Retronasal flavor perception
The retronasal (Latin : retro : 'back', 'again', 'behind'; nasal : 'relating to the nose') perception describes the transport of volatile, aromatic compounds from the oral cavity via the pharynx to the receptors in the nasal cavity. The aromas are released when food and drinks are consumed and trigger an olfactory stimulus.
General flavor perception
Aroma perception takes place at the olfactory center. There are around 10 million olfactory sensory cells , including 400 different ones with different receptors . This sensory perception not only provides information about how something tastes or smells, but it also serves as a warning system (inedible, poisonous food) and for communication ( pheromones ). In addition, emotional memories are linked to smells.
Fragrances or aromas can reach the olfactory organ in two ways :
1) orthonasal
This is the sensory perception commonly known as "smelling" e.g. B. smelling flowers or a cup of coffee. When you breathe in, fragrances in the air are transported through the nostrils into the nasal cavity to the olfactory receptor cells and perceived.
2) retronasal
When food is consumed, the released, volatile aromatic substances are transported through the pharynx into the nasal cavity to the olfactory receptor cells. Since the process is linked to the eating process, the perceived flavor profile is often incorrectly referred to as taste. The fact that it is more a question of smelling can be illustrated above all in the case of a cold. The typical aromatic substances of a food are only perceived to a limited extent or not at all (one has the feeling that the food no longer "tastes" good).
The retronasal flavor profile can differ from the orthonasal profile due to various factors (e.g. chewing or saliva).
Example: Flavors in fresh Valencia late orange juice
| connection | Concentration [µg / kg] | orthonasal aroma value | retronasal aroma value |
|---|---|---|---|
| ( R ) - limes | 85 598 | 228 | 1 339 |
| acetaldehyde | 8 305 | 332 | 831 |
| Butyric acid ethyl ester | 1 192 | 1 192 | 11 920 |
| 3-hydroxyhexanoic acid ethyl ester | 1 136 | 4th | 18th |
| 3-methyl-1-butanol | 639 | <1 | 2.6 |
| Myrcene | 594 | 42 | 36 |
| ( R ) - α-pinene | 308 | 62 | 9 |
| Hexanal | 197 | 19th | 19th |
| ( Z ) -3-hexenal | 187 | 747 | 6 227 |
| Vanillin | 67 | 3 | 2 |
| ( S ) - 2-methylbutyric acid ethyl ester | 48 | 8,000 | 12,000 |
| Octanal | 25th | 3.2 | <1 |
| trans -4,5-epoxy- ( E ) -2-decenal | 4.3 | 36 | 287 |
| 1-octen-3-one | 4.1 | 4.1 | 410 |
| Methional | 0.4 | <1 | 10 |
Anatomy and functioning
When eating food, more processes take place than just the sensual perception of the five basic taste qualities (sweet, salty, sour, bitter and umami) on the tongue . The further aroma impression occurs via the retronasal perception. Here, the act of swallowing , with its protective and control processes, plays a central role.
First, the food is chewed, salivated and a swallowable bite ("bolus") is formed. The base of the tongue closes off the mouth with the soft palate to prevent premature swallowing. This means that even volatile substances cannot get into the nasopharynx (a).
The swallowing process is initiated reflexively via touch receptors on the palatal arches, the back of the throat or the base of the tongue. So that the bolus does not get into the crossing windpipe (trachea), it is closed by the larynx and throat cover ( epiglottis ). At the same time, the soft palate (velum palatum) seals the nasopharynx with the pharynx wall, so that no food can be pressed in by the pressure of the tongue (b).
The bolus is passed on via peristaltic muscle contraction, the locking mechanisms relax, the trachea and nasopharynx are open. Odor-intensive, volatile substances (e.g. esters , thiols, etc.) enter the nasal cavity ( cavum nasi ) with the breath of the first breath after swallowing (the so-called swallow-breath ). In the upper nasal passage ( meatus nasi superior ), where the olfactory organ ( organum olfactus ) is housed, aroma perception finally takes place (c).
However, the perception of basic taste qualities and aroma impressions does not follow a strict chronological sequence. If food is put into the mouth, volatile substances can enter the nasal cavity both orthonasally and retronasally (the velum and epiglottis are still open). This is also possible with food that has to be chewed heavily, as the velum and epiglottis are arbitrarily opened for a short time. A conscious control of the Velum can be learned and is z. B. used by wine gustators to get a better flavor impression.
Influences on retronasal aroma perception
Speed of aroma degradation
Flavorings are broken down by saliva constituents at different rates and are therefore not perceived at the same time.
