Sterilization Of Liquid Foods Research Articles

Numerical study of the effects of pulsed electric field on β-casein

As a non-thermal microbial inactivation technology, pulsed electric field (PEF) treatment can be used in liquid food sterilization. It is necessary to investigate the effects and mechanisms of PEF on the important contents of liquid food. In this study, molecular dynamics (MD) simulation and multiple structural analyses were employed to investigate the effects of PEF on β-casein (BCN) molecule. The investigation focused on examining the impact of PEF on molecular conformation, flexibility, electrostatic properties, and solvent interactions. Results found that high-intensity pulsed electric fields can cause irreversibly complete unfolding of BCN molecule within a picosecond timeframe. The applied PEF changed the dipole moment of BCN molecules, leading to the reorientation of residues towards the direction of the applied electric field. Furthermore, the electric field-induced movement of hydrophobic and hydrophilic residues within the BCN molecules was observed, resulting in concomitant changes in the solvent accessible surface area (SASA) of BCN molecule.Industrial relevance: PEF is an emerging non-thermal processing technology in the food industry. MD simulations were employed to investigate the conformational changes of BCN under different pulse electric fields and exposure times. Our study elucidates the fundamental mechanism of PEF's interaction with protein molecules and may contribute to improving the functional properties of this protein. Analysis at the molecular level can be experimentally validated, providing a theoretical foundation for the widespread application of PEF technology in protein-containing food systems.

Non-Conventional Induction Heat Treatment: Effect of Design and Electrical Parameters on Apple Juice Safety and Quality

The proposed non-conventional induction heating, which combines an MSCP and VDC structure, was proved to have excellent thermal effect. Different from other electric field sterilization, this electrotechnology operates with no electrodes, and it is a continuous-flow process with short-duration (about 20 s). In current study, the parameters related to temperature rise were investigated, including applied voltage, frequency, the diameter of the secondary coil and heating tube, as well as their length, etc. It was demonstrated that a smaller diameter of the heating tube, parallel connection sample coils, and higher frequency were beneficial for the inactivation of microorganisms. At 500 Hz, the optimal condition is 800 V, d1 = 2 mm, and L1 = 10 cm. Notably, the system could inactivate all microorganisms and maintained the physicochemical properties of apple juice at 40 kHz. It suggests that this structural design has the potential for industrial applications and the proposed induction heating can realize the rapid sterilization of liquid food without applying electrodes.

Changes in structure and emulsifying properties of coconut globulin after the atmospheric pressure cold plasma treatment

Atmospheric pressure cold plasma (ACP) treatment, a non-thermal sterilization technology with great potential in coconut milk, can maximize the retention of the taste and flavour. However, it is unavoidable to have an impact on the coconut milk components. In this study, coconut globulin (CG), a component important for coconut milk stability, was selected to explore the effect of the ACP treatment on the structure and emulsifying properties of CG. After the ACP treatment, the structure of CG unfolded, which was the increase in random coils and reduction in intrinsic fluorescence intensity. In addition, the carbonyl and S–S bond content increased, while the free –SH content decreased. Compared with untreated CG (440.57 nm), the particle size of CG after the ACP treatment decreased, especially at 60 kV 60 s (207.63 nm) and 60 kV 90 s (204.20 nm). Simultaneously, poor modification and excessive modification of CG have similar surface hydrophobicity and interfacial tension to untreated CG. Notably, moderate modification (60 kV 60 s and 60 kV 90 s) resulted in the unfolding of CG molecules and the exposure of hydrophobic groups, increasing their adsorption at the oil-water interface. As expected, the emulsifying ability and emulsifying stability of CG were significantly improved after the ACP treatment at 60 kV 60 s and 60 kV 90 s. In conclusion, moderate ACP treatment could improve the emulsifying properties of CG by modifying its structure. This study provides new insights into the effect of ACP on food components during liquid food sterilization.

