Pasteurization Of Liquid Foods Research Articles

Exploring the impact of the process parameters on the thermal treatment of viscous food fluids in a tube-in-tube heat exchanger

Thermal treatments are essential to abate the microbial load in food matrices and ensure food safety. Heat exchangers (HEs) are commonly adopted for the pasteurization of liquid foods, thanks to their simple structure and ease of use. In particular, tubular HEs are often employed with viscous fluids and products containing fibres and pieces. The aim of pasteurization is to ensure that every point of the product reaches and maintains the target temperature for an adequate amount of time. To this end, it is essential to guarantee uniformity and prevent portions of fluid from reaching an insufficient temperature, and others from being overheated. To evaluate the thermal treatment inside a tube-in-tube HE, computational fluid dynamics (CFD) was used to simulate a pilot plant. Three different fluids with shear-thinning temperature-dependent non-Newtonian behaviour were evaluated. A CFD simulation campaign was carried out reproducing, for each juice, the thermal treatment under different operating conditions. Then, the results were analysed with statistical techniques to evaluate the impact of each operating parameter on the treatment, highlighting how high viscosity greatly impacts the thermal treatment, resulting in lower average temperature and temperature uniformity, while causing an increase in the pressure drop. The results of the simulation campaign were also used to generate a reduced order model (ROM) of the device, that could be exploited to estimate the outcomes of a treatment both as averaged values on a section or at a specific point like “virtual sensors”. The ROM could be also adopted to design and evaluate alternative treatments by performing numerical optimization based on given objectives and constraints. Finally, as the ROM can be implemented in real-time, it could be used to monitor and control the functioning of food plants, detecting deviations from the expected conditions and possible failure conditions.

Effects of ohmic heating with different voltages on the quality and microbial diversity of cow milk during thermal treatment and subsequent cold storage

Ohmic heating (OH), an innovative heating technology, presents potential applications in the pasteurization of liquid foods. Therefore, the study was conducted to evaluate the effect of OH at various voltage gradients (10 V/cm, 12.5 V/cm, and 15 V/cm) and water bath (WB) on microbial inactivation, physicochemical and sensory properties and microbial flora of pasteurized milk. Results indicated that OH with higher voltage could effectively inactivate microorganisms in milk, requiring less heating time and energy. Moreover, OH treatment at higher voltages could decelerate lipid oxidation and better maintain the sensory quality and essential amino acids content of milk. Additionally, all treatments significantly altered the microbial community, and during storage, the microbial community in milk treated with 10 V/cm and 12.5 V/cm OH remained relatively stable. OH treatments with voltage gradients exceeding 12.5 V/cm could effectively inactive microorganisms and maintain the quality attributes of milk.

Near-infrared spectroscopy for the inline classification and characterization of fruit juices for a product-customized flash pasteurization.

The feasibility of inline classification and characterization of seven fruit juice varieties was investigated by the application of near‐infrared spectroscopy (NIRS) combined with chemometrics. The findings are intended to be used to optimize the flash pasteurization of liquid foods. More precise information of the kind of product in real time had to be achieved to enable a more product‐specific process. Using the method of partial least squares discriminant analysis, the fruit juice varieties were classified, showing a classification rate of 100% regarding an internal and 69% regarding an external test sets. A characterization by the extract content, pH value, turbidity, and viscosity was made by fitting a partial least squares regression model. The percentage prediction error of the pH value was <3% for internal and external test sets, and for the Brix value prediction errors were about 4% (internal) and 20% (external). The parameters viscosity and turbidity were found to be unsuitable. Despite this, the strategy applied to gain more product‐specific information in real time showed to be feasible. By linking the results to a database containing potentially harmful microorganisms for various types of fruit juices, a more product‐specific calculation of the necessary heat input can be performed. To demonstrate the practical relevance, a comparison between conventional and product‐adapted process control was performed using two fruit varieties as examples in case of Alicyclobacillus acidoterrestris. Thus, with more accurate product information, achieved through the use of NIRS with chemometrics, a more precise calculation of the heat input can be achieved.

