Retronasal

The sense of smell in humans is not limited to detection of those volatile molecules inhaled through the nose, termed orthonasal olfaction. Molecules released at the back of the mouth, particularly in the chewing of food, can make their way up through the nasopharynx to the olfactory epithelium, termed retronasal olfaction. This system is activated when air is exhaled. Orthonasal olfaction is used to detect the scent of flowers and perfumes, food aromas, the presence of skunks, and the like. Retronasal olfaction detects the volatile molecules released from food. It is retronasal olfaction that makes a major olfactory contribution to the taste of food. And it is retronasal olfaction that helped to elicit Proust s profound reaction to a madeleine dipped in tea. 

Eor a thoughtful analysis of orthonasal and retronasal olfaction, see G. M. Shepherd, Nature316-321 (2006). 

Coppola, D. M. and Coltrane, J. A. (1994). Retronasal or internasal olfaction can mediate odor-guided behaviors in newborn mice. Physiology and Behavior 56,729-736. 

Tikk, M. Tikk, K. T0rngren, M. A. Meinert, L. Aaslyng, M. D. Karlsson, A. H. Andersen, H. J. Development of Inosine Monophosphate and Its Degradation Products during Aging of Pork of Different Qualities in Relation to Basic Taste and Retronasal Flavor Perception of the Meat. J. Agric. Food Chem. 2006, 54, 7769-1711. 

Compound Odour descriptor Retronasal threshold (pg/L) Orthonasal threshold (pg/L) Amount in fresh orange juice (pg/L) Amount in processed orange juice (pg/L)... 

Roberts, D.D. and Acree, T.E. 1995. Simulation of retronasal aroma using a modified headspace technique Investigating the effects of saliva, temperature, shearing, and oil on flavor release. J. Agric. Food Chem. 43 2179-2186. 

This unit discusses the use and design of the two mouth simulators, the retronasal aroma simulator (RAS) and the model mouth, that have successfully been verified to produce an effluent with volatile ratios similar to that found in human exhaled breath during eating. Though at a glance the apparatuses seem very different, they produce relatively similar effluents. Of obvious notability is the difference in the size of the reservoir the RAS reservoir is 1 liter and the model mouth reservoir is 70 ml. When determining which apparatus to use, carefully consider concentration needs, absorption characteristics of compounds, and shear resistance of the food. 

Retronasal aroma simulator (RAS, available from DATU) with temperature-controlled water jacket or water bath... 

Flavor perception results from interactions between a consumer and stimulants in a food. For the aroma part of flavor, the stimulants are volatiles that bind to receptor proteins found on the olfactory epithelium. These stimulants can reach the receptors by two routes, orthonasal or retronasal. The retronasal route is used when odorants are drawn from the mouth during eating through the nasal pharynx to produce aroma. 

The composition of volatiles released from a food is different when it is sniffed (via orthonasal route) and when it is eaten (via retronasal route). This is partially due to conditions in the mouth that selectively affect volatility, thus altering the ratio of compounds that volatilize from a food system. Mouth temperature, salivation, mastication, and breath flow have all been shown to affect volatilization (de Roos and Wolswinkel, 1994 Roberts et al., 1994 Roberts and Acree, 1995 van Ruth et al., 1995c). The ideal gas law describes the effects of temperature. Saliva dilutes the sample, affects the pH, and may cause compositional changes through the action of the enzymes present (Burdach and Doty, 1987 Overbosch et al., 1991 Harrison, 1998). Mastication of solid foods affects volatility primarily by accelerating mass transfer out of the solid matrix. The gas flow sweeps over the food, creating a dynamic system. The rate of the gas flow determines the ratio of volatiles primarily based on individual volatilization rates and mass transfer. 

The model mouth and the RAS will produce effluents carrying a ratio of volatile compounds that is similar to the ratio of volatiles leaving the human nose when the same food is consumed. The RAS effluent will be -200 times more concentrated than the human breath. The RAS produces a time average representation of the retronasal breath composition. 

Burdach, K.J. and Doty, R.L. 1987. The effects of mouth movements, swallowing, and spitting on retronasal odor perception. Physiol. Behav. 41 353-356. 

Deibler, K.D. 2001. Measuring the effects of food composition on flavor release using the retronasal aroma simulator and solid phase microextraction. Ph.D. dissertation, pp. 131. Cornell University, Ithaca, New York. 

Deibler, K.D., Acree, T.E., Lavin, E.H., Taylor, A.J., and Linforth, R.S.T. 2000. Flavor release measurements with retronasal aroma simulator. In 6th Wartburg Aroma Symposium, April 11, 2000, Eisenach, Germany. 

Pierce, J. and Halpem, B.P. 1996. Orthonasal and retronasal identification based upon vapor phase input from common substances. Chemical Senses 21 529-543. 

Roberts, D.D. 1996. Flavor release analysis using a retronasal aroma simulator (olfactory). Cornell University, New York. 

Roberts, D.D. and Acree, T.E. 1995. Simulation of retronasal aroma using a modified headspace... 

Roberts, D.D., Lavin, E.H., and Acree, T.E. 1994. Si mulation and analysis of retronasal aroma. In 4th Wartburg Aroma Symposium Aroma Perception, Formation, Evaluation (M. Rothe and H.-P. Kruse,... 

PTFE polytetrafluoroethylene PUFA polyunsaturated fatty acid PV peroxide value PVDF polyvinylidene difluoride PVP polyvinylpyrrolidone PVPP polyvinylpolypyrolidone RAS retronasal aroma stimulator RDA recommended dietary allowance RF radio frequency RFI relative fluorescence intensity RI retention index RNU relative nitrogen utilization ROESY rotational nuclear Overhauser enhancement spectroscopy RP-HPLC reversed-phase HPLC RPER relative protein efficiency ratio RS resistant starch RT retention time RVP relative vapor pressure S sieman (unit of conductance)... 

Besides texture and color, flavor (taste and smell) is an important property of foodstuffs. Smell is caused by volatile compounds coming into contact with a distinct area in the nose, the so-called "regio olfactoria" [1], Volatile flavor compounds are denoted odorants or odor compounds, if they have been perceived nasally (before eating) and aroma compounds if they have been perceived retronasally via the throat (during eating). Therefore, in the literature the terms flavor, odor or aroma compounds are often synonymously used. 

In general, any analytical equipment or procedure used in the field of natural products chemistry and environmental engineering is also helpful in aroma analysis 64,65 The history and principles of such art are described in detail elsewhere and will not be featured here. Gas chromatography (GC), GC-mass spectrometry (MS), and nuclear magnetic resonance (NMR) are the most frequently used techniques along with rather specialized setups such as proton transfer reaction-mass spectrometry66 (PTR-MS) used in retronasal aroma analysis (see Chapters 9.02, 9.06, 9.10-9.11). 

The third question derives from the large diversity in physico-chemical properties of the different wine impact compounds. Some of them are quite hydrophobic and are released very easily from the wine matrix, while some others are quite hydrophilic and will be released with difficulty (Ferreira et al. 2006). The former are major constituents of the headspaces on a glass of wine, while the latter will reach the pituitary only when the level of liquid in the glass is very small or when the wine is swallowed. These differences in behavior, still not completely understood, may explain why different odors are perceived when the glass of wine is full or when it is nearly empty (Petka et al. 2006) and why sometimes there are marked differences between ortho and retronasal perceptions. 

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