Progress 10/01/00 to 09/30/05
Outputs
During the five-year duration of this project, a comprehensive mechanistic description of hamburger cooking was developed. In cooking hamburger patties, thermal destruction of pathogens is of prime concern for food safety. We identified the mechanism of heat transfer prevalent during contact-cooking processes, such as grilling used for cooking hamburger patties. This mechanism involves moving boundaries that separate different regions within a patty. When an initially frozen hamburger patty is heated on a grill, two moving boundaries describe the energy transport mechanism; the first boundary separates the frozen and unfrozen region, and the second identifies the interface where water vaporizes. We validated the existence of multiple moving boundaries with experimental data. The presence of moving boundaries was shown to exist in a variety of other food processes such as freezing, thawing, baking, and immersion frying. This mechanistic description provided the
framework of a unified theory that may be used as a basis to describe many industrial food processing operations. The computer-aided simulation of the contact heating process allowed us to determine the cooking time as a function of different grill design and operating variables including plate temperatures, patty thickness, and gap separation between plates. Using an industrial-scale grill, we validated the predicted results. The predictive models were used to recommend design and operating variables for optimum performance of industrial grills. This project involved active collaboration with other stations for data on food properties for use in computer models. Air impingement technology has recently become popular in industrial freezing and baking equipment. There is a woeful lack of scientific information needed to design and operate such equipment with high energy efficiency and desired processing capacity. We developed predictive procedures to estimate spatial variations of heat
transfer in impingement systems. We conducted a comparative study of air flow distribution from an array of circular-opening nozzles and rectangular slot jets using flow visualization techniques. The air jet was impinged on a flat metal surface in each case. A Helium-bubble generation device in conjunction with a CCD camera system was used for the purpose of visualization. The results demonstrated that with a suitable optimization procedure, rectangular slot jets may provide more uniform heat transfer coefficient distribution than conventional round jets. A computer-aided mathematical model was developed to study fluid flow and heat transfer in the outside boundary layer and internal freezing in a food product subjected to air impingement. External air flow was simulated using a commercial computational package. Overall, freezing time predictions from 0 C to -18 C predicted by the simulation model were within 5% of experimentally determined freezing times in model foods. Research
collaboration with other stations helped identify experimental methods to study air impingement.
Impacts
Computer-aided simulations of hamburger patty cooking were used in developing design recommendations for equipment manufacturers to ensure food safety in cooking. An improved understanding of air-impingement processing is aimed at designing new generation of energy efficient processing equipment.
Publications
- Sun, S., Singh, R. P. and OMahony, M. 2005. Quality of meat products during refrigerated and ultra-chilled storage. Journal of Food Quality 28:30-45.
- Palou, E., Welti-Chanes, J., Singh, R. P., Lopez-Malo, A., Guerrero, L. G., Carrillo, J., Ramirez, J. M. and Athmaram, K. 2005. Remote experiments for food engineering. Journal of Food Engineering 67:129-133.
- Anderson, B. and Singh, R. P. 2005. Moisture diffusivity in Tylose gel (Karlsrouhe test material). Journal of Food Science 70(5):331-337.
- Singh, R. P. and Sarkar, A. 2005. Thermal properties of frozen food. In Engineering Properties of Foods, Edited by Rao, M. A., Rizvi, S. S. H. and Datta, A. K. Chapter 5, pp. 175-207.
- Singh, R. P. 2005. Food engineering. In The Engineering Handbook, Edited by Dorf, R. CRC Press. Chapter 189, pp. 189-1 - 189-14.
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Progress 01/01/04 to 12/31/04
Outputs
Particle Image Velocimetry (PIV) is a powerful technique for determining flow fields. However, its application in food engineering has been limited due to difficulties in replicating intricate geometries with transparent materials. One important application is the study of the airflow during the cooling of packaged strawberries to improve cooling rate and uniformity. In this work a transparent model of a one pound strawberry package was developed. Also, a suitable working fluid and the flow rate needed to replicate the flow conditions were determined. The strawberries were modeled as spheres, whose diameter was calculated based on the average volume of strawberries. The basket model dimensions replicate those of the real basket. The material and fluid were selected based on refraction index and oil viscosity. The non distortion of a grid of lines placed behind the system indicates a refraction index match. To obtain the flow rate, a Reynolds number matching was
performed. The void space inside a strawberry basket was characterized by sectioning a resin cast of it and the average open space and wetted parameter were obtained. The model, consisting in 30 acrylic spheres of 1.59 cm arranged in a body-centered cubic structure inside an acrylic basket of 9.5 x 6.8 x 12.7 cubic cm, reproduced the packaging factor of the real system and replicated the geometric relation of the real package cross section area. The material and fluid were Pyrex glass and a mix of Aniseed and Baby Oil (1:5 v/v, 10.2 cP). The working fluid flow rate that matches the operating conditions of the real system was 590 cubic cm/s. The set of design and experimental conditions obtained in this study allows the use of PIV to elucidate the effect of vent design, upstream velocity and strawberry distribution in the airflow field inside the strawberry package.
Impacts
PIV is useful in non-invasively determining fluid flow around solid objects such as strawberries. Packages designed with this new information will assist in reducing the post harvest losses in strawberries.
Publications
- Erdogdu, F., Zorrilla, S. E. and Singh, R. P. 2004. Effects of different objective functions on optimal decision variables: A study using modified complex method to optimize hamburger cooking. Lebensmittel-Wissehschaft und-Technologie 38:111-118.
- Singh, R. P. and Erdogdu, F. 2004. Virtual experiments in food processing. RAR Press, Davis.
