Microwave-assisted Pasteurization Research Articles

Modeling and experimental validation of the time-temperature profile, pectin methylesterase inactivation, and ascorbic acid degradation during the continuous flow microwave-assisted pasteurization of orange juice

This work evaluated the effect of microwave-assisted pasteurization on pectin methylesterase (PME) and ascorbic acid (AA) in orange juice (OJ) and proposed a model to predict the time-temperature profile of the process and consequent effect on inactivation and quality. Fresh OJ was pasteurized in a pilot-scale unit at four processing temperatures (70, 80, 90 and 100) °C, five holding times, using two heating systems (conventional and microwave). The experimental overall heat transfer coefficient was determined from the heat loads and correlated with Reynolds and Prandtl numbers. The best-adjusted correlation was used to predict the time-temperature profile considering a unidimensional mathematical model for flow and heat transfer. Predicted and experimental temperatures showed differences below 0.9 °C for all conditions. The model was able to predict PME inactivation and AA retention, indicating that microwave pasteurization of OJ can be as efficient as conventional heating on PME inactivation with less impact on AA.

Experimental validation of a multiphysics model for the microwave-assisted pasteurization of apple juice

A microwave cavity designed for continuous flow thermal processing of liquid foods was evaluated for the pasteurization of fresh apple juice. A three-dimensional model was built based on the assembly of the MicroThermics Lab25-UHT/HTST EHVH unit (2450 MHz, 6 kW). Simulations were implemented using the Finite Element Method in COMSOL Multiphysics 6.0. The physics for electromagnetic waves, laminar flow and heat transfer were combined iteratively to solve and predict the electric field intensity, the velocity profile and the temperature distribution within the fluid domain. To validate the model, cloudy apple juice was processed in the unit with flow rates of 0.4 and 0.8 L/min and pasteurization temperatures of 70, 80 and 90 °C. Cavity outlet temperature was measured and compared with simulation results. Multiphysics model showed good temperature prediction with average absolute error of 1.6 °C. Temperature distribution results were useful for determining hot and cold spots within the tube and showed an important temperature gradient at the outlet cross section of the tube. The main results show that the proposed model is reliable for predicting time-temperature histories during thermal processing, and can be used for process evaluation and product quality improvement.

Industrial applications of selected JFS articles

Industrial applications of selected <i>JFS</i> articles

Dielectric properties of Mexican sauces for microwave-assisted pasteurization process.

The dielectric properties and specifically the complex relative permittivity of foods are key elements for the design of pasteurization processes with high frequency electromagnetic waves. Mexican sauces are recognized worldwide for their flavor and nutritional properties. In this work, the complex permittivity of four of the most representative sauces of Mexican cuisine (chipotle chili, habanero chili, red and green sauce) is presented. The permittivity was measured with the open coaxial probe method at temperatures of 25, 40, 55, 70, 85 °C and in the frequency range of 500MHz to 6GHz. Additionally, moisture content, specific heat, viscosity, water activity, density and electrical conductivity are reported, these last three at 25 °C. Dielectric properties were affected by the sauce formulation. The loss factor of each sauce sample at any temperature presents significant changes in relation to the frequency. At 915 and 2,450MHz, , which would cause a thermal runaway effect or the uncontrolled rise in temperature in the sauces during the microwave pasteurization. At 5,800MHz, , which would give better control for microwave heating than at 915 and 2,450MHz. At 915MHz, the loss factor of all sauces is higher than at 2,450 and 5,800MHz, therefore, more rapid heating can be produced. Moreover, at 915MHz, microwaves exhibit higher penetration depth than at 2,450 and 5,800MHz; therefore, at 915MHz, the greatest uniform microwave dielectric heating would be achieved. Thus, 915MHz is the frequency recommended for the studied sauces pasteurization. PRACTICAL APPLICATION: This work provides the dielectric properties of Mexican sauces at different temperatures and their penetration depths in the microwave range, which are key information for further microwave-assisted pasteurization process and for getting safer sauces for consumers. Moreover, this research supplies suggestions about what frequency for ISM (Industrial, Scientific and Medical) applications is the best for microwave-assisted pasteurization according to the penetration depth of the electromagnetic wave in the sauces and microwave dielectric heating speed of the sauces.

