Source: UNIVERSITY OF NEBRASKA submitted to NRP
IMPROVING THE SAFETY OF PREPARED, BUT NOT READY-TO-EAT MICROWAVEABLE FOODS THROUGH HEAT TRANSFER AND PATHOGEN DESTRUCTION MODELING
Sponsoring Institution
National Institute of Food and Agriculture
Project Status
COMPLETE
Funding Source
OTHER GRANTS
Reporting Frequency
Annual
Accession No.
0214255
Grant No.
2008-51110-04340
Cumulative Award Amt.
(N/A)
Proposal No.
2008-01676
Multistate No.
(N/A)
Project Start Date
Sep 1, 2008
Project End Date
Aug 31, 2013
Grant Year
2008
Program Code
[111]- National Integrated Food Safety Initiative
Recipient Organization
UNIVERSITY OF NEBRASKA
(N/A)
LINCOLN,NE 68583
Performing Department
BIOLOGICAL SYSTEMS ENGINEERING
Non Technical Summary
Prepared, but not ready-to-eat (NRTE) microwaveable foods are convenience foods that comprise a considerable portion of foods consumed in the U.S. NRTE foods are partially cooked or contain partially cooked or raw ingredients and some of these products may appear ready-to-eat. These foods rely on proper heating or cooking before consumption for achieving food safety. However, most NRTE foods are cooked in microwave oven that provides uneven heating. The problem of uneven heating is severe when the product is frozen, because ice absorbs microwave energy to a lesser extent than liquid water, leading to defrosted sections of food warming faster while frozen sections remain cold. Most NRTE food packages provide cooking instruction without regard for the size, power, or condition of the microwave. Improper cooking and uneven heating in microwave ovens resulted in recent outbreaks and recalls of packaged frozen foods. The overall goal of this proposal is to improve the safety of NRTE microwaveable foods through heat transfer, pathogen destruction, and risk assessment modeling. The overall outcome of this study is to develop educational and outreach materials for a. processors by providing recommendations and guidelines to modify package and product parameters to improve the uniformity of heating and to develop clear cooking instructions b. consumers to understand the performance of their microwave ovens and to interpret the cooking instructions c. students to understand and apply modeling techniques for food safety applications.
Animal Health Component
40%
Research Effort Categories
Basic
50%
Applied
40%
Developmental
10%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
5015010110020%
5015010201010%
5015010202010%
5045010302010%
7125010110020%
7125010201010%
7125010202020%
Knowledge Area
504 - Home and Commercial Food Service; 501 - New and Improved Food Processing Technologies; 712 - Protect Food from Contamination by Pathogenic Microorganisms, Parasites, and Naturally Occurring Toxins;

Subject Of Investigation
5010 - Food;