- Singh, R. P. and Anderson, B. A. 2004. The major types of food spoilage: an overview. In: Understanding and Measuring the Shelf-life of Food. Editor, R. Steele, Woodhead Publishing Limited, Cambridge. p 3-23.
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Progress 01/01/03 to 12/31/03
Outputs
There is a need to develop faster thawing methods, especially since current methods can be undesirably slow (still air) or are very expensive and cause uneven thawing (microwave). One possible method to speed thawing is using jets of air at high velocity impinging on the food surface. A mathematical model was developed to study the feasibility of using impingement to improve thawing rates. A finite difference code was created in Matlab, utilizing the enthalpy method. Heat transfer during thawing of a meat analog (Tylose), were compared between impingement and still air. The convective heat transfer coefficients used in the model were measured in the laboratory. The thawing times predicted by the model were verified through experiments and found to have good agreement. The heat transfer coefficient during impingement thawing was found to range from 20 to 160 W/square m-K. The model was used to predict thawing times from -20 C to 0 C, using air at 5 C. Thawing in a
refrigerator (still air) took more than 24 hours. The model demonstrated that the thawing time could be reduced to less than three hours by impinging with air at 20 C for two hours, followed by air at 5 C for the remaining time. This study demonstrated that the use of air impingement technology could significantly shorten thawing times. This mathematical model can be utilized to improve experimental design and operating conditions for impingement-assisted food processing. Strawberries are packaged and cooled in polymeric clamshell packages that are stacked in corrugated trays. Mathematical modeling of the flow and heat transfer is an ideal approach to improve the cooling efficiency for such package systems. Modeling by solving the turbulent Navier-Stokes equation is constrained by computation time. Modeling by using porous media assumptions may be restricted by the validity of the porous media assumption itself. The objective of this research was to compare the two possible modeling
approaches for cooling strawberries in clamshell packages: appropriate porous media model and the k-e turbulence model. Using the k-e turbulence model, individual clamshells were modeled for various pressure gradients across the packages and the results were added in parallel and series configurations to model trays. Modeling of the entire tray was also done using Darcy-Forchheimer-Brinkman (DFB) theory of airflow through porous media. The results of the simulations were compared to experimental data for cooling of strawberries collected from lab-scale experiments and field trials. Simulations using the turbulence model showed agreement within 10 percent for experiments with individual clamshells. But when added together for the entire tray the agreement was less than 20 percent. Porosity of the stacked strawberries was determined to be 0.44. Using the porosity data and assuming strawberries as ellipsoids, the DFB model gave simulation results that agreed to the order of 15 percent
for the entire tray. The DFB model was less accurate in predicting spatial variations of temperature and pressure compared to the k-e model. Computation times were significantly shorter for the DFB model.
Impacts
Impingement-assisted systems have become popular in new generation of food process equipment. We are using a laser-based system to visualize movement of air around complex shaped foods. This information is necessary to improve process efficiency and product quality. Improved understanding of fluid flow in strawberry packages is aimed at designing clam-shell packages that minimize product spoilage.
Publications
- Anderson, B. A., Sun, S., Erdogdu, F. and Singh, R. P. 2004. Performance evaluation of household refrigerators during thawing and freezing of selected mean products. International Journal of Refrigeration 27(1):63-72.
- Anderson, B. A., Sarkar, A., Thompson, J. F. and Singh, R. P. 2004. Commercial forced air cooling of packaged strawberries. Transactions of American Society of Agricultural Engineers. (In Press)
- Anderson, B. A. and Singh, R. P. 2004. Factors determining spoilage. A Chapter in Understanding and Measuring the Shelf life of Food, Steele, R., Ed., Woodhead Publishing Limited, Cambridge, England. (In Press)
- Sarkar, A. and Singh, R. P. 2004. Air impingement food processing. In Advancements in Thermal Processing of Food Products. Richardson, P., Ed. Woodhead Publishing Limited. Cambridge, UK. (In Press)
- Sarkar, A. and Singh, R. P. 2004. Thermal properties of frozen foods. In Engineering Properties of Foods, 4th Edition. Datta, A. K., Rao, M. A. and Rizvi,S.S.H., Ed., Marcel Dekker, Inc., New York. (In Press)
- Wang, L. and Singh, R. P. 2004. Finite element modeling and sensitivity analysis of double-sided contact-heating of initially frozen hamburger patty. Transactions of American Society of Agricultural Engineers. (In Press)
- Anderson, B. A., Singh, R. P. and Rovedo, C. O. 2003. Use of phytoglycogen extracted from corn to increase the bowl-life of breakfast cereal. Journal of Food Process Engineering 26(3):315-322.
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Progress 01/01/02 to 12/31/02
Outputs
Air impingement systems commonly used in textile and paper drying are gaining new applications in food processing operations. To determine spatial variation in heat transfer in impingement systems used for baking, thermocouples were placed slightly below the surface of the dough. It was found that heat transfer coefficient increased as the boundary layer developed. At a nozzle-to-plate distance of 5.3 times jet diameter, heat transfer coefficient was highest at stagnation, but a secondary maximum was found at a radial distance of approximately 1.7 cm. Dough shaped as a cylinder produced different heat transfer characteristics than did flat dough. In another study, experimentally obtained heat transfer coefficients (h) were modeled with a computational fluid dynamic (CFD) package. Measurements were done for single, double and triple slot and circular jets impinging on a flat plate. The h-value variations under the jet were studied for various jet diameter (D), lengths
(L) and nozzle to plate spacing (H). Maximum h-values varied from 80 to 140 W/m_K at stagnation point for circular and slot jets for velocities from 15 to 30 m/s, and h-values dropped by 50 to 75% of maximum at a radial distance of 4 cm for circular jets and 30 to 60% for slot jets. Results show good agreement with existing semi-empirical models for heated conditions. The experiments in conjunction with visualization and modeling indicate turbulent structures in the jet wake cause considerable energy dissipation for Reynolds number of 25000 and above for D/L ratios of 2 and D/H ratios of 8 and above.
