Progress 10/01/00 to 09/30/05
Outputs
Deep-fat frying is a process that has evolved from almost little information to an in depth understanding of the thermal and mass transfer mechanisms involved in it. One important discovering was the mechanism related to oil absorption in fried products. The product structure before frying, pore size distribution, and capillary pressure all play an important role in defining final oil content in fried products. Another technique, vacuum frying, has also been evaluated in by our group. This technique has the advantage of produce high quality and safer food products compared to the traditional (atmosphere) frying processes. The last advances made in vacuum frying were the study done in acrylamide formation in potato chips. Maillard reaction between asparagine and reducing sugars during heating of foods is considered a major pathway for the formation of the possible human carcinogen acrylamide. The objectives of this research were to determine the influence of asparagine
(Asn) and glucose (Glu) concentration on acrylamide content in potato chips. Potatoes of the Atlantic variety were sliced and washed in tap water. Removal of amino acids and reducing sugars from the slices was accomplished by submerging in water at 60C for 5 minutes followed by 15 minutes in a 50% ethanol solution at 40C. Slices were kept overnight at 4C before infusing with solutions of asparagine and glucose at different concentration levels resulting in 16 combinations. An electric bench-top type fryer was used to fry the potatoes at 165C for 4 minutes. At none, low, medium, and high concentrations of Glu and at constant Asn concentration (low), the acrylamide contents of the chips were 214, 2137, 5923, and 9770 ppb. At a constant Glu concentration (Low) and at none, low, medium and high concentrations of ASN, acrylamide contents were 123, 2137, 2557, and 5584 ppb, respectively. Asparagine and glucose content in the raw product influence tremendously in the final formation of
acrylamide: as asparagine and glucose concentration increase, acrylamide formation increases as well. Vacuum frying (10 Torr) was studied as a possible alternative to reduce acrylamide formation in potato chips. The cultivar Atlantic was used to determine the kinetics of acrylamide formation during traditional and vacuum frying at different temperatures. There was a 94% decrease in acrylamide content when potatoes were fried to the same final moisture content (1.5%w.b.) under vacuum compared to those fried under atmospheric conditions. Acrylamide accumulation under vacuum frying was modeled using first-order kinetics, and during traditional frying, it was modeled using the logistic kinetic model. The behavior of the kinetics of acrylamide content in potato chips fried under the two processes was different mainly due to the different temperatures used. During traditional frying, higher temperatures are used (150C to 180C) and acrylamide after some time is produced but starts degrading,
producing a constant level of acrylamide content at longer times. During vacuum frying (10 Torr), acrylamide increased exponentially (but at lower levels) for all frying times.
Impacts
Asparagine and glucose content in the raw product influence tremendously in the final formation of acrylamide. Ways of reducing asparagine and/or reducing sugars in potatoes will reduce acrylamide formation in processed potato products. Results showed that the kinetics of acrylamide content during traditional frying was modeled by using a special case of the logistic kinetic model. Acrylamide content increased and eventually reached an equilibrium value. The influence of time on acrylamide accumulation in vacuum fried chips was best described by first order kinetics. Acrylamide content during vacuum frying kept increasing exponentially.
Publications
- Granda, C., and R. G. Moreira. 2005. Kinetics of acrylamide formation during traditional and vacuum frying of potato chips. Journal of Food Process Engineering.28(5):478-493.
- Granda, C., R. G. Moreira, and Elena Castell-Perez. 2005. Effect of raw potato composition on acrylamide formation in potato chips. Journal of Food Science. In press.
- Granda, C. 2005. KINETICS OF ACRYLAMIDE FORMATION IN POTATO CHIPS. M.S. Thesis. Biological and Agricultural Engineering Department, Texas A&M University.
- Granda, C, R.G. Moreira, and S.E. Tichy. 2005. Asparagine and Glucose Concentration on the Formation of Acrylamide in Potato Chips. IFT International Meeting, New Orleans, July 2005.
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Progress 01/01/04 to 12/31/04
Outputs
Potatoes and other foods that have a high content of the amino acid asparagine and high accumulation of reducing sugars are subject to the formation of acrylamide upon frying. The objectives of this research were: (1) to analyze the level of acrylamide formed during deep fat frying of potato chips; and (2) to evaluate means of reducing acrylamide in potato chips by using different potato cultivars and vacuum frying. Several potato cultivars were used in this research, including Innovator (I), NDTX 4930-5W (N), ATX 854 04-8W (ATw), Atlantic (A), Shepody (S), ATX847806-2Ru (ATr), and White-Rose (W). An electric bench top (atmospheric conditions) type fryer was used to fry the potatoes. Three temperatures were used: 150, 165, and 180C. The vacuum frying experiments were performed at 118, 125, and 140C and vacuum pressure of 10 Torr. The potatoes were sliced (1.5 mm thick) and fried for different times. For potatoes fried at 165C (for 4 min) and atmospheric conditions,
the acrylamide contents were 5021+55 ppb (W) to 552+25 ppb (I), 358+50 ppb (N); 397+25 ppb (ATw), 646+55 ppb (A), 466+15 ppb(S), and 537+14 ppb (ATr). Vacuum frying reduced acrylamide formation by 94%.Results showed that both cultivar and modified frying systems could play an important role in reducing acrylamide formation in fried potatoes. As the frying temperature decreased from 180C to 165oC, acrylamide content in potato chips reduced by 51% during traditional frying and by 63% as temperature decreased from 140C to 125oC in vacuum frying. Increased frying time increased acrylamide formation during traditional frying for all temperatures and frying methods analyzed. However, the effect on acrylamide concentration was greater for the traditional frying than the vacuum frying.
