Progress 08/31/04 to 01/30/07
Outputs
OUTPUTS: Formulations were developed which included adding to the liquid whole eggs, water and oil to minimize texture hardness attribute, citric acid to reduce the pH of the mix to 6.1 to prevent greening, xanthan gum at 0.35% to prevent syneresis, pre-gelatinized modified food starch at 0.25 to 0.5% and calcium caseinate at 0.28 to 0.5% to develop a consistent moderate texture hardness attribute similar to that of a commercially produced frozen reference pre-cooked egg patty. Various pre-thermal processing treatments were also tried to help develop the scrambled egg flavor but most of these treatments either had no effect or had adverse effects on color and texture. The best way to impart the scrambled egg flavor in the retorted product was the addition of a scrambled egg flavor concentrate and liquid margarine instead of plain vegetable oil.Thermal processing in the pilot plant retort showed the advantages of the high temperature short time process in reducing processing time and
minimizing thermal degradation of the product.
PARTICIPANTS: Romeo T. Toledo Rakesh Singh Jagan Damodarsamy Raghunandan Kandala Rutgers State University University of Tennessee
TARGET AUDIENCES: Companies that supply rations for defense personnel are the interested parties.
Impacts
With a rapid come-up time, total process for MRE eggs at 130 C (266 F) required only 11 min hold after retort reached 130 C to achieve an Fo of 8.0 min. A long come-up of 13 min and 11 min hold at 130 C resulted in a total process time of 24 min to reach the target Fo value of 8.0 min. A fluffy textured retorted egg was obtained by using a hold time at 100 C with a minimal overpressure to allow the egg to expand while gelling. However, in tests at the Demo site, excessive expansion resulted in slow heat transfer because the expanded pouches blocked the flow of the heating medium over the pouches thus extending the process time to achieve commercial sterility. An optimized overpressure during the gelling phase (retort temperature at 100 C) would limit this expansion and still achieve the desired fluffy texture. However, there was not enough time in the project to optimize this part of the process. Observations on the processing runs done at the Demo site indicate that
retort temperature distribution in the retort must be uniform to avoid overprocessing of some pouches in the high-temperature sections. Since the processes are at least 7 stages (Filling up of retort, come-up to 100 C, hold at 100 C, come-up to 130 C, hold at 130 C, emptying of heating medium, cooling) a rapid transition between stages is necessary for the process to be short and successful. This will involve having a separate reservoir of high temperature water so that water at the appropriate temperature is introduced into the retort during the transition between processing phases rather than simply heating the water in the retort with added steam. Although hold time at 130 C to achieve commercial sterility is in the 20 min range, the total process time is much longer because of the long time involved in the transition between phases. Fo values on the April 2004 Demo site run using the Stock retort in a cascading spray mode was 9.2 min while a repeat of this process in October 2004
resulted in a Fo value of 14.9 min. Tremendous overprocessing resulted in very poor product quality. Adjustments to the retort to improve temperature distribution, a careful study of critical factors involved in heat penetration, and establishment of a scheduled process which was filed with FDA. Sensory data indicate that this product rated in the higher range of "slightly dislike" so it does not compare in quality to the non-thermally processed egg products. However preliminary results on an omelet type product with sausage and potatoes produced using the rapid retort process are encouraging suggesting that the rapid retort process may have potential on products other than plain eggs.
Publications
- Damodarasamy, J.S. 2005. Rheology and microstructure of ready-to-eat retorted egg product. M.S. thesis, University of Georgia, Athens, GA.
- Kandala, R. N. 2005. Improvement of quality attributes of commercially sterile egg products by the use of improved formulation and optimized thermal process. Ph. D. Dissertation, University of Georgia, Athens, GA.
