Virendra M. Puri

Finite element modeling of heat and mass transfer in food materials during microwave heating — Model development and validation

Abstract A three-dimensional finite element model (FEM) was developed to predict temperature and moisture distributions in food materials during microwave heating. The FEM was tested with analytical solutions and commercial software (TWODEPEP, ANSYS) calculated values. The FEM predictions compared favorably with analytical solutions (within 0.066% of maximum temperature) and values calculated from commercial softwares (within 0.14% of maximum temperature). The three-dimensional FEM was also verified using experimental data from microwave oven heated cylinder- and slab-shaped potato specimens. A fluoroptic temperature measurement system and the near infrared (NIR) technique were used to measure temperature and moisture distributions, respectively. The FEM predicted temperature in potato samples agreed with measured results. The absolute maximum difference for slab geometry after 60 s of heating was 8.1 °C (or relative difference of 15.5% from the measured value), whereas, for the cylindrical geometry, it was 8.7 °C (or relative difference of 11.4%). The absolute moisture differences after 60 s of heating between FEM predictions and measured values for potato slab and cylinder were within 1.97% wet basis (or relative difference of 2.4%) and 1.85% wet basis (or relative difference of 2.1%), respectively.

Finite element analysis of microwave heating of solid foods

Abstract Microwave heating of solid food with rectangular and cylindrical geometries were analysed using TWODEPEP, a two-dimensional commercial finite element software. Absorbed microwave power density at any location in the test material was derived as a function of dielectric properties and geometry of the material. The model was experimentally validated by using sodium alginate gel as a test material. The temperature predictions by finite element analysis and the experimental measurements were very similar in slab-shaped samples. In cylindrical samples, the experimental data and the finite element predicted values of temperatures were close to each other at all regions except at the central region. Sensitivity analyses showed that variation in thermal diffusivity, dielectric properties, and incident microwave power resulted in significant variation in the temperatures as predicted by the finite element method.

The finite-element method in food processing: A review

Abstract The finite-element method has been successfully used to model several food-processing operations. Much of the activity to date has focused on heating and cooling, freezing and thawing, and heat and mass transfer, including drying and mechanical damage. Most of the studies have been confined to two-dimensional and/or axisymmetric regions undergoing transient response. A limited number of research results have been reported for three-dimensional and/or coupled heat, moisture, and stress analysis in food products. This review indicates that there still exists considerable potential for the use of the finite-element method in food-processing. Some other areas where the pay-off can be significant include baking, extrusion, aseptic processing, microwave heating, and optimization of food quality in terms of texture, nutrient retention, and microbial degradation during thermal processing.

Development and validation of a dynamic growth model for Listeria monocytogenes in fluid whole milk.

Listeria monocytogenes, a psychrotrophic microorganism, has been the cause of several food-borne illness outbreaks, including those traced back to pasteurized fluid milk and milk products. This microorganism is especially important because it can grow at storage temperatures recommended for milk (< or =7 degrees C). Growth of L. monocytogenes in fluid milk depends to a large extent on the varying temperatures it is exposed to in the postpasteurization phase, i.e., during in-plant storage, transportation, and storage at retail stores. Growth data for L. monocytogenes in sterilized whole milk were collected at 4, 6, 8, 10, 15, 20, 25, 30, and 35 degrees C. Specific growth rate and maximum population density were calculated at each temperature using these data. The data for growth rates versus temperature were fitted to the Zwietering square root model. This equation was used to develop a dynamic growth model (i.e., the Baranyi dynamic growth model or BDGM) for L. monocytogenes based on a system of equations which had an intrinsic parameter for simulating the lag phase. Results from validation of the BDGM for a rapidly fluctuating temperature profile showed that although the exponential growth phase of the culture under dynamic temperature conditions was modeled accurately, the lag phase duration was overestimated. For an alpha0 (initial physiological state parameter) value of 0.137, which corresponded to the mean temperature of 15 degrees C, the population densities were underpredicted, although the experimental data fell within the narrow band calculated for extreme values of alpha0. The maximum relative error between the experimental data and the curve based on an average alpha0 value was 10.42%, and the root mean square error was 0.28 log CFU/ml.