Field Of Science
2010 - Physics; 2020 - Engineering; 3020 - Education; 1100 - Bacteriology;
Goals / Objectives
Goal: The overall goal of this proposal is to integrate heat transfer and thermal destruction models in a risk assessment model to assess risks of microwave cooking with a goal of improving the uniformity of heating of a Prepared, but not-ready-to-eat (NRTE) food in a domestic microwave oven. The specific objectives are to: I. Develop a holistic microwave cooking model to understand how microwaves interact with NRTE food components and resulting heating patterns. a) Determine the temperature dependent dielectric and thermal properties. b) Unify and extend existing microwave heating models to produce a holistic microwave cooking model to simulate relevant scenarios associated with consumption of NRTE food products. c) Develop recommendations for packaging design, layout and sizing of various food components in the package based on their dielectric properties. II. Develop and validate microbial destruction model for Salmonella spp. and integrate it with the heat transfer model a) Develop a database of the lethality parameters for Salmonella spp. in individual components and validate the values in composite NRTE foods. b) Validate the integrated model by conducting microbial challenge studies. III. Conduct risk analysis of microwave cooking of frozen food products. a) Develop a risk assessment model for microwave cooking by incorporating the holistic heat transfer and microbial destruction models and dose-response curve to estimate risk. b) Conduct sensitivity analysis to identify critical factors that can contribute significant risks to consumers of frozen microwaveable food products. c) Estimate the risks of specific behaviors and pre- and post-cooking regimes associated with consuming frozen ready to eat scenarios. IV. Develop and deliver traditional and non-traditional programs of microwave cooking safety of NRTE food products for academia, industry and consumers a) Develop and deliver course materials related to heat transfer, microbial destruction, and risk assessment models to undergraduate and graduate students in engineering and food science. b) Develop and deliver easy to understand extension tools (fact sheets and bulletins) on assuring safety of microwavable foods through selection of microwave ovens, translation and adoption of cooking instructions, and safe cooking instructions. c) Deliver the integrated heat transfer and microbial destruction model and the risk assessment tool for processors on designing and developing safe microwavable foods and appropriate cooking instructions to assure safety of frozen ready to eat foods. Expected Outcomes: We expect to have a holistic heat transfer, microbial destruction , and risk assessment models for microwave cooking. These models will be used to develop recommendations and guidelines for processors to develop safe microwavable foods. We expect to come up with several recommendations for consumers to analyze the performance of microwave oven and recommendations for processors to prepare clear cooking instructions for microwave ovens of various performance levels. This will significantly reduce the risk of NRTE foods.
Project Methods
Objective I. Develop heat transfer model: Dielectric, thermal, and physical properties of complex food products will be determined and used in the heat transfer model. We will unify and extend a model that couples Maxwell's equation with thermal equations to model the cooking of frozen NRTE foods with active packages in a domestic microwave oven. The models will be validated by monitoring the temperature real-time during microwave cooking using fiber optic temperature measurement system. Objective 2. Develop microbial model: A five strain cocktail of Salmonella spp. will be used. The D and z-values values for Salmonella spp. will be determined. The integrated heat transfer and thermal destruction model will be evaluated by inoculating the five strain mixed cocktail of Salmonella spp. using in each food product. The product with then be heated in the microwave for various times and Salmonella spp. populations will be enumerated. Objective III. Develop risk assessment model: The risk assessment model will include the food, the microwave oven, the microwave cooking and heat transfer models, consumer practices, pathogen destruction model, and dose response curves. A fully developed model will be implemented using a Monte Carlo simulation of the entire food-oven-cooking-microbial-consumption-dose/response system. We will conduct sensitivity analysis will help in identifying the importance of uncertainties in the model which will in turn identify data gaps and needs to further improve the model. Simulations will be conducted to evaluate the mitigation efforts on reduction of final risk. Objective IV. Educational and instructional materials: Course materials in the areas of heat transfer, microbial destruction, and risk assessment models will be developed and delivered to undergraduate and graduate students in engineering and food science. Easy to understand extension tools (fact sheets and bulletins) will be developed on assuring safety of microwavable foods through selection of microwave ovens, translation and adoption of cooking instructions, and safe cooking instructions. For the processors of the NRTE microwavable foods, the fact sheets will be developed to provide information on design of foods for microwave heating, design of packaging to maximize the uniformity of microwave heating to assure microbiological safety and developing proper cooking instructions for the consumer. Analysis of Results: Both our heat transfer and microbial destruction models will be validated by extensive experimental observation of temperature distribution and microbial enumeration. Risk assessment model can be validated by comparing the estimated risk to foodborne illness outbreaks in the United States compiled by CDC and FSIS. Evaluation methods: For evaluating educational materials, appropriate pre/post-course assessment tools will be developed and implemented. Evaluation of the extension intervention video modules and traditional class room modules will be done using a newly developed evaluation system similar to TEVAL, an evaluation method in use at the University of Nebraska.

Progress 09/01/08 to 08/31/13

Outputs
Target Audience: Food industries especially the manufacturers of frozen microwaveable food products, students, and consumers. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? The project has provided training and professional developement to 1 post-doctoral fellow, 3 graduate students, 2 undergraduate students, and 3 visiting student interns. How have the results been disseminated to communities of interest? In addition to presenting results at scientific meetings, we presented results at the International Microwave Power Symposium Workshop for several industry participants. We interacted with several food companies, that resulted in follow-up funding. What do you plan to do during the next reporting period to accomplish the goals? Nothing Reported

