Food Senses Gustation PDF

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Summary

• Physiology
o Counting papillae
• Genetics
o PTC test
• Where; location of taste
o Tongue-taste map
• How intense; sensitivity
o Taste threshold
• Cognition; awareness
o Taste adaption
...

Description

FOOD501 Food and the Senses: Taste; gustation Tutorial WORKSHEET 1: STUDENT’S COPY Exploring factors contributing to taste talent: 

Physiology o Counting papillae



Genetics o PTC test



Where; location of taste o Tongue-taste map



How intense; sensitivity

Papillae cover the tongue.

o Taste threshold 

Cognition; awareness o Taste adaption

Each papilla contain multiple taste buds.

Exercise 1: Counting papillae Taste buds, made up of about 50 to 150 gustatory cells, are located on small bumps on the tongue called papillae. On the surface of protruding tips of these cells are receptors that bind to small molecules related to taste. The receptors relay taste stimulus information through sensory nerves to the brain where it is perceive as taste. Simply examining your tongue can determine your ‘taster type’. The number of taste buds (only papillae on which the taste buds are located are visible to the eye) have been correlated with the intensity at which you taste most things; the more taste buds the more you taste.

Taste buds are filled with gustatory cells. Each cell tip protrudes through a pore on the papilla surface. Nerves carry signals from each cell to the brain.

Each cell tip is covered with different taste receptors that detect various compounds contributing basic tastes. Stimulation of receptors sends signals to the brain.

Figure 1: Sensory structures of the tongue

Materials



Blue water-soluble food colouring (CAUTION: stains fabrics)



Small shallow dish



Measuring spoon



Water

FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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

1 cotton bud for each person



Paper towel



Magnifying glass and mirror

Instructions

1. Mix a few drops of colouring with water into the shallow dish. 2. Lightly apply dye towards the front of the tongue using a cotton bud (Do NOT double dip; use a clean cotton bud if required). You could define the area in which you are undertaking the papillae count by applying a reinforcement ring on the tongue. 3. Using the magnifying glass and mirror (or electronic device, observe and describe the appearance of your tongue. Is it mostly blue with a few pink spots, or is it mostly pink with very little blue – lots, or somewhere in between – a moderate count. The pink spots are papillae on your tongue, and the more papillae the more taste buds. 4. Record results for the group in Table 1.

Exercise 2: PTC test Phenylthiocarbamide (PTC) is an organic molecule that has the unusual property of either tasting very bitter, or being virtually tasteless, depending on the genetic makeup of the taster. The ability to taste PTC is a dominant genetic trait. Determination of PTC sensitivity is one of the most common human genetic test. PTC correlates strongly with some bitter substances found in nature, many of which are toxins. Therefore, the PTC test may also predict responsiveness to bitter cruciferous vegetables (cabbage, kale, broccoli), herbs (mustard leaves), fruit (grapefruit, pomegranate), coffee and ‘hot’ spices (chillies). However, your reaction to PTC is not a universal indication of your reaction to other substances. Just because you cannot taste PTC does not mean you cannot taste 6-npropylthiouracil (PROP), another bitter chemical used for testing, or other bitter foods. Your unique tongue anatomy, genetic heredity and medical history, overlaid with your culturally influenced experience of food, all affects your food choices. Materials

Filter paper impregnated with a tiny amount of PTC. Instructions

1. Place PTC paper on the tongue for 30 seconds. 2. Record results for the group participants in Table 1.

FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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OBSERVATIONS Table 1: Counting papillae and PTC test results Student Describe the appearance of your tongue 1 Moderate number of large round papillae Papillae Briefly describe PTC Student Predicted taster type test response count 1 M Taster Mild (taste like cumin None

