Get a Feel for Texture

Local Oven in Sunnyvale, Texas, uses Citrafiber to improve the texture of its baguettes. We evaluated the five properties given above using three types of wheat bread as a reference for Local Oven’s gluten-free baguettes and a separate retail gluten-free product from another manufacturer (see Table 1).

For these five physical properties, the Local Oven product scored much closer to wheat bread than the other retail gluten-free bread. A quick survey of the gluten-free marketplace shows that many new products are introduced every month. The properties of these products are getting closer and closer to those of traditional wheat products. This is good news for the gluten-intolerant population, as well as for those who simply choose to be gluten free.

Energy Snacks

Recently, we have seen a growing number of high-energy snack foods introduced to the market. Fruit flavors seem to dominate these brands. The products themselves are often bite-sized, chewy nuggets containing fruit juice, sugar, and other quick-energy supplements.

click for large version

Figure 3. Measurement of firmness (compression stroke) and stickiness (return stroke) on three energy snack foods.

Every brand is distinguishable from the others, at least partially, by a collection of physical properties: firmness, chewiness, and stickiness. Compression testing is a great way to measure these properties and can be done easily using a texture analyzer. Bite-sized pieces of soft and somewhat sticky snacks must be held in place for such testing. The device shown in Figure 2 is an adjustable vice that provides a convenient way to quickly position and secure samples. Of the physical properties we can address with a texture analyzer, firmness and stickiness can be measured with a single compression test by penetrating the sample with a small cylindrical probe. Firmness is measured on compression stroke and stickiness on the return stroke (see Figure 3). This test, which is quick and easy, appears to detect significant differences between two of the three samples.

Pie and Pasta Filling

The quality and consistency of the filling inside ready-to-eat pasta and pies is of great concern to manufacturers and consumers. There are texture accessories available to make testing easy for both smooth fillings like cheese in ravioli and pie fillings containing chunks of fruit (see Figure 4a and Figure 4b). Both are best measured using extrusion fixtures. During a test, the analyzer records the force required to squeeze the filling through an aperture or across a mesh that is chosen according to the size of the solids. The maximum force and the total work of extruding the filling are the important result parameters.

Figure 4a. Back extrusion used to measure fruit purée.

Figure 4b. Ottawa cell for extruding assorted soft samples through one of two interchangeable bases.

Dips and Spreads

Pourable dips can be measured for viscosity but, if the sample is too thick to pour, a spreadability test may be more appropriate. A set of matched cones allows sensitive measurements of spreadability between samples to be evaluated. Several female cone-shaped cups are supplied with the set. Each is filled with sample material and set aside to be conditioned if needed. During the test, the male cone is driven into the sample, forcing the material out in a back extrusion process. Because of the conical shape of the matched probe and cup, the load force resulting from driving the cones together typically shows a nearly exponential increase. Differences in spreadability can easily be seen on the resulting graph and the measured/calculated parameter. Peak force and work area, respectively, are the important parameters.

Fresh Vegetables

Fruits and vegetables are commonly tested for ripeness or firmness using radius-tipped probes known as Magness Taylor probes. These probes are used in a penetration test. Firmer products, like young crisp apples, result in higher loads. Other types of tests can yield additional, interesting information for the researcher. For example, a university conducting shipping research on russet potatoes wished to know the forces that fresh russets can withstand without damage. The higher they are piled, the greater the force upon the potatoes at the bottom becomes. A half-inch ball probe was used to approximate the smallest radius by which one potato would press against another one. Figure 5 shows several repeatable tests indicating that potatoes can withstand more than 15 kg of force applied by this small radius probe before damage occurs. Such information can help assure transportation without damage.