Brookfield AMETEK has participated as a sponsor of the Surimi School conducted at the Marine Experiment Station of Oregon State University. The Project Director is Dr. Jae Park, who is recognized around the world as a leading expert in the Surimi Industry. With the introduction earlier this year of Brookfield's new CT3 Texture Analyzer, there is now a new, low cost instrument to perform the Surimi Industry standard punch test.
In a direct quote from Dr. Park he states - "CT3 can easily replace the RT instrument without changing the value of gel texture. The CT3 will give more accuracy and consistency because you can calibrate the unit whereas the RT instrument does not have a calibration function. The CT3 can get customer services from Brookfield easily. If my understanding is right, CT3 is the right one to select for your future purchase."
Operational details of the CT3 in the surimi application are explained in this application note.
The punch test is typically used as a grading tool for the strength of the gelatin formed when surimi is processed (cooked) into analog seafoods. The test has historically been done using a 5mm ball probe. The important parameters resulting from this test are the Peak Load at which the surimi gel ruptures, and the distance the sample deforms before it ruptures. These two parameters define the grade of surimi. High grade equals high gel strength.
The following graphs show force and deformation curves as several surimi samples were tested. Such curves can be recorded using Texture Pro CT software to control the CT3 Texture Analyzer when running the test. However, software is not necessary. The load and deformation test results will show on the screen of the CT3 so it can be used as a stand-alone, bench top instrument. Typical surimi results are shown in Graph I.
The Y-axis of the graph shows force required to deform the sample. The X-axis tracks the probe travel to 15mm, and its return. All three surimi samples punctured at approximately 14mm of deformation with a mean peak force of about 250 grams. Other grades of surimi will puncture at different deformation distances or peak force.
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Ranges of different surimi samples are shown in Graph II. The curves labeled "Firm but Fragile Gel" punctured after deforming only 6mm at a force of 250g. A much more "rubbery" gel is seen in the two curves labeled "Firm, Strong Gel". This gel did not puncture until it was deformed 12mm.
The graph at the bottom shows a very weak gel with no real puncture peak. The result of such a test is simply the force required to penetrate the sample, but no gel puncture peak is present. Testing a cup of yogurt, for instance, would generate a similar curve.
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Strong gel surimi, typically preferred for making most seafood analogs, has a higher value. In a puncture test the strong gel exhibits a deformation of greater than 10mm at its puncture peak. Such surimi will exhibit an abrupt peak load, then a rapid and large drop in load after the gel ruptures. This characteristic is shown in Graphs I and II.
Recent developments in the CT3 now enable it to be operated more easily for all grades of surimi. The most significant change is that the test will automatically end when the surimi ruptures. This is accomplished by allowing the operator to enter three test parameters:
|Trigger value -||A load threshold used to indicate that the probe has contacted the sample. Once the sample surface is reached, the probe speed changes to the test speed and deformation (the distance the probe travels) begins being recorded. Deformation is the distance the probe travels after contacting the sample.|
|Correction value -||The magnitude of the decrease, in measured load, required to indicate the gel has ruptured. When the gel ruptures there is usually a sharp decrease in force. Historically, surimi machines use either 30g or 50g as the correction value. The CT3 uses a default value of 30g, but this can be changed from 5g to 99g.|
|Test Speed -||The rate of descent of the probe into the gel. The test speed of the CT3 can be set from 0.1mm/s to 10 mm/s. The standard surimi test uses a test speed of 1mm/s. This is the default speed in the CT3. The operator can change it, but be aware that changing the test is likely to change the gel strength result as well.|
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Most surimi gels have a clearly defined peak and a sharp drop in force when the gel fractures. The load curves from such gels are shown in graph II as firm gels. The red curve in graph III does not have a clearly defined peak. A drop in load force, termed a correction factor, is necessary to recognize a gel rupture. By default the correction factor is set to 30g, but it is adjustable from 5g to 99g. In the red curve there is no drop in force as large as the correction factor of 30g. The CT3 would not detect a peak in this gel because there is none. In such a test, the probe would continue down through the gel until it hit the base table, and then retract to HOME starting position. Should this happen, there is no damage to the machine.
For most surimi gels the 30g correction factor will work well. Remember that you do have the option of changing the correction value for special surimi products if the need arises.
The CT3 is a very easy to use, operator friendly instrument for a variety of applications including surimi gel strength. At the conclusion of a surimi gel strength test, the instrument display will show:
Peak Load: The value in grams of the highest peak just prior to gel rupture.
Def@Peak: The distance in centimeters that the gel deformed before it ruptured.
Gel Strength: A value resulting from multiplying peak load times deformation at peak. This value is shown in g:cm.
Calibration of a CT3 can be verified on site with the appropriate calibration weight set. Calibration weight sets are available for each load cell range of the CT3.