Article

Developing model food systems with rice based products for microwave assisted thermal sterilization

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Abstract

Model foods are effective tools to evaluate heating patterns and determine hot and cold spot locations in food packages during microwave-assisted thermally sterilization (MATS) processes. Previous research on model food development has focused on high-moisture foods, with limited information on medium-moisture foods (0.2–0.6 g water/g food). This research aimed to develop rice model foods to simulate medium-moisture food during MATS processing. The optimal composition of a rice flour gel (RFG) model food was 0.3 g/g rice flour, 0.135 g/g tapioca starch, 0.001 g/g xanthan gum, 0.005 g/g D-ribose, and 0.559 g/g water, and a rice to water ratio of 1:1.2 g/g with 0.005 g/g D-ribose for the rice grain (RG) model. The temperature sensitivities of the models' color parameters could be applicable for safety and quality attribute modeling; the RFG model had a larger range of z-values (11–31 °C) than the RG model (18–27 °C). Validation results showed that the RG model food received more thermal energy than the RFG model, with thermal treatment equivalents at 121 °C of 60.3 and 6.5 min, respectively. The heating pattern in RFG medium-moisture model food was consistent with high-moisture models in MATS processing. Model foods developed in this research could be helpful tools for microwave process development for medium-moisture foods.

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... Microwave technology is applicable for a wide range of food processes such as pasteurization, sterilization (Auksornsri et al., 2018;Bornhorst et al., 2017a;Cinquanta et al., 2010;Jain et al., 2017;Tang et al., 2007; J. Wang et al., 2018), cooking (Li et al., 2019;López-Berenguer et al., 2007), blanching (Severini et al., 2016;van Nguyen et al., 2019), baking (İçöz et al., 2004), frying (Su et al., 2016), puffing (Kraus et al., 2013;Pompe et al., 2020), and drying (Ambros, Mayer, et al., 2018;Cuccurullo et al., 2018;Lv et al., 2016). As resource efficiency and sustainable processing become increasingly important, microwave technology is gaining additional ground in these fields based on the trend toward electricity produced by renewable energy sources (Al-Ali et al., 2020;Berteli et al., 2007;McLoughlin et al., 2003). ...
... • M-1 (2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4one), • M-2 (4-hydroxy-5-methyl-3(2H)-furanone), • M-3 or HMF (5-hydroxymethylfurfural). Figure 8 depicts the formation of M-1 and M-3 as a result of the Maillard reaction pathway between amino acids (mainly lysine, histidine, arginine, and methionine) and d-glucose (Lau et al., 2003;Kim & Taub, 1993;Kim et al., 1996). While the quantification of the M-1 marker is mainly appropriate for monitoring pasteurization processes (Auksornsri et al., 2018;Tang et al., 2007), the M-2 marker is more suitable for microwave sterilization (J. Wang et al., 2018). ...
... Marker yield was quantified by high-performance liquid chromatography (HPLC) and/or mass spectrometry (Kim & Taub, 1993;Kim et al., 1996). Due to varying compositions of reactants in natural food products, in recent publications a uniform reaction rate was ensured by defined addition of reactants to homogeneous model food systems, for example, based on whey protein gels, mashed potato, rice, and others (Auksornsri et al., 2018;Bornhorst et al., 2017aBornhorst et al., , 2017bLau et al., 2003). Additionally, instead of time-consuming laboratory analysis, heating intensity was quantified by the extent of brown coloration as a result of Maillard reaction. ...
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Article
Limitations of microwave processing due to inhomogeneities of power input and energy absorption have been widely described. Over‐ and underheated product areas influence reproducibility, product quality, and possibly safety. Although a broad range of methods is available for temperature measurement and evaluation of time/temperature effects, none of them is sufficiently able to detect temperature differences and thermally induced effects within the product caused by inhomogeneous heating. The purpose of this review is to critically assess different methods of temperature measurement for their suitability for different microwave applications, namely metallic temperature sensors, thermal imaging, pyrometer measurement, fiber optic sensors, microwave radiometry, magnetic resonance imaging, liquid crystal thermography, thermal paper, and biological and chemical time‐temperature indicators. These methods are evaluated according to their advantages and limitations, method characteristics, and potential interference with the electric field. Special attention is given to spatial resolution, accuracy, handling, and purpose of measurement, that is, development work or online production control. Differences of methods and examples of practical application and failure in microwave‐assisted food processing are discussed with a special focus on microwave pasteurization and microwave‐assisted drying. Based on this assessment, it is suggested that infrared cameras for measuring temperature distribution at the product surface and partially inside the product in combination with a chemical time/temperature indicator (e.g., Maillard reaction, generating heat‐induced color variations, depending on local energy absorption) appear to be the most appropriate system for future practical application in microwave food process control, microwave system development, and product design. Reliable detection of inhomogeneous heating is a prerequisite to counteracte inhomogeneity by a targeted adjustment of process and product parameters in microwave applications.
... Microwave technology is applicable for a wide range of food processes such as pasteurization, sterilization (Auksornsri et al., 2018;Bornhorst et al., 2017a;Cinquanta et al., 2010;Jain et al., 2017;Tang et al., 2007; J. Wang et al., 2018), cooking (Li et al., 2019;López-Berenguer et al., 2007), blanching (Severini et al., 2016;van Nguyen et al., 2019), baking (İçöz et al., 2004), frying (Su et al., 2016), puffing (Kraus et al., 2013;Pompe et al., 2020), and drying (Ambros, Mayer, et al., 2018;Cuccurullo et al., 2018;Lv et al., 2016). As resource efficiency and sustainable processing become increasingly important, microwave technology is gaining additional ground in these fields based on the trend toward electricity produced by renewable energy sources (Al-Ali et al., 2020;Berteli et al., 2007;McLoughlin et al., 2003). ...
... • M-1 (2,3-dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4one), • M-2 (4-hydroxy-5-methyl-3(2H)-furanone), • M-3 or HMF (5-hydroxymethylfurfural). Figure 8 depicts the formation of M-1 and M-3 as a result of the Maillard reaction pathway between amino acids (mainly lysine, histidine, arginine, and methionine) and d-glucose (Lau et al., 2003;Kim & Taub, 1993;Kim et al., 1996). While the quantification of the M-1 marker is mainly appropriate for monitoring pasteurization processes (Auksornsri et al., 2018;Tang et al., 2007), the M-2 marker is more suitable for microwave sterilization (J. Wang et al., 2018). ...
... Marker yield was quantified by high-performance liquid chromatography (HPLC) and/or mass spectrometry (Kim & Taub, 1993;Kim et al., 1996). Due to varying compositions of reactants in natural food products, in recent publications a uniform reaction rate was ensured by defined addition of reactants to homogeneous model food systems, for example, based on whey protein gels, mashed potato, rice, and others (Auksornsri et al., 2018;Bornhorst et al., 2017aBornhorst et al., , 2017bLau et al., 2003). Additionally, instead of time-consuming laboratory analysis, heating intensity was quantified by the extent of brown coloration as a result of Maillard reaction. ...