Designing thinner wall ethylene-vinyl alcohol copolymer and polypropylene-based semi-rigid trays for microwave-assisted thermal sterilization and pasteurization processes

Abstract The goal of this research was to design a thinner wall tray for microwave-assisted thermal processing technologies. Three-layer (PP//EVOH//PP) sheets of different EVOH- and PP-layer thicknesses were coextruded. The sheets were then thermoformed into 8-oz trays with dimensions of 150 × 100 × 50 mm (L × W×D). Trays were filled with model foods and subjected to conventional and microwave-assisted pasteurization and sterilization processes. Barrier and mechanical properties were assessed before and after processing. Oxygen ingress, weight loss, and color kinetics were measured over a storage period of 3–6 months at 7, 23, and 37 °C. The newly-designed trays showed comparable or better performance in terms of O2 ingress and weight loss, with a 24 % reduction in wall thickness. Therefore, thinner EVOH and PP-based trays hold promise for use in microwave-assisted sterilization and pasteurization processes. This will result in a reduced carbon footprint and provide more economical alternatives to other forms of packaging that are currently available.

Industrial applications of selected JFS articles

Industrial applications of selected <i>JFS</i> articles

Impact of high-pressure and microwave-assisted thermal pasteurization on inactivation of Listeria innocua and quality attributes of green beans

In response to the increasing consumer demand for high-quality, minimally processed ready-to-eat (RTE) meals, the food industry has shown strong interests in exploring new processing technologies for production of safe RTE meals with an adequate shelf life in cold distribution chains. The purpose of this research was to understand the effect of high-pressure processing (HPP) and microwave-assisted thermal pasteurization on the quality attributes of green beans.The pasteurization conditions were selected as 600 MPa at 25 °C for 10 min for HPP and 70 °C for 2 min for processing with microwave-assisted pasteurization system (MAPS). Survival of L.innocua ATCC 51742 in green bean brine solution was analyzed right after the pasteurization processes. The quality attributes of the green beans, such as color, chlorophyll content, texture, vitamin C content, and pH, were further determined during storage at 2 °C for 36 days and 10 °C for 20 days.High-pressure treatment resulted in a 3.7-log CFU/g reduction in L. innocua ATCC 51742, whereas MAPS processing showed a 9.0-log CFU/g reduction. Both pasteurization processes provided significantly better green color retention when the beans were stored at 2 °C than when they were stored at 10 °C. Regardless of the pasteurization methods, the change in the greenness (a*) value of the beans followed similar trends during storage. Both methods caused an increase in the total color difference (ΔE) and a decrease in hue angle (yellowness) during storage (p < 0.05), but they had no significant effect on firmness, total chlorophyll content, and pH of the green beans. After the pasteurization processes, the vitamin C content of the HPP-treated green beans decreased significantly in comparison with the MAPS-treated beans (p < 0.05). This work reveals that both pasteurization treatments have a similar impact on quality attributes of green beans and that MAPS processing is more efficient in inactivating L. innocua ATCC 51742.

Comparative evaluation of flavour and nutritional quality after conventional and microwave-assisted pasteurization of cloudy apple juice

Novel processing technologies have been under study to improve pasteurization and to meet consumer demands for safe foods with fresh-like characteristics. Twelve processing conditions using two heating technologies (microwave and conventional) were carried out in a pilot-scale unit and an evaluation of flavour (sugar, acid and volatile) and nutritional (phenolic compounds and antioxidant capacity) attributes was performed in cloudy apple juice samples with similar holding conditions. Volatile profiles of the microwave-pasteurized juice were more similar to the non-pasteurized juice compared with conventionally pasteurized juices using multivariate analysis. Sugar-acid ratios were not different between fresh and pasteurized juices. In general, changes in the phenolic contents of pasteurized samples were independent of the processing technology, but increased during thermal treatment due to the extraction from the juice material in suspension. Outcomes of this study suggested the potential of microwave processing technology to retain the fresh-like qualities after thermal processing because of the shorter heating time.

Dielectric Properties of Beverages (Tamarind and Green) Relevant to Microwave-Assisted Pasteurization.

The dielectric properties of the studied beverages, how they behave at different temperatures, and the penetration depth reached by microwave at the allocated frequencies, provide important parameters for further heating treatments, such as heating (microwave-assisted pasteurization) and for modeling/simulation purposes.