Actual taster type Taster

2

M

Taster

Tolerant

3

F/M/L

Tolerant/Taster/Hyper

Tolerant/Taster/Hyper

4

F/M/L

Tolerant/Taster/Hyper

Tolerant/Taster/Hyper

5

F/M/L

Tolerant/Taster/Hyper

Tolerant/Taster/Hyper

6

F/M/L

Tolerant/Taster/Hyper

Tolerant/Taster/Hyper

Expected relationship: Few = Tolerant-taster (No taste of PTC), Moderate = Taster (Gradual response), Lots = Hyper-taster (Extreme response) 1. Provide a brief explanation of you and your group’s results and any identified relationship between papillae ‘count’ and the results of the PTC test. NOTE: If your experience differed from what the exercise was supposed to demonstrate, state the expected result and then describe what you and your group experienced. There was a slight variation in the ability to taste bitter in relation to papillae count. I had a moderate count and a mild PTC response. Another group member had a moderate count and no PTC response. The expected taster type in both cases was “Taster”.

(4 MARKS)

FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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Exercise 3: The tongue-taste map Slight differences in the intensity at which we taste things in each area of the tongue formed the basis for the development of the tongue-taste map. However, the tongue-taste-map became over simplified with the assumption that areas of lower sensitivity were areas of no sensitivity. Refer to the Tutorial PPT for more information. Materials



5 ml distilled white vinegar to provide a clean one dimensional sour taste



Small shallow dish



Measuring spoon



3 cotton buds for each person – use a clean end when applying sample to each area within the mouth to avoid cross contamination.



Water and disposable paper cup for each taster

Instructions 1. Pour vinegar into a small shallow dish.

A

2. Cleanse your palate by rinsing your mouth out with cold water

and wait a few minutes each time before applying vinegar. E

B

3. Dip the cotton swab into the vinegar and apply to your

tongue/mouth in distinct places (A – F) as shown in Figure 2, being careful to only touch the tasting location you are exploring. F; inside cheek 4. Record your observations in Table 2.

C D

Figure 2: Swab locations on tongue

OBSERVATIONS As you touch the swab around your mouth, note what you experience? Table 2: Tongue taste map results Location A B C D E F

Observations Definite soure taste + slightly sweet Not as sour Definite sour taste Sweet and sour but not as intense None None

Rate acidity (sourness)

Tongue taste map; areas of taste sensitivity

8/10 6/10 8/10 7/10 0/10 0/10

FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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Exercise 4: Taste threshold Each person lives in their own ‘taste world’ and differ in their sensitivity to the same compounds. To illustrate this point we will determine your taste threshold for sweetness. A similar exercise could be done for sourness (using vinegar) and saltiness (using salt). None of the basic tastes are stimulated by a single chemical and so we can have different thresholds for taste detection of chemicals that taste the same. For example, sucrose and lactose both taste sweet to people, but the concentration at which the sweet taste of lactose is detected is approximately three times greater for lactose than for sucrose. There are also some sweet substitutes that are extremely potent. Cyclamate is 30–50 times sweeter than sucrose and Aspartame is 200 times sweeter than sucrose which means that the threshold concentration would be much lower for these chemicals than for sucrose. Substances sensed as bitter typically have very low thresholds, probably because many natural poisons are bitter therefore this tasting ability has a protective function. Some people are more sensitive tasters than others, but they are not necessarily better tasters. Your ability to identify tastes and smells improves with repeated exposure as you become more accomplished with training, and experience. Paying more attention to the food you prepare and/or consume also adds to its enjoyment. Merely liking or disliking a food is a simple hedonistic judgement; food appreciation is very different. Materials

The serial dilutions are prepared by the lecturer prior to class. Lecturer:



Water at room temperature, preferably distilled



4 x 600 ml breakers labelled A, B, C and D



Kitchen scales



50 g castor sugar (sucrose)



4 teaspoons

Instructions

Make a serial dilutions of sugar solutions by: a. Pour 450 ml of water into breaker A. Add 50 g of sugar and stir until it is dissolved. This gives you a 10% sugar solution. b. Pour 50 ml of the 10% sugar solution into breaker B. Add 450 ml of water and stir. This gives you a 1% sugar solution. c. Pour 50 ml of the 1% sugar solution into breaker C. Add 450 ml of water and stir. This gives you a 0.1% sugar solution. d. Pour 50 ml of the 0.1% sugar solution into breaker D. Add 450 ml of water and stir. This gives you a 0.01% sugar solution. FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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IN CLASS: Materials



4 x 250 ml breakers labelled A, B, C and D



Small plastic sample cups, 4 each



Jug with water and disposable paper cup for each taster

Instructions

1. Pour 100 ml of each sample into the correspondingly labelled 250 ml beaker. Taste

2. Cleanse your palate by rinsing your mouth out with cold water and wait a few minutes each time before sampling. 3. Taste sweetened waters, starting with the D, then C, B and A (i.e. least sweet to most sweet). 4. Cleanse the palate and taste the next sample once the sweet taste has gone. 5. Record your observations in Table 3.