Modeling time-temperature history and sterilization value of mango puree under conventional and microwave assisted pasteurization

Abstract Continuous pasteurization of liquid foods has to provide the desired lethality level to guarantee food safety with minimum degradation of quality attributes (sensorial and nutritional characteristics) and high energy efficiency. To optimize quality and cost, a thermal process should be modeled considering flow, heat transfer and mass dispersion principles; however, flow through helical tubes and microwave heating require a complex 3D multiphysics approach. Herein a simplified 2D approach is presented to model a hybrid pasteurization unit with conventional and microwave heating under laminar flow to predict axial and radial distributions of temperature and residual activity of a microorganism or enzyme. A study case of 20 °Brix mango puree (power law fluid) processing is used to test the model based on an existing pilot plant unit. Results were useful to compare conventional and microwave heating regarding the process sterilization value and model can be used for process analysis, design and optimization.

An Improved Electroporator With Continuous Liquid Flow and Double-Exponential Waveform for Liquid Food Pasteurization

Pulsed electric field (PEF) pasteurisation keeps treated liquid food fresh and nutritious compared to traditional thermal pasteurisation. However, PEF adoption is still limited on an industrial scale due to a lack of practical systems. As a result, a great deal of research has gone into overcoming the limitations of the existing systems. Keeping this in mind, the current study contributes to the improvement of the electroporator. The heterogeneous electric field’s distribution raises the temperature of the treated food samples. Liquid laminar flow is a reason for heterogeneous electric field’s distribution in continuous treatment. Hotspots may also be created by using an inefficient high-voltage waveform in addition to the heterogeneous electric field distribution. This study rectifies the heterogeneous distribution by proposing an improved coaxial treatment chamber and double-exponential waveform to replace the exponential-decaying waveform. A static mixer provides an increased mixing, i.e. disrupting the laminar flow, inside the treatment zone. COMSOL based computational model was developed to study flow behaviour and corresponding temperature distribution in the proposed coaxial treatment chamber with sieves. Based on the model, it has been concluded that coaxial electrodes with sieves provide more homogeneous flow properties inside the treatment chamber. The effectiveness of the double-exponential (DE) waveform was validated using MATLAB. A three-stage Marx generator giving the DE waveform was designed and constructed. The performance of the improved treatment chamber together with the DE waveform, known as the electroporator, was studied using chemical and microbial analysis. Untreated, PEF treated, and thermal treated orange samples were stored at 4°C for 9 days before being examined. The lowest microbial growth was observed in both the PEF treated with sieves and thermally treated food samples than the untreated sample. However, treated juices’ visual and chemical colour analysis showed that the PEF-treated sample acquired a brighter appearance than a thermally processed sample. Thus, this study provides significant findings in developing and utilising an electroporator to inactivate microorganisms.

Inactivation of polyphenol oxidase by microwave and conventional heating: Investigation of thermal and non-thermal effects of focused microwaves

Emerging technologies, such as focused microwave heating of liquid foods, have been studied to reduce quality losses due to the high temperatures of conventional processing. Besides faster heating, microwaves can also have non-thermal effects on inactivation; however, this is a controversial issue. The objective of this study was to compare conventional and focused microwave heating under similar conditions for the inactivation of two polyphenol oxidases (PPOs): mushroom tyrosinase in buffer and the PPO present in coconut water. Small samples under stirring were treated at temperatures between 50 and 90 °C and three kinetic models were adjusted considering the whole time-temperature history. The Weibull model could best describe inactivation in both heating processes, which was more effective with microwave heating for temperatures over 70 °C. Validation runs show that the model can satisfactorily describe the PPO inactivation. This study contributes for the design of liquid food pasteurization by focused microwave technology.

