Aim: The aim of the study was to identify the
factors associated with taste perception.

 

Protocol & Results:
See Appendix

 

Discussion

 

Food
consumption is influenced by an individual’s perception of taste (Hilary et al
2015). From an evolutionary stand point it allows for the identification and
avoidance in the consumption of hazardous substances and identification of
nutritious substances. Pleasurable tastes tend to be favoured whilst those
perceived as unpleasant are avoided.

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There are five
known characteristics of taste which can be categorised including: sweet, salty,
bitter and unami. There is emerging evidence to propose that other
characteristics should join the fundamental categories which include; metallic,
fat and astringent.

 

Flavour
perception arises from multiple sensory afferents, including olfactory,
gustatory and somatosensory fibres (Small and Prescott, 2005). Visual stimuli
allows for identification of food while smell is regulated by the olfactory
system. Substances emit odours which enter the nasal cavity and are detected by
sensory cells called olfactory receptor neurons (ORN). The ORN alongside
sustentacular cells (SC) and basal cells (BC) reside in the nasal cavity,
making up the olfactory sensory epithelium, each with a unique receptor site.
The main function of the ORC is to detect odorants in airborne molecules passing
through the nasal cavity to encode and transmit sensory information to the
olfactory bulb in higher cortical centres (Theimer, 1982).

 

As an odorant
enters the nasal cavity it binds to its designated receptor cell which triggers
a G-Protein coupled receptor (GPCR) to dissociate itself and break away from
the ORC, in return, causing a cascade of events inside the cell. The GPCR binds
to an ion channel which allows positive ions from outside the cell to pass
through causing depolarisation of the cell, signalling an action potential for
the signal to pass through. The signal passes through the cribriform plate to
the glomerulus, activating mitral cells to send projections to the brain. Projections
are sent to the frontal lobe which allows for conscious identification, hypothalamus,
amygdala and limbic system which associate memories and emotions to a
particular stimulus. This process allows for the brain to perceive taste from
the odorant which initially entered the nasal cavity.

 

When the brain
is stimulated by the scent of food, it signals the production of saliva which
plays an integral role in taste perception. Saliva acts as a solvent for
substances to diffuse to taste receptor sites (Matsuo, 2000) while stimulates
the flow of gastric juices which is essential as proper nourishment may not be
established without the secretion of gastric juices (Lyman 1989). Throughout
this process saliva chemically interacts with substances which can result in an
alteration of taste sensitivity (Matsuo., 2000).

 

Disturbances in olfaction can result at any level of the
olfactory pathway and can occur from a multitude of diseases include aging,
sinus disease, respiratory tract infection, neurological degenerative diseases
and head trauma.

 

The gustatory
system is responsible for the perception of taste and is comprised of cells
located in the oral cavity where gustatory papillae house a host of taste
receptor cells (TRCs) in taste buds (Liu et al., 2016). Expressed within the
tongue and palate epithelium, the TRCs’ are morphologically different which are
classified as type I, II, III and basal (IV) cells (Lieu et al., 2016). TRCs’
are responsible for detecting each of the 5 basic taste characteristics, sweet,
unami, bitter, sour and salty (Chen et al. 2011).

TRCs’, T1R1,
T1R2 and T1R3 are involved in the identification of sweet, bitter and unami compounds
(Breslin 2006). Both T1R1s and T2Rs are located within type II taste receptor
cells. G Protein couples receptors (GPCRs) T2Rs mediate bitter taste (Alder,
2000).

Intracellular
proton concentration change is thought to trigger the taste of sour substances
created via protonated acids permeating the cell membranes, releasing protons
(Lyall et al., 2001). PKD2L1 and PKD1L3 are the associated channels for
triggering sour taste (Huang et al., 2006). Meanwhile, Sodium (Na+) permeates
through the cation channels (ENaC) on the apical taste buds leading to
de-polarisation which in return allows for the taste salt to be detected (Liu
et al., 2016).

