Thermal measuring and testing – Temperature measurement – By electrical or magnetic heat sensor
Reexamination Certificate
2001-03-12
2004-08-17
Verbitsky, Gail (Department: 2859)
Thermal measuring and testing
Temperature measurement
By electrical or magnetic heat sensor
C374S163000, C374S141000, C374S102000, C099S342000
Reexamination Certificate
active
06776523
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to thermal processing of materials, and more particular to a method and system for generating temperature measurements for such processing, and to a detectable particle for use in such a method and system.
BACKGROUND ART
It will be appreciated by those having ordinary skill in the art that thermal processing of particulate-containing food products is difficult to accomplish in an efficient but effective manner. Particulate-containing food products are also described in the art as multi-phase food products, or as multi-phase foods, in that these products include liquids and solids.
Traditionally, thermal processing of particulate-containing food products involved the placing of the product in individual cans, followed by thermal treatment of the product within the can. The process is generally effective in removing microbial contamination and in providing a food product that is safe for consumption. However, this process is labor and machinery-intensive and time-consuming. Thus, this process lacks efficiency.
Continuous thermal processing generally involves the thermal processing of the food product as a stream or flow in one line while processing the containers or cans in which the food will be stored in another line. The food product is then placed in the container under appropriate conditions wherein microbes and their spores are excluded. Continuous thermal processing thus enables unlimited package size, yielding increased efficiencies and reduced costs to the industry and ultimately to the consumer. Continuous thermal processing is sometimes also called aseptic processing in the art.
In the United States each continuous thermal process for use in the treatment of food must be described in a document to be filed with the United States Food and Drug Administration (FDA) for approval before it can be implemented in industry. Because of the problems associated with uniform treatment in the continuous thermal process, the FDA subjects these documents, hereinafter referred to as “FDA process filings”, “process filings” or “FDA filings”, to rigorous scrutiny.
To gain FDA approval, a process filing must demonstrate biovalidation of the process, among other information. As is known in the art, biovalidation refers to data showing that the process was effective in removing contamination of the food product by microbes and their spores. To determine biovalidation, conservative residence time distribution measurements are required. Lengthy test runs must be performed to generate the conservative residence time distribution measurements. Such test runs require a great deal of time and involve the loss of a great deal of the food product, as the food product that is part of the test run cannot be salvaged. The time required for and food product lost in such test runs have prevented the wide scale adoption in the industry of continuous thermal processing of particulate-containing food products.
The current state of the art for process evaluation and validation of continuous thermal processes for particulate-containing food particles, including low acid multi-phase foods, has evolved over a number of years through the joint efforts of the Center for Advanced Processing and Packaging Studies and the National Center for Food Safety and Technology. Currently, it consists of a three (3)-stage sequence. The first stage of the sequence primarily includes process modeling and simulation that provides predicted scenarios for the efficacy of process with respect to microbial lethality. The second stage of the sequence includes experimental measurements of real or simulated particle residence times while flowing through the system for a sufficient number of replications for each particulate product component to provide statistically acceptable (i.e. representative) data for particle velocities to ensure that a portion of the fastest moving particles has been captured and their residence times recorded for modeling purposes. The third and final stage of process evaluation and validation is a biological validation consisting of the use of thermoresistant bacterial spore loads within simulated food particles to demonstrate the achievement of appropriate cumulative thermal time and temperature by the implemented process—sufficient to lethally injure all bacterial spores present within the test particles.
Procedures disclosed in the art attempt to implement these stages by using various methods of particle residence time measurement. For example, U.S. Pat. No. 5,261,282 to Grabowski et al. discloses the use of implanted radio frequency transponders to identify simulated particles passing through a continuous process system. U.S. Pat. No. 5,741,979 to Arndt et al. discloses the use of dipole antenna marker implants in the particles and microwave transducer detectors to measure particle residence times.
Segner et al., “Biological Evaluation of a Heat Transfer Simulation for Sterilizing Low-Acid Large Particulate Foods for Thermal Packaging”, Journal of Food Processing and Preservation, 13:257-274, (1989); Tucker, G. S. and Withers, P. M., “Determination of Residence Time Distribution of Food Particles in Viscous Food Carrier Fluids using Hall effect sensors”, Technical Memorandum 667, Campden Food and Drink Research Association (CFDRA), Campden, Glos., U.K. (1992); “Case Study for Condensed Cream of Potato Soup”, Aseptic Processing of Multi-phase Foods Workshop, Nov. 14-15, 1995 and Mar. 12-13, 1996 (published 1997); U.S. Pat. No. 5,750,907 to Botos et al.; U.S. Pat. No. 5,739,437 to Sizer et al.; and U.S. Pat. No. 5,876,771 to Sizer et al. all disclose the use of permanent magnets for implants (single tag type) and a variety of magnetic field sensors to detect and record their passage through several system segments and locations.
The necessity for measurements of particle residence time and subsequent biological process validation using bacterial spores is a result of the current inability to measure temperature in the “cold spot” (the slowest heating point within a particle) of the fastest moving, slowest heating particle present in the continuously thermally processed multiphase product. Several techniques have been proposed in the art for this purpose and can be grouped into two groups: techniques implementing cross sectional imaging/tomography of the entire flow profile and techniques implementing thermosensitive implants in specific particle locations.
Magnetic resonance imaging thermometry, such as that disclosed by Litchfield et al., “Mapping Food Temperature with Magnetic Resonance Imaging”, National Research Initiative Competitive Grant Program, Cooperative State Research, Education, and Extension Service, United States Department of Agriculture (March 1998), is a non-obstructing and non-contact method, but is not rapid enough to provide in-line real time measurements. It took eight seconds to image a single 64×64 cross-sectional temperature map. During this time a considerable quantity of product would pass the detector unmonitored. It is also extremely complex and cumbersome for these types of measurements, requiring complicated technology, highly trained personnel, and specialized power and power conditioning. Due to all these factors, the number of windows/cross sections that can be observed and monitored within the process equipment is very limited, i.e. the detection of the initial location where the lethal thermal treatment temperature is achieved cannot be determined for all possible cases. The applicability of detection through stainless steel equipment walls without special ports or windows is unclear.
Similar shortcomings are evident with the other tomographic/cross sectional imaging techniques implementing ultrasonic tomography and tomographic reconstruction, such as that disclosed in U.S. Pat. No. 5,181,778 to Beller. Particularly, due to system complexity, the number of observed cross sections is limited. Another problem with the Beller system is the potential for misidentifying the thermal profiles occurring within or
Adles Eric
Simunovic Josip
Swartzel Kenneth R.
Jenkins & Wilson & Taylor, P.A.
North Carolina State University
Verbitsky Gail
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