Pasteurization Of Liquid Foods Research Articles

Behavior of the surviving population of Lactobacillus plantarum 564 upon the application of pulsed electric fields

The behavior of the surviving population of Lactobacillus plantarum 564 growing in MRS broth after pulsed electric field (PEF) treatments of different intensities was monitored by isothermal calorimetry, optical density and plate counts. Bacterial cells were treated with monopolar square pulses at varying nominal electric field strengths and number of pulses, corresponding to applied energies of 34.6, 65.8 and 658.1 J/cm3. After the PEF treatment, samples were inoculated into the MRS broth and incubated at 37 °C. The presented results show that surviving bacterial cells resume growth after a treatment-dependent delay. Both the untreated and treated cultures had similar growth rates, but the latter showed a higher growth rate during the late-growth phase, and the growth rate increased with the intensity of applied electric field. After the PEF treatment, the surviving population of bacteria was less susceptible to killing by further PEF application, showing that this subpopulation was less sensitive to the PEF treatment and could grow again. The application of pulsed electric field (PEF) technology as a non-thermal alternative to traditional pasteurization of liquid foods has received considerable attention during the last years. Effective inactivation for most of the spoilage and pathogenic microorganisms has been shown in fruit and vegetable juices and milk with little or no impact on nutritional and sensorial properties of the food. However, very little is known about the growth abilities of the surviving population. Ensuring food safety requires a better understanding of the behavior of the surviving populations of microorganisms which may be recovering from sub lethal injury, such as PEF-induced stress. This paper reveals that the surviving population of the bacteria subjected to the PEF treatment could grow again, showing higher growth rates as the intensity of the PEF treatment increased. Also, the new bacterial population showed higher resistance to further PEF treatment. Therefore, for industrial application of the PEF technology, an in-depth characterization of surviving microorganisms in the treated product is required. Moreover, the evidence of bacterial persistence indicates that the PEF technology, as a non-thermal alternative to traditional pasteurization, could not completely replace thermal treatment, but can be applied as a supplement treatment.

Combination of Microsecond and Nanosecond Pulsed Electric Field Treatments for Inactivation of Escherichia coli in Water Samples

Inactivation of microorganisms with pulsed electric fields is one of the nonthermal methods most commonly used in biotechnological applications such as liquid food pasteurization and water treatment. In this study, the effects of microsecond and nanosecond pulses on inactivation of Escherichia coli in distilled water were investigated. Bacterial colonies were counted on agar plates, and the count was expressed as colony-forming units per milliliter of bacterial suspension. Inactivation of bacterial cells was shown as the reduction of colony-forming units per milliliter of treated samples compared to untreated control. According to our results, when using microsecond pulses the level of inactivation increases with application of more intense electric field strengths and with number of pulses delivered. Almost 2-log reductions in bacterial counts were achieved at a field strength of 30 kV/cm with eight pulses and a 4.5-log reduction was observed at the same field strength using 48 pulses. Extending the duration of microsecond pulses from 100 to 250 μs showed no improvement in inactivation. Nanosecond pulses alone did not have any detectable effect on inactivation of E. coli regardless of the treatment time, but a significant 3-log reduction was achieved in combination with microsecond pulses.

Pasteurization of grapefruit juice using a centrifugal ultraviolet light irradiator

Studies are lacking on the nonthermal pasteurization of liquid foods using UV irradiators that centrifugally form very thin films to overcome the problem of limited penetration depth of UV. Grapefruit juice inoculated with Escherichia coli or Saccharomyces cerevisiae was processed at the following conditions: UV dose 4.8–24mJ/cm2; treatment time 3.2s, cylinder rotational speed 450–750rpm, cylinder inclination angle 15–45°, outlet temperature 11°C, and flow rate 300ml/min, and was stored for 35days. Appropriate dilutions of the samples were pour plated with TSA and TSA+3% NaCl for E. coli and Sabouraud dextrose agar (SDA) and SDA+5% NaCl for S. cerevisiae. Nonthermal UV processing at 19mJ/cm2, 450rpm and 15° reduced E. coli in grapefruit juice by 5.1log10. A dose of 14mJ/cm2 reduced S. cerevisiae by 6.0log10. Inactivation increased linearly with increasing UV dose. The inactivations at 600 and 750rpm were similar, and were better than at 450rpm. The results at 30° and 45° were similar, and were better than at 15°. The occurrence of sublethal injury in either microorganism was not detected. Storing UV processed grapefruit juice at 4 and 10°C reduced the surviving E. coli to below 1log10cfu/ml in 14days. Processing UV juice reduced the population of S. cerevisiae to less than 1log10cfu/ml where it remained for 35days during refrigerated storage. These results suggest that grapefruit juice may be pasteurized using a nonthermal UV irradiator that centrifugally forms a thin film.