Impacts
These studies demonstrate that the combined use of flow visualization, measurement of spatial variations of heat transfer coefficient, and modeling can lead to a better understanding of air impingement processes. The new information provides guidelines for equipment manufacturers to design systems with improved heat transfer characteristics.
Publications
- Chakraverty, A. and Singh, R. P. 2001. Postharvest Technology Cereals, Pulses, Fruits and Vegetables. Science Publishers, Inc., Enfield, New Hampshire, Plymouth, United Kingdom.
- Singh, R. P. and Heldman, D. R. 2001. Introduction to Food Engineering, 3rd Edition. Academic Press, Inc., San Diego, California.
- Wichchukit, S. A., Zorrilla,S. E. and Singh, R. P. 2001. Contact heat transfer coefficient during double-sided cooking of hamburger patties. Journal of Food Processing Preservation 25:207-221.
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Progress 01/01/01 to 12/31/01
Outputs
Most of the impingement systems used in the food industry utilize jets with a circular opening. However, jet systems with a two-dimensional opening, and arranged parallel to each other, promise to have a more uniform convective heat transfer coefficient distribution. This may result in uniform cooking, freezing, or thawing characteristics while applying impingement systems. In the present work, a comparative study of flow distribution patterns from an array of four circular-opening nozzles and a two- dimensional jet was conducted using flow visualization techniques. The jet was impinged on a flat metal surface. A Helium-bubble generation device in conjunction with a CCD camera system was used for the purpose of visualization. The relative spatial distribution of convective heat transfer from the two types of jets was studied at jet exit with airflow velocities of 15, 20 and 25 m/s. A previously described setup for measurement of spatial heat transfer coefficient was
used for the temperature ranges of 25 C to 80 C. For the same exit air velocities, the laminar jets show a slightly lower convective heat transfer coefficient (averaged over the entire area) but a more uniform heat transfer coefficient distribution pattern as compared to the array of circular jets. The flow patterns indicate that the lower convective heat transfer may be attributed to the reduced turbulence in the boundary layer while using the two-dimensional jet as compared to the circular jets where the jets interact with each other to increase the turbulence effect. The results show that with a suitable optimization procedure, two-dimensional jets may give a much better product quality than conventional round jets due to uniform heat transfer coefficient distribution.
Impacts
Air impingement systems have been used in various industrial applications such as textile and paper drying and electronic cooling. More recently, air impingement systems are developing as a promising thermal processing technique for industrial food processing operations. In our studies, we are developing new design information that will allow uniform heating/cooling of foods.
Publications
- Reveco, J. Rovedo, C. and Singh, R.P. 2001. Textural properties of popcorn cakes. Proceedings of the International Conference on Engineering and Food. (ICEF8). pp45-48
- Lee, J.H., Yoo, S.B., Sohn, J.M. and Singh, R.P. 2001. Web and CORBA interfaces of food thermal conductivity database. Proceedings of the International Conference on Engineering and Food. (ICEF8). pp 2081-2085
- Lima, I. and Singh, R.P. 2001. Mechanical properties of a fried crust. Journal of Texture Studies 32 (1) 31-40
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Progress 01/01/00 to 12/31/00
Outputs
The process optimization of hamburger cooking involves not only the microbiological product safety and the efficiency of the process, but also the desirable levels of texture and sensory quality. The objective of this work was to determine the effect of plate temperatures and gap thickness between plates on the texture quality of beef patties during double-sided cooking, in an attempt to relate the results to any change in the heat transfer mechanism of the patties. Frozen ground beef patties (12 mm thickness) were cooked on a clamshell grill (Taylor, Rockton, IL) at different plate temperatures (177C to 218C), for different gap thickness between plates (9.65 mm to 11.05 mm) during 130 s. The patty texture was determined using a Texture Analyzer (TA.XT2) immediately after frying. A 61 mm x 80 mm slice was removed from each patty using a stainless steel borer and tests were performed using a Kramer Shear probe with five blades at a speed of 5 mm/s. Texture Profile
Analysis of the patties was also performed. Five 2.3-mm-diameter cylinders were removed from each patty with a core borer. Each core was compressed twice to 75% of its original height using a 40-mm-diameter aluminum cylinder probe at a speed of 5 mm/s. A decrease in the gap thickness resulted in an increase of the maximum shear force, the firmness and work needed to shear. Furthermore, the work needed to shear was affected by a change in temperature. The hardness of the patties decreased and their cohesiveness increased when the gap thickness was decreased. The cooking temperature only affected the springiness of the patties. The gap thickness and the temperature did not affect the gumminess and chewiness of the patties. No adhesiveness was observed. These results relate the main textural attributes of the patties to physical and chemical changes that occur during cooking.
Impacts
Improving texture of the cooked products will allow food processors to increase their market share.
Publications
- Zorrilla, S.E., Rovedo, C.O., and Singh, R.P. 2000. A new approach to correlate textural and cooking parameters with operating conditions during double-sided cooking of meat patties. Journal of Texture Studies. In Press.