Impacts
What was accomplished under these goals? Objective 1. Microwave heat transfer model: We developed a dielectric properties measurement system, consisting of an impedance analyzer, a high-temperature coaxial cable, a micro-climatic chamber, a high-temperature probe, and stainless steel test cell. For accurate measurement of temperature dependent dielectric properties, especially at frozen conditions, a multi-point temperature calibration protocol were developed. We collected dielectric properties of various food products such as whey protein gel, mashed potato, lasagna ingredients, and pizza ingredients from -20 to 100 °C in triplicates. We measured packaging material properties using split-post dielectric resonators. Dielectric properties of food and package material were used in an electromagnetic model to demonstrate the effect of packaging on heating uniformity. Temperature-dependent thermal conductivity using a thermal properties analyzer and specific heat capacities using a differential scanning calorimeterwere measured. We developed methodologies to size the food products based on their thermal and dielectric properties to improve the microwave heating uniformity. The same protocol was used for varying the thickness of food products. The properties were provided to the heat transfer model. We first developed a coupled electromagnetic and heat transfer model for a homogeneous model food (gellan gel). Simulated spatial and temporal pro?les were found in good agreement with experimental temperature pro?les. The predicted transient temperature pro?les were close to the observed temperature pro?les with the global average RMSE value of 2.02 °C. Then, we extended the model to simulate cooking of a multi-compartment food consisted of nine chicken nuggets and mashed potato and multi-component foods (lasagna, pizza). The model was validated by 6 minutes of cooking in 1100 W oven. To simulate rotation of food in turntable, we developed a custom built algorithm in MATLAB that interacts with COMSOL Multiphysics software. Finally, a comprehensive and holistic microwave cooking model that includes multiphysics of heat, mass and momentum transfer was developed to simulate microwave heating of a model food (mashed potato) using a porous media approach. Transient temperature profiles at six locations collected by fiber optic sensors showed good agreement with predicted results, with the root-mean-square-error ranging from 1.0 to 11.2°C. The simulated spatial temperature profiles of the top and bottom layers of the mashed potato showed similar hot and cold spots when compared to thermal images acquired by an infrared camera. The holistic multiphysics microwave cooking model was used for sensitivity analysis on various mass and momentum transport properties to identify the significant properties that drive water transport during microwave cooking. The sensitivity analysis shows that, the diffusion coefficient of vapor and the evaporation rate constant greatly influenced the predicted temperature and total moisture loss, while the intrinsic permeability of vapor and the diffusion coefficient of water have little influence. We developed a methodology to assess heating and non-uniform heating to identify the best location to place the food in the turntable during microwave cooking. The study suggested that the best location to place food in a microwave oven is not at the center but near the edge of the turntable to achieve uniform heating. Objective 2: Development of cooking instructions for microwaveable foods and validate the adequacy of these cooking instructions for destruction of Salmonella spp. in three food matrices (i) mashed potato, (ii) chicken nuggets and (iii) pot-pies. Two household microwave ovens (2,450 MHz frequency) of low (700 W) and high (1,350 W) power were used. Commercial mashed potato flakes were obtained and prepared following manufacturer’s instructions. Twelve individual temperature profiles were obtained during heating of mashed potato for each microwave oven. Times required to reach 70.0, 72.2 and 73.8°C at the geometric center of the mashed potato were calculated and heating times were selected based on 90, 95 and 99% upper confidence limits (UCL) and the chi-square value. The adequacy of the heating times to eliminate Salmonella spp. was validated by placing a portion (0.3 g) of mashed potato inoculated with Salmonella spp. (8.73 log CFU/g) at the geometric center of the container and heating for the specified times in each microwave oven. Salmonella spp. survival after microwave heating was determined by plating and enrichment methods. Microwave heating of mashed potato to a target temperature of 70°C resulted in the elimination of Salmonella spp. (8.73 log CFU/g reduction) in mashed potato when heated in either of the microwave ovens. Similar to the mashed potato, temperature profiles of frozen chicken nuggets during heating were obtained by placing different numbers (4, 6 or 8) of chicken nuggets at either the (i) edge or the (ii) center of the carousel and heated for specific times for each microwave (700 W and 1,350 W). Incorporation of standing time in addition to the heating time eliminated Salmonella spp., regardless of the power of the microwave, location and the number of chicken nuggets. Microwaveable pot-pies were identified as the food involved in salmonellosis outbreaks. Microwave heating instructions were developed based on end point temperatures obtained at multiple locations in the product subsequent to heating. The heating instructions were validated using microbial challenge studies. Inclusion of standing times subsequent to heating resulted in elimination of Salmonella spp. in the pot-pies. Objective 3. ­Risk Assessment: A quantitative risk assessment model was developed in @risk software to estimate the risk salmonellosis associated with the consumption of not-ready-to-eat, frozen chicken nuggets, cooked in a microwave oven. Prevalence of Salmonella contamination in chicken was modeled as a binomial distribution (p value of 0.446). Three power levels (low-700 W; medium-1000W; and high-1250 W) of microwave ovens were studied. Cooking time of 1 and 1.5 minutes was evaluated and standing time of 0, 1, 1,5, and 2 minutes were evaluated. Ten replications were performed to estimate temperature distributions using fiberoptic thermal sensors and thermal imaging camera. Fiberoptic sensors provided the temperature of chicken nuggets at the center, while the IR camera provided variation in temperature within the chicken nuggets at the center plane, immediately after cooking. The measured temperatures were fit to a probability distribution function. The predicted temperatures were then integrated with the thermal inactivation kinetics of Salmonella to determine the survivors after the selected cooking and standing time. A dose-response curve was used to estimate the illnesses due to consumption of contaminated chicken nuggets. Monte-Carlo simulation was performed. In addition to microwave wattage and cooking time, standing time was found to be a sensitive factor. Objective 4. Outreach activities: Property measurement protocols were included in an undergraduate course, “Engineering Properties of Biological Materials”. The heat transfer models were disseminated at several meetings. As a result, a large food company is currently funding the follow-up work to utilize the models to improve the heating uniformity. Few food companies have been using the state-of-the-art property measurement system developed during this study to collect properties of various food products. Another large food company is currently evaluating our new cooking instruction development methodology for their food products. We also developed simple equations to size different food components based on thermal and dielectric properties.

