Chapter 15: Sensory Evaluation and Food Product Development
UNIT 11: SENSORY EVALUATION
15.1 What is Sensory Evaluation?
Sensory Evaluation – the assessment of all the qualities of a food item as perceived by
the human senses.
• This involves tasting, food colour, texture, flavor, aftertaste, aroma, tactile
response, and auditory response.
• Aka sensory analysis but this is more correctly used regarding statistical analysis.
A Scientific Method
• Sensory evaluation is a scientific method – involves identification of a problem,
statement of a hypothesis, and an experimental strategy to investigate the
problem. Data collection and analysis leads to a conclusion that answers the
original question, accepting or rejecting the hypothesis.
A Quantitative Science
• Human responses to stimuli are quantified using statistical approaches.
Sensory Science in the Food Industry
• Involved in quality assurance and product research and development.
15.2 Sensory Odour, Flavour, and Mouthfeel Perception
Two types of senses are involved in sensory perception: Chemical (taste and odour) and
physical (sight, sound, and touch).
Character notes – the sensory attributes of a food that define its appearance, flavor,
texture, and aroma.
• Organ of taste is the tongue
• Taste – the sensation derived from food as interpreted through the tonguetobrain
• Four primary taste sensations (sweet, salty, sour and bitter), as well as the fifth
one (umami – “delicious”, along with meaty and savoury suggestions) that all
trigger brain response through neurotransmitter release.
• Tastants – taste buds that are located primarily on the surface of the tongue that
detect various food stimuli molecules perceived to have taste.
• Taste buds – epithelial receptor cells organized into clusters of 50 – 150 that are
embedded into papillae.
• Humans possess several types of papillae – foliate, circumvallate, fungiform and
• The number of taste buds is highest in newborns, and declines with age. • The chemical PROP is used to test taste sensitivity and place people into the
supertaster (greatest number of fungiform papillae), medium taster, or nontaster
Transduction and Sensitivity
• The tongue is linked to the brain via the CNS.
• Taste transduction – the brains response to taste stimuli.
• Depolarization – occurs when a positive charge accumulates in the cell, making
the membrane potential less negative than normal, and more positive. Neuronal
signaling accompanies this via neurotransmitter release.
• Sweet, salty and sour transmissions all follow this mechanism, but the
transduction of bitter taste appears to be more complex, with several mechanisms
2. Odour (aka fragrance and aroma)
• Odour – the sensation derived from food as interpreted through the olfaction
• Components include either olfactory sensations (such as fruity or rancid) as
perceived by the olfactory nerve, or nasal feelings (such as cool or pungent
sensations) perceived by the nose’s tactile nerves.
• Olfaction – refers to the perception of odours by the nerve cells in the nasal area.
• Odourants – airborne molecules that possess odour are sensed by the olfactory
epithelium (the outer layer of receptor cells located on the roof of the nasal
• Cilia – tiny, hair like structures that cover the olfactory epithelium that sense
• The interaction between odourants and receptor cells initiates a cascade of events
that are related to the production of ion channel electrical signals..
• 1 – 2 seconds is the optimal contact time between odourant and the nasal
receptors, exposure beyond this requires the receptors to readjust for 20 seconds
before a new fullstrength sensation can occur.
• Sensitivity involves being able to detect something at a low threshold of
concentration, and being able to differentiate one odour from another.
• Results from the chemical stimulation of the tongue taste buds, the olfactory
apparatus, and the organs of feeling present within the mouth, throat, and nose.
• Flavour – an overall impression combining taste, odour, mouthfeel factors, and
• Trigeminal nerve is an important neural region that runs through the entire facial
area, with nerve endings in important areas like the nasal and oral cavities –
• This perception refers to the sensation of astringency, burning, cooling, and
warmth. • Flavour can be influenced through the use of enhancers.
• Aftertaste – perceived after the initial primary taste response and should be
viewed as residual sensations that linger on the tongue after swallowing.
