Chapter 15: taste

Flavor

the combination of true taste (sweet, salty, sour, bitter) and retronasal olfaction

PTC

people who are super tasters have a viceral reaction to this People who are non-tasters (3/4ths of population)

Four types of papillae

1. filiform : small structures on the tongue that provide most of the bumpy appearance Have no taste function Most dominant form Might just be there to give the tongue texture / break down food but unclear 2. Fungiform papillae: Mushroom-shaped structures (max diameter 1 mm) distributed most densely on edges of tongue especially the tip Average of six taste buds per papilla are buried in the surface 3. Foliate papillae: fold of tissue containing taste buds. Located on the rear of the tongue lateral to the circumvallate papillae, where the tongue attaches to mouth 4. Circumvallate papilla: circular structures that form an inverted V on the rear of tongue (three to five on each side) - on a trench and the buds are in the trench Mound like structures surrounded by a trench Much larger than fungiform papillae Don't need to memorize which one is which - but know that each one is responsible for info at a diff place on the tongue

Tastant

Any stimulus that can be tasted Categories: 1. Salty or sour: made up of small, charged particles that ack directly in the microvilli membranes allow some types of charged particles to enter but not others - Small ion channels in microvilli membranes allow some types of charged particles to enter but not others 2. Sweet or bitter: perceived via G protein - coupled receptors (GPCRs) similar to that in the olfactory system

Survival value of taste

Bitter - might signal poisons Sour - configured to detect acidic solutions that might harm the body Sweet and salty - our bodies need sodium and sugar to survive

Connection between taste and smell

Brain imaging studies - Brain processes odors differently, depending on whether they come from nose or mouth Food industry adds sugar to intensify sensation of fruit juice - Incase in sweetness (a pure taste sensation) increases perceived olfactory sensation of fruit

Umami

Candidate for 5th basic taste Comes from monosodium glutamate (MSG) - Glutamate: important neurotransmitter -- Safety issues: in human consumption --- Can lead to numbness, headache, flushing, tingling, sweating, and tightness in the chest if sensitive individual consume a large amount ---- Chinese restaurant syndrome -- For most people MSG does not pose a problem in small doses - thus FDA requires that food packages disclose when MSG is added --- Just a fear of it --- Does increase savory taste --- Could help w/ the palatability of food for people who have experienced a loss of appetite

Bitter

Cannot distinguish between tastes of different bitter compounds - Coffee isn't just bitter, why we can recognize it - Either bitter or it's not, all or nothing response Many bitter substances are poisonous Ability to turn off bitter sensations - beneficial to liking certain vegetables - A lot of taste preferences are formed in your environment Bitter sensitivity is affected by hormone levels in women, intensifies during pregnancy - To protect the child - Worse early on in pregnancy, when the child is more susceptible to harm

Sour

Comes from acidic substances At high concentrations, acids will damage both external and internal body tissues

Taste buds

Create neural signals conveyed to brain by taste nerves Are embedded in structures - papillae (bumps on tongue) Contain taste receptors (bud protects) Send info to brain via cranial nerves

Sweet

Evoked by sugars Many different sugars taste sweet - Glucose: principle sources of energy for most animals - Fructose: even sweeter than glucose - Sucrose: common table sugar; combination of glucose and fructose 2 step g protein ??? Single receptor responsible for all sweet perception - Different sweeteners stimulate different parts of receptor - Artificial sweeteners stimulate this receptor as well

Fat

Like protein, fat is an important nutrient Fat molecules evoke tactile sensations like oily, viscous, creamy, etc in the mouth - Rats have fatty acid receptors on their tongues...and humans may too But it seems that digesting fat in the gut produces conditioned preference for the sensory properties of the food containing fat - Liking for the food is increased once fat binds to gut receptors

What happens when we cannot perceive taste but can still perceive smell?

Patient case: damaged taste, but normal olfaction - could smell lasagna, but had no flavor Similar effect created in lab: Chorda tympani anesthetized w/ lidocaine - Chorda tympani: the branch cranial nerve VII (the facial nerve) that carries taste info from the anterior, mobile tongue (the part you can stick out)

Inhibition

Plays an important role in processing taste info in the brain Function: to protect our whole mouth perception of taste when we have injuries to the taste system (like the tongue)

Insular cortex

Primary cortical Insular is actually activated when they feel social disgust / if they are told that someone drank a glass of pee intentionally (not as reactive when people are told that it was by accident)

Salty

Salt is made up of two charged particles - Cation and anion Ability to perceive salt is not static - Low-sodium diets will increase sensitivity to salty foods over time Liking for saltiness is not static - Early experiences can modify salt preference -- Chloride-deficiency in childhood leads to increased preference for salty foods later --- Might be evidence for taste specific hungers (if your body is deficient in a nutrient you might crave it) -- Gestational experiences may affect liking for saltiness --- Children until the age of 4 are not fans of salt - slow development of salt preference --- Also what your mother eats in utero affects preferences later in life

Four basic tastes

Salty sour Bitter Sweet Umami is the proposed 5th taste

taste

Sensations evoked by solution in the mouth that contact the receptors on the tongue to the roof of your mouth

microvilli

Slender projections on the tips of some taste bud cells that extend into the taste pore - contain the sites that bind to taste substances - not tiny hairs -- Extensions of the cell membrane

How do taste and smell help us choose what to eat and what not to eat?

Smell: helps us identify object in the environment Taste: helps us identify nutrient and antinutrients

Different flavored foods placed on tips of infants' tongues

Sweet food evokes a smile like expression followed by sucking Sour produces pursing and protrusion of lips Bitter produces gaping, movement so spitting and sometimes vomiting movements

Neural pathway

Taste buds -> cranial nerves -> medulla -> thalamus -> cortex Happens bilaterally!

Orbitofrontal cortex

The part of the frontal lobe of the cortex that lies above the bone (orbit) containing eyes - received projections from insular cortex - involved in processing of temperature, touch, smell, and taste, suggesting if may be an integration area

retronasal olfactory sensation

The sensation of an odor that is perceived when chewing and swallowing force an odorant in the mouth up behind the palate into the nose - such odor sensations are perceived as originating form the mouth, even though the actual contact of odorant and receptor occurs at the olfactory mucosa

health consequences of taste sensation

Variations in sensory properties of foods and beverages affects food preferences and therefore diet - For instance, some vegetables have a bitter taste and so might be avoided by supertasters Valerie Duffy and colleagues showed that among men getting routine colonoscopies, those tasting PROP as the most bitter had the most colon polyps Note that fats also taste bitter to supertasters, so this may cause them to eat fewer high-fat foods, which could lower risk for heart disease

Recent studies of heirloom tomatoes

Volatile compounds contribute to perceived sweetness - Volatile compounds contribute greatly to retronasal olfaction - These volatiles may increase perceived sweetness w/out adding more sugar - Potential way to increase sweet flavor w/out adding more calories

Quinine

prototypically bitter tasting substance

Specific hungers theory

the idea that deficiency of a given nutrient produces craving (a specific hunger) for that nutrient Cravings for salty or for sweet are associated w/ deficiencies in those substances However, the theory has not been supported for other nutrients, such as vitamins - Other than you being cognizant of a lack of a certain nutrient