Real-time wireless temperature measurement during high pressure processing

Identification
How does it work?
What can it be used for?
What can it not be used for?
Implementation
Related Facilities
Further Information

Identification

Key words	high pressure treatment, process control, real-time temperature monitoring, compression heating
Latest version	2013/01/16
Completed by	DIL

How does it work?

Primary objective

To control high pressure processing by transmitting real time temperature data using a wireless transmission system.

Working principle

Preserving food with pressure is a gentle method to kill germs and bacteria ([1],[2],[3]). Structure, vitamins and micronutrients suffer little change when sticking to specific process parameters ([4],[5]). During high pressure processing, a temperature increase of the pressurized material occurs (e.g. 3°C/100 MPa for high water content foods [11]). To avoid or minimize over-processing, an online process–control device is necessary ([6],[7]).

This tool collects data inside the high-pressure vessel and transmits them for further processing to a PC or other evaluation units outside the high-pressure-chamber.

The principle of this technology is based on the measurement of temperature inside the high pressure vessel using a wired thermal resistor as probe to change the frequency of a Voltage Controlled Oscillator (VCO). The thermal resistor is very small (Ø1.5 x 1 mm with isolation, operating range 55°C 150°C), so it has little effect on the measured product, also the reaction time to temperature changes is very short. It is connected to a capsule (Ø85 x 180mm) which contains an electronic power device (battery operating time 5:30h) and ultrasonic transmission system. To measure one probe a bandwidth of 5 – 10 kHz is needed. The operating frequency for data transmission is selectable from 16 kHz to 80 kHz depending on the structure-borne noise of the high-pressure system. A sensitive microphone on the outside of the vessel records the frequencies transmitted by the capsule. With a Fast Fourier Transformation, a computer immediately does the backward translation into temperature-related data and could be used to control the preserving process. Due to its analogue method of operation, the resolution of the device is very fine (± 0.1°C). The measurement range is tested in temperatures from 0 80°C and within 0.1 to 600 MPa (conditions currently used in food processing by high pressure). It is possible to connect further probes (temperature, pressure or in development pH-value) to the capsule to get additional data from inside the vessel. For each transmission 5-10kHz bandwidth is needed. The capsule is placed within the chamber or in the handling basket. The wired thermal resistor is placed in contact with the packed foods to measure. Due to the working principle, each probe has to be calibrated first, before it is used at high pressure.

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Additional effects

Higher treatment capacity and productivity of the high pressure equipment as a result of:

Reduction of processing time
Avoidance of over-processing

Important process parameters

Operating frequency for data-transmission: 16 to 80kHz

Lowest measurable temperature: 0°C Highest measurable temperature: 80°C Pressure range: 0.1-600MPa Battery operating time: 5:30 h (up to 500 charge-cycles) Environment: no restriction inside a high pressure vessel

Important product parameters

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What can it be used for?

Products	For all kind of products for which temperature in a high pressure vessel should be measured (e.g. Meat, fish, vegetable and fruit products).
Operations	Temperature measurement, real-time process control, pasteurisation, structure forming
Solutions for short comings	High quality preservation. Real-time monitoring to avoid over-processing or control of new manufacturing processes in the future

What can it NOT be used for?

Products	-
Operations	High pressure thermal sterilisation High Pressure sterilisation
Other limitations	A correct measuring needs the probe to be connected with the measured product or packaged product The sensor (capsule + probe) is a standalone device and is placed within the handling basket. In a further development, the equipment could be integrated into the basket itself, so no extra space will be needed. Depending on the processing time multiple measuring positions could be needed, especially at high temperature, because a temperature gradient could occur ([8,9,10,11]).
Risks or hazards	Depending on the number of probes, temperature non-uniformity might be not detected

Implementation

Maturity	Prototype available for high pressure vessels (industry machines)
Modularity /Implementation	Extendible to additional sensors (pressure, pH)
Consumer aspects	Easy to use
Legal aspects	Machinery Directive 2006/42/EC Regulation (EC) No 1935/2004 (materials in food contact)
Environmental aspects	Optimizing production processes, energy saving ([7])

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Further Information

Institutes

DIL, University of Erlangen-Nürnberg

Companies

Hiperbaric, Uhde-HPT

References

[1] Knorr, D. (1999). Novel approaches in food-processing technology: new technologies for preserving foods and modifying function. Current Opinions in Biotechnology 10: 485-491.

[2] Hendrickx, M. and D. Knorr (2002). Ultra High Pressure Treatment of Foods. New York, Kluwer Academic/ Plenum Publisher.

[3] Patterson, M. F. (2005). A Review: Microbiology of pressure-treated foods. Journal of Applied Microbiology 98: 1400–1409.

[4] Heremans, K. (1982). High pressure effects on proteins and other biomolecules. Annual Review of Biophysics and Bioengineering 11: 1-21.

[5] Heremans, K. (1995). High pressure effects on biomolecules. High Pressure Processing of Foods. D. A. Ledward, D. E. Johnston, R. G. Earnshaw and A. P. M. Hasting. Nottingham, Nottingham University Press.

[6] Ardia, A. (2004). Process considerations on the application of high pressure treatment at elevated temperature levels for food preservation. Department of Food Biotechnology and Food Process Engineering. Berlin, Berlin University of Technology: 94.

[7] Toepfl, S., Mathys, A., Heinz, V. Knorr, D. (2006). Review: Potential of emerging technologies for energy efficient and environmentally friendly food processing. Food Reviews International, 22(4), 405-423.

[8] Grauwet et al. (2011) Temperature uniformity mapping in a high pressure high temperature reactor using a temperature sensitive indicator. J Food Eng 105, 36–47.

[9] Hartmann, C. & Delgado, A. (2003) The influence of transport phenomena during high-pressure processing of packed food on the uniformity of enzyme inactivation. Biotechnology and Bioengineering 82, 725-735.

[10] Rauh, C. et al. (2009) Uniformity of enzyme inactivation in a short-time high-pressure process. Journal of Food Engineering 91, 154-163.

[11] Mathys, A. & Knorr, D. (2009). The Properties of Water in the Pressure/Temperature Landscape. Food Biophysics, 4(2), 77-82.

Patents:

[1] EP 0689391 B1 (1996).

[2]EP 0752211 B1 (2001).

[3] EP 1100340 B1 (2001).

[4] DE 3734025 C2 (1989).

[5] EP 1112008 B1 (2001).

[6] EP 1201252 B1 (2002).

[7] EP 0683986 B1 (2001).

[8] EP 0748592 B1 (2000).

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