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Progress 01/01/99 to 12/31/99
Outputs
The textural quality of ready-to-eat (RTE) cereals is based on the initial crispness and the ability to retain it after immersion in milk. Because cereals lose crispness quickly when immersed in milk, any attempts to improve the textural characteristics of immersed product are of value to the cereal processor. The objectives of this study were to compare the bowl life of different RTE cereals, and to improve their texture characteristics by using an edible coating. The texture characteristics of eight different RTE cereals were determined using a Kramer Shear probe with five blades (Texture Analyzer). Fifteen grams of samples were weighed for each experiment. Each test was performed at four different immersion times (0, 2, 3 and 5 minutes) in milk at 8C. Similar tests were performed with RTE cereals covered with an edible coating (under patent review). The coating was prepared as a solution with a product extracted from corn and distilled water (1g/10 ml). Samples
were sprayed on both sides with the edible coating and dried for 10 minutes in an oven at 110C. Samples were allowed to reach room temperature before each experiment. The texture retention (ratio of the peak force of the samples immersed in milk over the peak force of the dry product) was determined. Cereals naturally covered with a sugary coating showed the best percentage of texture retention in milk. The texture retention of other cereals analyzed was less than 40% for 2 minutes in milk. When covered with an edible coating, the texture retention of these samples dramatically improved (higher than 80% and 60% for 2 and 5 minutes immersion in milk, respectively). The bowl life of selected RTE cereals can be improved with the addition of an edible coating, particularly for products with low texture retention in milk.
Impacts
The newly discovered edible coating is used for improving the textural properties for breakfast cereals. This edible coating is expected to be a desirable alternative to the traditional sugar-based coatings.
Publications
- Rovedo, C.O., Pedreno-Navarro, M.M., and Singh, R.P. 1999. Mechanical properties of a corn starch product during the post-frying period. Journal of Texture Studies 30(3):279-290.
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Progress 01/01/98 to 12/01/98
Outputs
During the post-frying period, crispness of fried foods rapidly deteriorates due to moisture redistribution inside a product. To study this phenomenon, mechanical properties of a corn starch product with added gluten, amylose and amylopectin were determined. Fried products were prepared with corn starch, distilled water and different gluten contents. Puncture test was used to determine the hardness of the crust for slabs with 0 percent and 30 percent gluten, fried for 10 min. at 180 C. The hardness of the crust decreased during the first 30 min. of post-frying storage at 4 C. The addition of 30 percent gluten significantly decreased the initial puncture force in the crust region, but had minimal effect for 4.5 h of post-frying storage. The residual stress of the samples increased with time of storage, indicating an increase in firmness. The influence of moisture content on the dynamic mechanical properties of the crust region of a fried starch product was
investigated. The dynamic mechanical properties were measured with a Rheometrics Solid Analyzer using a three point bending test. Thin rectangular samples of crust region were used. Temperature sweeps (25-200 C) and frequency sweeps (0.1-15 Hz), at a deformation level of 0.1 percent, were performed and storage and loss modulus were determined. The results indicated a plasticizing effect of water. These studies provided new information on the influence of moisture content on the glass transition of the crust.
Impacts
(N/A)
Publications
- PINTHUS, E.J., SINGH, R.P., SAGUY, I.S. and FAN, J. 1998. Formation of Resistant starch during deep-fat frying and its role in modifying mechanical properties of fried patties containing corn, rice, wheat, or potato starch and water.
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Progress 01/01/97 to 12/01/97
Outputs
The heat and mass transfer processes that occur during contact heating in hamburger patties cause protein denaturation and changes in physical and thermal properties. Among these changes, the shrinkage and cooking loss are directly related to the rates of heat and mass transfer in the patties. Consequently, these transfer processes may alter the safety and quality of the cooked patties. The objective of this study was to determine changes in dimensions and cooking loss as a function of heating time and temperature during single-sided cooking of hamburger patties. Frozen hamburger patties were obtained from a fast-food restaurant. A laboratory-scale single-sided grill was used in this study. The patties were cooked for 300 seconds at three grill temperatures: 160, 180, and 200 degrees C. The diameters and locations of the top surface of the patties were recorded using a video camera during cooking. Video images were transferred into a computer to determine the
diameters and top surface locations at different cooking times. A combined dimensional change of upward bulging and increase in thickness of up to 27 percent was observed when the patties at an initial temperature of -16 degrees C were cooked on a grill set at 160 degrees C temperature. The maximum reduction in diameter was 23 percent and the maximum cooking loss was 46 percent. Mathematical expressions describing the changes in dimensions and cooking loss for different heating time and temperature were developed.
Impacts
(N/A)
Publications
- Hertlein, J., R.P. Singh and H. Weisser. 1995. Prediction of oxygen transport parameters of plastic packaging materials from transient state measurements. Journal of Food Engineering. 24, pp. 543-560.
- Singh, R.P. 1995. Food processing - Food preservation and storage. Encyclopaedia Britannica Online. Chicago, IL.
- Singh. R.P. 1995. Food processing - Frozen and prepared foods. Encyclopaedia Britannica Online. Chicago, IL.
- Singh, R.P. 1995. Principles of heat and mass transfer. In frozen and refrigerated doughs and batters. (Ed) Lorenz, K. American Society of Cereal Chemists. pp. 193-217.
- Singh, R.P. 1996. Food Engineering. In the Engineering handbook. (Ed) Dorf, R. CRC Press Inc. Boca Raton, FL. pp. 1779-1791.
- Singh, R.P. 1996. Computer applications in food technology - Use of spreadsheets in graphical, statistical, and process analysis. Academic Press. San Diego, CA.
