Summary of the course Principles of Sensory Science (HNH30506_2020_1) including a summary of all the knowledge clips, lectures, tutorials, practicals and an example exam.
UPDATE: including a written summary with extra information on the course
,Index
WEEK 1 .............................................................................................................................................................. 0
CLIPS .........................................................................................................................................................................................0
Introduction to Sensory Science ......................................................................................................................................0
Descriptive Analysis Methods ..........................................................................................................................................0
Smell ...................................................................................................................................................................................2
Taste ....................................................................................................................................................................................3
Trigeminal Sensations .......................................................................................................................................................5
TUTORIAL - GOOD SENSORY PRACTICE .......................................................................................................................................5
Sensory checklist ...............................................................................................................................................................5
LECTURE: INTRODUCTION TO GROUP WORK ................................................................................................. 6
WEEK 2 .............................................................................................................................................................. 6
CLIPS .........................................................................................................................................................................................6
Threshold Measurements .................................................................................................................................................6
Thresholds ..........................................................................................................................................................................7
TUTORIAL - DISCRIMINATION TESTING ........................................................................................................................................7
Discrimination tests ...........................................................................................................................................................7
Statistical analysis ..............................................................................................................................................................9
Summary.......................................................................................................................................................................... 10
TUTORIAL - SIGNAL DETECTION THEORY AND ADVANCED TOPICS ............................................................................................. 10
The signal detection theory (SDT) ................................................................................................................................ 11
Discrimination index (d’) ................................................................................................................................................ 12
ROC curve ....................................................................................................................................................................... 13
WEEK 3 ............................................................................................................................................................ 13
CLIPS ...................................................................................................................................................................................... 13
Selection and orientation .............................................................................................................................................. 13
The panel leader............................................................................................................................................................. 14
Training a sensory panel................................................................................................................................................ 14
PRACTICAL – DISCRIMINATION ................................................................................................................................................. 15
Introduction ..................................................................................................................................................................... 15
Tests ................................................................................................................................................................................. 15
LECTURE – STATISTICS IN SENSORY SCIENCE ............................................................................................................................. 17
PCA .................................................................................................................................................................................. 17
One-way ANOVA – mixed models................................................................................................................................ 18
WEEK 4 ............................................................................................................................................................ 19
CLIPS ...................................................................................................................................................................................... 19
Texture ............................................................................................................................................................................. 19
Color ................................................................................................................................................................................ 21
Visual perception ............................................................................................................................................................ 21
Interaction between the senses .................................................................................................................................... 22
Hedonic sensory methodology..................................................................................................................................... 24
Context & bias in sensory science ................................................................................................................................ 25
PRACTICAL – FIND YOU BLISS POINT ......................................................................................................................................... 26
WEEK 5 ............................................................................................................................................................ 27
LECTURE – TEMPORAL DYNAMIC METHODS .............................................................................................................................. 27
Dynamic sensory methods ............................................................................................................................................ 27
Time events during eating............................................................................................................................................. 31
EXAMPLE EXAM ...................................................................................................................................................................... 31
1
,Week 1
Clips
Introduction to Sensory Science
Most of the time, the color of the food gives you expectations about the flavor of the food.
When you use your nose there is a difference in flavor perception compared to when you close
your nose. The information of all the senses is integrated in the brain. Flavor perception is a
multidimensional sensation.
Sensory science has strong connections with
other areas. Sensory evaluation evokes,
measures, analyzes and interprets responses
received by the senses. There are 3 basic test
methods:
People cannot switch easily between an analytical
and hedonic mindset. Analytical sensory tests are
mostly done in sensory booths to ensure control and a high internal
validity. You use a trained panel and that is why you can have a high
validity with a small panel. With hedonic tests the internal validity is
lower and that is why you need more people in your panel.
Psychophysics is the relation between physical properties of a food
and the sensory response. Psychohedonics is the relation between
the physical properties of a food and the liking of a food. The
psychohedonic function is also called a wundt curve and the
optimum concentration is called the bliss point. The perception is
different per person. This can be influenced by age, gender and
satiation. To prevent the order-effect you need to randomize your
samples. You also have to take the frame of reference into account.