Impacts
The variety of potato has an important effect on the formation of acrylamide in potato chips. Potato cultivars with high reducing sugar content produce more acrylamide during frying.
Publications
- Granda,C., R.G. Moreira, and S. E. Tichy. 2004. Reduction of Acrylamide Formation in Potato Chips by Low Temperature Vacuum Frying. Journal of Food Science, 69(8):405-411
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Progress 01/01/03 to 12/31/03
Outputs
We have analyzed the acrylamide content of potato chips fried under vacuum and atmospheric conditions in our lab. The method used for acrylamide measurement was a slight modification of the LC/MS/MS protocol developed by FDA scientists (FDA, 2002). The method uses a Waters C-48 Atlantis HPLC column [isocratic run of 90% water and 10% methanol (0.1% formic acid added)]. Preliminary results showed that potato chips (Variety Superior) fried at 165C for about 5 minutes in an atmospheric fryer had higher acrylamide content than chips fried in vacuum frying. Over frying (potato chips fried for 8 min resulting in a darker color) produced even higher acrylamide content. An affinity based bio-sensing technique was developed using an anti-transmissible spongiform encephalopathy monoclonal antibody as a bio-recognition molecule. Fluorescein iso-thio-cynate (FITC), labeled with a prion epitope (QYQRES), was used as a decoy for prions. Experiments done in 0.1M phosphate buffer
revealed that the dye fluorescence increased with the pH of the buffer and was influenced by solvent polarity. Binding studies conducted at pH 6, 7, and 8 showed that the optimum pH for the antibody-decoy binding was 7. Maximum differences between control and antibody samples were observed at pH 7. The optimum incubation time was found to be less than 4 hours for the control, antibody, and the prion samples at room temperature. Prion detection curves were established at 4 and 10 nM antibody decoy concentrations. The lowest detectable prion concentration in phosphate buffer was 8 nM. Experimental conditions determined in the phosphate buffer were used to implement the technique in gelatin and baby formula. Prion detection curves were generated in 0.01, 0.4, 1.0 and 2.0 mg/ml of gelatin solution. The gelatin interfered with the binding and the displacement reaction of antibody, decoy and prion. Addition of an anionic surfactant, sodium dodecyl sulfate (SDS) at 0.3 mg/ml to gelatin
samples facilitated prion detection in gelatin. The lowest detectable concentration of prion in gelatin was 0.5 nM at 0.4mg/ml gelatin. The baby formula samples produced light scattering and the intrinsic peak of baby formula at 526nm interfered with the dye peak at 514nm. Serial dilutions of baby formula were done to reduce the interference. Prion detection curves were then obtained at 1.31 and 5.34 mg/ml baby formula and 0.454 mg/ml of Triton-X-100 was added to the baby formula samples. The lowest detectable concentration of prion was 2 nM for baby formula. This developed bio-sensing technique can be used to detect prion in gelatin and baby formula solutions. Addition of surfactants assisted prion detection in foods, while high concentrations of gelatin and baby formula had an adverse effect on the detection system.
Impacts
Experimental results on the vacuum frying of potato chips showed that by controlling the oil temperature and the vacuum pressure a final product with low oil content can be obtained. Acrylamide formation can be reduced if the frying process temperature is reduced, so vacuum frying seems to be a technique to look in depth. The second project was aimed at the engineering and design of novel nanoscale monitoring devices whose speed, sensitivity, stability, and ease of use exceed the current methodology. The primarily application for these devices in this proposal is for the detection and analysis of microbiological agents, food allergens, toxins, and other bioactive compounds found in foods, food additives, and dietary supplements. The proposed work will provide the new detection methodology critical to keep hazardous substances out of the food supply. The results demonstrate that the described nanoparticle based sensors can be synthesized, that they can be optimized for
maximum signal generation and for a variety of applications.
Publications
- Limanond, B, M.E. Castell-Perez, and R.G. Moreira. 2003. Quantifying Texture Changes in Corn Tortillas due to Staling. J. of Texture Studies, 33(1):215-219.
- Brescia, G, R. G. Moreira, L. Braby, and M.E. Castell-Perez. 2003. Monte Carlo simulation and dose distribution of low energy electron irradiation of an apple. J. Food Engr. 60 (1): 31-39
- Kumar; V.R, R.G. Moreira, and M. Barrufet. 2003. Modeling the structural changes of a food product during frying. J. Food Engr. 60(2): 165-175.
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Progress 01/01/02 to 12/31/02
Outputs
We are developing several prototype nanoparticle based sensor systems. The principle behind sensor consists of binding a targeting agent (either an antibody, as shown, or an enzyme or a piece of DNA) to a gold nanoparticle. We will conjugate a fluorphore to a decoy (a competitive inhibitor of the analyte of interest). If the gold particle is close to the decoy (within 10 nm), quenching of fluorescence will be observed. If the particle is an intermediate distance from the decoy (between 10 nm and 40 nm), then enhancement of fluorescence will be observed. Once the decoy is bound to the targeting agent, then we can test for the presence of the analyte of interest. If the analyte is present, then the analyte will displace the decoy, and the fluorescence signal of the sample will change. For the case of a quenching based sensor, the analyte will displace the decoy bound to the antibody. As the decoy moves far away from the gold nanoparticle, its fluorescence intensity will
increase. The increase in fluorescence intensity is related to concentration of analyte present in solution.