Publications

  • Type: Journal Articles Status: Submitted Year Published: 2014 Citation: Chen J, Pitchai K, Birla S, Negahban M, Jones D, Subbiah J. Heat, mass, and momentum transport during microwave heating of mashed potato in domestic oven. Part I: 3-D finite element model development and validation. Journal of Food Science.
  • Type: Journal Articles Status: Submitted Year Published: 2014 Citation: Chen J, Pitchai K, Birla S, Negahban M, Jones D, Subbiah J. Heat, mass, and momentum transport during microwave heating of mashed potato in domestic oven. Part II: Sensitivity analysis of parameters. Journal of Food Science.
  • Type: Journal Articles Status: Published Year Published: 2014 Citation: Pitchai K, Chen J, Birla S, Gonzalez R, Jones D, Subbiah J. 2014. A microwave heat transfer model for a rotating multi-component meal in a domestic oven: Development and validation. Journal of Food Engineering. 128, 60-71.
  • Type: Journal Articles Status: Submitted Year Published: 2014 Citation: Chen J, Pitchai K, Birla S, Gonzalez R, Jones D, Subbiah J. 2013. Development of a multi-temperature calibration method for the measurement of dielectric properties applied to microwaveable food. Submitted to IEEE Transaction on Dielectrics and Electrical Insulation Society.
  • Type: Journal Articles Status: Accepted Year Published: 2013 Citation: Chen J, Pitchai K, Birla S, Gonzalez R, Jones D, Subbiah J. 2013. Temperature-dependent dielectric and thermal properties of whey protein gel and mashed potato. Transactions of ASABE. 56(6), 1457-1467.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Chen J, Pitchai K, Birla S, Gonzalez R, Jones D, Subbiah J. 2013. Multiphysics Modeling of Microwave Heating of a Multiphase Model Food System. 2013 Institute of Food Technologists Annual Meeting and Food Expo, Chicago, IL, July 13-16.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Pitchai K, Chen J, Birla S, Gonzalez R, Jones D, Subbiah J. 2013. Simulation of microwave heating of a frozen lasagna meal. 2013 Institute of Food Technologists Annual Meeting and Food Expo, Chicago, IL, July 13-16.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Chen J, Pitchai K, Birla S, Gonzalez R, Jones D, Subbiah J. 2013. Multiphysics modeling of microwave heating of food undergoing heat, mass and momentum transport. 2013 American Society of Agricultural and Biological Engineering (ASABE) annual international meeting, Kansas City, MO, July 21-24.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Pitchai K, Chen J, Birla S, Gonzalez R, Jones D, Subbiah J. 2013. Measurement of complex permittivity of thin microwavable susceptor films using split post dielectric resonator. 2013 American Society of Agricultural and Biological Engineering (ASABE) annual international meeting, Kansas City, MO, July 21-24.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Chen J, Pitchai K, Birla S, Gonzalez R, Jones D, Subbiah J. Development of Calibration Protocol for Measuring Temperature Dependent Dielectric Properties. 47th Annual Microwave Power Symposium, June 25  27, Providence, Rhode Island, USA.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Pitchai K, Chen J, Birla S, Gonzalez R, Jones D, Subbiah J. 2013. Simulation of microwave heating of frozen chicken nuggets. 47th Annual Microwave Power Symposium, June 25  27, Providence, Rhode Island, USA.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2012 Citation: Chen J, Pitchai K, Raj J, Birla S, Gonzalez R, Jones D, Subbiah J. 2012. Temperature dependent dielectric and thermal properties of whey protein gel. 46th annual microwave power symposium, Las Vegas, NV, June 20-22.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2012 Citation: Pitchai K, Raj J, Chen J, Birla S, Gonzalez R, Subbiah J. 2012. Developing microwave heat transfer model for frozen mashed potato packed in microwavable tray. 2012 American Society of Agricultural and Biological Engineering (ASABE) annual international meeting, Dallas, TX, July 29- Aug 1.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Subbiah J, Chen J, Pitchai K, Birla S, Jones D. 2013. Microwaveable food product design based on thermal and dielectric properties. Presented at the short course, Microwave Trends, Sponsored by International Microwave Power Institute, Oct 9-10, 2013, Omaha, NE.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Valenzuela?Martinez, C., Redondo-Solano, M., Summers, E., Subbiah, J., Thippareddi, H. (2013). Development and Validation of Microwave Heating Instructions for Pot Pies to Assure Food Safety. Des Moines, IA: IAFP Annual Meeting Proceedings.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: alenzuela?Martinez, C., Redondo-Solano, M., Summers, E., Subbiah, J., Thippareddi, H. (2013). Development and Validation of Microwave Heating Instructions for Chicken Nuggets to Assure Food Safety. Des Moines, IA: IAFP Annual Meeting Proceedings.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Summers, E., J. Subbiah, D. Jones, B. Tameru, 2013. Risk assessment modeling of microwave cooking of frozen, not-ready-to-eat food products. ASABE Annual Meeting, Kansas City.
  • Type: Conference Papers and Presentations Status: Published Year Published: 2013 Citation: Subbiah, J. 2013. Microwaveable food product design based on thermal and dielectric properties. Invited presentation at the International Microwave Power Symposium Fall Short Course, October 10, 2013, ConAgra Foods, Inc., Omaha.