Perception is always relative, and it is determined by the reference.
Descriptive Analysis Methods
Introduction
Descriptive analysis uses panelists that are trained to detect and describe differences among
products. The analysis is a method aiming to provide a quantitative measure of the sensory
properties of a set of products. The descriptive analysis techniques can be divided into two
method groups, dynamic methods and static methods. Dynamic methods are developed to
get a sensory description of food that develops over time and static methods only measure
snap shots at a certain timepoint. There are differences between methods; the generation of
sensory descriptors, degree of subject training and use of reference materials and scaling can
differ.
,Flavor Profile Method
The flavor profile was the first descriptive method that was used. The flavor profile method
uses a consensus technique à trained subjects discuss about the flavor of the food together.
They use reference materials. This way the subjects come to an agreement “consensus” of the
flavor.
The scores can range from “not present” to “strong”. A score is given to every single attribute
and to the total product. This method is barely used anymore because of the many limitations.
The method is qualitative, so you cannot use statistical analysis. You only make a profile of the
flavor. You can only profile a small part of the sensations (only flavor).
Quantitative Descriptive Analysis
With the Quantitative description analysis (QDA) you can test all modalities and you can use
statistical analysis. The QDA uses data from individual panelists (instead of a group). The
circumstances must be the same for all the panelists à sensory booths. The panelists are
trained to get consensus and reference standards are used. A statistical outcome can be that 2
apples differ significantly from each other.
There are limitations to this method: it takes time to invest in panel training and monitoring and
there are no absolute intensity scores.
Texture profile
With the flavor profile method, you were not able to test the different textures. We needed a
texture profile method for evaluation of different foods. Texture profiling is about the
mechanical, geometrical, fat and moisture characteristics of foods from the first bite through
complete mastication. The texture changes during these processes.
The method uses a fixed sensory vocabulary related to physical standards. Scoring is done with
intensity scales labelled with references. All texture
properties can be divided into three different groups:
- Geometrical characteristics
- Mechanical characteristics
- Other
The texture profile method needs a high degree of training.
Sensory spectrum
This method is based on the texture profile method. Focusing only on the texture was a
limitation. The sensory spectrum method uses standardized attributes, standardized vocabulary
and response scales with references. There is a high involvement of a panel leader as the
attributes are set beforehand. Standardization makes it possible to make comparisons between
foods and even between different cultures. The limitations are that there is a high degree of
panelist training.
1
,Rapid sensory profiling methods
Rapid sensory profiling methods are new. First, we have verbal-based methods, which allow
the panelists to use their own set of attributes. There is no need for training. Verbal-based
methods are Flash profile and CATA.
- For Flash Profile 5-10 panelists are used. The panelists receive a batch of products and
add their own attributes based on differences between the products. With the attributes
they rank the products by intensity. The method uses ranking and that is why we get
ordinal data.
- With Check All That Apply (CATA) a consumer/ expert panel is used. They receive a
prepared list of attributes and they can tick all the attributes that apply on that product.
Secondly, we have similarity-based methods. The methods are based on overall differences or
similarities between products. Similarity-based methods are sorting and napping.
- With sorting panelists have to place products with similar characteristics in the same
group. They are free to decide the number of groups and the number of products in a
group. It is possible to label the groups à labelled sorting.
- By napping you are screening many samples. The panelists need to place products on a
‘napkin’ based on their similarities. Products that are very different are placed more apart
and products that are similar are placed very closely. You can also add terms or labels à
ultra-flash profile. With partial napping you only focus on one modality at a time.
Smell
Functions of smell
Smell can be very important when it comes to social functions. Animals choose their partner by
the smell of their partner. It is also stated that we can smell the age of a person or if someone is
sick by their odor. Odors are also associated with emotions, mood and memory. Smell is also
an important warning system for our body; fire, toxins, spoiled foods. Losing the sense of smell
can also be a signal of developing neurological diseases. Smell also place a role in the
anticipation phase of eating but also during consumption. Orthonasal smell is used during
food anticipation and retronasal smell is used during flavor perception.
