced (pasteurization by high hydrostatic pressure) and some perhaps with a more important role in the future (pulsed electric fields). Nevertheless, processing is not the only factor that affects the quality of these products. It is also necessary to consider the conditions for refrigerated storage and to control time and temperature.

Carotenoid profile modification during refrigerated storage in untreated and pasteurized orange juice and orange juice treated with high-intensity pulsed electric fields

A comparative study was made of the evolution and modification of various carotenoids and vitamin A in untreated orange juice, pasteurized orange juice (90 degrees C, 20 s), and orange juice processed with high-intensity pulsed electric fields (HIPEF) (30 kV/cm, 100 micros), during 7 weeks of storage at 2 and 10 degrees C. The concentration of total carotenoids in the untreated juice decreased by 12.6% when the juice was pasteurized, whereas the decrease was only 6.7% when the juice was treated with HIPEF. Vitamin A was greatest in the untreated orange juice, followed by orange juice treated with HIPEF (decrease of 7.52%) and, last, pasteurized orange juice (decrease of 15.62%). The decrease in the concentrations of total carotenoids and vitamin A during storage in refrigeration was greater in the untreated orange juice and the pasteurized juice than in the juice treated with HIPEF. During storage at 10 degrees C, auroxanthin formed in the untreated juice and in the juice treated with HIPEF. This carotenoid is a degradation product of violaxanthin. The concentration of antheraxanthin decreased during storage, and it was converted into mutatoxanthin, except in the untreated and pasteurized orange juices stored at 2 degrees C.

Effect of high-intensity pulsed electric fields processing and conventional heat treatment on orange-carrot juice carotenoids

Liquid chromatography (LC) was the method of choice for quantification of carotenoids (including geometrical isomers) to evaluate the effects of high-intensity pulsed electric field (HIPEF), a nonthermal preservation method, with different parameters (electric field intensities and treatment times), on an orange-carrot juice mixture (80:20, v/v). In parallel, a conventional heat treatment (98 degrees C, 21 s) was applied to the juice. HIPEF processing generally caused a significant increase in the concentrations of the carotenoids identified as treatment time increased. HIPEF treatment at 25 and 30 kV/cm provided a vitamin A concentration higher than that found in the pasteurized juice.

Modelling inactivation of Listeria monocytogenes by pulsed electric fields in media of different pH

A study of the effect of square-wave pulsed electric fields (PEF) on the inactivation of Listeria monocytogenes in McIlvaine buffer of different pH (3.5-7.0) was conducted. L. monocytoges was more PEF sensitive at higher electric field strengths (E) and in media of low pH. A treatment at 28 kV/cm for 400 mus that inactivated 1.5, 2.3 and 3.0 Log10 cycles at pH 7.0, 6.5 and 5.0 respectively destroyed almost 6.0 Log10 cycles at pH 3.5. The general shape of survival curves of L. monocytogenes PEF treated at different pH was convex/concave upwards. A mathematical model based on the Weibull distribution accurately described these survival curves. At each pH, the shape parameter (n value) did not depend on E. The relationship between n value of the Weibull model and the pH of the treatment medium was described by the Gompertz equation. A multiple linear regression model using three predictor variables (E, E2, pH2) related the Log10 of the scale paramenter (b value) of the Weibull model with E and pH of the treatment medium. A tertiary model developed using McIlvaine buffer as treatment medium predicted satisfactorily the inactivation of L. monocytogenes in apple juice.

Modeling of Escherichia coli inactivation by UV irradiation at different pH values in apple cider

This study examined the effects and interactions of UV light dose (1,800 to 20,331 microJ/cm2) and apple cider pH (2.99 to 4.41) on the inactivation of Escherichia coli ATCC 25922, a surrogate for E. coli O157:H7. A predictive model was developed to relate the log reduction factor of E. coli ATCC 25922 to the UV dose. Bacterial populations for treated and untreated samples were enumerated with the use of nonselective media. The results revealed that UV dose was highly significant in the inactivation of E. coli, whereas pH showed no significant effect at higher UV doses. Doses of 6,500 microJ/cm2 or more were sufficient to achieve a greater than 5-log reduction of E. coli. Experimental inactivation data were fitted adequately by a logistic regression model. UV irradiation is an attractive alternative to conventional methods for reducing bacteria in unpasteurized apple cider.

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.

Modelling and optimization of inactivation of Lactobacillus plantarum by pulsed electric field treatment

AIMS

The effect of critical pulsed electric field (PEF) process parameters, such as electric field strength, pulse length and number of pulses, on inactivation of Lactobacillus plantarum was investigated.

METHODS AND RESULTS

Experiments were performed in a pH 4.5 sodium phosphate buffer having a conductivity of 0.1 S m-1, using a laboratory-scale continuous PEF apparatus with a co-linear treatment chamber. An inactivation model was developed as a function of field strength, pulse length and number of pulses. Based on this inactivation model, the conditions for a PEF treatment were optimized with respect to the minimum energy required to obtain a certain level of inactivation. It was shown that the least efficient process parameter in the range investigated was the number of pulses. The most efficient way to optimize inactivation of Lact. plantarum was to increase the field strength up to 25.7 kV cm-1, at the shortest pulse length investigated, 0.85 micros, and using a minimum number of pulses. The highest inactivation of Lact. plantarum at the lowest energy costs is obtained by using the equation: E=26.7tau0.23, in which E is the field strength and tau the pulse length. An optimum is reached by substituting tau with 5.1.

CONCLUSIONS

This study demonstrates that the correct choice of parameters, as predicted by the model described here, can considerably improve the PEF process.

SIGNIFICANCE AND IMPACT OF THE STUDY

The knowledge gained in this study improves the understanding of the limitations and opportunities of the PEF process. Consequently, the advantage of the PEF process as a new option for non-thermal decontamination can be better utilized.

Improved model based on the Weibull distribution to describe the combined effect of pH and temperature on the heat resistance of Bacillus cereus in carrot juice

The effect of pH and temperature on the thermal inactivation of different strains of Bacillus cereus was modeled. Inactivation tests were carried out in carrot broth, following a full factorial design at four levels for temperature (from 90 to 105 degrees C, depending on the strain) and pH (6.2, 5.8, 5.2, and 4.7). Individual inactivation curves were analyzed by applying the Weibull model function (with percent discrepancy close to 20% for most cases), and the effects of pH and temperature on the scale parameter (designated D(beta)) and the shape parameter (beta) were also studied. Temperature and pH did not have a significant effect on the shape parameter (beta). The effect of temperature on the scale parameter was modeled by the zeta concept. The scale parameter decreased with pH, although the behavior of the strains was not homogeneous. Two global models with a small number of parameters were developed, providing a satisfactory description of the thermal inactivation of B. cereus, with percent discrepancy ranging from 18 to 25%.