High Voltage Pulse Generator Based on a Novel Magnetic Isolated Drive Circuit

In order to meet the requirements of high voltage, high power, and compactness for pulse generators used in the field of liquid food sterilization, an all-solid-state Marx generator based on a novel magnetic isolated drive is proposed. The drive circuit uses the magnetic core to transfer the control signal, which adopts core stacking and inverse paralleled secondary side winding. It only needs one drive signal to realize synchronous conduction of the main switch or bypass switch and the complementary conduction of both. The maximum pulse width of drive signal is not limited by the magnetic core saturation. The topology is simple, and the problem of high voltage isolated drive of Marx generator is solved. Based on the novel magnetic drive, a 31-module solid-state Marx generator is built and a prototype test is carried out. The test results show that the maximum instantaneous power of this generator is 1.3 MW (30 kV, 43 A) with a pulse width of 3–10 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s and an adjustable repetition frequency of 0–1 kHz.

Design Parameters on Impingement Steam Jet Heat Transfer of Continuous Liquid Food Sterilization

The effect was clarified of the design parameters on the heat transfer of an impingement steam jet applied to continuous liquid food sterilization with the aim of high heating performance. The study investigated the effects of the steam and water Reynolds number, jet-to-target spacing to jet diameter ratio, and steam temperature on the Nusselt number. The Reynolds number was defined based on steam and water injection plate configurations in turbulent flow. The Nusselt number of the steam temperature at 120 °C was greater than at 125 °C and 130 °C and higher heat transfer was noted at a water nozzle number of two. The Nusselt number was the highest at the jet-to-target spacing to jet diameter ratio (H/d) of 1 and then tended to be constant for H/d above 3. The present study was compared with jet impingement correlations from Huber and Viskanta, and from Martin. In addition, the Ranz and Marshall correlation of a conventional direct steam injection was compared with the impingement method. The sterilization temperature tended to increase as the steam temperature and the number of steam nozzles was increased while the number of product nozzles was decreased.

Application and Mechanism of Nanofluid in Liquid Food Sterilization

Application and Mechanism of Nanofluid in Liquid Food Sterilization

Pulsed Electric Field Treatment of Raw Milk and Its Effect on Protein-Free Amino Acids Transition

As a nonthermal microbial inactivation technology, pulsed electric field (PEF) treatment technology shows potentials in liquid food sterilization and other biological applications. The purpose of this study is to investigate the effect of PEF treatment on sterilization, the physical and the chemical properties of raw milk. Fresh raw milk samples were subject to PEF process with electric field strength ranged from 15 to 35 kV/cm for 1.25&#x2013;5 ms in this study. The sterile rate and the shelf-life were evaluated and compared for PEF-treated, pasteurized, and untreated raw milk samples. It was demonstrated that similar inactivation effect was achieved as compared with pasteurization when raw milk was PEF-treated for 5 ms using 35-kV/cm field strength. The concentration of protein and free amino acids (FAA) was also measured and the results indicated that the PEF process promoted the protein-FAA transition as the concentration of FAA in the raw milk sample increased by as much as 14&#x0025;. It is also shown that the input energy density of PEF treatment can be the deciding factor which affects both inactivation of microorganisms and the transformation of composition in the liquid food.

Preparation of Antarctic Krill Oil Emulsion and Its Stability under Catalase Treatment.