Impacts
This project is aimed at the engineering and design of novel nanoscale monitoring devices whose speed, sensitivity, stability, and ease of use exceed the current methodology. The primarily application for these devices in this proposal is for the detection and analysis of microbiological agents, food allergens, toxins, and other bioactive compounds found in foods, food additives, and dietary supplements. The proposed work will provide the new detection methodology critical to keep hazardous substances out of the food supply. The results demonstrate that the described nanoparticle based sensors can be synthesized, that they can be optimized for maximum signal generation and for a variety of applications.
Publications
- Limanond, B., Castell-Perez, M.E. and Moreira, R.G. 2002. Quantifying Texture Changes in Corn Tortillas due to Staling. Journal of Texture Studies, Volume 33, 1: 35-45
- Limanond, B., Castell-Perez, M.E. and Moreira, R.G. 2002. Modeling Staling of Corn Tortilla. Journal of Food Engineering. 53(3): 237-247.
- Spadaro,V.; D.H. Allen, J.T. Keeton, R.G. Moreira and R. M. Boleman. Biochemical properties of meat and their correlation to tenderness. 2002. Journal of Texture Studies. 33:59-87.
- Garayo, J. and R.G. Moreira. 2002. Vacuum frying of potato chips. J. of Food Engr. 55(2):181-191
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Progress 01/01/01 to 12/31/01
Outputs
Vacuum frying was used as an alternative technique to develop low oil content potato chips. The effect of oil temperature (118, 132, 144 C) and vacuum pressure (16.661, 9.888, and 3.115 kPa) on the drying rate and oil absorption of potato chips and on the product quality attributes such as shrinkage, color, and texture was investigated. Furthermore, vacuum-fried potato chips (3.115 kPa and 144 C) were compared to potato chips fried under atmospheric conditions (165 and 192 C). During vacuum frying, oil temperature and vacuum pressure had a significant effect on the drying rate and oil absorption rate of potato chips. However, these two parameters had no significant effect on the final moisture and oil content of potato chips. Potato chips fried at lower vacuum pressure and higher temperature had less volume shrinkage. Color was not significantly affected by the oil temperature and vacuum pressure. Hardness values increased with increasing oil temperature and
decreasing vacuum levels. A higher drying and oil absorption rate was obtained when atmospheric frying was compared to vacuum frying. Potato chips fried under vacuum conditions (3.115 kPa and 144 C) had more volume shrinkage than potato chips fried under atmospheric conditions (165 and 192 C). The vacuum-fried potato chips were slightly harder and lighter in color than the potato chips fried under atmospheric conditions. It was concluded that vacuum frying is a process that could be used to produce potato chips with lower oil content and desirable color and texture.
Impacts
Experimental results on the vacuum frying of potato chips showed that by controlling the oil temperature and the vacuum pressure a final product with low oil content can be obtained. Further studies need to be carried on to better undertand the phenomenon of oil absorption during the process.
Publications
- Kawas, M.L. and R.G. Moreira. 2001. Effect of degree of starch gelatinization on product quality attributes of tortilla chips during frying. Journal of Food Science. 66(2):195-210.
- Moreira, R.G. 2001. Impingement drying of foods. Symposium in "Advances in Drying Technology in the Food Industry". Journal of Food Engineering.49(4):291-295
- Braud, L., R.G. Moreira and M.E. Castell-Perez. 2001. Mathematical modeling of impigiment drying of corn tortilla. Journal of Food Engineering. 50(3):121-128.
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Progress 01/01/00 to 12/31/00
Outputs
Superheated steam impingement drying of foods has proven to provide better energy efficiency and product quality and could be a reliable alternative for production of fat-free potato chips (not-fried). Our objectives were to determine the effect of drying operating conditions (temperature, convective heat transfer coefficient, h) on the drying rate and quality (texture, density, porosity, shrinkage, and nutritional value) of potato chips. Potato chips were dried up to the equilibrium moisture content. At 145C and 160 W/m2C, particle density and porosity showed an increase from 1.09 to 1.54 g/cm3 , and from 0 to 0.779, respectively. However, bulk density decreased from 1.09 to 0.34 g/cm3. Same behavior was observed for all other drying conditions. Particle density did not exhibit significant changes with temperature and h values. Porosity of chips dried at 160 W/m2C was higher than for those dried at 100 W/m2C (0.779 and 0.75, at 145C). During drying, change in
thickness was 50% for 155C and 62.5% for 130 and 145C drying conditions. Potato chips became crispier as drying time increased. No significant differences in crispness of chips (peak force in Newton) due to drying conditions was observed. However, chips were harder (4.19 N) at 115C, 100 W/m2C than the chips dried at higher temperature (145C). Results show the potential of producing a fat-free potato chip using steam impingement drying. A mathematical model of impingement drying of corn tortillas was developed based on governing equations for heat and mass transfer during the drying process. Mass transfer within the product was modeled as diffusion-driven mass flux. Heat transfer was driven according to Fourier's Law of conduction. Boundary conditions for drying in both air and superheated steam were developed for incorporation into the model. Convective heat transfer accounted for heat flow into the product at the surface. When drying in air, convective mass transfer prevailed; in
superheated steam, differences in vapor pressure between the drying medium and the product surface accounted for mass transfer.The explicit finite difference scheme was employed for model solution. A simulation program was written to predict temperature at the center of the product and average moisture content during drying. Results were validated with data collected in previous studies at varying drying temperatures and convective heat transfer coefficients.Temperature predictions followed the trends observed in previous experiments with both air and steam drying at temperatures ranging from 115 to 145 C. Temperatures at the product's center initially rose to the boiling point, remained at this temperature during a phase of latent heating, and finally rose to the temperature of the drying medium. Moisture content predictions in air drying also followed the experimental trends; however, steam condensation unaccounted for by the model resulted in under predictions in the moisture
content in steam drying at low drying medium temperatures. At high drying medium temperatures, drying in superheated steam was faster than drying in air.