Progress 09/01/11 to 08/31/12

Outputs
OUTPUTS: A model was developed and validated for microwave heating of multi-compartment foods (mashed potatoes and chicken nuggets). Pot pies are usually covered with grid pattern susceptor for crisping of dough. A framework for simulation of active package such as shielding and susceptor assisted microwave heating of food products was developed and validated. The model is being used for simulating microwave heating of pot pies. A COMSOL-MATLAB interface algorithm was developed for simulating realistic scenarios of microwave heating of products which involves rotating of food products along with a turntable. A preliminary model has been developed to take into account of the water and vapor transport occurs during long microwave cooking of frozen food items. Dielectric and thermal properties of dough, pasta, sauces, cheese, and chicken nuggets were measured as a function of temperature. Protocols for developing cooking instructions for frozen microwaveable foods are being developed based on temperature profiles at various locations followed by microbial challenge study. Based on temperature profile, a 99% upper confidence level for reaching 165 degrees F was determined. That cooking time was then validated using microbial challenge study. For the inoculation of the chicken nuggets, the product was first thawed overnight and inoculated at the center of the product with a five Salmonella spp. cocktail strain to attain a final population of 7.20 log CFU/g. After inoculation, chicken nuggets were frozen to a temperature of -9 degrees C and stored until used. Chicken nuggets (four, six or eight) were placed inside the microwave oven at two different positions and cooked based on the calculated cooking times. A quantitative risk assessment model (QRAM) to estimate the probability of a serving of chicken nuggets to cause illness to the consumer due to contamination of Salmonella has been developed. The QRAM is based on the prevalence of contaminated chicken at the time of manufacturing and a set of parameters which describe the retail to consumption pathway. It incorporates the holistic heat transfer and microbial destruction models as well as the dose-response curve to estimate risk. The modeling software @Risk is used to perform Monte Carlo simulations. This QRAM integrates the range of current household microwave ovens and consumer behavior in that it looks at microwaves of different wattages (700 W, 1000 W, and 1200 W), different cooking times (based on package directions), and different standing times (time between completion of cooking and consumption). Experimental microwave cooking data using an infrared thermal imaging camera and fiber optic sensors is incorporated into this QRAM to capture the range of final temperatures in the product i.e. non-uniform heating of microwave ovens. Sensitivity analysis is performed to identify critical pre- and post-cooking steps that can contribute significant risks to consumers of frozen microwaveable food products. PARTICIPANTS: Jeyamkondan Subbiah, University of Nebraska Harshavardhan Thippareddi, University of Nebraska David Jones, University of Nebraska Sohan Birla, University of Nebraska TARGET AUDIENCES: Food industries, customers PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
Microwave heat transfer model has been continually refined to improve accuracy The current model has been found to be useful for identifying the trends and helps in food packaging and product design. Protocols for developing cooking instructions for frozen microwaveable foods are being developed based on temperature profiles at various locations followed by microbial challenge study. Based on temperature profiles, a 99% confidence limit was used to identify the cooking time. Our findings indicated that Salmonella spp. is able to survive in chicken nuggets even when temperatures reached higher that 73.8 degrees C. However, the application of two minutes of standing time to the cooked samples completely destroyed Salmonella spp. cells and negative samples were observed even after enrichment. Initial runs on the QRAM show that microbial growth from retail to home storage was negligible and the biggest factors contributing to the final risk lies in the initial prevalence and ineffective microwave cooking. This QRAM aims to highlight areas for both the manufacturer and the consumer to address in order to reduce the occurrence of food borne illness related to microwave cooking of frozen NRTE food products. One of these areas is the tremendous need for consumer education on interpreting cooking instructions for their respective microwave ovens.

