descriptive analysis for sensory evaluation
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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