“Texture is not an independent function in the total sensory reaction of a consumer. If all a company did was measure texture profiles, they could miss flavor release and perception,” says Herbert Stone.

Texture is the crucial attribute of chewing gums with long-lasting flavor and soft, pleasing mouthfeel; pasta with the right texture that cooks in less than five minutes; a protein bar with a year-long shelflife; and low-fat ice cream that melts in the mouth and is smooth, not chewy.

Formula ingredients that directly impact product texture also influence other characteristics, such as flavor release, product stickiness on the palate and lips or even shelflife, such as its staling rate.

For example, if thickening ingredients are substituted in a formulation, when or how long the flavor is perceived may be affected. “Corn might mask more of the flavor in the product, whereas rice starch might not mute the notes as much,” says Ricardo Rodriguez, a food scientist at a rice supplier.

“The texture of a product is one of the first feelings that a consumer experiences,” says Herbert Stone, president of Tragon Corp. Depending upon the texture, the flavor of the product could linger or dissipate rapidly.

Texture is important because it is relative to how the manufacturer wants the consumer to experience the product, explains Stone. “If a product looks like mashed potatoes and consumers put it in their mouth and it acts like water going down their throat, they are going to be disappointed.”

When evaluating a product’s sensory appeal during product development, it is most optimal to identify every element of interaction the consumer will have with the product. The sensory experiences of seeing, touching, tasting and hearing are all integrated, making sensory evaluations very complex.

A trained sensory panelist can extrapolate crunch into the type of breakage (small or large pieces) of a chip, and whether it dissolves immediately or only after consecutive bites.

Texture Toss-up

Alina Szczesniak, PhD, considered by many to be the “mother of texture,” greatly contributed to the science of food texture. She and other scientists at General Foods developed the Texture Profile (TP) method. This method used trained panelists to analyze, quantify and place in sequence perceived food textural properties--from when a food is first placed in the mouth, during mastication (biting and chewing), until the final piece is swallowed.

Over the years, sensory methods have been refined, altered and new concepts purposed. Today, vigorous discussions continue as to the best sensory methods for tasks ranging from quality control evaluations to the capturing of a consumer's food experience for new product development efforts. A crucial element is cost of the method for results produced.

The decision as to whether to establish a descriptive analysis program generally revolves around the resources required. Costs include employee time, fees for outside professional assistance, salaries for panelists from the outside community (if applicable) and supplies, notes Alejandra Muñoz, president of IRIS: International Resources for Insights and Solutions LLC (IRIS).

The total time required to train a panel can contribute significantly to cost and, therefore, a program's feasibility. Panel recruitment, program development, training site selection, material acquisition, actual panelist training, validation studies and possible reorientation are some of the basic steps in this process. Muñoz divides factors impacting a training program's duration into five categories that can be interactive, to some extent.

1. Descriptive Method. The method chosen affects the training program's duration. For example, the “Free Choice Profile” method requires relatively little panelist training. The QDA (“Quantitative Descriptive Analysis”) method requires an “intermediate” length of time. Here, time is saved by factors such as limiting the product categories covered in the training (focusing on perhaps only one). Lastly, the “Flavor and Texture Profile” methods and their derivatives require long training periods. This is due to training the panel on multiple products; having them learn and apply a developed, technical lexicon (word list); and having the panel employ intensity references.

2. Types of Panels. A universal panel is trained on several product categories such as soups, burritos and ice cream. A product-specific panel focuses on one category, such as salad dressings.

3. Type of Product Category for a Product-specific Training. Training a panel to evaluate chocolate requires a longer program, because chocolate is more difficult to describe when compared to other categories, such as potato chips.

4. Sensory Dimension or Number of Attributes. The more product characteristics a panel is trained to evaluate (color, aroma, taste, texture, etc.), the more time is required.

5. Level of Training. A sensory scientist needs to decide whether a semi-trained or well-trained and -calibrated panel is desired.

“Measuring texture is different from measuring flavor in that, with texture, it is necessary to specify not only the attribute definition, but also the exact evaluation procedure to be followed by a panel, including the amount and size of the sample used for evaluation,” explains Muñoz.

Panelist Trip-ups

“Descriptive analysis is not something we are born with; we have to learn it,” she points out. And not all humans have equal sensory abilities. It is important that panelists describe and discriminate differences well. Usually 30% of panelists screened for a testing will not be able to do that, Stone explains. Identifying and removing that 30% from the panel is very necessary.