OBSERVATIONS Table 3: Taste threshold results Beaker Sugar solution Observations concentration (%) Very very light sweetness D 0.01 C

0.1

B

1

A

10

Tastes mostly like water, but can taste something very faint that is definitely not water Light sugary taste Very sweet and overwhelming taste

2. Explain how this exercise could be changed to determine more accurately an individual’s taste threshold for sour and other basic tastes (sweet, salty, bitter). Substitute sugar for another suitable substance dependant on the taste eg using sodium chloride to test for salt threshold; repeat the steps. Make sure the ingredient is simple so as to not confuse with other tastes. Wait longer between samples to reset pallet.

(4 MARKS)

FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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Exercise 5: Taste adaption This exercise introduces the concept of sensory adaption which will be addressed again in lectures and in the smell tutorial. Materials



5 Tbsp. sugar



Water



Measuring spoons



2 x 250 ml beakers, labelled A and B



2 teaspoons



Small plastic sample cups, 2 each



Water jug and disposable paper cup for each taster

Instructions

1. Measure 1 tablespoon sugar into the first beaker (A). Add 200 ml of warm water and stir briskly to dissolve the sugar. 2. Measure 4 tablespoons sugar into the second beaker (B). Add 200 ml warm water and stir briskly to dissolve the sugar. Taste

3. 4. 5. 6. 7. 8. 9.

Taste the mildly sugary water first (A). Note how sweet it tastes. This is your virgin taste. Now taste the extra sugary water (B). Note how sweet it tastes. Without cleansing your palate, go back and taste the first glass (A). Repeat sequence A, B, A several times. Now cleanse your palate by rinsing your mouth out with cold water and wait a few minutes. Then go back and taste the first cup of sweetened water (A). Record your observations in Table 4.

OBSERVATIONS Table 4: Taste adaption results Taste Rather sweet A B A

Observations

Overwhelmingly sweet Very mild Cleanse palette

A

Rather sweet

FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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REQUIRED READING  Roche, L. (2011). Not your grandfather's five senses. Retrieved 28/2/13 from

http://www.lorinroche.com/instincts/instincts/21senses.html 3. Explain how the senses could be divided into fewer categories based on the type of stimulus but then also subdivided into a greater number of senses based on the specialised sensory receptors. Illustrate your answer with particular reference to the sense of taste. If you were to use the nature of a stimulus to determine senses, then there would be 3 rather than the usual 5. These are mechanical, chemical, and light. For taste, because the taste receptors in the mouth rely on certain sensory cells registering chemicals, taste is a chemical sense. On the other hand, each of these 3 senses can be broken down into more specific senses when we consider how specialised cell receptors are used to differentiate between stimuli. For example, even though taste is a chemical sense, we can perceive different types of taste, depending on which cell receptors the chemicals interact with (4 MARKS) (TOTAL: 12 MARKS X 0.5 = 6 MARKS)

Bibliography Stuckey, B. (2012). Taste what you're missing: The passionate eater's guide to why good food tastes good. New York, NY: Free Press. Sensory Science: Testing Taste Thresholds. Scientific America. Retrieved 31/6/15 from http://www.scientificamerican.com/article/bring-science-home-taste-thresholds/ Physiology of Taste. Retrieved 17/6/15 from http://www.vivo.colostate.edu/hbooks/pathphys/digestion/pregastric/taste.html

FOOD501 Food and the Senses: Taste; gustation Tutorial – WORKSHEET 1: LECTURER’S COPY

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