Compression and Tension

Texture analysis is the science that measures the mechanical properties of food products and correlates these findings to the way that human beings use their senses to evaluate foods. More than 65 years of research have resulted in a set of definitions that relate peoples’ sensory properties to instrumental measurements based on a standard test known as Texture Profile Analysis or “TPA.”

Food Products

The image at right shows an example of a texture analyzer with cylinder probe used to measure the firmness of sliced bread. The TPA test is a two-cycle procedure that pushes the probe into the bread a defined distance, measures the resistant force, pulls back out, then repeats the same compression cycle. Figure 1a shows the graph of force versus time for the two-cycles; force is on the y-axis, time is on the x-axis. Note that the peak load P1 in the first cycle is higher than the peak load P2 in the second cycle. Once the bread compresses during the first cycle, it does not fully recover to its original position. The texture analyzer records the probe position and the force load is measured throughout the TPA test, which generally takes less than 30 seconds to perform. Figure 1b shows an alternative way to present the same data using distance (position of the probe) on the X-axis. These measurements are used in mathematical calculations that define properties of the sliced bread, such as “springiness” and “chewiness.”

Table 1 lists the defined properties that can be quantified with measurements from a texture analyzer. The two primary characteristics are “hardness” and “adhesiveness.” “Hardness” is exactly what it sounds like—how firm is the object that is under compression. French bread with a crusty exterior will give significantly more resistance to the probe compared to the sliced white bread. “Adhesiveness” is the amount of work required to extract the probe from the food item. Another way of thinking about this is how sticky the food item might be and how difficult it is to pull the probe away. For bread there is no resistance when the probe is extracted, but for salad dressings there can be noticeable resistance.

Using the data related to the hardness and adhesive force measurements, other parameters such as “springiness” and “chewiness” are calculated. Note that “springiness” is exactly what you might think—how much does the bread spring back after being compressed. “Chewiness” on the other hand is an expression that you instinctively understand, but the mathematical calculation shown in the Table may seem complex—the product of hardness, corrected cohesiveness, and springiness. Rest assured that food scientists have successfully used the various terms in Table 1 to characterize food items for years.

Packaging

Exploding QC interest in the use of texture analysis to certify the physical properties of food products coming out of the manufacturing process is now spilling over into related industries, like packaging materials for these same products. Texture analyzers, as explained above, are nothing more than simple instruments that compress or pull apart an item and measure the force and energy required to make it happen. They mimic the consumer who uses the sense of touch when evaluating a food item by hand or when popping the food item into the mouth and taking bites. Texture analyzers can also qualify the integrity of the packaging used to ensure that the food item survives transit from the manufacturing plant to the supermarket shelf to the end user who consumes the item.