5.5.1 Sensory product attributes

A food can be defined at different levels (Cardello, 1996) when considering the sensory properties. There are basic properties of the food that can be recognised by the individual's sensory system and then, by using learning and memory, these sensations are changed into the sensory product attributes perceived by the individual. Taste and aroma are combined in an overall flavour, e.g. an acidic taste with a citrus aroma are combined into an orange flavour; and the mouth feel, biting and chewing are combined in an overall texture - for example consider sticky toffees and hard toffees. Having identified the sensory product attributes, the individual can score them on a liking (hedonic) scale from dislike very much to like very much. Bringing the like/dislike scoring together with other properties of the product brings the consumer to acceptance or rejection of the product. The stimulus, sensation, perception and the response are combined in the individual and the product as shown in Fig. 5.8.

Fig. 5.8 Building sensory attributes for consumer acceptance.
(- click to enlarge)

The core is physical and chemical properties of the product, which are the basis for sensory properties. But in a food these sensory properties interact with each other, and the consumers have perceived sensory reactions.

Sensory product attributes have to be firstly identified before measurement and hedonic testing. Classifying the sensory product attributes is complex when one moves beyond shapes, sizes, basic tastes of sweet, salty, bitter, sour; and the colour standards of lightness, hue and chroma. Texture can include the finger feel and the mouth feel; the finger feel including firmness, softness, juiciness; mouth feel including the mechanics of chewing such as hardness, cohesiveness, viscosity, elasticity; the geometrical characteristics such as particle size, shape and orientation; and other mouth feels such as moistness and greasiness. These are in a simultaneous or sequential effect during eating, and give a total final reaction on swallowing. For example in testing the texture of black beans (Watts et al., 1989), the descriptions in Table 5.5 were used by a trained texture panel. The magnitudes of these biting and chewing attributes, and also the duration of chewing were determined.


Table 5.5 Measuring the texture of black beans

Hardness: bite down once with the molar teeth on the sample of two beans and evaluate the force required to penetrate the sample. Particle size: chew the sample (two beans) for only two or three chews between the molar teeth, and then rub the cotyledon between the tongue and palate and assess the size of the particles which are most apparent. Seedcoat toughness: separate the seedcoat from the cotyledon by biting the two beans between the molar teeth and rubbing the cotyledon out between the tongue and palate. Then evaluate the force required to bite through the seedcoat with the front teeth. Chewiness: Place a sample of beans (two beans) in your mouth and chew at a constant rate (one chew per second), counting the number of chews until the sample is ready for swallowing.

Source: From Watts, Ylimaki, Jeffrey and Elias, 1989, by permission of IDRC, Ottawa, Canada.


Developing terms for flavours and aroma is much more complex. For example one can take four or five representative commercial samples of the product type (category) or some of the product prototypes with different levels of ingredients, and ask a sensory panel to list the flavour characteristics, then in discussion try to organise the different descriptions into flavour types and use a reference list to group them into categories, as in Civille and Lyon (1996). A reference substance (usually a chemical compound but can be a simple substance) is found for that particular flavour category and used by sensory panels in the future. Flavour terms have been built up as shown in Table 5.6 for some specific foods. These terms have standard descriptions, for example burn is 'chemical feeling factor associated with high concentrations of irritants to the mucous membrane', heat is 'chemical burning sensation in the mouth and throat'. To explain the difference, the reference sample for burn is vodka and for heat is red pepper.


Table 5.6 Descriptions of flavours of vegetables

Corn Cucumber Eggplant (aubergine) Red peppers Parsley Cardboardy Astringent Bitter Bitter Barny/barnyard Grassy Bitter Cooked Burn Bitter Legumy Cucumber Heat Heat Fishy Metallic Green Metallic Pungent Grassy Salty Sour Mouth numbing Raw Green Starchy Sweet Raw Sweet Hay Sweet Watermelon Sweet   Salty Woody       Sweet

Source: From Civille and Lyon, 1996, copyright ASTM, reprinted with permission.


Other sensory characteristics are temperature, pain and sound. A product such as ice cream has its own temperature effect, and there are effects of temperature on the sensitivity of the consumer to flavours and aromas as well as on the volatility of the aroma materials. Consumers expect a certain temperature of foods for eating. Although a canned stew is safe and edible if eaten from the can, can designers have gone to great lengths to design methods of quick heating to make the stew acceptable. Some pains are expected for example in eating very hot curries, drinking a 'straight' whisky, licking an ice block, but some are unacceptable such as finding a hard nut that hurts your teeth. Sound affects the acceptability of many products, for example the snap of raw celery and the crack of a biscuit indicate freshness. Some important factors in the overall sensory character of the product are the order of appearance of the attributes, the magnitude of the attribute and the duration of the attribute.