Effect of pulsed light treatment on inactivation kinetics of Escherichia coli (MTCC 433) in fruit juices

The inactivation kinetics of Escherichia coli (MTCC 433) inoculated in the tender coconut water, orange and pineapple juice was investigated using a laboratory model continuous flow pulsed light system with a fixed flow rate of 100 ml/s and the experimental data were fitted with different inactivation models. The E. coli inactivation was examined by the effect of pulsed light fluence rate (0.18, 2 and 5.6 W/cm2) and exposure time (between 0 and 15 s). Log reduction of maximum 4.0, 4.5 and 5.33 was determined in orange, pineapple juice and tender coconut water, respectively, when treated with the pulsed light doses of 95.2 J/cm2, which follows the FDA recommendation. The Weibull, Biphasic and Log linear plus tail models were compared to predict the survival curves of E. coli. Inactivation kinetics of E. coli for liquid foods used in this study were best fitted by weibull model (R2 = 0.9926 to 0.9989; RMSE = 0.0462 to 0.0981). The E.coli inoculated liquid foods treated with pulsed light resulted in flattening out of the cells from the edges due to its membrane integrity degradation which were examined using scanning electron microscopy. Pulsed light could be an effective alternative non-thermal treatment for the pasteurization of liquid foods.

Release of Electrode Materials and Changes in Organoleptic Profiles During the Processing of Liquid Foods Using Pulse Electric Field Treatment

Application of pulsed electric fields (PEFs) is an alternative treatment to thermal pasteurization of liquid foods, which inactivates microorganisms without degrading flavor, texture, and nutrients compared to other conventional technologies. This article scrutinizes the applicability of PEF processing of carbonated beer using a titanium electrode based sealed processing chamber that provides not only effective use of the highest electric field but also eliminates edge effects, and at the same time reduces turbulence by providing steady and uniform flow of the fluid under treatment. The release of metal ions during PEF processing is evaluated by using inductively coupled plasma atomic emission spectrometry (ICP-AES). As metal ions directly affect the organoleptic properties of beer, a sensory evaluation is conducted with the panelists comprised of brewing experts. It has been found that the released amounts of metal ions are lower than the detection levels of ICP-AES, and much lower than what is accepted in consumable foods (<2 parts per billion). Supporting the metal analysis data, the sensory panel also reported nonoff flavors in the PEF-processed beer. The treated and untreated beer samples are aged at 5 °C, 22 °C, and 34 °C for ten days. The shelf-life analysis is conducted for PEF-treated and untreated beer samples. The organoleptic property profile of the beer treated at 4 kV by PEF shows the potential of extending shelf life at least for 90 days. In addition, analytical indicators like the deterioration of trans-iso-α-acids confirm no chemical changes in beer before and after PEF treatment under the conditions studied.

Molecular dynamics simulation of high-pressure CO2 pasteurization reveals the interfacial denaturation of proteins at CO2/water interface

While mirobial and enzyme inactivation by CO2 is a promising non-thermal method for cold pasteurization of liquid foods, the poor understanding of the underlying molecular mechanism limits the development of this procedure. The complexity of the process along with the high-pressure conditions have disabled the experimental techniques to establish microstructural information for this phenomenon. In this work, molecular dynamics simulation method was used to find microscopic insights about this system. Myoglobin protein and lysozyme enzyme have applied as models in the simulations. It was found that CO2 and water make a distinct biphasic system in the experimental pressures of pasteurization process. Although many hypothesizes have attributed the enzyme inactivation to the solubilized CO2 molecules in the aqueous phase, we have shown that enzymes can be inactivated by an “interfacial denaturation” mechanism. Results show that the protein migrates from pure aqueous phase to the CO2/water interface and becomes denatured there. The molecular mechanism includes releasing the hydrophobic cores to the CO2 phase and escaping of the hydrophilic surface residues to the aqueous phase. These two phenomena denature the protein to a flat and extended conformation. Moreover, chemotrypsin inhibitor 2 protein was used to obtain the effect of distance from interface in the denaturation process. It was found that the distance from interface is critical in both performance and rate of the denaturation. Our simulations not only shed some lights on the molecular mechanism of CO2 pasteurization methods, but it can also be a basic computational model for further technological design and development.

