- Taste is one of the most important aspects of stevia
- One of the ways the taste of stevia is evaluated is by using a scientific method called sensory evaluation
- Words used to describe the flavor of stevia include sweet, bitter, licorice, astringent and metallic
- Sensory evaluation methods rely mostly on human assessors and include discrimination testing, descriptive evaluation and consumer testing
When choosing to sweeten foods and beverages with stevia, there are three key aspects to consider: functionality, health and taste. Of these, taste is of upmost importance and much of the technical information around stevia revolves around understanding how the sweet tasting compounds within the stevia plant, called steviol glycosides, some of which impact both bitter and sweet taste perception. The taste of stevia is very complex and can taste different depending on what application you put it into, such as beverages, dairy, baked goods, cereals and sweets.
What is Sensory Evaluation?
A scientific method known as sensory evaluation is used to assess the taste of many varieties of stevia for a multitude of applications. Sensory evaluation is used to evoke, measure, analyze, and interpret those responses to products that are perceived by the five senses of sight, smell, touch, taste, and hearing (Lawless, 2010). People who conduct sensory evaluation research are referred to as sensory scientists. Sensory scientists evaluate products using panels of human taste evaluators and a series of standardized methods. Statistical techniques are applied to results to draw inferences and make conclusions. Most large consumer goods companies have departments dedicated to sensory evaluation.
Taste and Flavor
With stevia, much of the sensory evaluation research focuses on the sense of taste. Taste is the sensation produced when a substance in the mouth reacts chemically with taste receptor cells located on the taste buds. The five basic tastes perceived by the tongue are sweet, sour, salty, bitter and umami. Of these, sweet and bitter are the tastes prevalent in stevia and most stevia related sensory research focuses on maximizing sweet taste and minimizing bitterness. Beyond sweet and bitter, emerging research indicates that stevia may change the perception of other tastes such as salty (Toldrá, 2012). Human taste perception, especially for bitter tastes, can vary greatly among individuals due to genetic variation (Bachmanov, 2014). Understanding this variability is a challenge for sensory scientists working with stevia.
The five basic tastes are part of a larger sensory experience known as flavor. What most people think of as taste is really flavor. Flavor is the combined sensation from three modes of sensory perception: aromas identified within the nose, basic tastes perceived on the tongue and mouthfeels that stimulate nerves in the oral cavity (figure 1). Aromas can be perceived in two ways: 1) retronasal olfaction which is when aromas drift up the back of the throat during eating and drinking and 2) orthonasal olfaction which occurs during sniffing (Rozin, 1982).
Sensory Evaluation Tools Used to Evaluate Stevia
Sensory evaluation methods mainly rely on human assessors and commonly fall into three main categories: discrimination testing, descriptive evaluation and consumer testing (see Table 1).
Sensory scientists rely on many of these techniques to evaluate stevia. Discrimination testing is often utilized to determine if a product made with stevia is similar in taste to its full sugar counterpart. For example, a triangle test might evaluate a full sugar version of ice cream versus one with a 25% reduction in sugar using stevia. Taste panelists would be served three samples, two of the same and one that is different. If panelists consistently fail to pick out the odd sample, the conclusion would be that the reduced sugar version is similar to the full sugar version.
Descriptive evaluation is used to describe the sensory attributes of foods and beverages made with stevia. This type of sensory test is usually performed with highly trained taste panelists who use a standardized vocabulary called a lexicon to describe the sensory attributes of samples. The lexicon for stevia includes terms such as sweet, bitter, licorice, astringent and metallic. If stevia is placed into a food such as ice cream, then the taste panel would also rely on the lexicon for that product to determine how stevia changes the sensory profile. For example, in soft ice cream utilizing stevia to replace sugar, reduced sugar versions had less total flavor, were thinner in texture and melted faster (Alizadeh, 2014). Reducing sugar in foods and beverages is technically challenging and findings such as these provide clear direction on progress and next steps.
A trained descriptive evaluation panel can also measure the temporal, or time related, changes in flavor and texture over time (Cliff, 1993). This technique is often referred to as time intensity. For instance, in an ice cream made with stevia, a time intensity panel might measure how quickly the sweet taste develops, how long it lasts in the mouth and the duration of the sweet aftertaste.
Consumer research utilizes untrained taste panelists who typically are product category users. In the case of stevia, the most important question is if users of a food or beverage will find the reduced sugar versions acceptable. This can be accomplished by asking consumers how much they like or dislike products using a scale or by asking them which product they prefer. It is also common to ask consumers their opinion on the amount of certain sensory attributes using a scale called ‘just-about-right’. For example, you might ask a consumer if the sweet taste in a sample of vanilla ice cream is too little, just right, or too much. These methods are all referred to as quantitative consumer testing and numerical scores are analyzed using statistics.
Consumer research can also be qualitative, which seeks to understand the abstract and subjective attributes of a product. This can be done by simply asking someone what they liked or disliked about a sample, referred to as an open-ended response. Another popular technique is to conduct a focus group, which is a moderated group discussion that seeks to understand consumers’ perceptions, opinions, attitudes and beliefs. For instance, food manufactures might utilize information from a focus group on sugar claims in food and drink products to better communicate sugar reduction in light of current consumer understanding (Patterson, 2012).
Understanding the mechanisms of taste and smell as well as the methods that sensory scientists employ allows for an informed decision when using stevia. This will empower more and more food and beverage companies to leverage stevia for the creation of great tasting products with less sugar and fewer total calories.
- Alizadeh, M. & Azizi-Lalabadi, M. Impact of using stevia on physicochemical, sensory, rheology and glycemic index of soft ice cream. Food Nutr. (Roma). (2014).
- Bachmanov, A. A. et al. Genetics of taste receptors. Curr. Pharm. Des. 20, 2669–83 (2014).
- Cliff, M. & Heymann, H. Development and use of time-intensity methodology for sensory evaluation: A review. Food Res. Int. (1993).
- Lawless, H. & Heymann, H. Sensory evaluation of food: principles and practices. (Springer Science & Business Media, 2010).
- Patterson, N. J., Sadler, M. J. & Cooper, J. M. Consumer understanding of sugars claims on food and drink products. Nutr. Bull. 37, 121–130 (2012).
- Rozin, P. "Taste-smell confusions" and the duality of the olfactory sense. Percept. Psychophys. 31, 397–401 (1982).
- Toldrá, F. & Barat, J. Strategies for salt reduction in foods. Recent patents food, Nutr. (2012).