Microwave-assisted pasteurization of beverages (tamarind and green) and their quality during refrigerated storage

Abstract Microwave-assisted treatments for the pasteurization of a tamarind and green (formulated with pineapple, nopal, guava, and lemon juice) beverages were studied. The beverages were treated with microwaves (490 W, 2450 MHz) in batches of 480 mL until reach the target temperature for the inactivation of the enzyme pectinmethylesterase (90 °C, with holding time of 12 s). Thermal images were taken after the treatments to guarantee the heating uniformity. Bottles were closed, cooled and stored in refrigeration for 21 days. The heating time was 255 s and 280 s for the green and tamarind beverages, respectively. Enzymatic activity was reduced 100% and microbiological accounts were depressed after MW-pasteurization. There were no significant changes in pH, titratable acidity and total soluble solids in tamarind beverage in comparison with untreated samples (p > 0.05). However, MW-pasteurization affected sensory attributes and color in the green beverage (p Industrial relevance Microwaves (MW) are an alternative among the emerging technologies for preservation of diverse fluid foods, with advantages such as, high efficiency, sustainability and reduction of time and costs. This study found viable MW-pasteurization to preserve the sensory, physicochemical and microbiological properties of the tamarind beverage even for 21 days under refrigeration. Despite a safe and stable product may be obtained, the color and sensory attributes should be improved for green beverage. The proposed batch microwave-assisted pasteurization is a short treatment, which can be applied in small facilities or rural zones, with potential to be scaled up it to an industrial level.

Inactivation kinetics of pectin methyl esterase in the microwave-assisted pasteurization of orange juice

The enzyme pectin methyl esterase (PME) kinetic inactivation study in orange juice was performed by conventional heat treatment (thermal bath) and focused microwave heating (synthesis microwave reactor). Experiments have been performed in batch, with temperatures ranging between 50 °C and 95 °C for time between 0 and 60 s for both processes. Non-isothermal processes were considered and histories of time-temperature have been acquired. The kinetic model adjusted considered two fractions of PME (thermosensitive and thermoresistant), and the kinetic parameters to microwave processes at Tref = 90 °C were z1 = 13.7 °C, z2 = 20.3 °C, D1 = 0.231 s and D2 = 130.8 s with α = 0.95. Comparative analysis of processes was performed graphically by residual enzymatic activity versus lethality. The results demonstrated the microwave-assisted thermal process was more effective than conventional one under the same conditions, indicating the possibility for some additive non-thermal effects. Innovative conditions of inactivation were achieved: i.e. 90% at 60 °C after 10 s and 99% at 80 °C after 20 s.

A New Chemical Marker-Model Food System for Heating Pattern Determination of Microwave-Assisted Pasteurization Processes

New chemical marker-model food systems with d-ribose and NaOH precursors as color indicators and gellan gels as chemical marker carrier were explored for the assessment of the heating pattern of in packaged foods processed in microwave-assisted pasteurization system (MAPS). In determining appropriate precursor concentrations, a solution of 2% (w/w) d-ribose and 60 mM NaOH was heated at 60–90 °C for 0–20 min. The solution absorbance at 420 nm increased linearly, while the color parameters L* decreased linearly with heating time at all processing temperatures. In storage, the produced brown color was stable at 4 and 22 °C within 7 days. The new chemical marker-model foods were prepared by mixing 2% (w/w) d-ribose and 60 mM NaOH with 1% (w/v) low-acyl gellan gum and 20 mM CaCl2·2H2O solution. The dielectric constant of the model food samples decreased with the addition of sucrose, and the loss factors increased with the addition of salt. After processing in the pilot MAPS, the heating pattern and cold and hot spots in the new chemical marker-model food system could be clearly recognized and precisely located through a computer vision method. This is the first time that the caramelization reaction was used as a time-temperature indicator in gellan gel model food. This study shows the possibility of using the new chemical marker-model food system for heating pattern determination of the MAPS.

Green Pea and Garlic Puree Model Food Development for Thermal Pasteurization Process Quality Evaluation.

Development and selection of model foods is a critical part of microwave thermal process development, simulation validation, and optimization. Previously developed model foods for pasteurization process evaluation utilized Maillard reaction products as the time-temperature integrators, which resulted in similar temperature sensitivity among the models. The aim of this research was to develop additional model foods based on different time-temperature integrators, determine their dielectric properties and color change kinetics, and validate the optimal model food in hot water and microwave-assisted pasteurization processes. Color, quantified using a* value, was selected as the time-temperature indicator for green pea and garlic puree model foods. Results showed 915 MHz microwaves had a greater penetration depth into the green pea model food than the garlic. a* value reaction rates for the green pea model were approximately 4 times slower than in the garlic model food; slower reaction rates were preferred for the application of model food in this study, that is quality evaluation for a target process of 90 °C for 10 min at the cold spot. Pasteurization validation used the green pea model food and results showed that there were quantifiable differences between the color of the unheated control, hot water pasteurization, and microwave-assisted thermal pasteurization system. Both model foods developed in this research could be utilized for quality assessment and optimization of various thermal pasteurization processes.