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Chapter
Microwave heat installations are attracting major interest in industry in view of cutting down process times and improving qualities. The number of industrial installations is still small as compared to the wide use of household appliances. There is great interest on the part of the food industry and most global food players are testing microwave applications in their Research and Development Laboratories. However, only a few applications have transferred to the production sites. On the laboratory scale, many applications were developed to a level giving evidence of better process results. Besides the numerous requirements for a reliable and stable design of an industrial microwave, many installations still suffer from little understanding with regard to quality control and requirements of food safety in accordance with Good Manufacturing Practice (GMP) standards. The fact that microwave processes often are not reproducible and that operators do not find the operation of the complex industrial microwave plants easy, adds to this. Due to the fact that there are only a few microwave vendors on the market, global companies fear to use equipment, where second source and intellectual property issues are still fraught with risk. Therefore, the use of microwaves remains a niche technology for the time being. The current chapter explains the requirements of industrial microwave plants and intends to show the potential for unique process results and corresponding economic data, which can be achieved using industrial microwaves. This chapter will help to assess industrial microwave technology with regard to its commercial use.
... Finally, these studies have not used the combination of a time-temperature indicator, such as Maillard reaction, and a temperature indicator, such as infrared thermography, for investigation of uniformity of microwave heat processing. It is worth mentioning that during the Maillard reaction and the corresponding development of brown color, the three time-temperature indicators of M-1 (2,3-dihydro-3,5-dihydroxy-6methyl-4(H)-pyran-4-one), M-2 (4-hydroxy-5-methyl-3(2H)-furanone), and M-3 (5-hydroxymethylfurfural) are formed (Kim et al., 1996) with strong correlations to the thermal impact (Auksornsri et al., 2018;Bornhorst et al., 2017). M-2 with its fast formation and first order kinetics, which is the same as thermal inactivation of bacterial pathogens (Gupta et al., 2011), is more appropriate for high temperature-short time processes, such as microwave sterilization. ...
... M-2 with its fast formation and first order kinetics, which is the same as thermal inactivation of bacterial pathogens (Gupta et al., 2011), is more appropriate for high temperature-short time processes, such as microwave sterilization. However, M-1 is suitable for low temperature-long time processes, such as pasteurization (Auksornsri et al., 2018). Therefore, the objectives of this study were (1) to compare the fixed frequency and frequency sweep loops on the uniformity of microwave heat processing in the solid-state microwave system; (2) to compare frequency sweep loops with different frequencies and different time steps on each frequency on heating patterns of processed samples; (3) to investigate the suitability of using the combination of Maillard reaction and infrared thermography for the determination of the temperature and heating patterns of the heated samples after microwave heat processing with different fixed frequencies and frequency sweep loops; and (4) to access the impact of the position of sample surfaces related to the microwave port position. ...
Article
One of the parameters that has the most influence in the uniformity of microwave heat processing is frequency. Unlike the traditional magnetron microwave system, it is possible to control and set up the frequency with the newly developed solid-state microwave system. The aim of this study was an investigation of the effect of fixed frequencies and frequency sweep loops (in the range of 2400 to 2500 MHz) on the uniformity of heat processing in circular gellan gel model samples containing Maillard reactive agents in a solid-state microwave system. Therefore, the purpose was to compare the solid-state system at fixed frequencies in which the megaton generator also works. While the magneton generator runs at random frequencies within a certain range, solid-state systems are capable of conducting heat processing at fixed frequencies. This novel characteristic will be evaluated through the implementation of different trials at various fixed frequencies. Additionally, the effect of changing frequencies is evaluated through frequency sweep loops, where the frequency of the solid-state system is changed in a pre-determined pattern. The results obtained from the time-temperature indicator of the Maillard reaction and the temperature indicator of infrared thermography showed that the heat processing of samples with the frequency sweep loops, even without turntable rotation, can be more uniform in comparison to those with fixed frequencies and turntable rotation. Moreover, the frequency sweep loops not only improved the uniformity of temperature distribution of the heated sample, but also increased the average temperature of processed samples and, thus, microwave heating absorption.
... Notably, the use of water as the heating medium can resolve the issues of temperature non-uniformity and prevent the formation of cold-spots and hot-spots on the edges of foods during microwave heating [8]. MATS is also the first and the only microwave sterilization technology for low-acid food approved by the U.S. Food and Drug Administration (FDA) [9,10]. Thus far, the U.S. FDA has approved the use of MATS for processing boxed mashed potato and sterilizing salmon packed in soft bags [8][9][10]. ...
... MATS is also the first and the only microwave sterilization technology for low-acid food approved by the U.S. Food and Drug Administration (FDA) [9,10]. Thus far, the U.S. FDA has approved the use of MATS for processing boxed mashed potato and sterilizing salmon packed in soft bags [8][9][10]. ...
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Article
The microwave-assisted induction heating (MAIH) system provides comprehensive heating by combining microwave heating (with 1300 W of power and 2450 MHz of frequency) in the top part and induction heating (with 1800 W of power) in the bottom part. In this study, fresh white shrimps were placed in a sealed crystallized polyethylene terephthalate (CPET) container and heated in the MAIH system at two temperatures (130 and 90 °C) from 60 to 120 s. Afterwards, the shrimp samples were rapidly cooled, and the changes in the shrimp quality, including the appearance, cook loss, aerobic plate count (APC), color values, and texture, during the heating process were analyzed. The results demonstrate that longer heating times decrease the APC levels, but increase the cook loss, color values (lightness, redness, and whiteness), and texture (hardness, cohesiveness and chewiness) of the white shrimp samples. In particular, the white shrimp is fully cooked and gains a completely red appearance, along with no APC detected after heating in the MAIH system at 130 °C for at least 80 s or at 90 °C for at least 100 s. In summary, to achieve a good appearance, no APC detected, and low cook loss, the following heating conditions are recommended for cooking white shrimp in the MAIH system: heating at 130 °C for 80 s or at 90 °C for 100 s. This novel MAIH technology allows food to be heated and sterilized after being packed, thereby eliminating the post-pollution issue. To the best of the authors’ knowledge, this is the first study to evaluate the use of MAIH in the application of food processing.
... The model food was developed to help us more readily determine the heating patterns of microwave-assisted thermal processing systems using the Maillard browning reaction [27,[32][33][34]. It has been shown that the Maillard reaction in model foods containing M-2 (4-hydroxy-5-methyl-3(2H)-furanone) chemical marker precursors follows a first-order reaction and that the corresponding color changes in the model foods reliably reflect the intensity of thermal inactivation of Clostridium botulinum spores [28,[34][35][36]. In contrast, in conventional retort heating methods (e.g., using only pressurized hot water and steam), the cold spots of microwave heating are not always located at the geometrical center or near the center because the heating pattern is related to the electric field distribution. ...