Flow properties of powders using four testers — measurement, comparison and assessment

Abstract The flow properties, i.e. cohesion and slope of the yield locus, of wheat flour and sugar were measured using four testers, namely, the triaxial cell, the direct shear cell, the Jenike shear cell and the rotational split-level (RSL) shear cell over a range of loading conditions. A statistical comparison was done at the 0.05 level of significance ( P ) to evaluate the performance of the four testers with respect to the yield loci. For wheat flour, the flow properties determined from the Jenike shear cell, the direct shear cell, the triaxial cell and the RSL shear cell experimental data were not significantly different. For sugar, however, the test results from the RSL shear cell were significantly different from the other three testers. Therefore, the four testers seemed appropriate for determining the flow properties of wheat flour and similar powders, whereas, the Jenike shear cell, the triaxial cell and the direct shear cell seemed appropriate for measuring flow properties of sugar and similar powders.

Decontamination of unpackaged and vacuum-packaged boneless chicken breast with pulsed ultraviolet light

The effectiveness of pulsed UV light on the microbial load of boneless chicken breast was investigated. Unpackaged and vacuum-packaged samples inoculated with an antibiotic-resistant strain of Salmonella Typhimurium on the top surfaces were treated with pulsed UV light for 5, 15, 30, 45, and 60 s at 5, 8, and 13 cm distance from the quartz window in the pulsed UV light chamber. The log(10) reductions of Salmonella (cfu/cm(2)) on unpackaged samples varied from 1.2 to 2.4 after a 5-s treatment at 13 cm and a 60-s treatment at 5 cm, respectively. The log(10) reductions on vacuum-packaged samples varied from 0.8 to 2.4 after the 5-s treatment at 13 cm and the 60-s treatment at 5 cm, respectively. The optimum treatment conditions were determined to be 5 cm-15 s for unpackaged samples and 5 cm-30 s for vacuum-packaged samples, both of which resulted in about 2 log(10) reduction (approximately 99%). The total energy and temperatures of samples increased with longer treatment time and shorter distance from the quartz window in the pulsed UV light chamber. The changes in chemical quality and color of samples were determined after mild (at 13 cm for 5 s), moderate (at 8 cm for 30 s), and extreme (at 5 cm for 60 s) treatments. Neither malonaldehyde contents nor color parameters changed significantly (P > 0.05) after mild and moderate treatments. Mechanical properties of the packaging material were analyzed before and after pulsed UV light treatments. The elastic modulus at both along-machine and perpendicular-to-machine direction and yield strength at perpendicular-to-machine direction changed significantly (P < 0.05) after extreme treatment. Overall, these results clearly indicate that pulsed UV light has a potential to be used for decontamination of unpackaged and vacuum-packaged poultry.

Inactivation of Listeria monocytogenes on unpackaged and vacuum-packaged chicken frankfurters using pulsed UV-light.

The effectiveness of pulsed UV-light on the microbial load and quality of unpackaged and vacuum-packaged chicken frankfurters was investigated. Samples were inoculated with Listeria monocytogenes Scott A on the top surfaces, and then treated with pulsed UV-light for 5, 15, 30, 45, and 60 s at 5, 8, and 13 cm distance from the quartz window in a pulsed UV-light chamber. Log reductions (CFU/cm(2)) on unpackaged samples were between 0.3 and 1.9 after 5-s treatment at 13 cm and 60-s treatment at 5 cm, respectively. Log reductions on packaged samples ranged from 0.1 to 1.9 after 5-s treatment at 13 cm and 60-s treatment at 5 cm, respectively. The temperature changes of samples and total energy (J/cm(2)) received at each treatment condition were monitored. The extent of lipid peroxidation and the color were determined by thiobarbituric acid-reactive substances (TBARS) test and CIELAB color method, respectively. Lipid peroxidation of samples did not change significantly (P > 0.05) after mild (5-s treatment at 13 cm) and moderate (30-s treatment at 8 cm) treatments. Significant differences (P < 0.05) in color parameters were observed after treatments of both unpackaged and packaged samples. Packaging material was also analyzed for mechanical properties. The elastic modulus, yield strength, percent elongation at yield point, maximum tensile strength, and percent elongation at break did not change significantly (P > 0.05) after mild treatment. Overall, this study demonstrated that pulsed UV-light has a potential to decontaminate ready-to-eat (RTE) poultry-based food products.