Depot effect
Aromatic substances that can not be broken down by saliva (such as pyrazines ) are adsorbed on the oral mucosa and only released again over time. The release takes place either directly into the gas phase of the oral cavity or by the saliva continuously detaching the substances. These aromas are perceptible for a long time and lead to long-lasting impressions, such as B. the aftertaste of coffee.
Coating effect
The food matrix (e.g. quark or chocolate) forms a longer-lasting film and is adsorbed directly on the lining of the mouth and throat. Flavors are continuously released from it and can be perceived for a long time.
Sensory training
People with trained perception perceive some aromas more strongly than laypeople, e.g. B. by deliberately opening the velum or stronger release of the aromas through continuous movement in the mouth.
Temperature of the food
Aromas change into a gaseous state at different temperatures, with higher temperatures promoting a release. For example, smelling an ice cream does not provide a significant aroma impression. The ice cream is warmed up in the mouth and the aromas released as a result are perceived retronasally.
Individuality of man
Taste preferences differ depending on age, gender, culture, origin and upbringing.
Analysis of aromas that can be perceived retronasally
Retronasal aromas can be determined in the exhaled air using proton transfer reaction mass spectroscopy (PTR-MS; in vivo aroma analysis ). With this system, the test person wears a nasal attachment, which consists of two glass tubes and is easily attached to the nostrils. The exhaled air is absorbed by this and passed on through another tube to the PTR-MS. There the individual components are separated and identified. This method is fast, highly sensitive and allows a large number of volatile components to be monitored simultaneously.
An alternative method is the retronasal aroma headspace simulator (“artificial mouth”). This device can be used to simulate the release of volatile components from food when chewing and swallowing. In addition, the flavoring substances can be identified. Artificial saliva is added to food in an airtight container and chopped up using a knife (this simulates chewing). The simulator also works at body temperature to create realistic operating conditions. The volatile components are removed from the gas phase and used for gas chromatography (GC) (principle of a headspace GC ). The separated substances can either be identified and quantified with an appropriate detector (e.g. flame ionization detector ) or “smelled” by a person and thus identified. The prerequisite for this is the aroma activity of the volatile components.
Importance and application
Since the exact processes are not yet fully understood and this could be used to further develop food, retronasal perception is particularly important for science and industry. A first theoretical application in a product was provided by the American startup The Right Cup , which by 2017 had developed a drinking cup with a scented silicone ring that was supposed to enable retronasal and orthonasal aroma perception. The scent of the silicone ring is supposed to give pure water a lemonade-like fruit taste. In practice, however, the orthonasal perception plays a role in the product, so that the comments on the very successful crowdfunding campaign were mostly negative. The start- up air up GmbH (formerly JOYCE / ten-ace) has been working as a spin-off of the Technical University of Munich on a drinking bottle that aromatizes water through retronasal aroma perception since 2017. Water is passed into the mouth together with volatile aromatic substances in the gas phase , where it separates from the water and is perceived retronasally.
Individual evidence
- ↑ a b c d e f C. Yeretzian, P. Pollien, C. Lindinger, S. Ali: Individualization of flavor preferences: toward a consumer-centric and individualized aroma science. In: Comprehensive reviews in food science and food safety Volume 3, 2004.
- ^ A b c L. McCandless: Acree's Artificial Mouth Takes the Guesswork Out of Tasting. In: New York State Agricultural Experiment Station August 20, 1997.
- ↑ M. Steinhaus, U. Arzberger: Aromastoffe - An important piece of food (medium) quality ( Memento of July 13, 2015 in the Internet Archive ) (PDF) Retrieved October 17, 2011.
- ↑ S. Raisig: Feeling, Tasting, Smelling - the Hidden Senses ( Memento of the original from July 5, 2016 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 1.4 MB). Retrieved October 17, 2011.
- ↑ a b c d e f R. Huch, KD Bauer: Mensch body disease. Urban & Fischer, 4th edition
- ↑ a b c d e f g h i j k A. Büttner: Having fun eating and drinking - Retronasal odor perception. In: Nachrichten aus der Chemie No. 52, May 2004.
- ↑ H.-D. Belitz, W. Grosch, P. Schieberle: Textbook of food chemistry. Springer Verlag, 6th edition, 2008. Table 18.28
- ↑ The Right Cup: Trick Your Brain, Drink More Water! Retrieved February 8, 2018 .
- ↑ JOYCE | Climate-KIC . In: Climate-KIC . ( climate-kic.org [accessed February 8, 2018]).
- ↑ air up - up for new taste? Taste only through fragrance! Retrieved July 7, 2019 .