- Banga, J.R., A.A. Alonso and R.P. Singh. 1997. Stochastic dynamic optimization of batch and semicontinuous bioprocesses. Biotechnology
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Progress 01/01/96 to 12/30/96
Outputs
Physical and thermal properties of foods are necessary when designing or evaluating the performance of food processing systems. For example, the knowledge of optical properties of oil can provide useful data for designing sensors that could monitor the condition of oil during deep fat frying. Oil deteriorates during frying due to hydrolysis by moisture, oxidation by air, and polymerization by high temperature. The effects of each of these conditions on the visible and near infrared light absorption in corn oil during frying were studied. The percent of total polar materials formed in corn oil, as the oil deteriorated under aggressive air oxidation at 185 C over 8 hours, was found to be highly correlated with the absorption changes measured in both visible and near infrared regions of the spectrum. A low-cost optical sensor was developed to predict the total polar materials in corn oil. In another project, specific heat, thermal conductivity, thermal diffusivity, and
density of cooked and grated tuna, with different levels of brine, were measured. The experimentally-determined thermal properties were found to be highly correlated with the water content of tuna. Another study focused on determining optimal processing conditions for the dehydrofreezing of papaya. Partial drying (50% weight reduction) of papaya particulates in 30 C air , followed with freezing in an air-blast freezer, yielded final product with highest firmness.
Impacts
(N/A)
Publications
- Singh, R.P. 1995. Principles of Heat and Mass Transfer. In Frozen and Refrigerated Doughs and Batters. (Ed) Lorenz, K. American Society of Cereal Chemists. pp 193-217
- Hertlein, J., R.P. Singh and H. Weisser. 1995. Prediction of oxygen transport parameters of plastic packaging materials from transient state measurements. Journal of Food Engineering. 24, pp 543-560
- Singh, R.P. 1995. Food Processing - Food Preservation and Storage. Encyclopaedia Britannica Online. Chicago, IL
- Singh, R.P. 1995. Food Processing - Frozen and Prepared Foods. Encyclopaedia Britannica Online. Chicago, IL
- Singh, R.P. 1996. Food Engineering. In The Engineering Handbook. (Ed) Dorf, R. CRC Press Inc. Boca Raton, Florida. pp 1779-1791
- Singh, R.P. 1996. Computer Applications in Food Technology - Use of Spreadsheets in Graphical, Statistical, and Process Analysis. Academic Press. San Diego, CA.
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Progress 01/01/95 to 12/30/95
Outputs
Knowledge of accurate information on food properties is essential in improving process efficiency and the development of new products. Thermal conductivity and thermal diffusivity are two important properties that influence the heating and cooling characteristics of foods. A new technique was developed for the simultaneous determination of thermal diffusivity and thermal conductivity in a single experiment using a differential scanning calorimeter (DSC). For the thermal diffusivity determination, the temperature in the DSC can be increased linearly with time. The average thermal diffusivities for potato, banana, pear, Red Delicious apple, Granny Smith apple, agar (1.5 percent) and glycerin were 1.784, 1.044, 1.202, 1.219, 1.373, 1.411, and 0.922 x 10-7 m-2/s, respectively, for a temperature range of 30-40 degrees C and 10 degrees C/min scanning rate. Measurements were made for sample volumes of less than 0.6 cm3 in less than 200s. Another study was aimed at
determining reliable procedures that may be used to measure selected textural properties of fried foods. The methods included compression, puncture and three-point bending. A potato model system was chosen. Samples were fried in Canola oil at three temperatures (160, 180, 190 degrees C) for 5, 10, and 15 min and tested in a dynamic mechanical analyzer. Average stress value for puncture test was 48.17E5 Pa. The three-point bending test is useful in determining the crust flexural properties.
Impacts
(N/A)
Publications
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Progress 01/01/94 to 12/30/94
Outputs
Optimization of food processing operations is often necessary to select the bestoperating conditions. A new optimization scheme was examined for its use in the air drying processes. The following optimization problems related with the air drying of foods were studied: maximization of nutrient or enzyme retention, minimization of process time, maximization of nutrient retention with a constraint on the final retention of an enzyme, and maximization of energy efficiency. These problems were successfully solved for three different model systems using a stochastic optimal control algorithm. The optimal policies obtained were significantly superior to the classical processes in several cases. Another study focused on the use of computer aided modeling of the modified atmosphere packaging of fruits and vegetables. A new mathematical model of a perforated polymeric package was developed. The experimental study involved the design of a perforated package for broccoli since the
recommended modified atmosphere for broccoli is difficult to attain by commonly available polymeric packages. A metal wire heated by a discharging capacitor was used to make 75 micrometer diameter perforations. Replicate polyethylene packages with perforations were prepared, filled with broccoli, and stored at 2-3 degrees C. The package atmosphere was monitored until the steady state conditions were reached. Atmospheres inside packages with perforations attained the recommended modified atmospheric composition, validating the prediction by the model.
Impacts
(N/A)
Publications
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Progress 01/01/93 to 12/30/93
Outputs
A broader knowledge of the water management system in the food industry from both quality and quantity standpoints is necessary to conserve water use in food processing. A comprehensive water accounting study was conducted in three food processing plants, a peach cannery, a tomato cannery, and a frozen product plant. This study was done with respect to quantity, quality and thermal energy of the influence and effluent streams of every unit operation in all plants. The flow rate was measured using a doppler ultrasonic flow meter for its non-invasive characteristic. Water intensive operations were found to be the vacuum peeler in tomato processing (52 GPM) and the lye peeler in peach processing (106 GPM). Water quality analysis was done for organic acids, sugars, total solids, total fixed solids, total suspended solids, COD, pH and pectins. In addition, the potential of by-products and energy recovery was evaluated. The data obtained in this study were used to program a
simulation of food processing water management system with the software packaging EXTEND on an Apple-Macintosh computer. Water accounting and plant simulation have been found to be useful in determining the potential of recycling water within a plant and the reduction of the overall water usage.
