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Drew Lambert, Technical Services Manager. Food Technology Corporation, Email: firstname.lastname@example.org
Texture, and the related mouthfeel of food, plays an essential role in how consumers evaluate the product. In some cases, these characteristics are even more important than those of taste, appearance, or smell. Texture refers to how the physical attributes of the food are processed by the brain during mastication. Mouthfeel is related to texture in that it refers to the interactions between the surfaces in the mouth and the food. In its most simple form, mouthfeel is exactly that: how it feels in the mouth. Terms such as hard, soft, crispy or crunchy, are used by consumers to describe food texture, some of which lead to further labels such as ripe, fresh or stale.
The consumer’s sensory relationship with a food extends beyond mouthfeel when making texture-based judgements regarding quality and acceptance. The relationship begins before this, and before the final taste test. The way a product feels when handled, whether being squeezed or tapped at the point of sale, mixed or pressed during preparation, torn or grasped when being lifted to the mouth is also significant. This texture-related interaction, communicated by the sense of touch, is termed finger feel.
The manner in which a food item, including its constituent ingredients, interacts with the equipment utilized in its production process is similarly a function of the texture. The acts of compressing, extruding and slicing, which a product may undergo in the journey from raw ingredient to serving suggestion, have parallels in the way the consumer finally enjoys the product (or not).
The principles of texture analysis grew from the recognition that there is a tangible benefit from understanding how to optimize the sensory experience for the end customer. Food Technology Corporation was established to do just this. Today, processors determine what is expected in relation to texture of their product, typically by consumer feedback through surveys and evaluation panels. Armed with this information, a scientific test method may be developed that allows the measurement and ultimately the control of these characteristics. The texture analyzer is the means by which the subjective becomes objective—by correlating the measured test data for products deemed ideal or off-spec.
The accuracy and relevance of the test is determined by the appropriate replication of the interaction between the consumer and the product. The physical deformation of the food sample should be in a manner that reproduces the way that the consumer experiences the product when making a critical decision based on texture. Similarly, a representative preparation and presentation of the test sample is fundamental to gaining valid results. The legendary FTC Kramer shear cell performs a combined compression and shear action on a bulk sample of a product, returning firmness/tenderness data as if biting or chewing.
The benefit of understanding the measureable parameters which correlate directly to desirable quality—and possessing the capability to test them—allows the producer to respond to external influences and trends. This extends to variability in raw ingredient supply and regulation revisions, whether safety, nutritional or environmental.
Industry-standard tests have evolved over the years which focus on standardization of textural qualities in raw ingredients, evaluation of produce at point of harvest and classification at early stages in the supply chain. These procedures, or the fixtures required to perform them, often take the name of the pioneering individuals who recognized the need to formally quantify the grading of food.
For example, gelatin Bloom strength testing returns a hardness value in response to compressing a gel of known mixture concentration, Magness-Taylor probes are used to test the ripeness of fresh fruit by penetration, and Warner-Bratzler blades shear meat as an established indicator of tenderness at the meatpacking and processing stage.
Canned and retorted products are a good example of products which have food safety regulations as an external influence. The thermal process by which these items are preserved will have an effect on the final texture. Typically hotter conditions and/or longer cook times needed to sterilize will cause reduced firmness in the product, which consumers could find less desirable. The required thermal processing profile is more crucial for the microbiological safety of the product than the food’s texture profile. However, sensory and instrumental texture analysis can be used to determine if this is going to be significant. If the variation still falls within the criteria determined by the initial testing, the product can be released. If it falls outside the criteria, processors may still be able to make formulation changes to keep the finished product within specification. Calcium for example, is a popular texture-modifying ingredient often added to canned products to help maintain a desirable texture and mouthfeel. Usually these changes to formulation are tested on a small scale, pilot process before applying them to full-scale processing lines. For these reasons, texture and mouthfeel are important characteristics to understand and control at all levels of the food production process.