Publications

  • Chen J., Pitchai, K., Birla, S., Gonzalez, R., Jones, D., Subbiah., J. 2012. Temperature dependent dielectric and thermal properties of microwavable model food. J. Food Engg., Submitted.
  • Pitchai, K., Birla, S.L., Subbiah, J., Jones, D. 2012. Assessment of heating rate and non-uniform heating in domestic microwave ovens. J. of Microwave Power and Electromagnetic Energy. Accepted.
  • Pitchai, K. Birla, S., Subbiah J. 2012. Coupled Electromagnetic and heat transfer model for microwave heating in domestic ovens. J. of Food Engineering, 112, 110-111.
  • Chen, J., Pitchai, K., Birla, S., Gonzalez, R., Subbiah, J. 2012. Simulation of microwave induced heat, mass, and momentum transfer in food product, COMSOL conference proceeding, Oct 12-15, Boston. MA
  • Pitchai, K., Raj, J., Chen, J., Birla, S., Gonzalez, R., Wiemann, D., Subbiah, J. 2012. Microwave heat transfer model for frozen food in a rotating turntable, Poster presented at Annual IFT meeting and EXPO at Las Vegas, 25-28 June.
  • Pitchai, K., Raj, J. D., Birla, S., Subbiah, J., Jones, D. 2012. Evaluation of different methods of coupling rotation with microwave heating modeling using Comsol Multiphysics, 46th Symposium of International Microwave Power Institute, LasVegas, 20-22 June.


Progress 09/01/10 to 08/31/11

Outputs
OUTPUTS: Non-uniform heating of foods in microwave ovens is a major concern in assuring microbiological safety of not-ready-to-eat food products. The non-uniformity is attributed by complex interaction of microwaves with foods. To understand this complex interaction, a comprehensive model was developed to solve coupled electromagnetic and heat transfer equations using finite-difference time-domain based commercial software. The simulation parameters, cell size, heating time step, and number of iterations for steady state electromagnetic field were optimized. The comprehensive model was validated by heating a model food (1% gellan gel) as well as chicken nuggets and mashed potatoes. The model was validated qualitatively by measuring the product temperature profiles on three planes in the gel and compared to the corresponding thermal images. Quantitative validation was performed by measuring the temperature of the gel at 12 locations using fiber optic sensors. Model spatial temperature profiles agreed well with the thermal image profiles at 2.45 GHz frequency. The root mean square error values ranged from 0.53 to 4.52 degrees celculius, with an average value of 2.02 degrees celcius. To take into account of rotation of load and turntable during microwave heating, a MATALB routine was developed to simulate microwave heating of rotating objects. Spatial temperature profiles agreed well with the thermal image profiles. The developed model is now be used for studying the sensitivity of various product and oven parameters. Microbial destruction kinetics for Salmonella in mashed potato (D and z values) have been collected. The comprehensive heat transfer model is now also being integrated with microbial inactivation kinetics parameters (D and z values) for evaluating food safety risk during microwave cooking. PARTICIPANTS: Individuals: 1. Jeyamkondan Subbiah, PI, University of Nebraska-Lincoln 2. David Jones, co-PI, University of Nebraska-Lincoln 3. Harshavardhan Thippareddi, co-PI, University of Nebraska-Lincoln 4. Sohan Birla, University of Nebraska-Lincoln 5. Krishnamoorthy Pitchai, University of Nebraska-Lincoln 6. John Diamond Raj, University of Nebraska-Lincoln 7. Carol Jazmin Valenzuela Martinez, University of Nebraska-Lincoln 8. Edel Victor, University of Nebraska-Lincoln 9. Jiajia Chen, University of Nebraska-Lincoln 10. Paul Weckler, co-PI, Oklahoma State University 11. Carol Jones, co-PI, Oklahoma State University 12. Grace Okiror, Oklahoma State University TARGET AUDIENCES: Target audiences include frozen foods product development scientists in food industry. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
We are working with a large frozen food manufacturer in using the model to improve the safety and quality of microwaveable food products. This should lead to better design of product whose cooking performance in terms of heating uniformity is superior. Improvement in heating uniformity will results in enhanced food quality and safety.