Impacts
(N/A)
Publications
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Progress 01/01/92 to 12/30/92
Outputs
During frying of foods, many factors including the type, temperature, and condition of the oil influence heat transfer from the metal heating element to the frying oil. As oil is used, degradation products are produced. These products influence the rate of heat transfer between oil and the food being fried. A study was conducted to measure thermal properties during the frying process. Convective heat transfer coefficients were determined using a lumped model for heat transfer in a high thermally conductive material. At 188 C oil temperature, the heat transfer coefficient was 288 and 246 W/sq m.C in coconut and canola oil, respectively. The repeatedly used soybean oil's heat transfer coefficient was significantly different than for the fresh soybean oil. Using magnetic resonance imaging, the mass transfer of oil and water inside a food material during frying was determined. Scanning electron microscopy was used to study the structural changes in a potato during frying.
Measurement of thermal conductivity of foods is usually done using either steady state or transient methods. Steady state methods are usually slow. A new method to determine thermal conductivity was developed using a Differential Scanning Calorimeter. An attachment was fabricated to hold small food samples and subject them to a thermal gradient. Using this new procedure thermal conductivity values were obtained for apple and turnip as 0.544 W/mC (at 39.1 C), and 0.666 W/mC (at 26.2 C), respectively.
Impacts
(N/A)
Publications
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Progress 01/01/91 to 12/30/91
Outputs
Pistachio is a relatively new crop in California. Upon harvest and dehulling, pistachio nuts contain 40% (wb) moisture. It must be dried down to 6% for reprocessing and storage. A number of hot air drying systems from other industries have been adopted for this purpose. In this study, a fixed deep bed dryer, a cross flow dryer with recirculation and a fluidized bed dryer were compared in terms of specific energy utilization rates. A computer-aided grain drying model was used to simulate the three drying processes. Properties required by the model were determined experimentally and extracted from literature. The cross flow dryer with recirculation was found to be the most economical from the energy utilization aspect. Magnetic Resonance Imaging (MR) was used to study the oil and water interface which develops during frying. Russett potato slabs (2 cm, 5 cm x 4 cm) were fried for 0, 5, 10, 15, 20 and 25 minutes, 165 degrees C. Two dimensional images showed the
development of an oil/water interface characterized by a sharp boundary layer. Advancement of this boundary layer relied on crust structure and water vapor flow from the sample. Scanning electron micrographs showed the melting of the starch granules to form the crust matrix and porous sample core. The results from these visualization studies are being used to develop experiments to quantify the oil and vapor transport mechanisms present during the frying of foods.
Impacts
(N/A)
Publications
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Progress 01/01/86 to 12/30/90
Outputs
Magnetic Resonance Imaging (MRI) was used to study the oil and water interface which develops during frying. Russett potato slabs (2 cm, 5 cm x 4 cm) were fried for 0, 5, 10, 15, 20 and 25 minutes, 165(degree)C. Two dimensional images showed the development of an oil/water interface characterized by a sharp boundary layer. Advancement of this boundary layer relied on crust structure and water vapor flow from the sample. Scanning electron microgaphs showed the melting of the starch granules to form the crust matrix and porous sample core. A simulation-economic evaluation model was developed to analyze alternative systems for concentrating tomato juice. Ten alternative schemes including multiple effect evaporation, recompression evaporation, and reverse osmosis were evaluated using this model. A basecase and two energy price projection scenarios were examined to show their potential impacts on each scheme's net present cost. Results showed that under an optimistic energy
future, two- and three-effect evaporators are the most economical schemes to use. However, under a scenario that doubles steam price, mechanical recompression and reverse osmosis systems become competitive with three-effect evaporators. Under a scenario that doubles both steam and electricity prices, results differ according to plant size with reverse osmosis systems being competitive in small to medium size plants.
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Progress 01/01/89 to 12/30/89
Outputs
Cooked, diced chicken meat was dehydrated by various air and freeze drying techniques. These included: freezing of the samples at -15C, -57C, and 196C before freeze-drying; fixed bed air drying, fluid bed air drying, and fluid bed air drying with a pretreatment of slow freezing of the sample. The dried material was then evaluated to determine the following physical properties: shear strength, friability, rehydration, surface area, density and pore space distribution. Moisture curves obtained during drying show that the material which was prefrozen followed by fluid bed air drying had a much faster drying rate than the other air drying methods. Friability testing showed air drying to produce a brittle, highly friable product, while freeze drying produced a more resilient overall product, but with a surface structure highly sensitive to abrasion. Equilibrium moisture contents (EMC) for in-shell pistachio (variety: Kerman) were determined at dry bulb temperatures 20,
30, 50, and 70C and relative humidities ranging from 10.0 to 86.4% using a static method. Results showed that the isostere equation gave a good agreement with experimental data. The isostere equation with appropriate parameters is useful for predicting EMC in drying, handling and storage of pistachio nuts.
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Progress 01/01/88 to 12/30/88
Outputs
Gas exchange in apples was modeled as a diffusion process with a first order chemical reaction. Five diffusion reaction parameters for Golden Delicious apples were determined, namely: diffusivity of the flesh to oxygen and to carbon dioxide, conductance of the skin to oxygen and to carbon dioxide, and the first order reaction rate constant. The internal gas concentration gradients and the transient gas exchange processes in apples placed in modified atmosphere packages were simulated. Thin layer drying of in-shell pistachios was conducted with air at dry bulb temperature from 40-60 (degree)C, relative humidities from 21-82% and velocities from 0.15 - 0.82 m/s. An exponential model was found to be adequate in describing the characteristics of the thin-layer drying of pistachios. Fixed and fluidized bed freezing were investigated with the purpose of determining optimum operating conditions. Out of the three products tested, green peas, cherries, and radishes, it was
found that smaller particles have a smaller optimum bed height for both fixed and fluidized bed freezing. In general, fluidized beds have a higher production rate (up to 30% or more) than fixed beds of the same height.