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Article
Microwave assisted thermal sterilization (MATS) is a novel microwave technology currently used in the commercial production of ready-to-eat meals. It combines surface heating of high-temperature circulation water with internal microwave heating in cavities. The heating pattern inside the food packages in a MATS process depends heavily on the electric field distribution formed by microwaves from the top and bottom windows of the microwave heating cavities. The purpose of this research was to study the effect of the electric field on 922 MHz microwave heating of ready-to-eat meals as they moved through the microwave chamber of a pilot-scale MATS system using the finite-difference time-domain (FDTD) method. A three-dimensional numerical simulation model was developed as a digital twin of the MATS process of food moving through the microwave chamber. The simulation showed that the electric field intensity of the MATS microwave cavity was greatest on the surface and side edge of the cavity and of the food. There was a strong similarity of the experimental heating pattern with that of the electric field distribution simulated by a computer model. The digital twin modeling approach can be used to design options for improving the heating uniformity and throughput of ready-to-eat meals in MATS industrial systems.
... As a result, significant efforts are made to ensure food safety and adequate management of the bacterial contaminants. Thus, processing may involve thermal sterilization [3,4], pulsed electric field treatment [5], cold-plasma treatment [6], natural bacteriocins [7,8] or nanotechnological methods [9,10]. The synergistic approaches when several different methodologies are combined frequently deliver promising results in food control [11][12][13]. ...
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Article
Foodborne pathogens are frequently associated with risks and outbreaks of many diseases; therefore, food safety and processing remain a priority to control and minimize these risks. In this work, nisin-loaded magnetic nanoparticles were used and activated by alternating 10 and 125 mT (peak to peak) magnetic fields (AMFs) for biocontrol of bacteria Listeria innocua, a suitable model to study the inactivation of common foodborne pathogen L. monocytogenes. It was shown that L. innocua features high resistance to nisin-based bioactive nanoparticles, however, application of AMFs (15 and 30 min exposure) significantly potentiates the treatment resulting in considerable log reduction of viable cells. The morphological changes and the resulting cellular damage, which was induced by the synergistic treatment, was confirmed using scanning electron microscopy. The thermal effects were also estimated in the study. The results are useful for the development of new methods for treatment of the drug-resistant foodborne pathogens to minimize the risks of invasive infections. The proposed methodology is a contactless alternative to the currently established pulsed-electric field-based treatment in food processing.
... Microwave heating has some advantages, such as energy-efficient and retaining food flavours and nutrients (Campañone and Zaritzky 2005;Atuonwu and Tassou 2018). Microwave heating technology has been widely used in the food industry to improve food quality in many operations, including cooking (Tian et al. 2016), drying (Duan et al. 2010), thawing (Chen et al. 2015(Chen et al. , 2017 and sterilization (Resurreccion et al. 2013;Auksornsri et al. 2018). ...
Many simulations employed in microwave heating simplify the geometric model of the microwave cavity to reduce the complexity of the model. Some detailed design features of the cavity, such as magnetron and cavity depression, are usually ignored. This study built detailed geometric models (DGM) and simplified geometric models (SGM) to investigate the changes in the electric field in a microwave cavity. A three-dimensional finite element model was developed to simulate rotating and stationary food (mashed potatoes) during microwave heating, and the simulation parameters and strategy during rotation were optimized. The simulations using DGM and SGM were compared by comparing the simulated transient temperature profiles and spatial temperature patterns with physical experiments. The results indicate that the temperature patterns of the DGM differed significantly from the SGM, and the simulation results of the DGM were closer to the experimental results. The presence of the magnetron, plastic bearing and detailed glass turntable had little influence on the electric field, but the dents had the great influence. The influence of dents on the heating uniformity was discussed in detail.
... Their results showed that measuring the internal temperature during MW treatment does not reflect the surface inactivation, where the temperature was lower. To locate the cold spot, the chemical marker method developed by Kim and Taub [59] was successfully used [60][61][62]. Combined with experimental investigations, numerical simulations are highly recommended to find the cold spot and to achieve an accurate study to develop a reliable MW decontamination process [57,63,64]. ...
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Chapter
Since food is generally of low thermal conductivity, heating by conventional methods remains relatively slow. Thanks to its volumetric and rapid heating, microwave (MW) technology is successfully used in many applications of food processing. In this chapter, fundamental principles of MW heating are briefly presented. MW drying and MW microbial decontamination are extensively reviewed as innovative methods for food preservation. However, the complex interactions between microwaves and materials to be heated are not yet sufficiently controlled. Moreover, MW heating heterogeneity and thermal runaway are the main drawbacks of this technology. Several methods have been proposed and investigated in the literature to overcome these problems in order to assure the microbiological safety and quality of food products.
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The quality changes of duck meat during thermal sterilization using microwave, stepwise retort and general retort heating were evaluated. Results showed that compared with stepwise retort and general retort, duck meat subjected to microwave showed significantly higher gumminess, chewiness, cohesiveness and resilience as well as glutamic acid, lysine and total amino acids. Low-field NMR revealed that the relative content of immobilized water after microwave and stepwise retort treatment was significantly higher than that after general retort treatment. The relative content of 1-octen-3-ol with characteristic mushroom aroma was significantly higher with microwave and stepwise retort heating than with general retort heating, while 2-pentyl-furan with poor taste was only detected with general retort heating. The muscle bundles subjected to microwave were neatly arranged, similar to those with no thermal sterilization. Overall, the meat quality after three thermal sterilization treatment was microwave > stepwise retort > general retort.
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Microwave (MW) pasteurization is an efficient and energy saving technology, but it has the disadvantage of thermal inhomogeneity. This study reduced the inhomogeneity of pasteurization by integrating ultrasound and microwave (IUM) treatment, and decreased adverse effect on the functional properties of liquid egg white (LEW) while ensuring the pasteurization effect. The particle size increased by 48.5 nm after IUM treatment, indicating egg white protein was slightly denatured and aggregated. However, the secondary structure changed little. Compared with traditional pasteurized LEW, lower apparent viscosity, higher zeta potential value and hydrophobicity of LEW treated by IUM (IUM-LEW) made the functional properties maintained or improved. Emulsification capacity (EC), emulsification stability (ES) and gel strength of IUM-LEW were increased by 6.83%, 7.41% and 77 g, respectively. This study provided an alternative to traditional pasteurization for LEW.
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Fungal contamination is a threat to food safety in West Africa with implications for food and feed due to their climate, which is characterised by high temperatures and high relative humidity, which are environmental favourable for fast fungal growth and mycotoxin production. This report gives perspective on studies on toxigenic fungi (Aspergillus, Fusarium and Penicillium) and their toxins, mainly aflatoxins, fumonisins and ochratoxins commonly found in some West African countries, including Benin, Burkina Faso, Gambia, Ghana, Ivory Coast, Mali, Nigeria, Senegal, Sierra Leone, and Togo. Only four of these countries have mycotoxins regulations in place for feeds and food products (Ghana, Ivory Coast, Nigeria, and Senegal). Food commodities that are widely consumed and were thoroughly investigated in this region include cereals, peanuts, cassava chips (flakes), cassava flour, chilies, peanuts, locust beans, melon, and yam products. In conclusion, authorities and scientists needed to consider research and approaches to monitor mycotoxins in foods and feeds produced and consumed in West Africa.