Making Antarctic krill oil into emulsion is a good way to utilize Antarctic krill, but proliferation of microorganisms cannot be ignored. H2O2 is widely used in the sterilization of liquid food since its decomposition products are environmentally friendly, although residual H2O2 should be removed for food safety. Adding catalase (CAT) is an effective means to do this. However, the enzyme activity center of CAT is the iron porphyrin group, which has the risk of accelerating lipid oxidation in the oil emulsion. Therefore, we hypothesized that CAT might not be suitable for the removal of H2O2 in Antarctic krill oil emulsion. In this paper, Antarctic krill oil emulsion was prepared, and then the effect of CAT on the emulsion was studied through visual observation, microscopic morphology observation, turbidity and stability, particle size, and ζ-potential; finally, the mechanism of CAT destroying the emulsion was explored from the perspective of lipid oxidation. The results showed that a stable Antarctic krill emulsion was prepared using Tween-80 as the emulsifier, with the oil concentration of 1% (v/v) and the ratio of surfactant to oil phase of 1:5 (v/v). The emulsion treated with CAT had undergone demulsification, stratification, and coagulation after 2 days of incubation, while the emulsion treated with superoxide dismutase (SOD) and bovine serum albumin (BSA) changed little. In addition, the thiobarbituric acid reactive substances (TBARS) value and the content of hydroxyl radicals in the CAT group increased significantly. The preliminary research results indicated that the effect of CAT on the emulsion related to the lipid oxidation caused by the iron porphyrin group at the center of the enzyme activity. All these results indicated that CAT was not suitable for the removal of residual H2O2 in Antarctic krill oil emulsion. Moreover, it is helpful to avoid the contact of Antarctic krill oil emulsion and CAT during the processing of the krill.

Effects of induced electric field (IEF) on the reduction of Saccharomyces cerevisiae and quality of fresh apple juice

The non-conventional technologies about continuous sterilization of liquid food were focused on recently, which is benefits for industrialization. In this study, the machine with an induced electric field was used to sterilize S. cerevisiae in apple juice and the juice quality also was researched. The optimal condition is 800 V, 400 Hz, 5 rpm and 2 mm. Furthermore, the sterilization of the IEF was attributed to non-thermal and thermal effects. The IEF treatment group has a reduction of about 4.6 logs (CFU/mL) in S. cerevisiae at 400 Hz, 800 V, and 2 mm, while the non-thermal group is nearly 2 logs (CFU/mL). The improvement of conductivity and the reduction of pH value imply that IEF might destroy the cell structure. Meanwhile, polyphenol compounds and amino acids in the IEF group were protected well than other groups. Generally, IEF is a potential technology for industrial sterilization of liquid beverages.

Influence of temperature dependence of viscosity on thermal process establishment using CMC-based liquid food model

Since determination of the slowest heating zone (SHZ) is a tedious task in thermal process establishment, mathematical simulation has been introduced. In this research, a numerical study on 2-dimensional natural convection in a cylindrical can during sterilization of liquid food (1% Carboxy-methyl cellulose, CMC) was performed to simulate the flow pattern and temperature distribution. SHZ and sterilizing value (F0) were also determined. Temperature dependent viscosity and density were assumed, while heat capacity and thermal conductivity were kept constant. To represent the actual mechanisms of heating in an overpressure retort, nonisothermal boundary condition (B.C.) was applied; the results were compared with isothermal B.C. The non-isothermal B.C. resulted in a slower heating rate and the simulated temperature profiles that agreed well with the experimental data (2.6% RMSE). Simulated SHZ was forced to move downwards from the geometric centre to the bottom of the can and stayed at about 10% of the can height from the bottom. SHZ moved closer to the wall (at r = R/2) as a result of the secondary flow due to natural convection. An increase in viscosity and thermal conductivity and a decrease in specific heat and density of higher than 5% resulted in a significantly lower F0-value.

Inactivation of yeast in apple juice using gas-phase surface discharge plasma treatment with a spray reactor

Non-thermal plasma technology can inactivate microorganisms that maybe used in the food processing industry. This study mainly aims to evaluate the effect of a gas-phase surface discharge plasma system with a spray reactor on yeasts (Zygosaccharomyces rouxii LB and 1130) in apple juice. This method avoids the limitation of liquid penetration depths in plasma treatment, expanding the processing capacity. Owing to this advantage, this approach can be used to industrialize liquid food sterilization. Experimental results showed that the number of Z. rouxii LB and 1130 cells decreased by about 6.58 and 6.82 log reductions, respectively, in apple juice after discharge plasma treatment for 30 min. The treatment used a voltage of 21.3 kV and inactivation followed the downward concave Weibull kinetics. Longer plasma exposure times with higher discharge voltages and regulated volume flow rate for both gas and liquid phases resulted in greater inactivation rates. Scanning electron microscopy revealed that the structures of plasma-treated cells were severely damaged during the discharge plasma process. Plasma-generated compounds in liquid, such as hydrogen peroxide and ozone in the liquid phase, are generally responsible for the inactivation of microorganisms.