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Progress 01/01/87 to 12/30/87
Outputs
During thawing of frozen foods in humid air, the ambient water vapor undergoes aphase change at the food surface. The surface phenomena during thawing were formulated into a mathematical model consisting of six stages, namely: frost formation, frost consolidation, transition, condensation, evaporation, and drying. This model coupled with another model developed for heat conduction with phase change inside food during thawing was tested for simulating thawing of frozen foods. A mathematical model based on chemical kinetic theory was derived to predict food quality change from time-temperature indicator response. The derivation was extended to develop a quality based interpretation of the shelflife of perishable foods. A storage investigation of mature green tomatoes showed that the quality prediction model satisfactorily predicted changes in tomato firmness induced by variable temperature storage. The gas exchange processes in fruits and vegetables consist of
biochemical reactions, such as respiration and ethylene generation which consume or generate gases, and the diffusive transport of these gases between the external atmosphere and the internal reaction sites. A formulation of the overall process as a generalized diffusion problem with a chemical reaction and use of the solutions of analogical problems was developed and tested for modified atmosphere packaging of commodities.
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Progress 01/01/86 to 12/30/86
Outputs
Heat transfer during the freezing of foods has been studied with the determination of convective heat transfer coefficients that are important during fluidized-bed freezing. Using air velocities of 7 to 9 m/s, similar to the ones used in commercial freezers, the coefficient values of 150 to 190 W/ sq m C have been obtained for spherical-shaped foods. A computer-aided simulation model of food freezing has been developed that can operate on a personal computer. The model involves prediction of temperatures as well as properties during freezing. Cryogenic freezing of orange segments has been conducted to determine process parameters that minimize damage due to the crystallization process. A rigorous mathematical model to study thawing of frozen foods has been developed. The unique features of this model include the changing boundary conditions during thawing, such as, formaton of frost, densificiation of frost into ice, melting of ice, and evaporation of water from the
surface of the thawing product. A comprehensive study has focused on the use of biosensors in monitoring heat abuse of a variety of foods during storage and distribution. Correlations have been developed between certain sensory and objective changes in quality attributes in foods and responses of the biosensors. A computer-aided model is being developed for use in inventory management of foods with the prime objective of minimizing quality changes caused by heat abuse.
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Progress 01/01/85 to 12/30/85
Outputs
To study the applicability of time-temperature indicators (TTIs) in monitoring quality changes in stored foods, the following twelve products were selected: frozen hamburger, bologna, peas, strawberries, salmon and ice cream; and refrigerated tomatoes, wrapped lettuce, unwrapped lettuce, fresh milk, sterilized milk and fruit cake. Frozen products were stored to a maximum of 6 months duration. Several constant and variable storage temperatures were used. At periodic intervals, the food products were examined for a minimum of four sensory attributes as well as one or two objective tests. The response of the indicators was also recorded. It was found that the indicators were useful in providing a good correlation with certain quality attributes indicating usefulness of these indicators in monitoring the handling and storage component of the food chain. A computer-aided calculation of temperature history during thawing of foods has been developed for use on
microcomputers. Good agreement between the numerical predictions and experimental data was obtained. Heat transfer in a frozen food subjected to varying boundary conditions was modeled on a microcomputer. The model can simulate heat transfer in a frozen pallet which may receive solar radiation at loading docks during handling and transportation. The model was tested using the Tylose test substance and frozen orange juice concentrate.
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Progress 01/01/84 to 12/30/84
Outputs
Diffusion of volatiles in porous foods and pore-size distributions in food materials was determined. Samples of freeze-dried white potato, carrot, stew beef and apple (varieties Granny Smith and Golden Delicious) were evaluated in terms of porosity by the method of mercury intrusion porosimetry. The two apple varieties were found to have the largest pore volume per gram of material whereas carrots showed to have the smallest. The experimental data on porosity of foods is being utilized in studying diffusion of simple gases in model and real food systems. To study the applicability of time-temperature indicators (TTI's) in monitoring quality changes in stored frozen foods, a performance valuation study was conducted. Several TTI's of four commercially-available types were exposed to constant temperatures of -18C and -12C and a temperature step change from -18C to +2C. This study has revealed the potential use of such indicators in management of storage and
transportation of perishable products. The influence of temperature of the drying air on changes in color of parboiled rice was determined. It was found that an increase in temperature of drying air from 50 to 140C caused a 20% change in color of milled rice. The results on color changes in rice due to drying conditions has allowed determination of upper limits of time-temperature exposure.
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Progress 01/01/83 to 12/30/83
Outputs
A comprehensive research program on developing thin layer drying equations for long-grain rice has been completed. Empirical exponential equations have been determined that are useful for air temperatures between 30 to 158 C. Parboiled rough rice has been found to have consistently higher values of diffusivity than untreated rough rice indicating lower resistance to moisture movements. To study diffusion of volatiles in porous foods a diffusion cell was designed and fabricated based on the Wick-Kallenbach approach on countercurrent gas diffusion under zero pressure gradient. Selected volatiles include propane, pentane, cyclopropane. Nitrogen is being used as a carrier gas. Diffusion through small pellets of coarse cereal flour is currently being studied. A mercury intrusion technique has been used to obtain macropore size distributions, cumulative pore size distribution, average pore size, particle density and macroporosity of freeze-dried apple (Granny Smith and
Golden Delicious), carrot, potato and stew beef. A freezing/thawing simulation program using the finite element method for axisymmetric bodies was developed. Available experimental freezing curves were compared with the predicted freezing curve using the computer program. A computer-aided simulation for rotary driers used in drying parboiled rough rice was developed.