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Article
The purpose of this study was to examine emotional and liking responses to foods designed for older adults and made using microwave‐assisted thermal sterilization technology (MATS). Six chicken pasta meals (three each with and without herbs) were formulated with three concentrations of salt at 100%, 75%, and 50%. Seventy‐six community‐dwelling older adults conducted sensory and emotional evaluations. Sensory testing involved measuring liking of various sensory attributes using a 9‐point hedonic scale, Just‐about‐right scales to measure appropriateness of the intensity of the attributes, and check‐all‐that‐apply questions to identify perceived flavor and texture attributes. EsSense25 methodology was used for capturing food‐evoked emotional responses. Significant differences existed in all measured sensory attributes and in 14 out of the 25 tested emotions across the six meals. Liking scores for all pastas with herbs and high salt pasta with no herbs were not significantly different for all tested attributes and fell between neither like nor dislike and like slightly on the 9‐point hedonic scale. These samples were also associated with positive emotions related to energy and activation. Low‐salt pastas with no herbs were consistently the least liked samples and evoked negative emotions. Results show that sodium content can be reduced by up to half when herbs are added to microwave‐processed pasta meals without compromising liking. Chicken pasta meals manufactured using microwave‐assisted thermal sterilization technology are acceptable to community living individuals 60 years and older. Emotional responses to the meal are positive. When formulating these meals, herbs can be added to lower sodium content formulations to improve liking and increase the number of positive emotions associated with the meal. Microwave‐assisted thermal sterilization, sodium reduction, emotional responses, consumer liking, older adults.
Chapter
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Chapter
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Food engineering, food chemistry, and consumer segmentation were used to evaluate ready-to-eat rice. The aromatic Louisiana Clearfield Jazzman (CJ) and Thai Jasmine (TJ), and a non-aromatic parboiled (PB) rice were hydrated during the first 10 min of processing with reciprocal agitation followed by static retort processing. The aroma compound, 2-Acetyl-1-pyrroline (2-AP) was more heat-stable in CJ than TJ rice but decreased 15-fold compared to the rice cooker method. Pareto analysis indicated that rice type and agitation had the main effect on amylose and total starch and chroma and hue. Color differences of rice agitated during hydration and between rice cooker or static retort processed rice, indicated only slight differences for each rice variety. Hydration of dry rice during retort cooking and similar starch, color, and aroma quality were achieved with reciprocal compared to static or rice cooker methods. Survey responses categorized consumers into three, mindsets driven by rice consumption, convenience, or packaging.
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Low-cost model foods were necessary for developing radio frequency (RF) and microwave (MW) thawing and tempering process for tuna to reduce experimental cost. In this study, grass carp mince with vegetable oil (1.0–8.0% wt), methylcellulose (MC, 1.0–8.0% wt) and NaCl (0.25–4.0% wt) were investigated for their effect on dielectric properties and tempering temperature distribution to simulate tuna. The dielectric properties of the model foods and tuna were both measured over 1–2500 MHz and −40 to +40 °C. The temperature distributions of tuna and the developed model foods after RF (27.12 MHz) and microwave (2450 MHz) tempering from −55 °C were both determined for comparison. Results showed that the dielectric properties of the model food of grass carp with 4.0% oil and 4.0% methylcellulose was the closest to that of tuna. Furthermore, the temperature distribution of grass carp mince with 4% Oil, 4% Methylcellulose and 1.0% salt addition matched that respective temperature distribution of tuna mince in both RF and MW tempering. The results laid a foundation for low-cost model food development for tuna in the tempering/thawing industry. Industrial relevance In industrial radio frequency and microwave thawing/tempering process development, using model food could largely save the economic cost. For the model food selection, low-cost fish usually has a similar composition as the precious fish species than other model food base. Thus, developing easy preparing model food based on low-cost fish mince is necessary and practical. Results in this study could be utilized in assisting frozen precious fish tempering/thawing process development in radio frequency and microwave, and also provide a new perspective for the model food base and additives.
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Background Starch is a vital component of the human diet and is widely used in food manufacturing. Its complex and subtle structure influences its physicochemical properties, thus affecting its application. Microwave heating has experienced increased popularity in the food industry for many diverse uses. Dielectric properties are crucial parameters reflecting the response of food to microwave treatment. Recent studies have often neglected the importance of dielectric properties when investigating the structural changes of starch in a microwave field. Scope and approach This review summarizes the dielectric and microwave absorption properties of starches and starch systems (with water and/or ions). The various possible structural changes of starch under a microwave field are also analyzed, from the macroscopic to the microscopic level (morphology, lamellar structure, crystalline structure and molecular structure), in an attempt to elucidate the essential features of the response of starch to microwave heating in terms of the dielectric properties. Key findings and conclusions Microwaves can directly or indirectly induce a series of changes in the morphology and internal structures of starch granules, closely related to the dielectric properties of the system and microwave input energy. The future research trend will be to regulate and manipulate the structural changes of microwave-treated starch systems from the perspective of changing their dielectric properties and to obtain microwave-treated starch-based food with desirable properties.
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Microwave-assisted thermal sterilizsation (MATS) technology combines the energy from microwaves of long-wavelength (915 MHz) along with hot water immersion to sterilize food in polymeric packages. MATS is presumed to be a successful sterilization method to eliminate pathogens including bacterial spores, improve the shelf-life of food products while the nutritive qualities and flavours are not affected (within consumer acceptance). From the regulatory point of view, it is a thermal technology for pre-packaged commercial sterilization of homogeneous and nonhomogeneous foods as accepted by the Food and Drug Administration (FDA). Scope and approach This review covers the technical progress, advantages and challenges associated with MATS technology with a comparison to conventional methods and its potential in the food industry. This comprehensive background study is worth considering while developing protocols and validation assays for MATS. Key findings MATS is postulated to not only eliminate the edge-heating issues, but it also reduces the heat exposure time to minimize the effect on heat-sensitive components while achieving maximum microbial inactivation. MATS technology has promising potentials and has been expected to have comparable results if not better to retorting in sterilization while ensuring better sensory qualities and attribute that influence consumer acceptance. Hence, bridging the gaps with enhanced efforts in the field of food safety and sensory science would not only provide an upper hand to the technology but would also increase commercialization by meeting the market needs.
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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.
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Microwave is an effective means to deliver energy to food through polymeric package materials, offering potential for developing short-time in-package sterilization and pasteurization processes. The complex physics related to microwave propagation and microwave heating require special attention to the design of process systems and development of thermal processes in compliance with regulatory requirements for food safety. This article describes the basic microwave properties relevant to heating uniformity and system design, and provides a historical overview on the development of microwave-assisted thermal sterilization (MATS) and pasteurization systems in research laboratories and used in food plants. It presents recent activities on the development of 915 MHz single-mode MATS technology, the procedures leading to regulatory acceptance, and sensory results of the processed products. The article discusses needs for further efforts to bridge remaining knowledge gaps and facilitate transfer of academic research to industrial implementation. © 2015 Institute of Food Technologists®
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This study aimed to determine the effects of different cooking methods on white, milled rice. Two methods were evaluated (the Excess, or American method, and the Pilaf method, also known as the Oriental, or calculated-water method), which are commonly used, both domestically and in the catering industry. The effects of the two cooking methods were assessed on four varieties of rice, American Long Grain, American Long Grain Easy Cook, Basmati, and Thai Jasmine rice. The study used sensory evaluation techniques and terminology previously used in the field of rice research. The aim of the study was to assess potential differences in sensory attributes and overall acceptability. Affective testing techniques (hedonic and relative-to-ideal scales) were used to measure consumer preference. A consumer questionnaire also investigated the effects of rice eating, buying and cooking behaviour on the preferred cooking method. The subjects taking part in the study were taken from a typical student population at Bournemouth University. In general, the Pilaf method resulted in rice products that were stickier, firmer and drier in texture, with a more acceptable flavour. Overall acceptability and preference for the Pilaf method was higher, except in the case of Basmati rice. Models of acceptability accounted for up to half the variation so sensory attributes could not be used to predict the acceptability of rice products reliably.