Evaluation and modeling of a microwave‐assisted unit for continuous flow pasteurization of liquid foods: Residence time distribution, time–temperature history, and integrated lethality

AbstractFocused microwave heaters have potential to replace heat exchangers in continuous flow pasteurization of liquid foods. The objective of this work was to evaluate a pilot scale unit used for microwave assisted pasteurization of low viscosity liquid foods in order to model the heat transfer and residence time distribution (RTD) to, subsequently, predict the average time–temperature history and estimate the level of heat treatment of the process and contributions from each step. RTD data using water showed that it was possible to assume plug‐flow (negligible axial dispersion). Heat transfer experiments using water provided heat transfer coefficients as functions of Reynolds number and microwave power absorption. Mathematical modeling was used to determine the temperature distribution along the product path, and results were validated. Integrated lethality calculated from the time–temperature histories (pasteurization at 70 °C) revealed the contribution of each process step. Results showed that focused microwave heating provided the necessary temperature increase in a very short time, with a lethality contribution of only 0.7% as compared to 59–68% when using only the conventional heat exchanger. The methods described can be useful for the evaluation of other continuous flow pasteurization units processing low viscosity liquid foods.Practical applicationsThe mathematical modeling approach and experimental methods presented herein can be used for the analysis of continuous flow pasteurization systems based on tubular heat exchangers and with low axial dispersion (plug flow), providing temperature and lethality distribution along the product path, showing the contribution from each section on inactivation. Specifically for the equipment used in the experiments, the obtained heat transfer and resident time distribution parameters will be useful to study the processing of low viscosity foods such as fruit juices and nectars on ongoing works from the group.

Development of continuous flow microwave and hot water bath system for destruction of spoilage microorganisms in food

A continuous pasteurization system was designed based on a domestic microwave oven. Broth was pumped through helical coils of glass tubing placed in the center of the oven cavity. Inactivation of two selected spoilage microorganisms, Bacillus cereus and Saccharomyces cerevisiae in broth were evaluated under continuous flow microwave heating conditions and compared with conventional batch heating in a well stirred hot water bath. Inoculated broth was heated in a microwave oven (700 W, 2450 MHz) under continuous flow conditions to selected exit temperatures of 90°C for B. cereus and 60°C for S. cerevisiae at five power levels (210, 280, 350, 420, 490 W) and five time intervals (1, 2, 3, 4, 5 minute). Broth treated in hot water bath at 90˚C for B. cereus and 60˚C for S. cerevisiae was taken as control. There was a decrease in B. cereus and S. cerevisiae count after microwave and hot water bath treatment (control) with increasing treatment time. Higher microbial inactivation was observed at lower power levels. For all the microwave power levels, higher inactivation of B. cereus and S. cerevisiae was observed in comparison to control, this may be due to some non thermal effects associated with microwave. Heating rate and flow rate also increased with the increasing power level with decrease residence time to kill the contaminants. In future, this system may be useful for effective pasteurization of liquid foods e.g. sugarcane juice and soymilk without affecting the taste of processed juices.

Concentrated high intensity electric field (CHIEF) system for non-thermal pasteurization of liquid foods: Modeling and simulation of fluid mechanics, electric analysis, and heat transfer

Abstract This study develops an integrated, multi-scale model of the pilot concentrated high intensity electric field (CHIEF) system using the finite element method (FEM). The CHIEF system is a novel non-thermal pasteurization technology that uses medium to low voltage (≤10 kV) frequency AC (60 Hz) power supply, and offers satisfactory pasteurization results for liquid food such as juice and milk. The model in this study provides accurate predictions for the fluid behavior, electric field distribution and temperature profile and is validated using experimental results. Results from the model shows that the CHIEF system can provide electric field up to 4000 kV/m with a power supply of 10 kV, enabling a 6-log reduction of bacteria kill. Furthermore, recommendations and optimizations are made based on the modeling results, which would benefit for the process scale-up and design.

Recommendations guidelines on the key information to be reported in studies of application of PEF technology in food and biotechnological processes

Abstract The application of pulsed electric field (PEF) technology as a non-thermal cell membrane permeabilization treatment, was widely demonstrated widely to be effective in microbial inactivation studies, as well as to increase the rates of heat and mass transfer phenomena in food and biotechnological processes (drying, osmotic treatment, freezing, extraction, and diffusion). Nevertheless, most published papers on the topic do not provide enough information for other researchers to assess results properly. A general rule/guidance in reporting experimental data and most of all exposure conditions, would be to report details to the extent that other researchers will be able to repeat, judge and evaluate experiments and data obtained. This is what is described in the present recommendation paper. Industrial relevance Pulsed electric field (PEF) treatment is a promising technology that has received considerable attention in food and biotechnology related applications food and biotechnology related applications of PEF include: i) “cold” pasteurization of liquid foods and disinfection of wastewater by microbial inactivation ii) PEF-assisted processing (drying, extraction or expression)