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Progress 01/01/82 to 12/30/82
Outputs
Using Fick's Law of Diffusion, experimental data on thin-layer drying of rough rice (variety S6) was analyzed to obtain diffusion coefficients. The diffusion coefficients were expressed as a function of temperature by the following expression, Diffusion Coefficient = 33.6 exp (-6420/ Absolute Temperature, K). These coefficients are useful to predict rice drying under different conditions of air temperature and humidity. Computer aided simulation of rice drying was extended to an industrial scale crossflow rice drier. Exit air temperatures and grain moisture content were measured at various locations in an Industrial drier. The predicted values were found to be in good agreement with experimental values for eight different trials. Tests conducted on a pilot scale drier showed large moisture and temperature gradients in the drier column, that causes non-uniformity of drying in crossflow driers.
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Progress 01/01/81 to 12/30/81
Outputs
Methods for measuring steam flow were reviewed, and recommendations made on procedures to use in food plants. Several energy accounting studies in thermal processing of foods were conducted. A water recycle system was installed on a conventional atmospheric cooker. Average savings in steam usage were found to be 25% over the conventional steam injection system.
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Progress 01/01/80 to 12/30/80
Outputs
The primary focus of research has been to study heat and mass transfer properties during drying of cereal grains, in particular rice. Following are major accomplishments: Diffusivity equations for the starchy endosperm and bran were determined for rewetted white and brown rice. Arrhenius type equations relating diffusivity and temperature were developed. Results suggest that diffusivities of starchy endosperm and bran determined from fresh (naturally moist) and rewetted materials are equal. Rough rice was considered a three-component material, and liquid diffusivities were determined for the hull, bran, and starchy endosperm. The starchy endosperm offered the least resistance to liquid moisture movement. The bran provides a more significant barrier to liquid moisture flow than the starchy endosperm. The greater resistance to liquid moisture flow is in the hull which has the lowest diffusivity of the three rough rice components. The percent volumetric reductions
that may occur in drying white, brown, and rough rice were determined. It was found that in the shrinkage of rough rice during drying, the volumetric reduction of the hull may be significantly less than that of the remaining portions of the kernels. Research has also focused on energy accounting of canning spinach, peaches, and tomatoes. For canning tomato products, it was found that the thermal and electrical energy intensities were 538 BTU/lb and 0.0126 kwh/lb, respectively.
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Progress 01/01/79 to 12/30/79
Outputs
A study was conducted to examine the rates of hydration in rice during soaking process, degree of starch gelatinization and diffusion of moisture in parboiled rice during drying. A mathematical equation describing simultaneous diffusion and reaction was used to describe both hydration and starch gelatinization. It was found that the rice hull offers significant resistance to water uptake. In addition, a given percentage of starch gelatinization is carried out more rapidly in brown rice than in rough rice. It was concluded that at temperatures below 85C, reaction of rice components with water is the limiting factor for parboiling, while diffusion of water in rice is the limiting factor for parboiling above the temperatures of 85C. Since rice hull provides significant resistance to moisture transfer, rice should be hulled before parboiling process. Improvements in quality of the product should also result if brown rice is parboiled (instead of rough rice) since for
same degree of starch gelatinization, brown rice parboils more rapidly than rough rice. Another experiment was designed and an apparatus was built to evaluate heat transfer to non-Newtonian fluids in annular flow. A unique aspect of the design was the use of a thin metallic film on the annular surfaces as a resistance heating element. Flow was restricted to the laminar region. Experimental results for the outer Nusselt number agree well with the analytical, numerical solutions of other researchers.
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Progress 01/01/78 to 12/30/78
Outputs
This research project is designed to contribute to Objectives B and D of the NC-136 project. The following two studies were initiated during 1978. Heat transfer in non-Newtonian fluids flowing in an annulus: Extensive literature search was conducted to develop both analytical and experimental techniques useful in determining heat transfer rates in non-Newtonian liquids heated in an annulus. No theoretical or experimental information on this topic was found. From similar studies on Newtonian fluids, an experiment was designed to get information that may be useful in designing tubular heat-exchangers for non-Newtonian fluids. The apparatus is currently being assembled with experiments planned in early 1979. Rice parboiling: This study involves examining the rates of hydration in rice during soaking process, degree of starch gelatinization during steaming process and diffusion of moisture in parboiled rice during drying. Equipment for conducting experiments is
currently being assembled.
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Progress 01/01/77 to 12/30/77
Outputs
This research project is designed to contribute to Objetive B and D of the NC-136 project. Specifically, the emphasis is to examine the heat transfer characteristics of non-Newtonian liquid foods. An extensive literature search on the topic has revealed the following: Only a limited number of past studies have focused on determination of the heat transfer parameters of non-Newtonian liquid foods. The influence of temperature on rheological parameters is available for a few liquid food products (such as tomato concentrate, banana puree, applesauce and pear puree). No theoretical/experimental information was found on heat transfer to non-Newtonian food products heated in an annulus. A paper by Fredrickson and Bird (Ind. and Engr. Chem. 50(3):347, 1958) gives theoretical development of non-Newtonian flow in annuli. Experimental information obtained from non-Newtonian heat transfer will be valuable in designing heat exchangers with minimum effects on product quality
deterioration with better energy-use efficiencies. In addition, these experiments should increase our analytical understanding of heat transfer for non-Newtonian liquid foods.
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