Impacts
The use of superheated steam to dry potato chips indicates that this technique can be used as a mean for reducing nutrient losses during drying. Structure and crispness of chips are different to those subjected to hot air drying. Fundamental modeling of tortilla chips during impingement drying with hot air and superheated steam will help understand the process and will provide better capabilities for designing the system for different food materials
Publications
- Kawas, M.L. and R.G. Moreira. 2000. Characterization of product quality attributes of tortilla chips during the frying process. J. of Food Engineering. 47(2):97-107.
- Singh, S.K., Castell-Perez, M.E. and Moreira, R.G. 2000. Viscosity and Textural Attributes of Reduced-Fat Peanut Pastes. Journal of Food Science, 65(5): 849-853.
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Progress 01/01/99 to 12/31/99
Outputs
Total oil content of tortilla chips at 60 s of frying was the highest for the freeze-dried sample (38.25%) and the lowest for the chips that were steamed and dried before frying (14.71%). The control sample (baked for 70 s before frying) total oil content was about 23.64% (w.b.). Oil absorption during frying was higher for the freeze-dried chips (20.85%), followed by the control (10.94%), and steamed-baked chips (3.48%). The degree of gelatinization was evaluated using WSI and WAI values. The chips that were steamed-baked-fried showed values of WSI = 1.4% and WAI = 9.21 g/g. The freeze-dried/fried had WSI = 5.82% and WAI = 3.0 g/g, and the control chips (baked-fried) WSI = 2.76% and WAI = 5.48 g/g. So, steaming yields lower solubility so higher starch gelatinization before frying. Freeze drying resulted in less starch gelatinization. Both WSI and WAI were highly correlated to total oil content for all treatment (1.000- 0.998. Pore size distribution was different for
the different treatments. The chips that were steamed and baked before frying showed an average pore size of 30-40 mm in diameter after baking increasing to 70 mm after frying. The average pore size of the control samples were around 90-110 mm in diameter after frying. The freeze-dried samples showed pore size around 40 mm in diameter. The structure of the chips analyzed using ESEM revealed that the control samples had large and irregularly shaped pores and a smooth starch matrix; the steamed/baked/fried samples showed larger pores and a smooth starch matrix; and the freeze-dried/fried samples had small pores and a rough starch matrix. Porosity increased from 0.32 to 0.55 during frying for the control chips and from 0.38-0.70 for the steamed-baked-fried samples, however porosity did not change during frying for the freeze-dried chips (0.33). The diameter of the samples changed very little during frying. It shrunk about 9% for the control, 7% for the freeze-dried/fried sample, and 11%
for the steamed-baked-fried chips. The control and steamed-baked-fried samples puffed (thickness increase due to bubbling) about 100% and 140%, respectively, however, the freeze-dried/fried chips only puffed 8%. No changes in thickness were observed during frying. The crunchiest chips were the control samples, the hardest the steamed/baked/fried chips, and the most brittle the freeze dried-fried tortilla chips. Isotherm: For the raw tortilla, the best curving fitting was obtained with the Chung and Pfost equation. Glass Transition Temperature: The mechanism of mass transport in tortilla chips during frying is coupled to the structure change. As the moisture is reduced during frying, the product structure changes from a rubbery to a glassy like structure. The change of structure happens at the crust/core boundary when the temperature of the product matrix is at the Tg. The glass transition temperature of raw tortilla follow the typical behavior of food carbohydrates. Tg for raw corn
tortilla can be predicted using Gordon-Taylor equation with k = 5.2.
Impacts
The degree of starch gelatinization in tortilla chips before frying affects the final oil content. It also affects the expansion and texture of the samples. Higher level of gelatinization before frying caused more expansion and stiffer texture. Pore size distribution was also larger than the control sample. Futher studies are needed to optimize the manufacturing of tortillas with good texture and low oil content.
Publications
- Guo, Z., Castell-Perez, M.E. and Moreira, R.G. 1999. Texture of masa and low-moisture corn tortilla using stress relaxation methods. Journal of Texture Studies 30(2): 197-215.