While there may be synergies in the desirable texture for the consumer and that which facilitates ease of production, this may not always be the case. A rich and creamy dairy product, which holds its shape well, flows consistently from the packaging and feels firm to the touch, may bring challenges to the efficiency of delivery from filler-line nozzles.
The use of a texture analyzer can enable the food manufacturing community to gain valuable control of their own production processes. Food processing equipment settings are directly influenced by the physical properties or the product being manipulated. Packaging choices are also strong influencers on customer acceptance and have texture-modifying implications. Packaging the product, the attributes of the packaging in terms of storage performance and environmental concerns are all decisions which can adversely affect the texture of the food at the point of mouthfeel.
Changing end-customer tastes further complicate matters—fat-free, sugar-free, meat-free, gluten-free, dairy-free, additive-free, preservative-free, GMO-free—such freedom of choice can cost a product its desirable texture. Fat content is a major factor in how we perceive quality in relation to texture, the mouthfeel of fatty food invokes a sense of richness associated with higher quality and the transmission of taste is also expedited by the structure of fats.
The texture comparison between reduced fat alternatives to a traditional formulation is a valuable application of texture analysis. Semi-solid dairy products, such as sauces, dips and yogurts can be tested for their thickness and consistency against benchmark data, using extrusion methods. The early quality perception for a product of this nature occurs as the consumer serves it, typically by spooning or pouring from its container. The flexibility and choice of accessories allows a producer to closely replicate this consumer interaction, by testing in the product’s own packaging, with the back extrusion method. This test type lowers a probe, acting as a plunger—either a cylinder or a flat, circular plate—into the sample, which is constrained in a cylindrical receptacle. The force is measured as the product is extruded back between the plunger and the cylinder. The peak value reflects the overall firmness, itself an indicator of a desirably thick texture. The area under the force-vs.-displacement graph calculates the energy required to initiate and maintain flow, adding further information for comparison.
The same product may be evaluated for its behavior in the critical elements of its processing. The flow through filling machine heads is simulated by forward extrusion, where the sample is constrained to flow out through a known diameter hole in the bottom of the containment cylinder, representing the nozzle bore. A close tolerance between the cylinder fixture and the plunger, ensures maximum forward extrusion. Varying the cylinder clearance and the hole diameter can return a wealth of data for the machine manufacturer to fully profile the behavior.
Similar texture analysis studies on fresh processed meats and vegetarian substitutes, with an equivalent desired texture for the consumer, may be used to optimize pressing and forming equipment.
Once a product is delivered into its packaging, this local environment is required to protect the food’s taste, appearance, smell and texture. Environmental regulations and consumer opinion is increasing the demand that packaging also protects the environment.
Useful shelf life in fresh bakery products and the need for a crisp, crumbly food item to arrive at the consumer in a non-crumbled state, are two customer acceptance criteria that are strongly influenced by the effectiveness of the packaging solution. Bread staling tests use compression to squeeze the product, with the knowledge that a lower peak force for a given displacement indicates a softer, fresher item. The increase in peak force as the product becomes stale—and hardens—over time can be measured for packaging alternatives.
Brittle foods may be evaluated for their break resistance, all at once ensuring a quality snap for the consumer and providing data to minimize the likelihood of transportation damage. The 3-point bend fixture can also appraise the shelf life qualities of these products, plotting the decrease in force required to break as staling causes softness.
The product must ultimately arrive at the customer safely, on time, and in acceptable condition. While the safety of food is the primary concern for all products, quality is also a major concern and needs to be monitored before complaints are raised. Companies can best meet consumer expectations through measurement (sensory testing and texture analysis) and control (formulation and processing parameters).
Taste may be the final test on the route to customer acceptance, however this sensory assessment remains very subjective, with an immeasurably fine line between love and hate.
Mechanical properties which determine physical texture are more certain and a texture analyzer can measure these attributes to calculate crispness, ripeness or tenderness. Producers should be taking control of what is objectively quantifiable, to ensure their unique selling point remains consistent in the face of external variables.
If the texture doesn’t feel right to the consumer, the product won’t even get the chance to be tasted.