Mathematical simulation of liquid food pasteurization using far infrared radiation heating equipment

In this study, pasteurization equipment using far-infrared radiation (FIR) was developed for liquid food. The temperature was measured at various conditions to investigate the heating effect. With the liquid food passing down an angled trough and FIR applied from above, the temperature changed with the radiation intensity (electricity supplied), the angle of the incline, and the flow rate. As the liquid film became thinner, the temperature could be heated to nearly 80°C. The pasteurization effect was verified using lactic acid bacteria as the target microorganism; the heat resistance of the bacteria was measured, the death of bacteria was confirmed, and the effectiveness of the equipment was verified. Furthermore, a mathematical model for FIR pasteurization was developed using a heat transfer equation and thermal death equation. The simulation could make predictions about temperature and the viable count of bacteria that compared very well with the experimental results. Moreover, the model simulated the change of temperature and viable count of bacteria at different flow rates, and showed that it is possible to sterilize at low temperatures with this equipment.

Experimental Measurements and Thermodynamic Modeling of CO2 Solubility at High Pressure in Model Apple Juices

High pressure carbon dioxide (HPCD) treatment can be used for the pasteurization of liquid foods. Solubility of CO2 in the liquid affects microbial inactivation. Measurement and prediction of CO2 solubility in a real or model system are of industrial relevance since the knowledge of the solubility limits will avoid the use of excess CO2. An experimental apparatus was set up to measure CO2 solubility in ternary mixtures of water−CO2−glucose and water−CO2−malic acid and in a quaternary mixture of water−CO2−malic acid−glucose at different concentrations of malic acid (0.01 and 2.68 g in 100 g of solution, corresponding to 7.5 × 10−5 and 0.02 mols in 100 mols of solution) and of glucose (4 and 12 g in 100 g of solution, corresponding to 0.02 and 0.07 mols in 100 mols of solution). CO2 solubility was also measured in a more complex solution of water−malic acid−ascorbic acid−pectin−glucose−sucrose, based on apple juice composition and in a commercial apple juice. The range of pressure tested was between 7.5 and...

Development of Liquid Food Pasteurization Equipment Using Far-infrared Radiation Heating

Development of Liquid Food Pasteurization Equipment Using Far-infrared Radiation Heating

Heat conduction in microbes exposed to pulsed electric fields

Nonthermal pasteurization of liquid foods by intense pulsed electric fields results in advantages over conventional heat pasteurization. Thermal damage to liquid foods can adversely affect the flavor and taste and result in loss of nutrients. Numerical modeling of heating parameters near the microbe during exposure to these intense electric fields is described. Boundary conditions at membrane interfaces included the continuity of temperature and continuity of heat flow. Temperature, heat flow vector, and heat source were included in the one-dimensional model. Two simulations are reported here. Simulation 1 consisted of a 0.5 /spl mu/m wide microbe suspended in liquid with conductivity of 0.01 S/m and was treated with an applied electric field of 40 kV/cm for 375 ns. Simulation 2 contained a 1.0 /spl mu/m wide microbe suspended in liquid with conductivity of 0.1 S/m and was treated with an applied electric field of 40 kV/cm for 1 /spl mu/s. Comparison is made with a uniform conductivity model (ohmic), and it is shown that significant differences exist in the heating parameters between the two models. For the parameters used in these one-dimensional simulations, conditions for electroporation were found to exist without a significant temperature rise in the microbe.