Traditionally, descriptive analysis was applied in a lab environment. This has changed. “We have learned that where one uses a product is not as important as the sensory questions that need to be answered about a product,” offers Stone. Some products need to be tested in the same type of environment in which they will be consumed (as opposed to a lab where everything is controlled), while other products need to be tested in isolation or in the context of other products, Stone adds.

For example, there are many ways that people eat chips. When evaluating a chip's sensory characteristics, should the chip alone be considered or the chip with dips? If it is used with dips, is it important to instruct the panelists to eat the chip in the most popular ways? If so, then it is important to confirm that the differences seen in a chip alone also are present when used with a dip.

Panelists should be taught to recognize distinct definitions and points of reference, adds Muñoz. “I refrain from speaking in terms of smoothness, because the opposite of smoothness could be so many other things such as chalky, gritty, grainy, lumpy or powdery. Without proper training, a panelist might describe something as grainy that technically is defined as lumpy,” she muses. “Two products may be smooth in different ways.”

Some of the products suggested for references by Szczesniak are not available anymore or have changed. Therefore, references need to be updated, as done by Muñoz in 1986. Additionally, more complex references may be needed since products have become more complex due to multiple textures. For example, pudding has a homogeneous consistency. “In comparison, measuring texture is more complicated in products with two to three textures,” Muñoz explains. A candy bar with a smooth chocolate covering over an interior of chewy caramel and solid nuts is a good example. As this product with different textures is chewed, different characteristics are perceived. The whole product might disappear gradually or component by component. While the three textures exist originally, a consistent rate of breakdown may be the most desired trait.

Predicting texture viscosity from other characteristics is generally unadvisable. For example, products that melt at the same rate do not necessarily have the same viscosity when dissolved in the mouth.

Although sensory methods provide information unavailable through instrumental analysis, instruments also possess certain benefits, such as availability or cost per sample analyzed. It is sometimes desirable for sensory scientists to try to correlate results from descriptive and instrumental analysis.

Instrumental Alliances

“A sensory panel is most useful when measuring the texture of semi-solids and solids, compared to that of liquids,” observes Muñoz. Also, the measurement of “thickness” or “thinness” of liquid products by taste panels correlates well with the measurement of viscosity by instrumental analysis. Thus, an instrument may be all that is needed.

A Brookfield viscometer or Bostwick Consistometer often can be used to tailor a product within a certain range. The Bostwick measures a thicker product like tomato paste, while a Brookfield viscometer measures sauces that are not as thick, such as a beverage. “The instruments are more like guidelines that then are followed up with a taste panel,” says Rodriguez. The taste panel can help narrow the specifications of the product based on less linear descriptions.

“It is also possible to visually measure viscosity,” observes Rodriguez. For example, it is easy to eyeball a beverage and know that it has the viscosity of water instead of a smoothie without setting up a panel or an instrumental analysis.

However, most measurements are not as simple—like determining how to measure snack chips that break too easily when used in a dip. Increased use of alternative starches might create a stronger chip, but it might make it more difficult to bite through the chip. In such a case, a manufacturer can determine if consumers like that new characteristic when compared to the traditional chip. They might enjoy it in a dip but not when they eat the chip solo. These are characteristics that cannot be culled from instrumental analysis.

Evidence shows that instrument measures are univariate; however, the brain is multivariate, so it is not surprising to find that there is not a one-to-one relationship between instrumental analysis and descriptive analysis, Stone suggests. Instrumental analysis is a methodology driven by physical chemistry, and it is not measured on a behavioral basis.

“When an instrument is measuring breakage (the amount of pressure applied to a chip before it breaks), you get a plot,” says Stone. “When the consumer puts a chip in his mouth and bites down, the experience is more complex. He is getting more than just 'crunch' plotted on a graph.”

“Nevertheless, instruments are always useful since they can be programmed for 24-hour usage. Humans can't be,” Stone adds. Taste panels functioning on every shift are impractical, but a battery of instruments can monitor production variations with routine testing.

“If you don't use the right methodology with measures of reliability and sensitivity built in, the tests won't make any difference,” Stone warns. “In sensory science, dependency is the rule, and independence the exception.”

Website Resources:

www.tragon.com -- A market research and sensory analysis company
www.iris-consulting.net -- Management consulting firm in sensory and consumer science
www.abingredients.com -- Information about starch ingredients
www.ag.auburn.edu/~ckerth/671/Sensory%20Panel%20Methods.pdf -- Information about descriptive analysis methodologies
http://zingerone.foodsci.cornell.edu/fs410/lectures/lect1.html -- Sensory evaluation methods

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