Flow property measurement using the Jenike cell for wheat flour at various moisture contents and consolidation times

Abstract The flow properties, i.e. cohesion and slope of the yield locus, of wheat flour at three different moisture contents (11.8%, 14.7% and 16.4%, dry basis) were measured using the Jenike shear tester with no time consolidation, i.e. instantaneous yield loci, over a range of loading conditions. The values of cohesion obtained for the three moisture contents were not significantly (P

Uniformity of Powder Die Filling Using a Feed Shoe: A Review

The process of die filling for achieving a uniform fill is a critical unit operation that is far from being sufficiently understood. Factors influencing powder flow from a feed shoe and powder deposition into a die are reviewed in this article. The factors include feed shoe speed, feed shoe holding time over the die, particle shape and size, powder size distribution, die shape and size, die configuration, filling intensity, filling direction, and the height of powder in the feed shoe. Devices suitable for evaluating the quality of powder deposition in dies need to be more: (1) specific to simulate the filling process, (2) versatile to encompass different filling parameters, and (3) able to provide quantitative evaluation. Recommendations to improve die deposition and density uniformity are given with respect to powder characteristics and die and feed shoe properties. New devices using load cells, pressure sensors, or tactile sensors to investigate powder deposition are important for further the investigation of the deposition process and spatial density uniformity. These primary measurement devices have the potential to bridge the knowledge gap and enable the development of discrete and/or continuum-concept computational models for the dynamic die-fill process.

Pulsed UV light inactivation of Salmonella Enteritidis on eggshells and its effects on egg quality.

The majority of Salmonella Enteritidis outbreaks have been related to the consumption of raw or undercooked eggs or egg-containing foods. Therefore, the U.S. Department of Agriculture mandates egg washing for all graded eggs by use of a detergent solution and sanitizer. These agencies and the egg industry have been investigating alternative decontamination techniques, which could better serve the public, minimize costs, and benefit both the public and the industry. Pulsed UV light is an emerging technology that is used to inactivate microorganisms quickly. In this study, the effectiveness of pulsed UV light was evaluated for the decontamination of eggshells. Eggs inoculated with Salmonella Enteritidis on the top surface at the equator were treated with pulsed UV light 1 to 30 s, at a distance of 9.5 and 14.5 cm from the UV lamp in a laboratory-scale, pulsed UV light chamber. Three eggs were used per treatment in each repetition, except for quality measurements, which involved six eggs per treatment in each repetition. A maximum log reduction of 5.3 CFU/cm2 was obtained after a 20-s treatment at 9.5 cm below the UV lamp at a total dose of 23.6+/-0.1 J/cm2, without any visual damage to the egg. After a 30-s treatment at 9.5 and 14.5 cm, the temperature of eggshell surfaces increased by 16.3 and 13.3 degrees C, respectively. Energy usage increased up to 35.3+/-0.1 and 24.8+/-0.1 J/cm2, after 30-s treatments at 9.5 and 14.5 cm, respectively. The effect of pulsed UV light treatments on egg quality was also evaluated. Pulsed UV-light treatments for 3, 10, and 20s at either 9.5 or 14.5 cm did not change the albumen height, eggshell strength, or cuticle presence significantly (P<0.05). This study demonstrated that pulsed UV light has potential to decontaminate eggshell surfaces.