Thermal pasteurization process evaluation using mashed potato model food with Maillard reaction products

Model foods with Maillard reaction product formation have been utilized to evaluate thermal sterilization processes, but these models are not optimal for pasteurization. Model foods for pasteurization applications have been developed, but studies on temperature sensitivity and validation are limited. The goal of this research was to assess the temperature sensitivity of chemical marker and color formation in mashed potato model foods and conduct validation testing using a microwave-assisted pasteurization system (MAPS) and conventional, hot water methods. Reaction kinetics were determined for chemical marker M-2 (4-hydroxy-5-methyl-3(2H)-furanone) and color formation (L* and a* values). Results showed that the thermal resistance constants (z-values) were 20.6–24.0 °C for M-2, 20.8–28.8 °C for L* value, and 10.3–25.6 °C for a* value. Correlation analysis between M-2, L*, and a* values and thermal lethality and cook value showed that model foods were most relevant for pasteurization process quality evaluation. Thermal treatment equivalent at the cold spot was approximately 11 min at 90 °C for all pasteurization processes. Model foods pasteurized in MAPS had less color change than those from hot water processes, implying the less severe MAPS process yielded better quality. Model foods and image analysis techniques used in this study could be helpful quality evaluation tools for pasteurization processes.

Food Quality Evaluation using Model Foods: a Comparison Study between Microwave-Assisted and Conventional Thermal Pasteurization Processes

Thermal process optimization has focused on traditional sterilization, with limited research on pasteurization or microwave-assisted thermal processing. Model foods have been developed as quality evaluation tools for thermal pasteurization processes, but there are no comprehensive studies demonstrating how these model foods could be used to evaluate and compare the resulting food quality after different pasteurization processes. The aim of this study was to develop a methodology using image and quantitative analyses for quality evaluation of pre-packaged food pasteurized using a microwave-assisted pasteurization system (MAPS) and traditional hot water method. Four pasteurization processes (MAPS and hot water method at 90 and 95 °C) were designed to have an equivalent accumulated thermal lethality at the cold spot of at least 90 °C for 10 min to control nonproteolytic Clostridium botulinum spores. Color-based time-temperature indicators in mashed potato and green pea model foods were quantified using image analysis. Results showed that median color values were useful in assessing overall color change, and interquartile range was an indicator of burnt areas. MAPS 95 °C was the best process because it had the smallest hot spot cook values and the least color change, while the 90 °C hot water process was the worst. Model foods and image analysis techniques were useful pasteurization process quality evaluation tools and made it possible to visualize the potential food quality change volumetrically, throughout a food package. In the future, these tools could be combined with computer simulations to optimize the quality of pilot-scale and industrial MAPS or conventional pasteurization processes.

Microwave pasteurization of pre-packaged carrots

This research investigated the application of 915 MHz microwaves in pasteurizing pre-packaged vegetables. A specially designed 915 MHz single-mode microwave-assisted pasteurization (MAP) system was used to process carrot cuboids in brine pre-packaged in 8-oz polymer pouches. Gellan gel was formulated and selected as the model food to simulate the real foods processed by the MAP system; heating patterns and cold spots of the pouched samples were detected by a chemical-marker based computer vision method. Two MAP processes (F90°C = 3 min and F90°C = 10 min) targeting Clostridium botulinum type E spores were developed and compared with conventional hot water (HW) processes resulting in equivalent microbial safety. Compared with an equivalent HW process, MAP process greatly reduced the total processing time, reduced the cook values and improved quality uniformity of the products. Quality evaluation showed the impacts of MAP processing on each quality attribute of carrot products depended on the specific quality parameter selected.

Morphological changes in multilayer polymeric films induced after microwave-assisted pasteurization

In-package pasteurization of ready-to-eat (RTE) meals using microwave-assisted pasteurization system (MAPS) has shown promise for improving the safety and quality of foods, since dielectric heating is more efficient than thermal conduction. However, MAPS can affect the oxygen transmission rate (OTR) and water vapor transmission rates (WVTR) of packaging, imparting a certain degree of quality deterioration to the pasteurized food. This study evaluates morphological changes in newly-developed 3 multilayer polymeric films used for lid-stock on trays subjected to MAPS. We measured changes in OTR and WVTR after MAPS treatment, and further correlated these measurements with melting enthalpy (ΔH), overall crystallinity, crystal structure, water absorption, and dielectric properties of films. The composition of tested films was: (Film A): polyethylene terephthalate (PET)/barrier PET/polyethylene (PE); (Film B): PET/Nylon-Polypropylene (PP) and (Film C): PET/low density polyethylene (LDPE)/Nylon/LDPE. Results show that the OTR and WVTR of the films significantly increased (P < 0.05) after both hot water and MAPS pasteurization. Films B and C exhibited a higher OTR after MAPS (52 mins) compared to hot water pasteurization (36 mins). The melting enthalpy (ΔH) of the films increased after pasteurization, and was correlated to the increase in overall crystallinity (1–4% increase) of the films. Increases in OTR and WVTR can be attributed to the fragmented crystal structures and smaller crystal size observed in X-ray diffraction. It is evident that the films absorbed water during MAPS, which altered their dielectric properties. In addition, it is likely that water absorption caused plasticization of the Nylon polymer, degrading the gas barrier properties of the film. Based on these findings, we recommend using a multilayer film with PET as barrier layer for MAPS treatment. Commercialization of novel microwave-assisted thermal pasteurization technology will require development of multilayer films which can sustain microwave and thermal stresses. Food processes influence oxygen and water vapor barrier properties of films which may affect the shelf-life of food sensitive to oxygen and water vapor. A better understanding of the influence of microwave-assisted thermal pasteurization process on film properties will help polymer industry in the design and development of improved film structures.

