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DESCRIPTIVE ANALYSIS

Andrew L Myrthong2014-12-126

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Introduction• Descriptive analysis is concerned with trying

to provide description of the sensory qualities of food

• It is one of three basic types of sensory test:–Difference Tests make comparisons between

foods– Affective Tests evaluate liking for foods. These

are sometimes called consumer tests–Descriptive Tests describe the sensory

attributes of a food

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Application of descriptive analysis

• The purpose of descriptive analysis is to obtain detailed description of– Aroma– Flavour– Oral texture

• It is used both to obtain qualitative descriptors of the product and to obtain quantitative evaluations of product.

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Uses of descriptive analysis include• Research and Development (long term studies)• New product development• Specifications for QA/QC purposes• Define product attributes for consumer tests• Track sensory changes over time• Long term changes for shelf life/packaging studies• Short term intensity measurement of specific attributes• Measure attributes for comparison with

instrumental/analytical measurements

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Qualitative aspects of descriptive analysis

• Appearance characteristics– Colour – hue, chroma, uniformity, depth– Surface texture – shine, smoothness/roughness– Size and shape – dimensions, geometry– Interactions among particles – stickiness, agglomeration, loose particles

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• Aroma Characteristics–Olfactory sensations• vanilla, fruity, floral, skunky•Nasal feelings–cool, pungent

• Flavour characteristics–Olfactory sensations• vanilla, fruity, floral, chocolate, skunky, rancid

–Taste sensations• salty, sweet, sour, bitter, umami (meatiness)

–Oral feeling factors• heat, cool, burn, astringent, metallic

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• Oral texture characteristics–Mechanical parameters - reaction of

product to stress• hardness, viscosity, deformation/fracturability

• Geometrical parameters - size, shape, orientation of particles in product–gritty, flaky, grainy, stringy

• Fat/moisture parameters - presence/release of fat, oil, water–oily, greasy, juicy, moist

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• Skin feel characteristics–Mechanical parameters - reaction of product

to stress• thickness, ease to spread, slipperiness, denseness

–Geometrical parameters - size, shape and orientation of particles• gritty, foamy, flaky

–Fat/moisture parameters - presence/release of fat, oil, water• greasy, oily, dry, wet

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Quantitative aspects of descriptive analysis

• The quantitative aspect or intensity expresses the degree to which a characteristic is present and is expressed by assigning a value on a scale

• The validity and reliability of the analysis is dependant on the – selection of scaling technique which should encompass

full range of intensities – but be sufficiently sensitive to pick up small differences

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Training of panellists

• Reference scales are used to ensure consistency between panellists across repeated evaluations

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Types of scale used• Category scales• Uses words to define intensity, such as

"none", "just detectable", "mild", "strong"• terms chosen to describe (as far as possible)

equal intervals - 9 point scale most popular• Line scales: mark a point on a line (typically

15 cm long)• Magnitude estimation (ME) scales• Free choice of first "score" • Subsequent scores assigned in proportion

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Overall impression

• As well as rating individual attributes, some kind of "overall rating" is sometimes needed. These may include– Total intensity of aroma or flavour– Balance/blend– Overall difference– Hedonic ratings

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Total intensity of aroma/flavour• Overal intensity of aroma or flavour is an

assessment of the overall impact the product will have on the consumer

Balance/blend (amplitude)• This is an assessment of the way the various

flavour or aroma characteristics fit together in the product

• It requires highly trained and skilled panel members and is not appropriate with all products

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Overall difference• In some situations, relative difference between

samples and controls is important. This involves a quantifying of the difference from the control (c.f. Duo trio test)

Hedonic ratings• This is a rating of the

overall acceptance of a product

• It is not appropriate with trained panels

• Used only with consumer tests since trained panels tend to weigh attributes differently from ordinary consumers and so their judgements are not "typical" of consumer preferences

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Common descriptive methods

A variety of procedures have been developed for descriptive testing. These include• Flavour profile• Texture profile• Quantitative descriptive analysis (QDA)• Spectrum analysis• Time-Intensity descriptive analysis• Free choice profiling

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Flavour profile• Uses panel of 4 - 6 trained panellists• Panel sit round table and evaluate one sample

at a time and record the ratings• Panel then discusses ratings and arrives at a

consensus• Advantage of small panelDisadvantages:• Consensus

method means risk of bias from dominant personality

• Danger of lack of consis-

tency and reproducibility

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Texture profile• Procedure similar to flavour

profile, but a wider range of scaling techniques may be used

• Results may be by consensus method or by statistical analysis

• Panel training involves understanding underlying mechanical principles

• Experience of a wide range of textural attributes

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Quantitative descriptive analysis

• Panelists develop agreed terminology beforehand• Panelists evaluate products one at a time

in separate booths• Panellists are discouraged from

discussing results afterwards• Scoring is by marking on a line• The results are analysed statistically• Can lead to inconsistency of results

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Spectrum descriptive analysis• Panelists score intensities with respect to

learned absolute intensity scales• A wide variety of standard descriptors are

provided• Scoring is both by use of descriptive terms

and by marking on a line• It is intended to provide consistent and

reliable data by providing a wide range of standards

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Time-intensity analysis• Panelists evaluate intensity of an attribute at

intervals over a period• Time-intensity response curve is generated• This should not be seen by the panelists

while it is being generated• Requires a well-trained panel to be

effective

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Free-choice profiling• Panelists are allowed to invent their own

terms to describe the sensory attributes of a set of samples

• Samples are from the same category of products

• Panelists develop their own scoresheets• These are aimed at identifying terms that

appear to measure the same attribute• Panel training requirements are minimal• Panel is closer to a consumer panel

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Let Us Sum Up• The consumer acceptance of

fruits/Vegetables and their products most often relies upon the inherent flavor and textural quality of the product

• Incorporating sensory evaluation will help in the selling of a consumer friendly product with increased acceptance

• When done properly, sensory information can provide reliable and useful information about fruits and vegetables and their products which no instrument can measure – their perceptual characteristics

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Thankyou