Progress 10/01/02 to 09/30/07
Outputs
Dr. Hansen is currently retired and the project has been completed. David Settle, the graduate student whose studies were funded from this project has completed his program of studies and sucessfully defended his MS thesis. He is currently employed with the Dairy Farmers of America. One of objectives of the research was to develop a sour cream product (16% milkfat) that could withstand the effectsof UHT processing to obtain a commercially sterile, shelf stable product using continuous flow microwave heating and aseptic packaging. Several formulations were generated and tested following pilot-scale processing using a 5 kW continuous flow microwave system. Further studies and test trials are being performed on the semi-industrial capacity, 60 KW system and additional research funding and support is continuously sought from industrial and other sources.
Impacts
The major impact will be safer and more nutritious sour cream, whipping cream and cottage cheese with six-month shelf life at refrigerated temperatures of 40 degrees F. The major benefit of the developed processes to the manufacturers and institutional users (restaurants, hospitals, hotels etc.) would be the extension of shelf-life, especially in conjunction with asceptic packaging. This would result in less spoilage, elimination of the need for refrigerated storage, transporation and distribution, and thus incresased profits. A shelf stable product would also enable the processors to expand the market and distribution range of their sour cream products - for example a single production facility could potentially distribute such products to the nation-wide market.
Publications
- No publications reported this period
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Progress 10/01/04 to 09/30/05
Outputs
During the report period, most of the research and development activities have concentrated on the study of dielectric properties of several alternative formulations of sour cream (using different stabilizers and milkfat contents). These studies implemented several new devices developed in our laboratory to enable performance of these measurements under representative sterilization-level temperatures and flow conditions. Using additional funding support from NCSU CALS and from the NSF Center for Advanced Processing and Packaging Studies we were able to acquire and implement a new dielectric property measurement probe and electronic calibration tools. These were installed and tested - currently the first known functional system capable of performing these measurements at sterilization temperature and pressure levels under conditions of full continuous flow. After the return to the renovated NCSU Department of Food Science building, experiments and measurements
continued using the continuous flow microwave installations. The investigated formulations for sour cream were processed using the 5 kW microwave heating installation and the produced materials are currently being analyzed for quality and functionality parameters. The results of these analyses will be used as a basis for selection of a single formulation to process/sterilize for commercial shelf stability and quality and functionality evaluation.
Impacts
The major impact will be safer and more nutritious sour cream, whipping cream and cottage cheese with six-month shelf life at refrigerated temperatures of 40 degrees F.
Publications
- No publications reported this period
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Progress 10/01/03 to 09/30/04
Outputs
Experimental studies were continued in order to establish a system and a processing protocol to address the identified issues with grainy texture of some processed products. Additional equipment and process line modifications were implemented in order to better evaluate, quantify and monitor the processing conditions that lead to these issues and to potential compromise of product treatment with some high-viscosity products. Several multi-point thermocouple-sensing arrays were custom-made and installed in the system. The data collection from these arrays was performed using a unique 80-channel thermocouple monitoring and data acquisition system. Additionally, static mixers (Admixers) were installed and tested in order to implement a secondary mechanism for thermal equalization of processed materials. The need for this additional equipment was identified for more viscous products. There have been recorded cases of under-processing and subsequent spoilage with other
(non-dairy) test products due to poor thermal equilibration subsequent to the last stage of heating and throughout the hold tube process segment. The cause of this problem was identified as one of the shortcomings of an otherwise beneficial temperature distribution within the flow-through, microwave transparent tubes. Specifically, with some viscous products, achieved distribution of temperature was recorded as preferential (hotter product in the center of flow and gradually lowered temperature toward the tube flow perimeter), i.e. inverse to the common temperature distribution found with the tube in tube or plate heat exchangers (cold flow segments in the center). For products with low thermal conductivity this could potentially result in thermal under-exposure of some flow segments (those closest to the tube walls) which could potentially cause product instability and spoilage during storage and distribution. Installation and testing of static in-line mixer devices have confirmed
the ability of this approach (a secondary passive temperature equalization device) to appropriately address this problem. As a result, several test batches of extended shelf life as well as shelf stable products have been produced. This development is expected to also serve to appropriately address the identified issues with dairy product texture since it will serve to equalize temperature distribution within the product prior to entrance into the hold tube process region as well as at selected points along the product cooling line.
Impacts
The major impact will be safer and more nutritious sour cream, whipping cream and cottage cheese with six-month shelf life at refrigerated temperatures of 40 degrees F.
Publications
- No publications reported this period
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Progress 10/01/02 to 09/30/03
Outputs
Process characterization has been done for both whipping cream and sour cream as well as for a number of variants such as fat content and various stabilizing systems. Dielectric measurements were performed for all investigated materials and theoretical microwave energy distribution profiles generated. Pilot plant scale heating studies were done and resulting temperature profiles collected using the pressurized circulating 5kW continuous flow microwave heating system and a custom developed thermocouple array installation. Three experimental test run trials were also performed with the semi-industrial capacity 60 kW continuous flow microwave heater/reactor integrated in the aseptic processing line with processed products filled into 250 ml cartons and 2 gal aluminum laminate aseptic bags. For the processing trials for sour cream fresh raw milk and cream were obtained from the NC State Dairy Plant. The sour cream was standardized to 16% fat content and blended with
modified cornstarch and gelatin at different levels. The mixture was heated to 165degrees F for 30 minutes and homogenized in a Gaulin homogenizer. The pressures used were 3000 psi on the first stage and 500 psi on the second stage. The mixture was subsequently cooled to 72 degrees F and inoculated with Streptococcus lactis and Leuconostoc citrovorum and held for 12 hours at 72 degrees in a temperature-controlled vessel. After a 9 hour period the titratable acidity of the mixture was tested until the titratable acidity reached .72. At this point the sour cream was transferred into a Marlen pump reservoir and pumped through the 60 KWIMS cylindrical microwave heater/reactor cavity where it was heated to 285 degrees F, subsequently held for 10 seconds in the hold tube segment of the system and rapidly cooled to 100 degrees F. It was then filled into 2 gallon aluminum foil laminated bags for storage studies using an astepo aseptic filler. The bags of sour cream were stored in the dairy
cooler at 38 degrees F and analyzed for flavor viscosity, texture and mouth feel. The flavor and texture of the ultrapasteurized sour cream were estimated to be equivalent to those of fresh sour cream. Initial processing runs were also performed with the whipping cream and are currently under analysis. An invention disclosure has been generated and accepted for management by the Office of Technology Transfer and Industrial Research at NC State University.
Impacts
The major impact will be safer and more nutritious sour cream, whipping cream and cottage cheese with six month shelf life at refrigerated temperatures of 40 degrees F.
Publications
- No publications reported this period
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