Publications

  • Pitchai, K., Birla, S.L., Subbiah, J., Jones, D., Thippareddi, H. 2011. Coupled electromagnetic and heat transfer model for microwave heating in domestic ovens, Journal of Food Engineering, Accepted.
  • Birla, S. L., Raj, J. D., Subbiah, J. 2011. Modeling of microwave heating of a rotating object in domestic oven, COMSOL conference proceeding, Oct 12-15, Boston. MA.
  • Pitchai, K. Birla, S. L., Raj, J. D., Subbiah, J. 2011. Modeling of Susceptor assisted microwave heating of food package in domestic oven, COMSOL conference proceeding, Oct 12-15, Boston. MA
  • Birla S. L., Pitchai K., Subbiah, J. 2011. A critical comparison of COMSOL and QUICKWAVE software for modeling of microwave heating in domestic oven. Proceedings of 45th International Microwave Power Institute Annual Meeting, June 8-10, New Orleans, LA
  • Pitchai K., Birla S. L., Subbiah, J. 2011. Effect of location of small loads on heating rate and uniformity in domestic microwave ovens. Proceedings of 45th International Microwave Power Institute Annual Meeting, June 8-10, New Orleans, LA


Progress 09/01/09 to 08/31/10

Outputs
OUTPUTS: 1. Development of heat transfer model for microwave cooking: Due to inherent nature of standing wave patterns of microwaves inside a cavity and dielectric properties of different components in a food, microwave heating leaves non-uniform distribution of energy inside a food item. Achieving heating uniformity plays critical role in improving the safety of microwavable products. To understand the complex microwave interaction of microwaves with foods, a comprehensive coupled electromagnetic and heat transfer model was earlier developed using COMSOL software. Due to limitations of this software in modeling real scenarios such as rotation of food items during microwave, another commercial software, Quickwave, based on finite difference time domain was employed. A comprehensive model has been developed and it was used for studying effect of various microwave and product parameters. Temperature dependent dielectric properties of gellan gel, mashed potato, chicken nuggets were measured using open coaxial probe method. 2. Evaluation of heating uniformity in microwave ovens A custom designed container was used to assess non-uniform heating of a range of microwave ovens using a hedgehog of 30 T-type thermocouples. The mean and standard deviation of temperature raise along the radial distance and sector of the container were measured and analyzed. The effect of radial distance of rings and sectors were analyzed using ANOVA to identify the best location for placing food in the turntable. PARTICIPANTS: Carol Jones, Oklahoma State University; Paul Weckler, Oklahoma State University. TARGET AUDIENCES: food industry, microwave manufacturers, and consumers. PROJECT MODIFICATIONS: Not relevant to this project.

Impacts
1. Development of heat transfer model for microwave cooking: Several model parameters such as mesh size, time step, magnetron frequency, magnetron input were determined for predicting reasonable transient temperature of a model food. The developed model was validated qualitatively and quantitatively with experimental heating profile of 1% cylindrical gellan gel subjected to 30 s of heating in a 700 W rated power microwave oven. Spatial and temporal temperature profiles were collected using thermal imaging camera and fiber optic sensors, respectively. After studying the effect of various simulation parameters, it was found that magnetron frequency is most critical parameters effecting level of power coupling with the load and resulting temperature profile. Now the model is being used for simulating real case scenarios such as multi-components foods. This study helped in understanding interaction of various product and microwave parameters and how they influences microwave-heating pattern of any food materials. The developed heat transfer model will be integrated with microbial inactivation model for predicting microbial population upon completion of cooking. 2. Evaluation of heating uniformity in microwave ovens Our experimental study using a custom designed container for assessing microwave heating uniformity suggested that the best location to place small food items in a microwave oven is not at the center but near the edge of the turntable for uniform and rapid heating.