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Progress 01/01/05 to 12/31/05
Outputs
Heat transfer into16 x 9 x 2 cm quad-laminate flexible pouches with eggs, processed in steam-air under cascading water was conducted. A Steritort with the rotary reel removed was utilized in the experiments. At least 20 gal per min of water cascaded over the tray which held the pouches. A series of parallel perforated plates maintained pouch thickness during processing and permitted the heating medium to cascade over two faces of each pouch. A sight glass on the recirculating water line ensured that the pump delivered water to the spray nozzles before starting the thermal process. The superimposed air pressure avoided rupturing the pouches. Thermocouples in the geometric center of each pouch and a data logger, permitted recording and transfer of temperature vs. time readings into an Excel file. The heat transfer model consisted of explicit finite difference equations in three dimensions in rectangular coordinates. The equations were based on an energy balance around a
control volume. Nodes with different incremental distances in the three directions were used in the analysis. Geometrical symmetry was assumed and calculations were based on one-eighth the volume of the container. The heat transfer program was written in MATLAB and run on a PC. Surface nodes included a convective heat transfer coefficient and iterations were made on values of the heat transfer coefficient that allowed a fit between the measured geometric center temperature and the calculated temperature vs. time data. Since eggs gelled at around 80 C, most of the heat transfer occurred during sterilization into a solid material. Thermal conductivity of the eggs measured on thermally processed eggs using the line heat-source probe were 0.498, 0.558, 0.602, and 0.648 W/mK at 60, 70, 80 and 90 C, respectively. Corresponding values calculated using a model based on the product composition were 0.548, 0.553, 0.556, and 0.559 respectively. All calculations with the heat transfer model were
based on a constant thermal conductivity of 0.55 W/mK. Density was 1020 kg/m3 used in all calculations. Specific heat measured by DSC was 3115, 3193, 3341, 3466, 3697, 3821 and 4109 K/kgK at 45, 60, 75, 90, 105, 130 and 130 C, respectively. There was a small difference in values when liquid egg was sued int he DSC compared to using a thermally processed egg. Values calculated using a model based on product composition predicted small changes from 45 to 130 C with values of 3715 to 3794 J/lgK. A constant specific heat of 3700 J/kgK was used in all calculations. Heat transfer coefficients were different during retort come-up, during the sterilization hold time and during cooling. A very high value of the heat transfer coefficient was observed during the retort come-up time due to the rapid flow of steam into the retort. the heat transfer data will be used in modeling thermal degradation of eggs during high temperature thermal sterilization.
Impacts
Good quality shelf-stable egg products will be available to the military and to civilian consumers in emergency relief. The long shelf-life of these products will permit stockpiling during times of low demand. Consideration of both safety and quality during the thermal process determination ensures the best quality product possible. The high temperature short time sterilization process already has proven to be able to produce a better quality product thanis now available in the military ration program.
Publications
- Kandala, R. 2005. Improvement of quality attributes of commercially sterile egg product by the use of improved formulaitona nd optimized thermal prosess. Ph. D. Dissertation, University of Georgia, Athens, GA.
- Damodarasamy, J. 2005. Rheology and microstructure of ready-to-eat retoreted egg product. M S Thesis, University of Georgia, Athens GA.
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Progress 01/01/04 to 12/31/04
Outputs
Viscosity of banana puree was determined at temperatures used in aseptic sterilization of the product. A dynamic stress rheometer with a pressure coquette fixture was used. the temperature range for the measurement was 30 to 120 C and shear rate from 10-5 to 103 per sec. Shear stress values ranged from 10 to 170 Pa. Banana puree exhibited an increase in apparent viscosity from 50 to 60 C and also from 110 to 120 C. Some hysteresis was observed as shear stress sweeps were conducted in a ramp-up and ramp-down sequence. Thermal conductivity measurements were also made on liquid eggs in order to develop a simulation model for heat transfer during thermal processing. K values were temperature dependent but values tended to level off after the gelation temperature of 65 C was reached. Values of thermal conductivity in the temperature range 100 to 125 C averaged 0.55 W/mK and ranged from 0.5 to 0.64 measured by the line heat source probe. Specific heat measured by
Differential Scanning Calorimetry ranged from 3100 to 3800 and averged 3700 J/kgK
Impacts
Thermal processing to produce shelf-stable low acid foods has always been associated with poor flavor in the commercially sterile product. The excessive deterioration in product quality during thermal processing is a consequence of the container thickness through which heat must travel to kill microorganisms in the interior of the container. Current research on the use of thin profile packages has shown that the thinner containers permit higher microbial lethalities in the center of the container in a much shorter time of exposure to the high temperature thus producing better quality products. By mathematical modeling of deteriorative chemical changes and microbial lethality associated with internal temperatures during processing a high temperature short time process was developed which resulted in excellent quality shelf-stable products. These procedures for thermal processing is being promoted by the Dept. of Defense to commercial contractors producing Meals Ready
to Eat items to improve the quality of military rations.
Publications
- Shah, A., Akoh, CC, Toledo, RT, and Corredig, M. 2004. Isolation of phospholipids from inedible egg. J. supercritical fluids. 30:303-313
- Gomez, F, Toledo, RT, Wadso, L, Gekas, V and Sjoholm, I, 2004. Isothermalcalorimetry approach to evaluate tissue damage in carrot slices upon thermal processing. J. Food Engineering. 65:165- 173.
- Jeong, HS, and Toledo, RT. 2004. Twin-screw extrusion at low temperature with carbon dioxide injection to assist expansion. J. Food Engineering. 63:165-173.
- Yilmas, Y and Toledo, RT. 2004. Health aspects of functional grape seed constituents. Trends in Food Science and Technology 15:422-433
- Yilmas, Y and Toledo, RT 2004. Major flavanoids in grape seeds and skins:antioxidant capapcity of catechin, epicathechin and gallic acid. J. Agric. And Food Chem. 52:255-260
- Ditchfield, C, Tadini, C, Singh, R.K. and Toledo, R. T. 2004. Rheological properties of banana puree at high temperatures.Int. J. of Food Prop. 7:571-2004
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