Article
Model foods as chemical marker carriers are needed to evaluate the heating patterns and location of hot and cold spots in developing microwave assisted thermal sterilization (MATS) processes. Previous research on model food development has been conducted for high moisture foods, with limited data on medium moisture foods (20–60% water). This research aimed to determine the dielectric properties (dielectric constants and loss factors) and penetration depths of rice grain (RG) and rice flour gel (RFG) model foods with moisture contents between 50 to 60% (wet basis) and of cooked rice (CR) over a frequency range of 300–3000 MHz at temperatures from 20 to 121 °C. The dielectric properties of rice models with 0% salt and 0.5% d-ribose closely matched the properties of CR; this indicated that rice model foods could be used to emulate CR for heating pattern and cold/hot spot detection in the development of MATS processes at 915 MHz and 2450 MHz. Therefore, rice model foods developed in this research could be useful in the future for the food companies, in order to visualizing the heating pattern and determining the location of cold and hot spots during MATS process of medium moisture foods, such as rice, pasta or macaroni used as main ingredient in ready-to-eat meal products.
Article
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.
Article
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.
Article
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.
Article
The effects of different concentrations of guar and xanthan gums on functional properties of mango kernel starch (MKS) were studied. Both guar and xanthan gum enhanced the water absorption of MKS. The addition of xanthan gum appeared to reduce the SP (swelling power) and solubility at higher temperatures while guar gum significantly enhanced the SP as well as solubility of MKS. The addition of both gums produced a reinforcing effect on peak viscosity of MKS as compared to control. Pasting temperature of MKS was higher than that of starch modified by gums indicating ease of gelatinization. Guar gum played an accelerative effect on setback but xanthan gum delayed the setback phenomenon during the cooling of the starch paste. Both gums were found to be effective in reducing the syneresis while gel firmness was markedly improved.
Article
The aim of this study was to determine the effect of various cooking methods on the white rice (WR), brown rice (BR) and parboiled geminated brown rice (PGBR) of the same variety, focusing on γ-oryzanol and tocols. The methods used for analysis of γ-oryzanol and tocols included solvent extraction and HPLC. The results indicated that PGBR had a higher content of γ-oryzanol and tocols compared to BR and WR, when different cooking methods (raw, steamed, boiled and fried) were used. Steaming method retained the higher γ-oryzanol content (53.6-62.2mg/100g) in both PGBR and BR, in comparison with boiling (53.0-60.6mg/100g) and frying (23.4-31.5mg/100g) methods. Frying reduced the γ-oryzanol content significantly regardless of the rice type. Regarding tocols, a similar trend was noticed in all the methods studied. Tocotrienol was the most abundant tocol found in PGBR and BR. Therefore, steaming is the best cooking method to preserved most of the bioactive compounds; however, a slight increase in total tocols was observed after frying. Copyright © 2015 Elsevier Ltd. All rights reserved.
Article
The goal of this study was to evaluate suitability of using mobile metallic temperature sensors in continuous microwave assisted sterilization (MATS) systems. A computer simulation model using the finite difference time domain method was developed to study the influence of microwave field on the accuracy of mobile metallic temperature sensors, ELLAB, in a MATS system in which food packages with embedded sensors traveled on a conveyor belt. Simulation results indicated that the metallic temperature sensors did not change the overall heating patterns within food samples. But when a metallic temperature sensor was placed in parallel to the electric field component within microwave cavities the field intensity had intense singularity at the sensor tip and caused localized overheating. The electric field singularity adjacent to the tip of the metallic temperature sensor can be avoided by placing the sensor perpendicular to the electric field component. The simulated heating patterns and temperature profiles were verified with experimental results. It was evident from both simulated and experimental results that the metallic temperature sensor could be used to capture temperature profile in a MATS system when placed in a suitable orientation.
Article
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 30 min. 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 30 min. 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 9 days. 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.
Article
Microwave pasteurization is a novel thermal processing technology in which non-uniform heating may be a major challenge. In this study, the suitability of using egg whites (EWs) and whole eggs (WEs) as model foods to evaluate the heating uniformity and to determine the cold and hot spots during microwave pasteurization was investigated. The samples were prepared from mixtures of water with commercial EW or WE powders at different solid concentrations (20%, 25%, 27.5%, and 30%) and salt contents (0, 50, 100, and 200 mM). Critical physical properties for desirable model food systems include appropriate dielectric properties, gelation temperatures, gel strengths, and water holding capacities (WHCs). The gelation temperature of liquid EW and WE were 70 and 80 °C; both fell in the pasteurization temperature range. At 915 MHz, the dielectric constants of liquid EW and WE samples and their heat induced gels decreased with solid concentration while the loss factor was not affected. Loss factors of liquid EW and WE samples increased linearly with salt addition, which could be explained by the linear increase of electrical conductivities by adding salt. The strength and WHC of heat induced EW and WE gels increased linearly with solid concentration, while salt addition had no significant effect. The results demonstrated the suitability of using EW and WE as model foods to determine the heating uniformity during microwave pasteurization process.
Article
The microwave assisted thermal sterilization computer simulation model (MATS-CSM) was developed to improve the previous computer simulation model for the microwave assisted thermal sterilization (MATS) system. Development of the new MATS-CSM included determination of optimum heating time step, evaluation of electromagnetic field distribution and the resulting heating pattern in food, and experimental validation of heating patterns. It was determined that the minimum number of discretization that would not cause immediate divergence of the EM-heat transfer solution was 32 steps corresponding to 97 mm and 5.6 s of displacement and heating time for every step, respectively. Furthermore, this study successfully demonstrated the symmetrical electromagnetic field distribution between top and bottom microwave entry ports and a staggered electric field pattern from one cavity of the MATS to the next. In addition, MATS-CSM confirmed that incorporating heat diffusion in the simulation model reduces the difference in hot spot and cold spot temperature by 65%. It also confirmed that water circulation reduces the edge heating effect, as observed in experiments. The heating pattern generated by MATS-CSM was verified experimentally through a chemical marker method. Based on the percent areal cross section of the weighted average temperature, there were no noticeable differences between the heating zones generated by the MATS-CSM and by the chemical marker method. The percent areal cross section of the cold area 1, cold area 2, and hot area by MATS-CSM were 35%, 25%, and 40%, respectively, and the cold area 1, cold area 2, and hot area by chemical marker method were 35%, 30%, and 35%, respectively.
