activity 8

What are papillae?

Small bumps on the human tongue that contain taste buds in their grooves.

Where are taste buds located on the tongue?

In the grooves of the papillae.

What are the four types of papillae found on the human tongue?

Fungiform papilla, filiform papilla, foliate papilla, and circumvallate papilla.

Approximately how many taste buds are present on the human tongue?

About 10,000 taste buds.

Approximately how many gustatory receptor cells are in each taste bud?

Approximately 50 gustatory receptor cells.

What must happen to chemicals (tastants) before gustatory receptor cells can detect them?

They must dissolve in the saliva.

What is the cellular mechanism of a gustatory receptor cell when stimulated by a tastant?

It transduces chemical energy into an action potential, which is transmitted to the gustatory cortex of the brain.

How many taste types can a single gustatory receptor cell detect?

A single type of taste (sweet, salty, umami, sour, or bitter).

What are the 5 basic taste types detected by gustatory receptors?

Sweet, salty, umami, sour, and bitter.

Are taste buds restricted to detecting only one taste based on tongue location?

No; while certain receptors are concentrated in specific regions, all taste buds have receptor cells that can detect all five tastes.

How can humans perceive complex flavor profiles in foods like chocolate or bread?

Because an assortment of different gustatory receptor cells become stimulated at once.

What happens to the human ability to detect different tastes as age increases?

The ability to detect different tastes decreases with age.

What chemical types give rise to sweet flavors?

Sugars and numerous other chemicals.

Why is sweetness typically associated with feelings of reward and pleasure?

Because sweet foods are high-energy sources, which the body desires.

What is the chemical composition of the sweetener Aspartame (NutraSweet, Equal)?

A combination of amino acids.

From what chemical group are Sucralose (Splenda) and Saccharin (Sweet'N Low) derived?

Sugar-like alcohols.

What are two examples of sweet-tasting substances that are toxic to humans?

Chloroform and glycols (e.g., antifreeze).

What chemical substances produce salty flavors?

Various ionized salts (such as NaCl, CaCl2, and KCl).

What chemical compound is table salt / road salt?

Sodium chloride (NaCl).

Which basic taste is the most recently recognized, though known in Japan for over a century?

Umami.

How is the flavor of umami described?

Savory and meaty.

What specific amino acid primarily elicits the umami taste?

Glutamate.

What is the most abundant amino acid in protein-based foods?

Glutamate.

Name protein-based or aged foods naturally rich in glutamate.

Meats, seafood, bouillon cubes, yeasts, mushrooms, and aged cheeses (e.g., parmesan).

Why is umami taste NOT usually detected in raw/fresh protein foods?

Because glutamate is bound to other amino acids.

What three processes release bound glutamate to produce an umami taste in foods?

Cooking, fermenting, or aging.

What common food additive is used as a flavor enhancer to elicit umami?

Monosodium glutamate (MSG).

What chemical property is the direct cause of sour flavors?

Acidity (presence of H+ ions / low pH).

On what substance is the sourness index based, and what is its index value?

Dilute hydrochloric acid (dilute HCl), which has a sourness index of 1.0.

What is the relationship between acid strength, pH, and sourness?

Stronger acid = lower pH = more sour taste.

What is the typical pH range of lemon juice and vinegar?

pH ~ 2–3

What is the typical pH range of citrus juices and sodas?

pH ~ 3–4

What is the typical pH of black coffee?

pH ~ 5

What is the typical pH of many sour candies?

Below 2

Which basic taste elicits the strongest gustatory response at the lowest concentration?

Bitter.

What group of plant-derived complex molecules is the primary cause of bitterness?

Alkaloids.

What physiological effects can alkaloids produce in humans?

Increased heart rate, blood pressure, alertness, addiction, hallucinations, and death.

Name examples of bitter alkaloids listed in the lab pre-info.

Caffeine, nicotine, cocaine, LSD, morphine, codeine, quinine, and poisons.

What is the evolutionary significance of detecting bitterness at very low thresholds?

Many naturally occurring bitter compounds are highly toxic, so detecting them at low thresholds acts as a protective trait against poisoning.

What three chemical paper tests are used to determine genetic taste thresholds in humans?

Phenylthiocarbamide (PTC), thiourea, and sodium benzoate.

On which chromosome are the genes for tasting PTC, thiourea, and sodium benzoate independently inherited?

Chromosome 7 (determined in 2003).

What percentage of most human populations can taste PTC paper as bitter vs. non-tasters?

70% can taste PTC as bitter; 30% are non-tasters.

What taste quality do PTC and Thiourea papers typically elicit in tasters?

Bitter.

What three different taste qualities can Sodium Benzoate paper elicit depending on the taster?

Bitter, sweet, or salty.

What genetic genotypes correspond to "super-taster/taster" vs. "non-taster" phenotypes for PTC?

Homozygous dominant or heterozygous = taster/super-taster; Homozygous recessive = non-taster.

[Similarity] What similarity do Sweet and Salty tastes share regarding their detection thresholds?

Both have a high threshold for a taste response, requiring a minimum concentration of 0.01 M.

[Similarity] What similarity do Sour and Umami tastes share regarding their detection threshold category?

Both have an intermediate threshold for a taste response (Sour: 0.0007 M, Umami: 0.0009 M).

[Differentiation] How do the minimum threshold concentrations (M) compare across all 5 basic tastes from highest to lowest?

Sweet (0.01 M) = Salty (0.01 M) > Umami (0.0009 M) > Sour (0.0007 M) > Bitter (0.000008 M).

[Differentiation] How do Aspartame and Sucralose differ in their chemical derivation?

Aspartame is a combination of amino acids, whereas Sucralose is derived from sugar-like alcohols.

[Differentiation] How do sourness indices rank among Tartaric, Citric, Acetic, and Carbonic acids?

Tartaric acid (0.7) > Citric acid (0.46) > Acetic acid (0.40) > Carbonic acid (0.06).

[Differentiation] How does taste perception of PTC/Thiourea compare with Sodium Benzoate paper?

PTC and Thiourea tend to taste consistently bitter, whereas Sodium Benzoate can taste bitter, sweet, or salty depending on the person.