Non Thermal Pasteurization for Orange Juice Using Pulsed Electric Field

Pasteurization is an act or a process to minimize or eliminate all forms of life, particularly microorganisms in food products. Its aim is to reduce or eliminate the number of viable pathogens, which are likely to cause diseases. Pasteurization can be in the form of thermal and non-thermal methods. Thermal pasteurization typically uses high heat and temperature to reduce or eliminate microorganisms. Although this method has been practiced and proven effective, the process is associated with many side effects. Due to this problem, new approaches using a non-thermal pasteurization to generate pulsed electric field (PEF) is proposed. In this paper, non-thermal sterilization using Cascaded H-Bridge Multilevel Inverter (CHMI) pulse power generator was evaluated in order to produce pulsed electric field in inactivating of microorganisms such as Saccharomyces cerevisiae and Escherichia coli in orange juice. The experimental set-up was conducted where an orange juice was placed inside the treatment chamber. The electrodes between the treatment chamber were applied with pulsed electric field up to 15 kV/cm by using the CHMI. The hardware development was implemented using MOSFET 2K3748 power devices and the gate signal generator was controlled by using dSPACE DS 1104. The experimental results show that, an output voltage of 1.2 kVp−p was effective to inactivate Escherichia coli and Saccharomyces cerevisiae. Thus, power consumption was decreased and energy was saved. The pulsed width of 1000 μs with repetitive rate of 50 Hz was generated from the hardware implementation. The results proved that the specifications of the experimental set-up meet the requirements for liquid food sterilization, particularly to inactivate Escherichia coli and Saccharomyces cerevisiae microorganisms in orange juice by using streaking plate techniques.

Effect of two viscosity models on lethality estimation in sterilization of liquid canned foods.

A numerical study on 2D natural convection in cylindrical cavities during the sterilization of liquid foods was performed. The mathematical model was established on momentum and energy balances and predicts both the heating dynamics of the slowest heating zone (SHZ) and the lethal rate achieved in homogeneous liquid canned foods. Two sophistication levels were proposed in viscosity modelling: 1) considering average viscosity and 2) using an Arrhenius-type model to include the effect of temperature on viscosity. The remaining thermodynamic properties were kept constant. The governing equations were spatially discretized via orthogonal collocation (OC) with mesh size of 25 × 25. Computational simulations were performed using proximate and thermodynamic data for carrot-orange soup, broccoli-cheddar soup, tomato puree, and cream-style corn. Flow patterns, isothermals, heating dynamics of the SHZ, and the sterilization rate achieved for the cases studied were compared for both viscosity models. The dynamics of coldest point and the lethal rate F0 in all food fluids studied were approximately equal in both cases, although the second sophistication level is closer to physical behavior. The model accuracy was compared favorably with reported sterilization time for cream-style corn packed at 303 × 406 can size, predicting 66 min versus an experimental time of 68 min at retort temperature of 121.1 ℃.