Article
Sugars and hydrocolloids are used in starch-based product formulations during processing for improving the final quality of foods. Effect of sucrose (0–30%) on thermal and pasting properties of 5% w/w tapioca starch (TS) – xanthan gum (Xan) mixtures was investigated using differential scanning calorimeter (DSC), rapid visco-analyser (RVA) and rheometer. Sucrose increased gelatinization temperatures and enthalpies of TS and TS/Xan dispersions. RVA pasting temperatures, peak viscosity, final viscosity, breakdown and setback values of TS/Xan mixtures increased with increasing sucrose concentration (p < 0.05). Addition of sucrose in all TS/Xan pastes increased the rate of viscosity breakdown during RVA heating under constant shear and temperature. Setback values of TS/Xan pastes increased with sucrose addition but decreased significantly with increasing Xan content. Xan enhanced thermal stability of steady shear viscosities to TS pastes with and without sucrose. Linear regression from pasting profile revealed a good relationship for predicting final viscosity. These results could facilitate the development of TS-based products with improved thermal and pasting properties.
Article
Short-time microwave (MW) sterilization is a feasible technology to produce high-quality shelf-stable sea cucumbers (SCs) (Stichopus japonicus). Selection of a model food matching the sea cucumbers in dielectric properties (DPs) is one of the most important steps for developing the MW processing. The test results revealed that rehydrated sea cucumber has much lower relative dielectric loss factor (9.73–5.62) than muscle foods, including salmon fillets and sliced beef, which were reported in the literature. The whey protein gel formulations that had been developed in our laboratory as a tool in heating pattern studies for those products are, therefore, not appropriate for sea cucumber. Adding 1.0% gellan powder sharply reduced the amount of whey protein concentrates needed to form firm gels and significantly lowered the dielectric loss factor. The dielectric properties of the sea cucumbers and model food samples with different formulations were measured using a custom-built temperature controlled test cell and an Agilent 4291B impedance analyzer in the temperature range 20–20°C. Based on comparison of the measured dielectric properties and the calculated microwave power penetration depths among the sea cucumbers and model foods, appropriate formulation with whey protein concentration 5%, whey protein isolation 3%, gellan gum 1%, d-ribose 0.5% and water 90.5% was chosen as the model food for the sea cucumbers for the purpose of MW processing development.
Article
The performance of organic and inorganic coated retort pouch materials on the shelf life of ready-to-eat (RTE) rice products was investigated. Two different retort pouch structures were used: the organic material coated retort pouch (ORG), organic material coated polyethylene terephthalate (PET)/biaxially oriented nylon (BON)/cast polypropylene (CPP); the inorganic material coated retort pouch (IND), aluminum oxide coated PET/BON/CPP. Two specific cooked rice products, plain and chicken-flavored cooked rice, were utilized for the comparison. For quantitative analysis, moisture content and lightness of the rice products were measured. The moisture content of both the plain and chicken-flavored rice packed in either pouch decreased slightly during the 12 week storage time after retort processing. However, there were no significant differences in quantitative analysis between the ORG and IND for both the plain and chicken-flavored cooked rice. A simple paired comparison test was used to evaluate the sensory characteristics of rice products. Overall, there were no significant sensory differences between the ORG and IND for both the plain and the chicken-flavored cooked rice. These results demonstrated that the newly developed ORG can be used as a retort pouch material for RTE rice products.
Article
The effects of cooking at elevated temperatures (80, 100, 120 and 140°C) and pressure levels (0, 0.1, 0.3 and 0.5MPa) on the textural and morphological properties of cooked Jasmine rice were investigated. The developed high pressure cooker was utilized to process Jasmine rice in excess water under isothermal conditions. Rice cooking at higher temperature produced softer and stickier grain texture as well as more off-white colour. Using scanning electron microscopy technique, the microstructure revealed that the soft texture at high cooking temperature corresponded well to the increase of pore size and thickness of the sponge-like texture of inner layer endosperm. As the temperature increased, the outer layer of cooked rice became less porous. Boiling significantly altered the external appearance (namely colour and exterior integrity) and texture of cooked rice while cooking pressure had a little or no effect.
Article
It is desirable to develop rapid commercial microwave and radio frequency sterilization processes to produce high quality shelf stable muscle foods, particularly aquatic foods. Whey protein gels containing d-ribose and salt were studied as a model food to determine heating patterns in salmon fillets during high temperature microwave sterilization processes. Dielectric constant (ɛ′) and loss factor (ɛ″) of whey protein gels with d-ribose (0.5g/100g, 1g/100g, and 1.5g/100g) at different salt contents (0, 0.1g/100g, 0.2g/100g, 0.3g/100g, 0.4g/100g, and 0.5g/100g) and frozen and thawed pink salmon (Oncorhynchus gorbuscha) fillets were determined over the frequency range of 27–1800MHz at temperatures ranging from 20 to 120°C. The dielectric properties of whey protein gels containing 1g/100g d-ribose and 0.2g/100g or 0.3g/100g salt closely matched the dielectric behavior of salmon fillets in both radio frequency (RF, 27MHz) and microwave (MW, 915–1800MHz) ranges. Altering the salt content had a greater impact on dielectric constant and loss factors at lower frequencies. These results suggest that whey protein gel may be a good model food for microwave sterilization process development, particularly for determining the locations of cold and hot spots in complex muscle foods.
Article
Short-time microwave (MW) sterilization is a feasible technology to produce high-quality shelf-stable sea cucumbers (SCs) (Stichopus japonicus). Selection of a model food matching the sea cucumbers in dielectric properties (DPs) is one of the most important steps for developing the MW processing. The test results revealed that rehydrated sea cucumber has much lower relative dielectric loss factor (9.73-5.62) than muscle foods, including salmon fillets and sliced beef, which were reported in the literature. The whey protein gel formulations that had been developed in our laboratory as a tool in heating pattern studies for those products are, therefore, not appropriate for sea cucumber. Adding 1.0% gellan powder sharply reduced the amount of whey protein concentrates needed to form firm gels and significantly lowered the dielectric loss factor. The dielectric properties of the sea cucumbers and model food samples with different formulations were measured using a custom-built temperature controlled test cell and an Agilent 4291B impedance analyzer in the temperature range 20-120 degrees C. Based on comparison of the measured dielectric properties and the calculated microwave power penetration depths among the sea cucumbers and model foods, appropriate formulation with whey protein concentration 5%, whey protein isolation 3%, gellan gum 1%, D-ribose 0.5% and water 90.5% was chosen as the model food for the sea cucumbers for the purpose of MW processing development. (C) 2011 Published by Elsevier Ltd.