• Retroinhalation – refers to the passage flavor stimuli from the mouth through
the pharynx up to the nose.
• Mouthfeel – the perceived sensation of food by the epithelial lining within the
oral cavity, which includes tactile sensation as well as thermal response.
• Small movements of the tongue press food against the gums and palate to
evaluate viscosity and texture.
15.3 Sensory Texture and Colour Perception
Has to do with the structure and composition of food, and it involves food
molecules, their perception, and measurement.
Texture perception occurs whenever a food is chewed or a beverage is swallowed,
and involves describing physical characteristics of a food.
o Mechanical, geometrical, afterfeel, food fat and moisture content.
Sensory cells perceive food particle shapes, sizes, thickness, and hardness and
transmit this information to eh brain like tast and odour information.
People remember the texture of a particular food item they consumed in the past,
and there is an expectation of the same texture if the item is consumed again.
Both sight and sound create an expectation regarding how the texture will feel
inside the mouth upon chewing.
Important texture notes are also detected as food is manually handled in
preparation for biting, chewing, and swallowing (i.e. tactile cells in fingers).
Mechanical Sensory Characteristics
Mechanical Sensory Characteristics – generally due to attractive forces
between the molecules in a food and the opposing force of disintegration.
Mechanical characteristics include:
o Hardness – described by the amount of force required to compress the
food between the teeth. Hardness intensitites range from soft through firm
o Cohesiveness – described by the degree to which a food will deform or
compress between the teeth before it breaks. Intensities range from easy to
disintegrate through difficult to disintegrate.
o Sensory viscosity – related to the force required to draw a fluid food from
a spoon across the tongue at a steady rate. Intensities range from thin to
thick through viscous.
o Chewiness – the length of time in seconds required to chew a food sample
at a steady rate (one chew per second) with a constant force applied that
results in a food consistency that is just ready to be swallowed. Intensities
range from tender to chewy through tough. o Adhesiveness – is the force required to remove food material that attaches
to the mouth (primarily the upper palate) during normal chewing. It is a
unique mechanical parameter because it is related to surface properties
rather than forces of attraction and breakage. Intensities range from sticky
to tacky through gooey.
Geometrical Food Characteristics
Geometrical characteristics – related to the size of discrete food particles
present in the food, as well as to their shape and orientation.
Related to size and shape ranging from chalky to gritty to grainy and course.
o Grainy indicates foodcontaining granules of a specified size.
o Coarse indicates relatively large particle size.
Particle shape and orientation can range from fibrous to cellular and crystalline.
o Fibrous indicates food composed of fibres.
o Crystalline describes foods composed of crystals.
Afterfeel – indicates that after certain foods are chewed and eaten or beverages
sipped, a “texture sensation residue” persists.
Fat and Moisture Content
The perception of the fat and moisture content in a food affects texture.
Foods differ in fat content, in the manner in which fat is absorbed into them
during preparation and food processing and release into the mouth on
consumption, and with respect to melting behaviours.
Moisture is also variable according to content, as well as to the rate and manner of
its absorption and release, from dry to moist to wet to watery.
Foods exhibit interactions in terms of taste, odour, texture and flavor, which can
generate a wide variety of effects.
o Ex: salt decreases sourness, or sucrose counteracts saltiness.
Sensory overload – a saturation of the sensory system that results in excessive
Pigment molecules are the chemical basis of colour.
Foods possess colour based upon wavelengths of reflected and absorbed visible
Visible light is part of the electromagnetic spectrum, and can be dissected into a
spectrum of colours from violet to red, each with a characteristic wavelength and
Reflected light energy in the range of 350 to 800 nm act as the stimulus to the
sensory cells of the eye, which in turn communicates to the brain, enabling us to
The top three criteria used to define food quality are freshness, good
appearance/colour and good taste.