- Emesih, G.C., R.G. Moreira and M.A. Barrufet. 1999. Evaluation of modified starches for improved oil recovery. Applied Engineering in Agriculture. 15(3):237-242.
- Murano, E.A.; P.S. Murano, R.E. Brennan, K. Shenoy and R.G. Moreira. 1999. Application of high hydrostatic pressure to produce safe and long-lasting fresh pork sausage. J. Food Protection. 62(5):480-483.
- Suhendro, E.L., H.D. Almeida-Dominguez, L.W. Rooney, R.D. Waniska and R.G. Moreira. 1999. Use of extensibility to measure corn tortilla texture. Cereal Chem. 76(4):536-540.
- Huang, M.; R.G. Moreira, and E. Murano. 1999. Use of hydrostatic pressure to produce high quality and safe fresh pork sausage. Submitted to J. of Food Processing and Preservation. 23(4):218-220.
- Book: Moreira, R.G.; Castell-Perez, M.E. and Barrufet, M.A. 1999. Deep-Fat Frying: Fundamental and Applications. Aspen Publisher. Boston, MA.
- Thesis: Miranda-Lopez, R. 1999. Effects of some anti-staling additives, pH and storage on the staling of corn tortillas. Ph.D. degree in Food Science and Technology, Texas A&M University.
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Progress 01/01/98 to 12/31/98
Outputs
The structure characteristic of snack food products is an important quality attributes for texture development. Superheated steam drying is proven to produce porous product and to be more efficient than hot-air drying. The objectives of this study were: To determine the drying behavior of tortilla chips under impingement superheated steam and hot-air drying; to evaluate the changes in physical properties (shrinkage, crispiness, starch gelatinization, and microstructure) of tortilla chips during drying. Tortilla chips were dried in a lab-size impingement dryer and the average moisture content and temperature profile measure on-line using a data acquisition system. The modulus of elasticity, shrinkage, pasting properties, and structure formation (using Environmental Scanning Electron Microscopy) were determined of-line. All properties and moisture and temperature data were measured as function of temperature (115, 130, and 145 C) and convective heat transfer coefficient
(100 W/m2 C, 130 W/m2 C, and 160 W/m2 C). The microstructure exhibited more pores and coarser appearance when dried at higher temperatures. Products dried under higher steam temperature and higher heat transfer coefficient gelatinized less during drying and had higher ability to absorb water. At elevated temperatures, superheated steam resulted in higher drying rates than air drying. Furthermore, there was a less starch gelatinization associated with air drying compared to superheated steam drying. Drying with superheated steam is more efficient than air drying and improves product quality.
Impacts
(N/A)
Publications
- Moreira, R.G. and M.A.Barrufet. 1998. A new approach to describe oil absorption in fried foods: a simulation study. Journal of Food Engineering. 35:1-22.
- Li, Y.B.; Seyed-Yagoobi, J. ; R.G.Moreira, R.G. and R. Yamsaengsung. 1998. Superheated steam impingement drying of tortilla chips. Drying Technology.
- Tsue-Er Lo, R.G. Moreira and M.E. Castell-Perez. 1998. Rheological properties of corn meal dough. Food Science and Tech. Intern.
- Tsue-Er Lo, R.G. Moreira and M.E. Castell-Perez. 1998. Modeling product quality during twin-screw food extrusion. Transactions of the ASAE.
- Tsue-Er Lo, R.G. Moreira and M.E. Castell-Perez. 1998. Effect of operating conditions on melt rheological characteristics during twin-screw food extrusio. Transactions of the ASAE.
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Progress 01/01/97 to 12/31/97
Outputs
The most important quality parameters of fried products are the fat content and texture. Impingement drying is a popular system for convective drying when rapid drying is desired. Temperature and magnitude of air circulation can be controlled using an impingement dryer before frying to obtain a high quality product. The objective of this project was to analyze the effect of steam impingement drying conditions on the drying rate, microstructure, shrinkage profile, and texture of tortilla chips. Tortilla chips were prepared with nixtamalized dry corn masa flour. The chip thickness was adjusted to 1.9 mm, and the chip diameter to 88 mm. The chips were placed between a pair of wire meshes and dried under the impinging superheated steam. The weight and diameter of the sample were measured at 2-minute intervals until an equilibrium was reached. The effect of different drying conditions (T of 115, 130, and 145C; h of 110 and 160 W/m2 C) on the drying rate, temperature
profile, texture, shrinkage, and microstructure was analyzed. The drying time varied from 8 to 18 min for tortilla chips dried at 145C and 115C, respectively (h=110W/m2C). The effect of h on the drying rate was negligible at a drying temperature of 145C, but the chips dried faster at h = 160W/m2C for T=115oC (15 min) and T=130C (12 min). Temperature history (measured at the center of the chip) showed that evaporation rate increased as steam temperature and airflow rate increased. By varying the temperature from 115 to 145C (h=110W/m2C), the work required to break the chips reduced from 254+42 N.mm to 29+9 N.mm. At 145C, the work values increased from 29+9 N.mm to 60+3 N.mm for h=110W/m2C and h=160W/m2C, respectively. The values of work showed a pick value at a moisture content around 0.3-0.4 d.b. for all conditions analyzed. Tortilla chips shrunk about 10% during drying. The structure of the chips was smoother for the chips dried at 115C than at 145C for the same h=110W/m2C. The chips
became harder and brittle as temperature and air flow rate (i.e., h) increased. Tortilla chips dried with superheated impingement steam had better color and flavor than those dried under hot air impingement drying. It is expected that this technique could be used before frying to produce tortilla chips with better texture and lower oil content.