Article
Chemical markers, such as furanone, are intrinsically formed in foods at elevated process temperatures, and have been successfully used as indirect indicators of heating patterns in advanced thermal processes such as aseptic processing, microwave sterilization and ohmic heating. However, very limited information is available on suitability of these chemical markers during combined pressure-heat treatment. The present study was conducted on the formation and stability of chemical marker M-2 (4-hydroxy-5-methyl-3(2H) furanone, a by-product of Maillard reaction) as a function of pressure, temperature and pH. Whey protein gels (containing 1g ribose/100g gel mix) at pH 6.1 and 8.3 were subjected to pressure assisted thermal processing (PATP; 350 and 700 MPa, 105 degrees C), high pressure processing (HPP; 350 and 700 MPa, 30 degrees C) and thermal processing (TP; 0.1 MPa, 105 degrees C) for different holding times. Unprocessed gel was used as control. The marker yield was quantified using HPLC. The initial concentrations of M-2 in the gels were 9.17 and 6.1 mg/100 g at pH 6.1 and 8.3, respectively. As expected, heat treatment at 105 degrees C, 0.1 MPa increased M-2 concentration. The marker yield increased with increase in holding time, following a first order kinetics and decreased with increasing pH. Pressure treatments from 350 to 700 MPa at 30 degrees C reduced the chemical marker formation for both pH values investigated. Marker formation during combined pressure-temperature (105 degrees C, 350 and 700 MPa) was influenced by both heat (which favored the marker formation) and pressure (which hindered marker formation). The net final concentration of the marker formed during PATP was higher than HPP, but lower than thermal treatments. This study suggests that 4-hydroxy, 5-methyl, 3(2H) furanone may not be a suitable marker for evaluating pressure-heat uniformity during PATP.
Article
Low-energy ion beam bombardment at energy levels in the range of 60–125 keV and ion fluences (dose) of 1 × 1016–5 × 1017 ions/cm2 was chosen for mutation induction in Thai jasmine rice (Oryza sativa L. cv. KDML 105) at Chiang Mai University. One of the rice mutants designated BKOS6 was characterized. The rice mutant was obtained from KDML 105 rice embryos bombarded with N+ + N2+ ions at an energy level of 60 keV and ion fluence of 2 × 1016 ions/cm2. Phenotypic variations of BKOS6 were short in stature, red/purple color in leaf sheath, collar, auricles, ligule, and dark brown stripes on leaf blade, dark brown seed coat and pericarp. The mutant's reproductive stage was found in off-season cultivation (March–July). HAT-RAPD (High Annealing Temperature-Random Amplified Polymorphic DNA) was applied for analysis of genomic variation in the mutant. Of 10 primers, two primers detected two additional DNA bands at 450 bp and 400 bp. DNA sequencing revealed that the 450 bp and the 400 bp fragments were 60% and 61% identity to amino acid sequence of flavanoid 3′hydroxylase and cytochrome P450 of O. sativa japonica, respectively.
Article
We conducted a study of model foods for use with microwave heating, in which the dielectric properties that are so important when microwave heating is used could be adjusted and fine-tuned. Agar gel was used as the base in the model foods, and sucrose and sodium chloride were used to adjust the dielectric properties. It was found that the addition of sucrose primarily changed the dielectric constant, whereas the addition of sodium chloride primarily changed the dielectric loss factor. Based on this discovery, we proposed a procedure for determining the concentrations of sucrose and sodium chloride to be added when applying a certain dielectric constant and dielectric loss factor. We created model foods in which the additions of sucrose and sodium chloride were made to mimic a gratin sauce in consistency, and conducted a heating experiment using microwaves. We found good agreement between the temperature increases in the model food and those in the real food.
Article
In this study, a novel approach to determine heating patterns using chemical marker (M-2) yield and computer vision was developed for packaged foods after microwave sterilization. Due to various constraints of temperature measurement devices such as fiber-optic temperature sensors, thermocouples, and infrared sensors, there is a need to develop an accurate and rapid method to determine heating patterns in packaged food trays after microwave sterilization. Yield of a heat sensitive chemical marker (M-2) was used as a coloring agent and digital images of the processed trays were analyzed using a computer vision system. A script in IMAQ vision builder software was written to obtain a 3-D heating pattern for the sterilized trays. Relationship between chemical marker (M-2) yield and cumulative thermal lethality (F0) was also studied. Validation of the locations of cold and hot spots determined by computer vision were performed by fiber-optics temperature measurement sensor. Results show that computer vision in combination with chemical marker M-2 and other accessories can be used as a rapid, accurate and cost efficient tool to specify the location of cold and hot spots after microwave sterilization.
Article
Thermal inactivation kinetic studies are necessary to determine heat resistances of spores in the development of new thermal processes for low-acid shelf-stable products. Most currently available sample holders used for solid and semi solid samples in the kinetic studies take long time to reach the target sample temperature, hence fail to provide isothermal condition. In this research, novel aluminum test cells were developed to facilitate easy loading and unloading samples in a hermetically sealed 1 ml cavity to evaluate the heat resistance of bacterial spores when heated at temperatures above 100 °C. Design of the test cell was governed by minimum come-up time. A finite element model based on the commercial software ‘FEMLAB’ was used to simulate transient heat transfer and finalize the test cell dimensions. Performance of the new test cell was evaluated against capillary and aluminum thermal death time tube methods in characterizing the heat resistance of Clostridium sporogenes PA 3679 spores in a phosphate buffer and mashed potato at 121 °C. D121 values of PA 3679 spores in both the phosphate buffer and mashed potato using the new test cells were not significantly different (P>0.05) from those by the capillary tube method. The results indicated that the new test cell is appropriate for studying the inactivation kinetics of bacterial spores in microbial validation of conventional and novel thermal processes for low-acid shelf-stable foods.
Article
Effects of pH (3, 7, and 9) and xanthan gum (XG) on freeze-thaw (FT) stability of tapioca starch (TS) pastes (6.0% or 24.0% w/w, total solids) were studied as a function of TS/XG mixing ratios (6.0/0.0, 5.7/0.3, and 5.4/0.6) and FT cycles (−20 °C, 22 h and 30 °C, 1 h up to five cycles). Syneresis results showed that xanthan was most effective in reducing the syneresis at pH 7 and this effect increased with increasing gum concentrations. At pH 3, however, xanthan was much less effective reflected by the highest syneresis produced within two FT cycles. DSC data demonstrated that neither transition temperatures nor enthalpies of the FT-TS/XG pastes were affected by pH and xanthan addition. Photographs of stained starch granules exhibited a phase separation between the added xanthan and starch polysaccharides at all pH values tested. SEM micrographs illustrated the largest ice crystals formation in the pH 3 pastes and in the 0.6% xanthan-added pastes of all pH values. Xanthan maintained textural properties of the tapioca starch pastes during FT treatments better at pH 7 and pH 9. Lower starch molecular weight (revealed by HPSEC) and a reduction in viscosity of xanthan solution caused by acid hydrolysis was probably the cause of the lower FT stability of starch pastes at pH 3.