The altered appearance and colour of rancid and spoiled foods have taught a
valuable lesson regarding food colour and its quality and even safety. USDA recognizes the importance of colour in grading orange juice.
o The analytical technique used is tristimulus calorimetry; the three
components are the shade of darkness of a sample plus two hue
Hunter tristimulus data – a system widely used for food analysis. Uses the
Hunter colour difference meter, which is a device used to measure colour based
off the Hunter Colour Solid.
o The L value, located vertically on the scale, measures lightness or
darkness (0 = black, 100 = white).
o Hue is measured by the a and b scales (+a = red, a = green, +b = yellow,
b = blue).
o The Hunter Colour Difference equation (ΔE)
ΔE = (ΔL) + (Δa) + (Δb) . 2
Appearance – includes interior product characteristics and things like food
15.4 Responses Contributing to Sensory Perception
Sensory study involves quantifying a response to a stimulus:
1. The stimulus interacts with the sense organ (tongue, nose, eye) and is converted
into nerve signals that travel to the brain.
2. The brain interprets the incoming signals and organizes them into perceptions.
3. A response is elicited from the subject based upon these perceptions.
Objectivity and Subjectivity
Sensation – corresponds with objective brain functioning (regarding the brain as
Perception – corresponds with subjective brain functioning (regarding the brain
as a thinking mental process).
Objective procedures – used to measure many features of food quality related to
flavor, texture, colour, and odour.
o Objectivity can be a good thing, because it eliminates bias. Instrumental
methods alone are insufficient indicators of product quality, since they do
not measure human subjective response.
Intensity has to do with the product stimulus, while sensitivity has to do with
panelist ability to sense.
Intensity – the degree to which a character note is present, as determined by its
product concentration and perception by a person (refers to its perceived
Timeintensity measurement – the measurement of sensory attributes evaluated
over a period of time following an initial exposure.
o This type of data is obtained when information related to timedependent
product attribute rates of change or duration in intensity desired. o A timeintensity curve shows the total duration of a taste, the maximum
intensity, the time required to achieve maximum, and the rate of intensity
decline to a minimum value.
Threshold – refers to distinct points of transition for sensory judgements
corresponding to concentrations of stimuli.
o Each person has a lower limit at which he or she first begins to respond to
a stimulus, and an extended range for the ability to differentiate low,
medium, and high levels of a stimulus, before a saturation point is reached
and further distinctions are not possible.
Detection threshold – the point at which a person initially responds to a stimulus,
the dividing line between lack of sensation to sensation.
A stimulus molecule’s potency is connected to how it is perceived.
Other thresholds of significance are:
o Recognition threshold – the point to which the identity of a stimulus is
o Difference threshold – refers to the minimum amount of stimulus change
that results in a change of sensation.
o Terminal threshold – the amount of stimulus above which any increase in
intensity cannot be detected without the use of reference standards.
15.5 Sensory Tests
Tests involve a large number of decisions, guided by a group of important principles:
• The objective of the specific project determines the sensory technique and test
chosen by the specialist.
• Trained panelists should not be used to obtain acceptability judgments.
• Consumer panels should not be used to obtain accurate descriptive information.
• Individuals who are involved with the research and development aspect of the
product should not serve on panels.
• Samples should be labeled with random 3digit codes to minimize bias.
• Sample order should be randomized to avoid artifacts due to the order of
• Panelist interaction during sensory evaluation is forbidden because it can bias the
Classification of Test Methods
Classified according to their primary purpose and most valid use (matching the
test method to the objectives of the project is critically important). Three classes
are most commonly used:
1. Affective Test Methods • Affective tests – attempt to quantify the degree of liking or disliking of one
product over another, and include preference, hedonic, and consumer acceptance
• Two main approaches to using consumers in sensory evaluation are in measuring
preference and measuring acceptance:
o Preference – allows the consumer a choice and asks for it to be made
between products on a hedonic (like, dislike) basis.
o Ranking – a form of preference testing that uses more than two samples
(which is not the same as rating). Panelists order a group of products with
respect to either their degree of liking or their perceived intensity of a