Impacts
(N/A)
Publications
- Huang,M. 1997. Use of high hydrostatic pressure to produce high quality and safe fresh pork sausage - MS Thesis.
- Emesih, G. 1997. Characterization of agricultural starch based biopolymers for use in oil and gas field production processes - Ph.D. Dissertation.
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Progress 01/01/96 to 12/30/96
Outputs
Research continued on measurement and modelling of thermal properties of foods.
Impacts
(N/A)
Publications
- Ramirez-Wong, B., V.E. Sweat, P.I. Torres, and L.W. Rooney. 1996. Evaluation of the Rheological Properties of Fresh Corn Masa Using Squeezing Flow Viscometry: Biaxial Extensional Viscosity. J. of Textural Studies 27(2).
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Progress 01/01/95 to 12/30/95
Outputs
Research continued on measurement and modelling of thermal conductivities of small grains. Thermal conductivity, density, porosity and moisture content of several grains were measured. Thermal conductivity of fried corn chips was measured by "sandwiching" the thermal conductivity probe between several layers of chips to minimize the amount of air spaces between the chips. Work continued on simultaneous measurement of thermal conductivity and thermal diffusivity of food materials.
Impacts
(N/A)
Publications
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Progress 01/01/94 to 12/30/94
Outputs
Research continued on measurement and modelling of thermal conductivities of small grains. Thermal conductivity, density, porosity and moisture content of several grains were measured. Thermal conductivity of fried corn chips was measured by "sandwiching" the thermal conductivity probe between several layers of chips to minimize the amount of air spaces between the chips. Work continued on simultaneous measurement of thermal conductivity and thermal diffusivity of food materials.
Impacts
(N/A)
Publications
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Progress 01/01/93 to 12/30/93
Outputs
Thermal conductivities of several grains have been measured with a line heat source thermal conductivity probe. Preliminary testing of porosity measurement is being conducted for the purpose of modeling thermal properties of grains based on water content, temperature and porosity.
Impacts
(N/A)
Publications
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Progress 01/01/92 to 12/30/92
Outputs
Thermal properties of various grains were measured. A technique was developed for simultaneous determination of thermal conductivity and thermal diffusivity using the line heat source probe and a finite element computer model.
Impacts
(N/A)
Publications
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Progress 01/01/91 to 12/30/91
Outputs
Thermal properties of a variety of grains are being measured using the line heatsource thermal conductivity probe. Grains include amaranth, barley, buckwheat, kamut, millet, oats, quinoa, long and short grained rice, rye, teff, and wheat The grains are first equilibrated to a moisture content of about 12% for comparative purposes. Water content and mass density of samples are being measured for subsequent modeling. Water content and temperature will be varied for selected grains.
Impacts
(N/A)
Publications
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Progress 01/01/90 to 12/30/90
Outputs
Thermal conductivity of breads and cakes was measured and modeled. The best model was of the form: k = C(1) + C(2) x porosity, where k is thermal conductivity and C's are constants. Porosity varied from 44% to 87%. Water content varied from 39% to 45%. Thermal conductivity was measured and modeled for fabricated foods consisting of various combinations of water, fat, protein and carbohydrate. Only the effects of water and fat content were significant for the samples used in this study. The best model was: k = -0.091 + .00233 x W + 0.368 x D + .0000231 x W, where W is water content (%) and D is density (g/cm). The model derived for fabricated foods worked well for predicting thermal conductivity of commercial food products. Rheological properties of margarines were measured and correlated to process conditions: heat exchanger surface area, rpm of heat exchanger mutator and product flow rate. Primary equipment settings of heat exchanger surface area, product
flow rate, and rotational speed of the scraped-surface heat exchanger had significant impact, while rotational speed of the secondary unit (whipper) demonstrated little effect on the product attributes of complex viscosity and cone penetration depth.
Impacts
(N/A)
Publications
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Progress 01/01/89 to 12/30/89
Outputs
Thermal properties of several types of bread were measured and modeled. Measurements were also made on compressed samples (0% porosity) for use in modeling. Best fit statistical models using SAS were compared to theoretical models for parallel configuration and for a discrete phase (air) in a continuous phase (bread solids). For the limited range of water contents used, the best model for thermal conductivity was k = C(1) + C * porosity. This study is important since there are very little thermal property data for porous foods. With one of the models used, it is possible to estimate thermal conductivity of bread knowing only the porosity and thermal conductivity of the solid phase. A study was initiated to relate rheological properties of margarines to process conditions. Variables include heat exchanger surface area, rpm of heat exchanger mutator and flowrate of product. One measurement of rheological characteristics used the cone penetrometer which is an industry
standard. Apparent viscosity was also measured. An experimental method for estimating shear history was used.
