Ever wondered why potato chips, French fries, or potato salads don’t have a consistently similar texture, even when produced by the same manufacturer or fast food chain? Consumers have a certain preference and expectation of how food should taste and what its texture will be like when they bite into and chew it. So, what prevents the manufacturer from achieving this goal?
There are a number of processes involved in converting a whole potato to the desired product that a consumer will enjoy. The crucial first step is to ensure that the required potato quality is established at the receiving dock. Qualitative inspection on all incoming shipments is a must. Potato evaluation can include defined physical tests for texture in order to pass and thereby ensure a smooth and predictable production process. The quality of the eventual end product, and in turn a healthy business profit, depend on this important inspection procedure when the potato is first received.
Visual inspection and tactile assessment of the potatoes by means of touching, squeezing, and poking with the human finger can be easily carried out. However, the drawback with this form of inspection is the subjective nature of the pass/fail test which may result in approving potatoes that should have been rejected or vice versa. Accuracy and quality are likely to suffer when a human inspector experiences fatigue or distraction related to the monotony of inspection tasks.
Fortunately, the subjectivity in the potato inspection procedure (or any fruit or vegetable inspection procedure for that matter) can be eliminated by using a Texture Analyzer (see Figure 1) fitted with a Magnus Taylor probe (see Figure 2). This combination of instrument and probe automatically provides an objective procedure for guaranteeing a quantitative quality assessment regarding the receiving, handling, and storage of potatoes.
By selecting a compression test using the Magnus Taylor probe, a technician can measure the force required to break through the potato’s skin and into the flesh. This simple test involves the penetration of the sample under controlled conditions. It assesse the physical textural characteristics of potatoes such as rupture point, internal flesh consistency, stickiness, and firmness.
The test set-up simply involves placing the potato sample on the fixture base table (see Figure 3). The test commences once the 5 mm diameter Magnus Taylor probe with hemispherical tip end is positioned about 10 mm above the test sample. The probe approaches the test sample at a pre-test speed of 1 mm/s. Data collection begins once the probe makes contact and detects a trigger force of 50 gm force. The Magnus Taylor probe then pushes through the potato skin at a speed of 2 mm/s and continues to penetrate into the potato flesh. When the test target distance of 15 mm has been attained, the probe withdraws from the potato and travels back to its starting position above the sample surface.
The Texture Analyzer can perform textural assessment tests in standalone mode and report force measurement values on the screen, or, when used with the optional software running on a PC, it can automatically control the Analyzer and collect data for graphical display (see Figure 4). The software also comes with analytical tools for data analysis; it can generate multiple plot overlays, print tabular data, and perform other time-saving routines.
The graphical plot in Figure 4 and the statistical results reported in Table 1 reveal that that the Russet Burbank potato sample is firmer than the Russet Norkotah. The graph for the Russet Burbank potato also shows a larger area under the positive curve, known as Hardness Work done, which is a measure of the energy required to penetrate the flesh within the potato. The test also provides a stickiness value for the potato sample, which is calculated by analyzing the negative part of the graph that is generated when the Magnus Taylor probe retracts from the potato flesh. The peak negative value on the graph indicates the maximum adhesion force. A higher negative peak value will mean a stickier sample.
The quantitative data obtained from the Texture Analyzer may be used to predict the potato’s maturity by correlating the information with sugar, starch, and water content levels contained in the flesh. These results can be effectively used for decision-making concerned with the receiving, handling, storage, and processing of potatoes.
The testing described above is quick and easy to perform, provides a consistently repeatable test procedure, and appears to detect significant differences between samples. Use of Texture Analyzers to make these types of simple measurements is growing because the results provide an objective approach for pass/fail determination. Similar testing can also be used to quantify the quality of other samples such as fruit and vegetables. The ability to measure physical properties that correlate to sensory characteristics make the Texture Analyzer an important tool in quality control for establishing and maintaining product consistency.
1) Abbot, J. A. 1999. Quality measurement of fruits and vegetables. Postharvest Bio. And Tech. 15(3): 207- 225
2) Crosby, Guy. “The Difference between Waxy and Mealy Potatoes” The Cooking Science Guy. Guy Crosby, 11 May. 2015.
3) Gould, W.A., 1999. Potato production, processing & technology. Citi Publications.
4) Magness, J. R., and G. F. Taylor. 1925. An improved type of pressure tester for the determination of fruit maturity. USDA Circular 250. Washington, D.C.: USDA.
5) Malcom D. G., and E. D. DeGarmo. 1953 Visual inspection of products for surface characteristics in grading operations. USDA Marketing Research Report No. 45. Washington, D.C.: US Government Printing Office