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. 
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 xe2x80x9cFDA process filingsxe2x80x9d, xe2x80x9cprocess filingsxe2x80x9d or xe2x80x9cFDA filingsxe2x80x9d, 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 processxe2x80x94sufficient 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.,  xe2x80x9cBiological Evaluation of a Heat Transfer Simulation for Sterilizing Low-Acid Large Particulate Foods for Thermal Packagingxe2x80x9d, Journal of Food Processing and Preservation, 13:257-274, (1989); Tucker, G. S. and Withers, P. M., xe2x80x9cDetermination of Residence Time Distribution of Food Particles in Viscous Food Carrier Fluids using Hall effect sensorsxe2x80x9d, Technical Memorandum 667, Campden Food and Drink Research Association (CFDRA), Campden, Glos.,  U.K. (1992); xe2x80x9cCase Study for Condensed Cream of Potato Soupxe2x80x9d, 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 xe2x80x9ccold spotxe2x80x9d (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.,  xe2x80x9cMapping Food Temperature with Magnetic Resonance Imagingxe2x80x9d, 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 64xc3x9764 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 outside of the particle.  For example, Beller discloses that the curve of the speed of sound versus temperature for potatoes approximately paralleled that of water above about 110xc2x0 C. This indicates a potential material and location misidentification of fluid vs. solid temperatures.  Additionally, standardization and calibration curves must be generated for each and every potential product component, necessitating a very laborious and lengthy measurement and calibration procedure prior to implementation.  The applicability of detection through stainless-steel equipment walls without special ports or windows is also unclear. 
Methodologies that implement thermosensitive implants include the local magnetic temperature measurement approach disclosed in U.S. Pat.  No.  5,722,317 to Ghiron et al.  Ghiron et al.  disclose the use of spherical paramagnetic particles for implants and detector coils around the pipes for sensors.  The approach then implements the correlation between the falling magnetic field strength and temperature increase to calculate the implant temperature from the signals of three sensor coils.  However, the negative correlation between the measured magnetic field and the increasing temperature employed by the Ghiron et al.  approach can cause a non-conservative temperature estimation, i.e. the resulting calculation can indicate a higher temperature than is actually present in the implant.  This is due to the fact that magnetic field reduction can be caused by a variety of factors other than temperature increase in the implant, such as the particle or the detection system being out of calibration, reduction of sensitivity of the detection system, and obstruction of detection by other materials such as other present food particles.  The complexity of the system disclosed by Ghiron et al.  also limits the number of observation points as well as the applicability at high-temperature, short time processing levels. 
The Campden and Chorleywood Food Research Association in Great Britain reports on the use of a Temperature Responsive Inductance Particle (TRIP) sensor, which can be placed in the food product.  The time temperature history of the sensor is purportedly monitored/logged in real time outside the processing equipment/environments.  See Research Summary Sheets, 1997-68, xe2x80x9cTRIPxe2x80x94A New Approach to the Measurement of Time and Temperature in Food Processing Systemsxe2x80x9d.  Most of the details of this methodology are not publicly available.  However, one of the accessible, limited reports indicates that the sensor size is about 5 mm in diameter.  This size precludes its use to measure the xe2x80x9ccold spotxe2x80x9d temperatures in aseptically processed particles.  Additionally, no disclosure is made with respect to capability for the monitoring through stainless steel equipment and current applicability to continuous processes. 
One common shortcoming of all available systems is the limited number of monitoring locations due to the complexity, cost or the necessity of having view ports or windows within the stainless steel processing equipment segments.  This is a serious disadvantage due to the fact that various product components, and especially product formulations, achieve thermally lethal temperature levels within particles at various points in the equipment stream path.  It is not therefore sufficient to have a port or a detector located at any specific fixed location along the process stream path.  While this port might detect lethal levels for one product or particle type, it would have to be repositioned or added downstream to ensure confirmation of lethal temperature levels for a faster moving or slower heating particle type or product.  The location point for a downstream detection unit, port or window might be arrived at by modeling, but is substantially impossible to predict reliably without actual experimental data.  This requirement therefore becomes an uncertain, expensive, multi-step trial and error procedure for each processed particle type and product formulation. 
Currently, there are no available continuous process particle temperature measurement systems, conservative or otherwise, in spite of the documented need by the industry as well as the above-noted several attempts to provide an appropriate method and system.  Thus, what is needed is a method and system that can conservatively generate temperature measurements in continuous thermal processing of particulate-containing food products, among other applications.  Such a method and system are lacking in the prior art. 
A method of generating a temperature measurement for a batch or a continuous stream of material is disclosed.  The method comprises: providing a particle having a signal that changes at a pre-determined temperature; inserting the particle into the batch or continuous stream; and detecting a signal change from the particle to thereby generate a temperature measurement for the batch or continuous stream. 
A system suitable for carrying out the method is also disclosed.  In a preferred embodiment, the system comprises: a particle having a signal that changes at a pre-determined temperature; and a detector for detecting a signal change from the particle to thereby generate a temperature measurement for the batch or continuous stream. 
Accordingly, it is an object of this invention to provide a novel method and system for generating a temperature measurement for a batch or continuous stream of material.  The object is achieved in whole or in part by the present invention. 
An object of the invention having been stated hereinabove, other objects will become evident as the description proceeds when taken in connection with the accompanying Drawings and Examples as best described herein below.