Impacts
(N/A)
Publications
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Progress 01/01/88 to 12/30/88
Outputs
Textural characteristics of fresh corn masa prepared with three cooking times, two degrees of grinding, and three levels of moisture content were evaluated. Masa texture was reported as adhesiveness, hardness, and as a ratio of compression/tension forces. Adhesivness was measured with a mechanical stickiness tester, and with an Instron compression test. Hardness and compression/tension forces were evaluated with the Instron. Masa adhesivness was affected by the interaction of cooking time and grinding, and by the interaction of cooking time and moisture content. Hardness and texture of fresh masa were affected by the interaction of cooking time and grinding, by the interaction of cooking time and moisture content, and by the interaction of grinding and moisture content. Results suggest that texture of fresh masa may be correlated to the water retention capacity of the masa. This is fixed through the conditions of cooking time and grinding. There were very good
correlations between the different methods used to measure fresh corn masa texture. Viscosity of seven vegetable oils was measured at 10 degree intervals from 20 C to 70 C. The effects of fatty acid composition, degree of saturation and temperature were studied.
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Progress 01/01/87 to 12/30/87
Outputs
Stickiness of corn masa was measured by successive compression and tension testson an Instron Universal Testing Machine. A ratio of compressive force to maximum tension force of 2 gave optimum stickiness for corn tortilla manufacture. This procedure was compared to an empirical stickiness measuring device used by some tortilla manufacturers. Effect of temperature on rate of water uptake in whole corn kernels was measured at 20, 30 and 40C. To simulate traditional tortilla processing 0.1% lime was added to the water. Soaking with an excess of water was compared to the case where just enough water was available to raise the water content to 30%.
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Progress 10/01/85 to 09/30/86
Outputs
Work focussed on studies of freezing and thawing of bread dough. In the first phase 10 gram micro-loaves were frozen in boiling Freon mixtures at -10, -20, -30, and -40 C. Loaves were then stored at different freezing temperatures from 0-3 months. Then samples were slowly thawed and baked. A freezing temperatures of -20 C produced the least changes in microbial population and baked loaf volume after 3 months of frozen storage. The next phase involved freezing and thawing of 165 gram loaves with temperature measurement with time for subsequent modeling studies. Six different dough formulas were included to test the effect of composition. Thermal conductivity of the bread doughs was measured; it ranged from 0.39 to 0.42 W/m -C. Water contents ranged from 41 to 43% and density was 845 kg/m. Surface heat transfer coefficients were measured for the freezing and thawing of unbaked bread dough loaves having dimensions of 11 cm x 6 cm x 4 cm. For freezing tests the
initial dough temperature was 20 C, and the freezing medium was boiling Freon-12 at -31 C. The surface heat transfer coefficient was measured with an aluminum cylinder 12 cm long and 4.5 cm in diameter; it started at 80 W/m -C and ended at 1100 W/m -C. For thawing the initial dough temperatures were -18 C or 10.5 C. The thawing medium was still air at 28 C. The surface heat transfer coefficients were 21 W/m -C and 24 W/m -C, respectively. There was some condensation of moisture on the dough surfaces during the initial stage of thawing.
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Progress 01/01/85 to 12/30/85
Outputs
Work continued on measurement of the thermal properties of cakes using a wide variety of types of cakes. Specific heat was found to vary from 2.1 to 2.6 KJ/Kg-C. Thermal conductivity ranged from 0.08 to 0.12 W/m-C for densities from 300 to 350 Kg/m and water contents from 22 to 37 percent. Then the cakes were compressed to remove void spaces. Compressed densities ranged from 1150 to 1190 Kg/m and thermal conductivity ranged from 0.25 to 0.31 W/m-C. The thermal conductivity of the compressed cakes was used as the thermal conductivity of the solid phase in modeling the thermal conductivity of the original porous cakes using models based on two phases: the cake solids and the void spaces. Several models from the literature gave good estimates of thermal conductivity of the porous cakes; these models are based on thermal conductivity of the continuous phase (cake solids), thermal conductivity of the discontinuous phase (air) and the porosity. These results should
provide insights into the modeling of the thermal properties of other porous food materials.
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Progress 01/01/84 to 12/30/84
Outputs
Thermal conductivity, specific heat and mass density were measured for chopped pecan nut meat at water contents from 4% to 20% mass densities from 700 to 1000 kg/mDT. Thermal diffusivity was calculated from the above properties. These data were compared to thermal conductivity, specific heat, and thermal diffusivity of several food oils and fats which were measured in our laboratory and other data from the literature. Models for these properties were developed, based on composition. Other fats and oils included in the study were pork fat, beef fat, butter fat, corn oil, soy oil, olive oil, coconut oil, peanut oil and cod liver oil. Thermal conducitivity, specific heat and mass density were measured for several low and intermediate moisture foods including dried fruits, sausages, cakes, jellies and pet foods. Thermal diffusivity was calculated. Effects of water content, temperature and density were studied. This provides a data base for estimating thermal properties
of lower water content foods for use in design of heating and cooling processes.
