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How to measure and analyse the texture of food, cosmetics, pharmaceuticals and adhesives.

Monday 25 September 2017

Sensory Analysis and Definitions of Food Texture

The process of sensory evaluation starts with a well trained sensory panel – a group of humans who will judge sensory qualities. 

To carry out a meaningful texture profile analysis, a panel of judges needs to have knowledge of the texture classification system, the use of standard rating scales and the correct procedures related to the mechanics of testing. Panellist training should start with a clear definition of each attribute.
Furthermore, the techniques used to evaluate the food product should be explicitly specified, explaining how the food product is placed in the mouth, whether it is acted upon by the teeth (and which teeth) or by the tongue and what particular sensation is to be evaluated. Panellists should be given reference standards for evaluation so they can practice their sensory evaluation techniques and the use of scales. 

The panel is given a list of rheological attributes that are relevant and important to the products they'll be judging. These attributes might include firmness, hardness, cohesiveness, chewiness, elasticity, springiness, etc. 

The next step is to perform an organoleptic sensory evaluation in which the trained panellists assign intensity levels on various descriptors/texture attributes. For example, for evaluating the texture of pickles, firmness may be considered one important attribute. In this case, panellists could be asked: "On a scale where 1 equals extremely soft and 9 equals extremely firm, how would you rate the firmness of pickles A, B and C?"

The following table gives a small sample of the qualities that a panel might be instructed to evaluate for a sample material. Notice that the meaning of each quality is not left to panel members' imagination, but is defined fairly rigorously. 

Example Sensory Techniques for Evaluating Food's Texture Characteristics

Place spoon with sample directly in front of mouth and draw liquid from spoon over tongue by slurping, evaluating the force required to draw liquid over tongue at a steady rate.

Sensory Characteristic: / Technique for Evaluating Characteristic

  • Hardness: Place sample between molar teeth and bite down evenly, evaluating the force required to compress the food.
  • Cohesiveness: Place sample between molar teeth; compress and evaluate the amount of deformation before rupture.
  • Springiness: Place sample either between molar teeth (if it is a solid) or between the tongue and the palate (if it is a semi-solid) and compress partially; remove force and evaluate the degree and quickness of recovery.
  • Adhesiveness: Place sample on tongue, press it against the palate and evaluate the force required to remove it with the tongue.
  • Fracturability: Place sample between molar teeth and bite down evenly until the food crumbles, cracks or shatters, evaluating the force with which the food moved away from the teeth.
  • Chewiness: Place sample in the mouth and masticate at one chew per second at a force equal to that required to penetrate a gum drop in 0.5 seconds, evaluating the number of chews required to reduce the sample to a state ready for swallowing.
  • Gumminess: Place sample in the mouth and manipulate with the tongue against the palate, evaluating the amount of manipulation necessary before the food disintegrates.
More complete set of Terms Used in Sensory Texture Profiling*

Term: / Definition

  • Adhesiveness: Force required to remove the material that adheres to a specific surface (e.g., lips, palate, teeth).  
  • Bounce: The rate at which the sample returns to the original shape after partial compression. 
  • Chewiness: Number of chews (at 1 chew/sec) needed to masticate the sample to a consistency suitable for swallowing. 
  • Coarseness: Degree to which the mass feels coarse during product mastication. 
  • Cohesiveness: Degree to which the sample deforms before rupturing when its bitten with molars. 
  • Denseness: Compactness of cross section of the sample after biting completely through with the molars. 
  • Dryness: Degree to which the sample feels dry in the mouth. 
  • Fracturability: Force with which the sample crumbles, cracks or shatters. Fracturability encompasses crumbliness, crispness, crunchiness and brittleness. 
  • Graininess: Degree to which a sample contains small grainy particles. 
  • Gumminess: Energy required to disintegrate a semi-solid food to a state ready for swallowing. 
  • Hardness: Force required to deform the product to given distance, i.e., force to compress between molars, bite through with incisors, compress between tongue and palate. 
  • Heaviness: Weight of product perceived when first placed on tongue. 
  • Moisture absorption: Amount of saliva absorbed by product. 
  • Moisture release: Amount of wetness/juiciness released from sample. 
  • Mouthcoating: Type and degree of coating in the mouth after mastication (for example, fat/oil). 
  • Roughness: Degree of abrasiveness of product's surface perceived by the tongue. 
  • Slipperiness: Degree to which the product slides over the tongue. 
  • Smoothness: Absence of any particles, lumps, bumps, etc., in the product.Springiness 
  • Degree to which the product returns to its original size/shape after partial compression (without failure) between the tongue and palate or teeth. 
  • Uniformity: Degree to which the sample is even throughout. 
  • Uniformity of Chew: Degree to which the chewing characteristics of the product are even throughout mastication. 
  • Uniformity of Bite: Evenness of force through bite. 
  • Viscosity / Force required to draw a liquid from a spoon over the tongue. 
  • Wetness: Amount of moisture perceived on product's surface.
*Note: Note all of these parameters can be measured by a Texture Analyser, particularly those relating to degrees of mouthfeel moisture.

After the taste panel has been instructed and rated various samples, instrument readings of the food product are made.

The instrumental technique must duplicate as closely as possible how the mouth manipulates the particular food product. The instrument should apply the same amount of force in the same direction and at the same rate as the mouth and teeth do during chewing.

Note that for some particular foods, springiness may be more important than fracturability or it may be that hardness is more important than brittleness. For example, in the case of pickles, crispness is usually considered to be the most important texture attribute. This is a complex characteristic related to hardness, elasticity and cohesiveness; viscosity and adhesion are less important. 

So pickles are not just cucumbers that have sat for a while in brine: a host of complex sensory and physical variables go into making a good pickle.

And sometimes there is no good correlation of any type between instrument readings and taste panel scores. The problem is that no instrument can manipulate a food product precisely the same way as the human mouth does during mastication. For example, an instrument may compress some food product between two flat plates, but a human would be biting down with incisors, which are sharp, rather than flat and the result is different. In fact, what an instrument measures may not relate at all to what the tongue perceives. 

Nevertheless, instruments that employ advanced sensor technologies, powerful computer capabilities and sophisticated, versatile software are invaluable tools for mouthfeel evaluation. They make it possible to establish quite strong correlations between results from taste panels and results from physical instruments. Today's instruments, such as the TA.XTplus Texture Analyser, can perform an entire TPA and are capable of measuring dozens of rheological food properties. 

Why not forget instruments entirely and rely exclusively on organoleptic taste panelling? The answer is simple. Once good correlation has been established between instrumental data and organoleptic data, the instrumental approach offers several advantages over sensory paneling. Compared to sensory panelling, instrumental results are obtained in much less time, at less cost and are more objective and accurate. 

Furthermore, instruments can be used in situations that are impractical for sensory panelling – for example, as a quality control tool to check rheological properties throughout the processing cycle. Instrument readings and rheological evaluation can easily be made at numerous steps and stages during the product design process.

For more information on how to measure texture, please visit the Texture Analysis Properties section on our website.

TA.XTplus texture analyser with bloom jar The
TA.XTplus texture analyser is part of a family of texture analysis instruments and equipment from Stable Micro Systems. An extensive portfolio of specialist attachments is available to measure and analyse the textural properties of a huge range of food products. Our technical experts can also custom design instrument fixtures according to individual specifications.

No-one understands texture analysis like we do!

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Watch our video about texture analysis Replicating Consumer Preferences Texture Analysis applications

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