Article
A custom-built temperature-controlled test cell and an Agilent 4291B impedance analyzer were used to determine the dielectric properties of a whey protein gel, a liquid whey protein mixture, and a macaroni and cheese product and their constituents. Dielectric constants, loss factors, and penetration depths for each sample over a temperature range from 20 to 121.1 °C, at frequencies of 27, 40, 915, and 1800 MHz are reported. As temperature increased, dielectric constants of whey protein products increased at 27 and 40 MHz, but decreased at 915 and 1800 MHz. Dielectric loss factors of whey protein products increased sharply with increasing temperatures at 27 and 40 MHz, but increased mildly at 915 and 1800 MHz. Similar results were observed with macaroni and cheese. The penetration depths of electromagnetic energy at 27 and 40 MHz were about four times as great as those at the microwave frequencies 915 and 1800 MHz in all tested samples.
Article
Chemical marker M-2 (4-hydroxy-5-methyl-3(2H)-furanone) can be used as a tool to evaluate heating patterns of foods in microwave sterilization. This research studied the kinetics of the M-2 formation in mashed potato as influenced by temperature and salt content. Mashed potato (83.12% moisture content) with 1.5% d-ribose was heated in the capillary tubes at four temperature levels. Chemical marker M-2 yield was obtained using high performance liquid chromatography. Formation of M-2 in plain mashed potato was a first-order reaction. The rate constant changed with temperature following an Arrhenius relationship. For kinetic parameters estimation, one-step non-linear regression was the best followed by modified two-step regression. Amino acid was the limiting element in the formation M-2 in mashed potato. The salt content of 0–1% had no influence on the chemical marker yield. Addition of l-lysine more than 1% resulted in too dark color after sterilization treatments.
Article
Physical properties and storage stability of tapioca starch (TS) can be modified using hydrocolloids. Xanthan gum (Xan) was investigated in this study for further application in TS-based products. The TS and TS/Xan mixtures at a total polysaccharide concentration of 5% w/w (db) were prepared. From RVA pasting profiles, pasting temperature, peak and final viscosities of TS pastes increased with increasing Xan concentration (p < 0.05) whereas the setback values indicating the short-term retrogradation were lower (p < 0.05). Flow curves of all TS and TS/Xan pastes from steady shear measurement exhibited shear thinning behavior. Water separation values of TS/Xan pastes were also lower than those of TS pastes alone from repeated freeze–thaw experiment, indicating Xan preventing the reassociation of starch molecules. The correlation between setback and water separation was investigated and proven to be a useful approach for predicting water separation from RVA setback value at any given freeze–thaw cycles. These results have important implications for the formulation of TS-based products with improved rheological properties and freeze–thaw stability.
Article
Determining the cold-spot in packaged foods is a critical step to ensure commercial sterility of the processed products in developing novel thermal processes. In dielectric heating (i.e. heating with microwave and radio frequency energy), the cold-spot is different from that of conventional heating. Chemical marker methods can be used to map heating patterns within foods systems. This study determined the kinetic parameters of the M-1 formation in whey protein gels at sterilization temperatures. Pre-formed whey protein gels containing 2% glucose sealed in capillary tubes were heated for different time intervals in oil baths at 116, 121, 126 and 131 °C. M-1 yields were determined by high performance liquid chromatography. Modified two-step, multi-linear and non-linear regression analyses were conducted to determine the kinetic parameters of marker formation. Kinetic parameters were validated with experiments using a pilot-scale radio frequency sterilization system. M-1 formation followed a first order kinetics. The predicted M-1 yields based on the kinetics model agreed with experimental results. Accurate kinetic parameters for M-1 formation should enable us to use M-1 for developing and validating advanced thermal processes.
Article
A major challenge in developing advanced thermal processess based on electromagnetic heating is to determine the location of cold spots in foods. A rapid and reliable method was developed in this study with the aim to effectively locate the cold spot in model food sterilized in microwave systems. The developed method involved application of chemical marker M-2 yield to a model food, mashed potatoes, using computer vision system and an image processing software IMAQ Vision Builder to capture and analyze color patterns after thermal processes. A systematic study was conducted to establish relationships among M-2 yields, color values from captured images of cut food samples, and thermal lethality (F0). Several factors including consistency of imaging background and positions of lights over the diffuser box were considered to standardize the method. To facilitate the comparative study of heating characteristic for different combinations of power levels and F0, a mapping scale using unheated and saturated mashed potato samples was developed by fixing the lowest and upper most gray-scale values. Color values equivalent to gray-level values were positively correlated to F0 and M-2 yield. The specified cold spot location determined by computer vision method was validated in a 915 MHz single-mode microwave sterilization system. The results showed that the computer vision method can potentially be used as an effective tool in microwave sterilization process development for regulatory acceptance and industrial applications.
Article
The kinetics of 4-hydroxy-5-methy-3(2H)-furanone (M-2) formation in a model food system (20% whey protein gel) was determined for studying cumulative time–temperature effects in high-temperature-short-time processes. M-2 was formed from d-ribose and amines through non-enzymatic browning reactions and enolization under low acid conditions (pH > 5). The order of the reaction for M-2 formation was determined by non-linear regression analysis and further confirmed by graphical method. M-2 formation followed a first-order kinetics and the rate constant temperature dependence was described using an Arrhenius relationship. The reaction rates and activation energy were determined using two-step, multi-linear and non-linear regression analyses. This study also demonstrated the use of M-2 formation in determining the cumulative heating effect in a model food system subjected to 915 MHz microwave heating.
Article
This research was to investigate the feasibility for developing a short-time sterilization protocol for a highly inhomogeneous food prepackaged in polymeric trays using 915 MHz microwave (MW) energy. A 915-MHz, single-mode, 10-kW pilot-scale MW system developed at Washing State University was used for this study. The inhomogeneous food consisted of sliced beef and gravy packaged in 7-oz polymeric trays. Specially formulated whey protein gel, matching the beef product in their dielectric properties, was chosen as a model food to emulate the real food for determination of heating patterns and cold spots inside food trays. The heating patterns and cold spots were detected using a chemical-marker-assisted computer vision method. Processing schedules to achieve desired levels of F0 for 7-oz trays of beef in gravy were established based on temperature histories measured at the identified cold spot location. The developed processing schedules were validated by inoculated pack studies using Clostridium sporogenes PA 3679 spores. The results of this study indicate that the 915-MHz single-mode MW sterilization technology is effective for processing of the inhomogeneous food. The procedure established could be used for developing MW sterilization processes for other packaged inhomogeneous foods, such as chicken meat in gravy in trays and salmon in sauce in pouches. The processing data collected could be helpful for industrial scale-up of the MW system.
The retrogradation of canned rice during storage
  • Narkrugsa
Narkrugsa, W., & Saeleaw, M. (2009). The retrogradation of canned rice during storage. KMITL Science and Technology Journal, 9, 1-8.
Apparatus and method for heating objects with microwaves
  • J Tang
  • F Liu
  • K Patfiak
  • E E Eves
Tang, J., Liu, F., Patfiak K., & Eves, E. E., (2006). Apparatus and method for heating objects with microwaves. US Patent 7119313 B2.
FAO Rice market monitor
World Food Situation (2016). FAO Rice market monitor. http://www.fao.org/economic/ est/publications/rice-publications/the-fao-rice-price-update/en/, Accessed date: 16 October 2016.