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Progress 01/01/83 to 12/30/83
Outputs
The effects of grinding action and temperature on particle size reduction of sorghum were investigated. Two varieties of sorghum with differing proportions of hard (vitreous) and soft (floury) endosperm were ground at temperatures of from 25 to -78C. Chemical and microscopic analyses showed that the structure and properties of the resulting products depended on both grinding action and temperature. In all cases and for all mills, the more vitreous grain (SC0283) sustained more starch damage than the less vitreous variety (CS3541). Thermal conductivity of defatted soy flour was measured with a line heat source probe at various process conditions (e.g., moisture content, bulk density and temperature) normally encountered in commercial extrusion texturization processes. These process conditions are moisture content from 9.2 to 39.1 percent wet basis, bulk density from 0.95 to 1.30 gm/cmDT and temperatures from 25 to 150C. Thermal conductivity varied from 0.070 to
0.460 W/m-C. An experimental model for predicting thermal conductivity of defatted soy flour based on bulk density, moisture content and temperature was developed using the experimental data and the PROC GLM in Statistical Analysis System (SAS). It was found that thermal conductivity of defatted soy flour increased with increasing moisture content, bulk density and temperature. Thermal properties of several low and intermediate moisture foods were measured and modeled including jellies and jams, dried fruits and comminuted meat products.
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Progress 01/01/82 to 12/30/82
Outputs
Defatted soy flour dough at 35% moisture content was extruded in a capillary viscometer at a Newtonian shear ratio of 100s - 1. The dynamic modulus and phase angle were measured at 10 Hz. As time increased, the dynamic modulus increased and the phase angle decreased. Samples removed from the extrudate were successively solubilized using water, buffer, mercapto ethanol and sodium - dodecyl sulfate. The insoluble fraction increased markedly and stabilized and was highly correlated to the dynamic properties of the extrudates which indicated this fraction may be most responsible for the extrudate properties. This research should help the design engineer to better predict the relationship between process conditions and the texture of an extruded product and lead to better control of product texture. Thermal conductivity and specific heat of pecan meat was measured at mass densitities of 0.7 to 1.0 g./cm.(3), at water contents from 3 to 88% and at temperatures from 5
degrees C to 35 degrees C. Thermal diffusivities were calculated. Thermal property research should provide data for the design engineer to develop more energy efficient food processing systems. Energy efficiencies of grinding grain sorghum, corn and wheat were measured for various bench size and pilot plant size grinders including hammer mill, pin mill, roller mill and Urschel Commitrol for varying temperatures and moisture contents. This basic research on grinding should lead to improved energy efficiencies in grinding processes.
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Progress 01/01/81 to 12/30/81
Outputs
Temperatures in the loin and round of 115 beef carcasses were monitored in a commercial slaughtering plant. Cooling rates were affected by carcass weight, thickness of fat cover and location of the carcass in the chill cooler. A finite elements computer model was developed to simulate the temperature in the loin during chilling. This will enable beef processors to predict cooling times for various chilling conditions. The energy required to grind grain sorghum was determined for a hammer mill, pin mill and roller mill. Effects of temperature and moisture content were determined. Particle size distributions were obtained for comparison of energy required per unit of new surface area generated. Thermal conductivity and thermal diffusivity of soy flour were measured for various moisture content and density levels. Results can be used to predict temperatures during heating processes.
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Progress 01/01/80 to 12/30/80
Outputs
Thermal conductivity of defatted soy flour was measured with a line heat source probe at room temperature for moisture contents ranging from 4 to 32% and bulk mass density from 330 to 710 kg/m 3. Thermal conductivity varied from 0.03 to 0.09 watts/m-C. Specific heat of sorghum flour was measured with a differential scanning calorimeter for moisture contents from 3 to 50% and temperatures from 35 to 150 degrees C. A prediction model was developed for modeling the specific heat of the sorghum flour. Thermal properties of flour and flour containing materials will make it possible to model heat transfer in cooking and baking processes. Experimental data for chilling rates of beef carcasses were obtained in a carcass chill cooler. The chilling rates were modeled as a function of carcass weight, thickness of fat covering on the carcass, and location of the carcass within lthe cooler. A finite element model was developed for modeling the temperatures in the loin area.
This information will make it possible to predict cooling times for a variety of chilling conditions including alternative processing methods for reducing energy consumption.
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Progress 01/01/79 to 12/30/79
Outputs
This research will lead to improved food processing with more efficient energy utilization while maintaining food quality. A model was developed theoretically and tested experimentally for predicting effects of shear rate, temperature, moisture content and temperature-time history on the apparent viscosity of defatted soy flour dough undergoing heat-induced protein denaturation in a stationary condition. A capillary rheometer was used for the experimental testing. Viscosity data obtained for various operating conditions were used to evaluate model parameters. A literature survey of surface heat transfer coefficients for food cooling, freezing and thawing applications was completed. A capillary rheometer was used to extrude defatted soy flour dough after given time-temperature treatments. Several extrudate properties (moisture loss, bulk density, swell ratio, rehydration capacity and texture) were measured and correlated with operating conditions and viscosity.
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Progress 01/01/78 to 12/30/78
Outputs
Results of this project will enable food processors to process food with increased quality while reducing food waste, energy used and costs. An experimental capillary food extruder has been designed, constructed and used to obtain experimental extrusion data which have been used to validate a protein extrusion texturization model. Flour moisture content, die length and die diameter were varied. Pressure loss through the extruder was the measured variable. Thermal conductivity of ground meat products containing various amounts of soy and cottonseed flour has been measured. A survey of surface heat transfer coefficients for food cooling and freezing applications was initiated. Shear tests were made on steeped corn to correlate shear properties with doneness in tortilla production. Other research involved investigation of plasma protein rheology interactions with heat treatments and ionic additives.
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