2
,People with partial smell loss have hyposmia and with
complete smell loss have anosmia. This can be due to
the age, respiratory tract infection, head trauma, toxins,
drugs, medication or a chronic disease. It has a large
impact on the quality of life.
Physiology of the olfactory system
Odors reach the odorant receptors à olfactory
epithelium à olfactory nerve (CN I) à olfactory bulb à
olfactory tract à rest of the brain. All odor nerves from
the same type will come together in the glomerulus.
Odor receptors are G-protein receptors. Small parts of
the receptor can recognize small parts of the odor. One receptor can detect different odors and
different odors can activate different receptors. This results in a pattern of glomeruli activation
which causes us to smell the odor. When we smell a rose and an orange there can be an
overlap of receptors that are activated, but the combination of the receptors is specific for an
odor. The activation can be different at different concentrations causing differences in odors.
Olfactory information is processed ipsilateral, meaning that information that enters the nose on
the left is also processed on the left side of the brain. Information from the olfactory bulb
directly travels to the piriform cortex without going through the thalamus. The piriform cortex is
closely connected to the limbic system (emotions), this is the reason why some odors can evoke
memories.
Odor perception and measurement
Human can discriminate more than 1 trillion olfactory stimuli. So, humans are not that bad at
smelling. We are not good at naming the odors that we receive. Positive labels increase the
pleasantness of an odor and a negative label deceases the pleasantness of an odor. The
pleasantness is flexible.
With Sniffin’Sticks you can measure the identification, discrimination and detection threshold
ability of a participant. UPSIT only measures odor identification. Olfactometer is a machine that
can deliver odors in a precise way. In general, it is hard to tell if you are good at smelling. The
sensitivity is different for different odors. Odor perception is also influenced by age,
experience, culture, genetics and general variation. Women are
better at identifying odors than men.
Taste
Functions of taste
We have 5 basic tastes; sweet, salty, bitter, sour and umami. Each
taste has 1 specific compound that represents that taste. Taste is a gatekeeper of the internal
system. Each taste is associated with its own physiological function. There is a relation with the
taste and the nutrient content.
3
, Taste perception and measurement
We can measure taste perception with different tests. The quality can be measured with an
identification test. The sensitivity can be measured with a threshold detection test. The
intensity is subjective and differs per person à psychophysical function. We can also test the
hedonics with a psychohedonic function. Taste blindness is when you cannot perceive a
specific taste. One of the most common taste blindness is the blindness to PTC (bitter). Taste
perception is a slow process, so it takes some time before you taste the stimulus.
The gustatory system
There is no taste map on the
tongue. Taste perception starts
on taste papillae that are
differently spread out. The
gustatory papillae contain taste
buds. In the taste buds there are
taste receptors.
The labeled line theory states
that each taste receptor cell can
bind and detect a taste quality.
There are different nerves that
send the information to the brain. The
across fiber pattern theory states that
taste receptor cells are not specific for
a taste quality and the nerves bring
the total information to the brain or
vice versa that the receptors are
specific but that the nerves are not. There is no consensus about what theory is the right one.
Umami, sweet and bitter tastes are bound to G-protein coupled receptors. Umami is detected
with a T1R1 + T1R3 receptor, sweet with T1R2 + T1R3 receptor and bitter with T2Rs. We have
more than 30 members of the T2Rs receptors. That is why we can like the bitterness in coffee
but dislike the bitterness in fruits. We cannot distinguish the bitter tastes perceptional (so we
taste them all like bitter), but we can like or
dislike the different kinds of bitter. Bitter and
sour are thought to signal via ion-channels.
Via 3 nerves the signal is transduced. The first
one is the facial nerve which is responsible
for sending the taste perception to the brain.
The second one is the glossopharyngeal
nerve which helps you decide if you should
swallow or not. The last one is the vagal nerve
that signals to the gut that food is on its way.
4
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