Sterilization Plant simulation of whole milk UHT Type through the Aspen plus

&lt;p&gt;The milk sterilization process aims to diminish or extinguish the microbial load present in the food in order to reduce possible damage arising of the metabolic processes of microorganisms that might be present in food. The system currently used in milk processing plants have direct injection principle oversaturated steam in a certain volume of milk in order to establish microbiological reduction, then the product is directed to a tank where flash evaporation condensed the steam is taken off after the product part to the homogenizer where fat molecules are broken making the standardized product. In this whole process is used a system called VTIS (Vacum Therm Instant Steriliser) developed by Tetra Pak company that consists of a piece of equipment back to the sterilization of liquid foods. The computational model used the Aspen plus programmable plataform that by means of unit operations allows you to predict the behavior of a process, this plataform lets you interactively vary some elements of the process in order to obtain desired results through the flowsheets of feed compositions and operating conditions. The ASPEN plus enables the realization of sensitivity analysis, generation of graphs and tables, estimation, regression of physic-chemical properties, settings of simulation models the operative data, equipment sizing, cost analysis, and data input sheets of calculations. As a result was able to reproduce a process without the need for costs.&lt;/p&gt;

Sterilization of liquid foods by pulsed electric fields-an innovative ultra-high temperature process.

The intention of this study was to investigate the inactivation of endospores by a combined thermal and pulsed electric field (PEF) treatment. Therefore, self-cultivated spores of Bacillus subtilis and commercial Geobacillus stearothermophilus spores with certified heat resistance were utilized. Spores of both strains were suspended in saline water (5.3 mS cm−1), skim milk (0.3% fat; 5.3 mS cm−1) and fresh prepared carrot juice (7.73 mS cm−1). The combination of moderate preheating (70–90°C) and an insulated PEF-chamber, combined with a holding tube (65 cm) and a heat exchanger for cooling, enabled a rapid heat up to 105–140°C (measured above the PEF chamber) within 92.2–368.9 μs. To compare the PEF process with a pure thermal inactivation, each spore suspension was heat treated in thin glass capillaries and D-values from 90 to 130°C and its corresponding z-values were calculated. For a comparison of the inactivation data, F-values for the temperature fields of both processes were calculated by using computational fluid dynamics (CFD). A preheating of saline water to 70°C with a flow rate of 5 l h−1, a frequency of 150 Hz and an energy input of 226.5 kJ kg−1, resulted in a measured outlet temperature of 117°C and a 4.67 log10 inactivation of B. subtilis. The thermal process with identical F-value caused only a 3.71 log10 inactivation. This synergism of moderate preheating and PEF was even more pronounced for G. stearothermophilus spores in saline water. A preheating to 95°C and an energy input of 144 kJ kg−1 resulted in an outlet temperature of 126°C and a 3.28 log10 inactivation, whereas nearly no inactivation (0.2 log10) was achieved during the thermal treatment. Hence, the PEF technology was evaluated as an alternative ultra-high temperature process. However, for an industrial scale application of this process for sterilization, optimization of the treatment chamber design is needed to reduce the occurring inhomogeneous temperature fields.

Inactivation of bacterial spores by UV-C light

This investigation evaluates the ability of UV light to inactivate bacterial spores of interest for food preservation. It also evaluates the effect of the absorptivity of the treatment medium on UV lethality and the effect of the simultaneous or sequential combination of UV light and mild heating. A UV dose of 23.72 J/mL reached 2.25, 2.93, 3.24, 3.85, and 4.05 Log10 reductions of Bacillus coagulans, Bacillus cereus, Alicyclobacillus acidocaldarius, Bacillus licheniformis, and Geobacillus stearothermophilus spores, respectively. The most UV-sensitive species (Bacillus stearothermophilus) was the most heat-resistant species. The shoulder phase of UV survival curves of the most resistant B. coagulans increased linearly with the absorptivity of the treatment medium whereas the inactivation rate decreased exponentially. The UV inactivation of B. coagulans increased synergistically when increasing the treatment temperature from 25 to 60 °C. A previous heat treatment (60 °C for 3.58 min) did not affect UV sensitivity of B. coagulans, but prior UV exposure (27.10 J/mL) sensitized bacterial spores to subsequent heat treatments. This investigation demonstrated the ability of UV light to inactivate bacterial spores during food preservation. UV technology, unlike other nonthermal technologies, is a real alternative to current heat sterilization treatments. For UV sterilization of liquid foods with a high absorption coefficient, the efficacy of UV light can be enhanced when combined with heat.