Inactivating microorganisms using a pulsed electric field continuous treatment system

High-voltage pulsed electric fields (PEFs) can be used to inactivate microorganisms in liquids. Applying PEF technology to food pasteurization is a promising nonthermal method, which may radically change food preservation processes and provide consumers with microbiologically safe, minimally processed, fresh-like products. A continuous-flow system in a laboratory-size prototype was constructed for the nonthermal pasteurization of liquid foods with PEF technology. Major components in the prototype include a high-voltage repetitive pulse generator, a coaxial liquid food treatment chamber, a fiber-optic temperature sensing instrument and a data acquisition system. Microbial inactivation tests were conducted in the continuous PEF treatment system. Repetitive high-voltage pulses with an exponential decaying waveshape were applied to the liquid food which was pumped through the treatment chamber. Test microorganisms selected for inactivation were Escherichia coli, Staphylococcus aureus and Saccharomyces cerevisiae. Over 6-order-of-magnitude reductions in the viability of selected microorganisms were achieved while the food temperature was maintained below 40/spl deg/C.

Electrical environment surrounding microbes exposed to pulsed electric fields

Inactivation of microbes by the application of intense pulsed electric fields (/spl sime/10 to 40 kV/cm) could result in low-temperature pasteurization of liquid foods. Advantages over conventional heat pasteurization include longer shelf-life, better flavor, and less enzyme damage. Numerical modeling of electrical parameters near the microbe during exposure to these intense electric fields is described. The continuity equation describes movement of positive and negative ions while Gauss's law yields the electric field after movement of the ions. One negative ionic species and one positive ionic species are assumed to be in the suspension fluid and protoplasm of the microbe. The microbe membrane is modeled as a nonconducting dielectric. With application of unidirectional electric fields, free volume and free surface charge densities form along the membrane. Comparison is made with a uniform conductivity model and it is shown that significant differences exist in parameters such as ion concentration, free surface charge density, free volume charge density, heat sources due to conduction current, and ionic injection at membrane surfaces.

Nonthermal pasteurization of liquid foods using high-intensity pulsed electric fields.

Processing foods with high-intensity pulsed electric fields (PEF) is a new technology to inactivate microorganisms and enzymes with only a small increase in food temperature. The appearance and quality of fresh foods are not altered by the application of PEF, while microbial inactivation is caused by irreversible pore formation and destruction of the semipermeable barrier of the cell membrane. High-intensity PEF provides an excellent alternative to conventional thermal methods, where the inactivation of the microorganisms implies the loss of valuable nutrients and sensory attributes. This article presents recent advances in the PEF technology, including microbial and enzyme inactivation, generation of pulsed high voltage, processing chambers, and batch and continuous systems, as well as the theory and its application to food pasteurization. PEF technology has the potential to improve economical and efficient use of energy, as well as provide consumers with minimally processed, microbiologically safe, nutritious and freshlike food products.

INACTIVATION of E. COLI FOR FOOD PASTEURIZATION BY HIGH-STRENGTH PULSED ELECTRIC FIELDS

Pulsed electric fields of very high field strength and short duration are effective in the inactivation of E. coli. Nine log reduction in E. coli viability was achieved using a stepwise pulsed electric field treatment where E. coli suspensions were treated repeatedly in batches. It was demonstrated that high-strength pulsed electric field treatment is adequate for pasteurization of liquid foods. A 40,000 volt pulse generator was constructed to supply high voltage electric pulses to a treatment chamber with two parallel plate stainless steel electrodes where fluid food was contained. the gap between electrodes was 0.51 cm and the chamber volume was 14 ml. Pulse electric field strength ranged from 35 to 70 kV/cm. Pulse width was selected at 2 μs. Number of pulses per treatment varied from 1 to 80. E. coli were suspended in a simulated milk ultra-filtrate (SMUF) and treated with pulsed electric fields in a batch mode. the suspension fluid was maintained at constant temperatures of 7, 20, or 33C. Maximum temperature change occurring during each pulse was 0.3C measured by a fiber optics temperature probe. E. coli viability before and after treatment were assayed by counting colony forming units (cfu).

Microbiologically safe continuous pasteurization of liquid foods

The pasteurization of food is aimed at eliminating the risk of food poisoning. Pasteurization is, in theory, very simple: the product to be pasteurized is heated to a certain temperature and kept at or above that temperature for a certain time. There are, however, many reasons why, in practice, pasteurized products sometimes present a microbiological health hazard. To minimize this risk, the Continuous Heat Treatments subgroup of the European Hygienic Equipment Design Group (EHEDG) has prepared guidelines for the microbiologically safe continuous pasteurization of liquid foods without particulates, as summarized below.