Current applications and new opportunities for the use of pulsed electric fields in food science and industry

ABSTRACT Several studies have demonstrated the feasibility of pulsed electric fields (PEF) for different applications in food industry. PEF technology is therefore a valuable tool that can improve functionality, extractability, and recovery of nutritionally valuable compounds as well as the bioavailability of micronutrients and components in a diverse variety of foods. Additionally, other studies have shown the potential of PEF treatments to reduce food processing contaminants and pesticides. This opens the doors to new PEF applications in the food industry. This review focused on some of the most renowned traditional and emerging PEF applications for improvement of osmotic dehydration, extraction by solvent diffusion, or by pressing, as well as drying and freezing processes. The impact of PEF on different products of biological origin including plant tissues, suspension of cells, by-products and wastes will be analyzed in detail. In addition, recent examples of PEF-assisted biorefinery application will be presented, and finally, the main aspects of PEF-assisted cold pasteurization of liquid foods will also be described.

Applications of pulsed electric field for food processing — Special issue

A wide variety of applications of pulsed electric field (PEF) that are based on cell membrane electroporation have been developed. In the food area these are focused on nonthermal microbial inactivation for food pasteurization, treatment of vegetable, animal and microbial cells to enhance the efficiency of mass transfer of water and other valuable compounds, in drying, extraction and infusion processes. Over past decades, much research on basic and applied aspects of PEF for the food industry has been carried out contributing to a better understanding of this innovative food processing technology. The lack of reliable and viable industrial equipment limited the exploitation of PEF in the food industry for several years. However recent developments in pulse power generators have permitted the design of appropriate PEF equipment at an industrial scale. First commercial applications of PEF technology have been achieved and it is expected that new ones will be launched in the near future. Thisspecialissueonthe useof pulsedelectric fields for foodprocessing contains manuscripts on recent developments in the field of PEF prepared by participants of the first edition of the “Training School on Applications of Pulsed Electric Fields (PEF) for Food Processing” that was held at the University of Zaragoza (Spain) in January 20–23 of 2004. The School was organized in the framework of the COST TD1104 Action — European network for development of electroporation-based technologies and treatments (www.electroporation.net) and joined for four days, 13 lectures and 33 students coming from 15 countries of four different continents belonging to both academia and industry. The aim of the School was to offer an overview of knowledge and understanding of the basic principles involved in food processing by PEF and to provide practical demonstrations in the use of PEF for liquid food pasteurization and improving mass transfer operations in the food

Environmental and biological factors influencing the UV-C resistance of Listeria monocytogenes

In this investigation, the effect of microbiological factors (strain, growth phase, exposition to sublethal stresses, and photorepair ability), treatment medium characteristics (pH, water activity, and absorption coefficient), and processing parameters (dose and temperature) on the UV resistance of Listeria monocytogenes was studied. The dose to inactivate 99.99% of the initial population of the five strains tested ranged from 21.84 J/mL (STCC 5672) to 14.66 J/mL (STCC 4031). The UV inactivation of the most resistant strain did not change in different growth phases and after exposure to sublethal heat, acid, basic, and oxidative shocks. The pH and water activity of the treatment medium did not affect the UV resistance of L. monocytogenes, whereas the inactivation rate decreased exponentially with the absorption coefficient. The lethal effect of UV radiation increased synergistically with temperature between 50 and 60 °C (UV-H treatment). A UV-H treatment of 27.10 J/mL at 55 °C reached 2.99 and 3.69 Log10 inactivation cycles of L. monocytogenes in orange juice and vegetable broth, and more than 5 Log10 cycles in apple juice and chicken broth. This synergistic effect opens the possibility to design UV combined processes for the pasteurization of liquid foods with high absorptivity.