Influence of Rotation Speed on the Sterilization of a Steamed Liquid Food Can Using Numerical Simulation

This paper presents an efficient way for the sterilization of a liquid food (liquid soup) can lying vertically and rotated axially by using a commercial computational fluid dynamics package (ANSYS FLUENT). Aside from the forced convection applied by rotating the can, the simulation involved effect of the natural convection with steam heating to 121°C around all of the can sides. The liquid food in the can was assumed to have constant properties, except for the density (Boussinesq assumption) and viscosity (temperature dependent). By solving the governing equations of mass, momentum and energy, we compared the temperature profile in the thermal sterilization which emphasizes the slowest heating zone (SHZ) of viscous rotation speeds compared to that of a stationary can. The simulation results of temperature profiles with different rotation speeds (5, 10, 15, 20, and 25 rpm) for different periods (1, 19, and 43 minutes) indicated that the combined effect of natural and forced convection causes the higher temperature to reach all of the locations of the SHZ with increased rotational speed. With the higher rotational speed, the heating process time is further reduced when reaching the same lowest temperature at the SHZ of the liquid food can.

Numerical Simulation of Liquid Food Sterilization in a Still Can

Cylindrical liquid can of water and CMC was simulated by solving the governing equations for continuity, momentum and energy conservation, using “COMSOL®” multiphysical coupling field software package which based on finite element method of analysis. Through finding out cold spot of 100 °C, 105 °C，110°C and 115°C in the can and sterilization minimum value spot, temperature and sterilization value were compared. The results indicated that there were differences between cold spot and F minimum value spot. thus, in order to ensuring food safety, the original sterilization time should be moderately prolong, especially for thinlyfluid.

Assessing the effect of different ultrasonic frequencies on bacterial viability using flow cytometry

This research investigated the effect of sonication at frequencies of 20, 40 and 580 kHz and approximately the same acoustic intensity on the viability and declumping of two micro-organisms (Escherichia coli and Klebsiella pneumonia). Two analytical methods were employed; viable plate counts (CFU ml−1) and flow cytometry to identify and quantify both live/viable and dead bacteria in the bulk liquid. Flow cytometry results for E. coli and Kl. pneumonia indicated a high sensitivity to 20 and 40 kHz frequency with a continuous decrease in the viable cells and an increase in dead cells during experiments. In contrast, results using the higher frequency of 580 kHz indicate predominantly deagglomeration of bacterial clumps rather than cell membrane disruption (Joyce et al. 2003). Results indicate a good correlation between flow cytometry and viable plate count methodology. Sonication has two different effects on bacteria (i) inactivation and (ii) declumping; however, the scale of these effects is dependent on intensity and frequency. Flow cytometry provides a method to distinguish between and quantify the effects through the observation of two subpopulations: (i) live/viable and (ii) dead bacterial cells. Treatment using power ultrasound has been shown to have a significant impact on microbial activity. This is the first time a study has compared the influence of a range of different frequencies, but at similar power settings on the survival of bacteria in phosphate buffer saline (PBS). This work is of importance for applications where ultrasound has been considered for use in industry as a means of disinfection including the treatment and pretreatment of water and also for the sterilization of liquid foods.

Bipolar Narrow-Pulse Generator With Energy-Recovery Feature for Liquid-Food Sterilization

This paper presents a bipolar narrow-pulse generator with energy-recovery feature for liquid-food sterilization. The generator is formed from a bidirectional flyback converter and active-clamp circuits which are further simplified to the proposed topology with the synchronous-switch technique. In the converter, the leakage inductance of the transformer will resonate with the active-clamp capacitors to recover the trapped energy and to reduce switching loss, improving efficiency by about 13%. In addition, the capacitors can reduce voltage stress significantly. Experimental results obtained from a prototype with the output of plusmn6-20 kV, depending on loads, and the peak power of 1.2 MW has confirmed these discussions.