Development of model food systems for thermal pasteurization applications based on Maillard reaction products

Model food systems with Maillard reaction products have been an effective tool to assess process lethality for microwave-assisted thermal sterilization. However, model food systems used for sterilization temperatures (110–130 °C) are not optimal for pasteurization temperatures (70–100 °C). The purpose of this research was to develop and assess model food systems to quantify process lethality and food quality for pasteurization applications, such as microwave-assisted pasteurization. Chemical marker M-2 (4-hydroxy-5-methyl-3(2H)-furanone) and color reaction kinetics were determined for egg white, mashed potato, and gellan model foods. M-2, L*, and a* value changes followed first order reaction kinetics and were significantly correlated to thermal lethality and cook value. Mashed potato was the optimal model food, in part because it had the greatest range of L* and a* reaction rates at 90 °C. Mashed potato model foods developed in this study could be used in the future to describe safety and quality reactions during pasteurization process evaluation.

Mathematical modeling and Monte Carlo simulation of thermal inactivation of non-proteolytic Clostridium botulinum spores during continuous microwave-assisted pasteurization

The objective of this study was to develop a mathematical method to predict the internal temperature history of products exposed to a microwave-assisted pasteurization system and use Monte Carlo simulation to analyze the inactivation of the spores of Clostridium botulinum Types B in beef meatball trays and Type E in salmon fillet trays. With a target of 6 log-reduction in the spores, the simulation showed >98.8% and 99.1% of the processes will achieve a minimum of 5-log reductions of C. botulinum Type B in beef meatball trays and Type E in salmon fillet trays, respectively. Sensitivity analysis showed that the heating temperature, time, and product heating rate in the Microwave-Assisted Heating section and the heating temperature in the Pre-Heating section are four most critical factors affecting the accumulation of lethality. The results of this study may be used to guide the development of more effective thermal processes in microwave-assisted pasteurization systems.

Chemical marker M2 (4-hydroxy-5-methyl-3(2H)-furanone) formation in egg white gel model for heating pattern determination of microwave-assisted pasteurization processing

Microwave-assisted pasteurization (MAP) is a potential thermal processing technology in which the non-uniform heating presents a challenge. This study evaluated the application of a chemical marker M2 (4-hydroxy-5-methyl-3(2H)-furanone) in an egg white gel model on the determination of possible heating patterns in prepackaged foods during MAP processing. The gel model samples were prepared by heating a homogeneous liquid egg white mixture (25% egg white, 1% D-ribose, 0.5% L-lysine) at 70°C for 30min. The chemical marker M2 formation was studied by heating the gel model samples in 75, 80, 85, 90, 95, and 100°C oil bath for 5, 10, 15, 20, and 30min. The marker yields were determined using high-performance liquid chromatography (HPLC). The color values of the heat-treated samples were measured using CIE L∗a∗b∗ and RGB models. The stability of M2 was evaluated at storage temperatures of 4 and 22°C for 1, 3, 5, and 9days. In order to validate the application of the new gel model system, the heating patterns of the gel models and marker yields of samples taken from 5 different locations of the MAP-processed gel models at 75 and 100°C were analyzed. Results showed that the M2 formation in egg white increased linearly with heat treatment time at 75–95°C, while a slight concavity was observed for samples treated at 100°C. Color parameters L∗ and G values were found to be significantly correlated with the heating temperatures. During storage, the M2 retention rate decreased with increasing time and temperature, while samples treated for longer times were more stable. Salt addition had no significant effect on the M2 yield within the studied time-temperature combination. The color change of egg white gel models due to different M2 yield after the MAP process could be clearly recognized using a computer vision method.