Publications

  • Birla S. L., Pitchai K., Subbiah, J., Jones, D. 2010. Heating performance assessment of domestic microwave oven. Proceedings of International Microwave Power Institute Annual Meeting, July 14-16, Denver CO.
  • Pitchai K.,Birla S. L., Subbiah, J., Jone, D. 2010. Effect of magnetron frequency on microwave heating pattern in domestic oven. Proceedings of International Microwave Power Institute Annual Meeting, July 14-16, Denver CO.
  • Birla, S., Pitchai, K., Subbiah, J. 2010. Development of real time temperature monitoring system for microwave cooking, Annual meeting of MidCentral ASABE section, April 9-10, 2010, Saint Joseph, MO.
  • Pitchai, K., Birla, S., Subbiah, J. 2010. Assessment of heating uniformity distribution in domestic microwave ovens, Annual meeting of MidCentral ASABE section, April 9-10, 2010, Saint Joseph, MO.


Progress 09/01/08 to 08/31/09

Outputs
OUTPUTS: Microwave heating is fast and convenient, but is highly non-uniform. When a food product contains raw or partially cooked food components, the non-uniform heating can result in inadequate cooking leading to microbiologically unsafe product. It is critical to have an understanding of how microwaves interact with food components in a domestic microwave oven to solve this problem. We approach this problem by developing a holistic computer model. We started with developing computer simulation model using finite element based COMSOL multi-physics software. To solve realistic scenarios of micorwave cooking, we have to solve thermal and electromagnetic governing equations simultaneously. Solving these equations took longer time to converge to the solution for even a simple domain using finite element method in COMSOL multi-physics. Then, we evaluated finite difference time domain method using QuickWave software for solving coupled equations. In this software, a user defined object has been developed to successfully simulate a range of microwave ovens and variety of regular solid food items. In order to predict accurate temperature profile, temperature dependent dielectric properties are essential. This work got delayed because of withdrawal of subcontract by USDA-ARS due to incompletion of paperwork. Recently, a new subcontract was awarded to Oklahoma State University, Stillwater for measuring temperature dependent dielectric properties. A setup has been assembled and a student has started collecting dielectric properties data for proposed products. D and Z values of E-coli and Salmonella have been compiled and data gap in the literature has been identified. These data will be collected in the coming months. For developing a risk assessment model for microwave cooking of not-ready-to-eat (NRTE) food products, variability and uncertainty existing in microwave ovens needs to be characterized. We have developed a setup to measure the variability in microwave energy distribution within the cavity of various microwave ovens. A 300-mm diameter container was divided into 36 compartments with same surface area. Same amount of water is added to each compartment. The container is then placed inside the oven and heated for few minutes such that the temperature increase was around 5-10 degrees Celsius. The temperature of each compartment was quickly measured by using a setup with 36 quick response thermocouples to be inserted into the container. The temperatures were also measured using an infrared camera. A setup has been developed to validate MW heating model using real time temperature mapping of the foods during microwave cooking. An IR camera (SC640 FLIR system) mounted on top of the microwave oven views through a screen placed on cut hole in top wall of the cavity. A computer algorithm is being developed to remove the screen effect from the thermal image. PARTICIPANTS: Carol Jones, Oklahoma State University; Paul Weckler, Oklahoma State University. TARGET AUDIENCES: Manufacturers of not-ready-to-eat food products, consumers. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.

Impacts
The computer simulation model has been developed and validated using model food (1% gellen gel cylinder, 80 mm diameter and 50 mm height). Simulation results qualitatively agreed well with the temperature profile obtained using IR camera. The results were presented and documented in the International Microwave Power Institute annual meeting proceedings. By developing heat transfer and pathogen destruction models to assess the risk of microwave cooking, this project will help to identify the significant factors that influences pathogen survival after microwave cooking), and to apply control measures (better package design) for reducing those pathogens. We are currently studying the effect of various system and process parameters on improving heating uniformity. The knowledge acquired in this project will be shared with interested academic and industry researchers in the upcoming International Microwave Power Institute meeting at Denver.

Publications

  • Birla, S. L., Pitchai, K., Subbiah, J. 2009. Development and validation of Microwave cooking model, In: Proceedings of International Microwave Power Institute Annual Meeting, July 8-10, Washington DC.
  • Pitchai, K., Hanson, B., Birla, S., Jones, D., Subbiah, J. 2009. Infrared real -time temperature monitoring of MW cooking: System development and validation. Presented at the American Society of Agricultural and Biological Engineer, Reno, June 22-25.
  • Birla, S. L., Subbiah, J. 2009. Applying Computer Simulations to Address Food Safety in Domestic Microwave Ovens, International Microwave Power Institute Annual Meeting, July 8-10, Washington DC.