 

The detection
of taste is not isolated to the oral cavity alone and taste receptors alone do
not produce taste. Emerging research has identified that the receptors which
detect bitter, sweet and unami are not soley restricted to the tongue and are
in fact distributed throughout the stomach, intestine and pancreas where they
aid the digestive process by influencing appetite and regulating insulin
production (Trivedi, 2012) 

 

Humans have a
sensory threshold which is unique to each individual where sensitivity to taste
qualities are detected from chemical compounds. The lowest level that a
stimulus is perceived is known as the detection threshold (Lie et al., 2016).
The recognition threshold is known as the minimum level that taste can be
characterised, for example; sweet, salt, bitter, sour, unami may be detected
(Lawless, 2010).

As taste
thresholds are unique to each individual, it may account for why some
participants in the taste ID study were able to correctly identify tastes while
others not. Each taste is associated with a
different physiological significance (Carpenter, 2003). Within the Taste ID, it
was evident that the taste bitter was one of the most identifiable tastes. It
could be argued that this is relatable to human evolution to allow for
detection of hazardous substances (Carpenter, 2003).

 

 

There are
multiple factors that alter an individual’s perception of taste, which is
important for food and beverage industries when developing new products. Taste
is mediated by viscosity, oral absorption, temperature and taste bud density (Murray
and Stofan, 1951)  

 

The effect of
temperature on taste perception has been extensively examined where it has been identified that there is a threshold range
between 20° and 30°C for detecting the five basic tastes. When food or drinks
are heated to temperatures above 30°C, McBurney et al., (1973) identified that detecting
weak tastes becomes more difficult.

Green and Frankman (1987) found
that as temperature rises, perceptions of sweetness and bitterness tend to
intensify whilst the perception of sour or saltiness remain the same.

 

Evidence demonstrates
that taste perception diminishes with age. 
A pilot study completed by Kenway et al., 2004 found that after 70 years
of age, taste threshold began to increase with their findings being compatible
with various other studies (Cowart, 1981; Stevens & Cain 1993; Schiffman
1997). Altered taste perception with age occurs due to the loss of taste buds
and change in taste cell membranes. The increase in taste threshold may account
for reports that food is tasteless or the preference for stronger tasting foods
such as very sweet or salty food. Deficits in these senses can reduce the
pleasure of food and place individuals at risk for nutritional deficiencies.
The use of flavour enhancing in foods for the elderly population has been shown
to have a significantly positive effect on oral intake (Schiffman, 1997)

 

Hunger will also effect the
perception of taste. (Walker –
FONA article) suggest that those individuals
experiencing hunger are more sensitive to sweet and saltiness however perception
of bitterness is not affected by hunger.

 

In the athletic
industry, sports drinks are widely consumed and are one of the best-researched
products in the world as they aim to enhance athletic performance by providing
fuel, hydrate the body, and replenish minerals lost through sweat (Molavi,
2015). Ingredients such as simple carbohydrates, electrolytes, and water
incorporate flavour thus enhancing the taste, whilst other necessary
characteristics such as temperature, colour and flavour variety all stimulate
consumers to buy the product (Molavi, 2015).  Olfactory, tactile and temperature regulation
all contribute to an individual’s decision on what beverage to consume (Murray
and Maughan 1951).

 

Within this
industry it is important to be aware of the effects of sustained exercise on
altering taste perception as it has been found to induce a broad-range of
physiologic responses including thermogenesis, fluid and electrolyte loss,
alterations in pH, changes in circulating glucose, and fluctuations in hormones
(Nakanishi et al (2015). 

In the same
study by Nakanishi et al., (2015), which compared the impact of exercise
intensity to four of the major tastes; sweet, sour, salty and bitter, it was
found that post-exercise sourness threshold was higher (p?0.05) following the
high intensity exercise compared to the low intensity exercise whilst sweetness
threshold decreased following the higher intensity exercise. This increase in
sensitivity to sweetness was strongly related to changes in blood glucose which
may be useful to indicate taste perception sensitivities in exercising individuals.
However, a relatively small sample size of ten participants was used in this
study that may make it difficult to generalise to the population therefore it
is suggested that further studies are conducted with larger sample size.

 

 

Taste
perception is a multi-faceted complex system which can be affected by a number
of factors. It is unique to each individual, however a significant factor identified
within the taste ID practical was how impairment of smell had such a profound
effect on taste perception and ability to pin point specificity of taste.

 

 

 

 

 

 

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