Liquid food pasteurization by pulsed electric fields: dimensionless analysis via Sherwood number for a comprehensive understanding

Pasteurization of liquid foods by pulsed electric fields has been a subject of research for many years. The biological membranes are damaged by the process of electroporation, allowing leakage of internal compounds and possibly leading to subsequent cell lysis. This work is a continuation and extension of a former study that correlated biological inactivation with a modified Sherwood number. The Sherwood number is normally used to describe mass transfer under an electromotive force. In the present work, the Sherwood model was modified; the electric field intensity E was replaced by the specific energy W specif a more general parameter, particularly when the chamber design results in a non-constant electric field. To deal with particular parameters, the length of the treatment chamber was also introduced. Experimental results were compared with the results obtained via the new model we propose. In addition, the model was able to satisfactorily describe results previously published in the literature. The model proposed is thus suitable for describing microbial inactivation in various systems, according to the chamber geometry, hydraulic regimes, electric signal shapes and durations, and the types of microorganisms (yeast and rod bacteria).

Continuous-Flow UV Liquid Food Pasteurization: Engineering Aspects

Ultraviolet (UV)-C treatments are a promising technology for liquid food pasteurization as an alternative to heat treatments. However, the design of efficient UV reactors to reduce pertinent microorganisms and comply with current food safety goals is still an engineering challenge due to the low penetration depth of UV light in liquid foods with high UV absorbance and suspended particles, and the variations in the residence time of the product in the UV reactors. This review focuses on physical aspects of UV radiation related to the essential product and processing parameters for the design of UV reactors. The UV equipment available for liquid food processing is described and the main drawbacks and advantages are discussed.

Metal release from stainless steel electrodes of a PEF treatment chamber: Effects of electrical parameters and food composition

Abstract The effects of electrical parameters (field strength E, total specific energy input W T and pulse frequency) and product composition on the release of the main metallic elements (Fe, Cr, Ni and Mn) of stainless steel (type 316L) electrodes of a continuous flow parallel plate PEF chamber into the treatment medium were investigated. Experiments were carried out by subjecting two different buffer solutions (McIlvaine and Trizma-HCl) with the same values of pH (7) and electrical conductivity (σ = 2 mS/cm) to PEF treatments (mono-polar exponential decay pulses, lasting 3.1 μs) at different intensities (E = 12–21–31 kV/cm, W T = 20–60–100 J/mL) and flow rates (2–3–4 L/h). The results showed that, for each field strength applied, the concentration of metallic elements increased upon increasing the total specific energy input. At constant total energy input, it was noticed that the metal concentration decreased upon increasing the field strength applied. These results were mainly attributed to the key role played by the pulse frequency in the charging process of the double layer capacitors at the electrode–solution interface. Moreover, it was shown that the amount of metal released from the electrodes markedly depended on the presence of halides in the composition of the processed product. Industrial relevance Electrochemical reactions at the electrode solution interfaces are unavoidable when typical conditions for PEF processing are applied. For the acceptability of PEF processing as a non-thermal method for liquid food pasteurization, the occurrence of these reactions should be avoided or minimized since they may determine undesired phenomenon of contamination of the food product, electrode-fouling and electrode corrosion. In this paper, electrode corrosion was studied, for the first time, in a continuous flow parallel plate PEF treatment chamber. The present investigation contributes to clarifying the effects of some electrical parameters and food composition on electrode corrosion or release of electrode materials under real PEF treatment conditions.

Continuous HTST pasteurization of liquid foods with plate heat exchangers: Mathematical modeling and experimental validation using a time–temperature integrator

The continuous thermal processing of liquid foods with a three-section plate heat exchanger (PHE), heat integration and a non-isothermal holding tube was modeled to derive the temperature history of the product and the lethality distribution. Sequential linear temperature changes were assumed along the process and plug-flow was considered with three options for residence time: space time (bulk velocity), experimental mean residence time and minimum residence time (theoretical or experimental). In order to validate and test the model, it was used to simulate the operation of a laboratory-scale plate pasteurizer processing an enzymic time–temperature integrator (TTI) at four temperature conditions (70, 75, 80 and 85°C). Previous studies of residence time distribution and heat transfer in the equipment provided important parameters for the simulation. Predicted results of temperature distribution were in excellent agreement with experimental values and the simulated process lethality was close to the value assessed with the TTI. A case study showed the effect of the adopted residence time and the over-processing associated with a non-isothermal holding tube with tubular connections.