Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
1999-04-30
2001-10-02
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S436000
Reexamination Certificate
active
06297505
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and a flow system for carrying out spectrometry for analysis of a liquid food product, possibly containing dissolved gases, in a process line in a liquid food product processing plant, especially milk and milk products in a dairy, and comprising the following steps: 1) providing a liquid food sample from the process line to a measuring branch, 2) thermostating the liquid food sample, 3) passing the thermostated liquid food sample to a sample cuvette, 4) measuring at least part of the absorbance spectrum of the liquid food sample in the sample cuvette. The invention also relates to a measurement cuvette for the flow system. The present invention is specifically intended for IR-measurements, e.g. MID-IR and/or NIR-measurements for a determination of the quantities of specified components in the liquid food product.
BACKGROUND ART
A presently used method includes providing a milk sample from the process plant in an open sample container or cup from which dissolved gases may escape, passing part of the degassed milk sample from the container through a measurement branch into a measurement cuvette, performing the test and passing the tested milk sample to a waste outlet.
The presently used test instrument includes generally a flow system, an IR spectrophotometer, and a computer comprising a PC with hard-disc, floppy disc drive, monitor and keyboard.
Instead of the above mentioned method it would be preferable to perform the test on-line and in-line in the process plant, and preferably in such a way that it also would be possible to let the tested milk sample be returned into the process line, to avoid the waste.
U.S. Pat. No. 5,137,738 discloses a system and a method for controlling the butterfat content of milk. The entire product stream is monitored continuously by the use of optical density sensors. The preferred sensors have stainless steel bodies and housings med Pyrex windows and mount directly on the product output lines and operate at full flow and pressure. U.S. Pat. No. 4,144,804 discloses a photoelectric monitoring system for continuously measuring the butterfat content of a sample of homogenized milk as the latter flows continuously through the processing system under the pressure of the homogenizer in the system. The known on-line sensors for milk products do not apply spectrometric analysis of the content. On-line spectrum measurement for determining a property of a product is known, e.g. as described in U.S. Pat. No. 5,452,232 for a hydrocarbon product. GB-A-2 104 681 describes an apparatus for the continuous investigation of chemical reactions by infrared absorption by use of an IR spectrophotometer having a through flow cell through which flows a continuous sample stream branched off from the reaction container. U.S. Pat. No. 4,910,403 describes a flow cell utilized on-line in the analysis of molten polymer. The flow cell includes diamond windows for passing mid to far infrared radiation through the molten polymer flowing through the flow cell.
Testing milk in-line in a process plant in a dairy presents several problems. One problem is due to dissolved air, which is normally present in the raw milk. If air bubbles are released and enter the measuring cuvette, the measurement result will obviously not show a correct analysis of the milk product itself. A further problem is that milk includes several components and specifically the fat globules can give reason to failures. According to the known art the temperature of the milk sample should be raised to about 35-42° C., and preferably homogenized to make reliable, reproducible measurements possible in an IR cuvette. Obviously, the milk in the process plant is generally kept at a low temperature to avoid the milk to be spoiled by some unwanted reactions, such as growing bacteria's.
A further problem is that thin layers of milk tend to adhere to the IR-windows of the cuvette. The measurements may be seriously deteriorated due to such milk coatings. Therefore, an IR cuvette needs regular thorough cleaning.
An in-line and on-line system must be able to measure reliably and normally without needing any regular calibrations and adjusting. Spectrometric measurements require the utmost stability of the components of the optical system. It is very important that the cuvette is extremely stable and not liable to suffer from wear. In fact the cuvette is highly exposed to wear as the liquid product and rinsing and cleaning solutions pass through the cuvette under high pressure and flow rates.
It has therefore until now not been possible to perform the desired testing procedures on milk in an in-line system. To the applicants best knowledge there does not on the market exist any reliable apparatus able to perform accurate and reliable in-line determinations of the quantities of the components in raw milk or in a milk product, e.g. fat, protein, lactose, urea and casein.
SUMMARY OF THE INVENTION
According to the invention the method as defined in the preamble comprises extracting the liquid food sample directly from the process line into the measuring branch, providing and maintaining a pressure that is at least as high as the pressure in the said process line, and before each measurement flushing the cuvette with part of the recently (latest) extracted liquid food sample, further having provided that the cuvette having windows of a pressure and wear resistant material, being especially resistant to mechanical and chemical influences of the kind appearing in dairies. The flushing is performed under a pressure of from 100-200 bars, preferably from 110-150 bars across the cuvette, so the flushing rate will be high enough to ensure a thorough removal of the old sample including a cleaning of the cuvette.
The high pressure ensures that dissolved air will stay dissolved in the liquid food. The pressure and wear resistant materials, preferably diamond windows, allow the cuvette to stand high pressures and high flow rates. Other window materials might break or move causing the cuvette to widen and to thereby causing the IR transmission loss through the cuvette to raise, thereby influencing the measurement result. Accordingly the pressure in the measurement branch should preferably be kept high, at least as high as the pressure in the process line at the location on which the sample is extracted, and during measurements the pressure shall be kept constant in the cuvette. Preferably, the pressure in the measuring branch exceeds the pressure in the process plant to ensure that dissolved air stays dissolved in the liquid food.
The method is specifically fitted for liquid food products such as raw milk or processed milk and other dairy products.
In one embodiment the measuring branch forms a closed system together with the process line. This means that the measuring branch only receives liquids flowing in the process conduit to which the measuring branch is connected.
Preferably, a regular (e.g. daily) cleaning of the measuring branch including the cuvette is performed when the dairy plant is subjected to the regular cleaning process and/or by flushing the branch with the same cleaning solutions used for cleaning the dairy plant. In an advantageous embodiment of the present invention at least one of the cleaning or rinsing liquids of the dairy may be used in the measuring branch for an adjustment, such as a standardization based on characteristics in the measured spectrum or spectra of the cleaning or rinsing liquids, especially characteristics originating from the appearance of ions belonging to the group comprising NO
3
-ions and PO
4
3−
. (By “standardization” is meant an adjustment of the instrument, (e.g. performed in the instrument software) made in order to make a plurality of spectrum measuring instruments performing in the same way so that copies of the same calibration software can be used on all the instruments and whereby all instruments will provide the same result when measuring the same sample.)
Preferably, the spectrometry is performed in the IR spectral ran
Frandsen Andreas Skærlund
Pedersen Søren Christian
Ridder Carsten
Thomsen Henrik
Foss Electric A/S
Hannaher Constantine
Israel Andrew
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