According to one study, while protein and hydrocolloids retain aroma compounds in thicker applications such as yogurt and spoon-able dressings, fat is more effective at retaining aroma flavor compounds in more fluid applications.

Abstracts, in brackets, were printed with permission from Academic Press, a division of Elsevier. Flavour Science, Volume 43: “Recent Advances and Trends" by Wender L.P. Bredie and Mikael Agerlin Petersen. Copyright 2006. For more information about this title and other similar titles, please visit—Ed.
As trends toward a fresher and bolder flavor impact continue to proliferate, product developers strive to maximize product quality and value. Many variables affect flavor perception in foods. Food systems are increasingly complicated, especially with popular food trends—salt, sugar and fat and increased fiber—all affecting flavor perception. Hydrocolloids, protein and fat are just a few factors that influence aroma and flavor release. For food processors, flavor-optimized modeling systems that vary viscosity, fat, protein and carbohydrate levels are valuable in predicting suitable flavor applications. Release behavior of flavor compounds in various applications is discussed in the following selected abstracts.

Research suggests the characteristics of individual hydrocolloid ingredients, such as those typically used in salad dressings and sauces, are more important to understanding flavor retention than the overall viscosity of the final product.

Taste Entrapment

Abstract: “Role of viscosity and hydrocolloid in flavor release from thickened food model systems,” E. Bylaite and A.S. Meyer.
[Release behavior of two aroma compounds, diacetyl and isoamyl acetate, from viscous food model systems having different viscosities was studied. Aroma partitioning and release rates were evaluated in pure water and in hydrocolloid solutions of sodium alginate, guar gum, locust bean and gellan at different concentrations and viscosities. The results showed that the aroma compounds were released differently from viscous solutions thickened to the same viscosity by different hydrocolloids. It was concluded that the nature of aroma compounds, type and concentration of thickener, and not the viscosity of the system, are determining factors in aroma release.]
Hydrocolloids often are chosen for applications based on processing limitations, physical characteristics of the end product and cost. However, cost issues become null if excessive amounts of flavor are required to compensate for poor flavor perception or retention in the product. 
Gums impact flavor release through their polymeric structure and physical chemistry. Lowering water content in a food system often increases physical and microbial stability of starch-based foods, but the increase in viscosity can also assist in binding more aroma compounds. Common polymers assist in the development of moisture barriers, shelflife enhancement and controlled release of flavors.
In the viscous food model systems discussed in this abstract, more diacetyl compounds were retained with locust bean and gellan at higher viscosities (880cP). The overall higher retention of isoamyl acetate compared to diacetyl observed in all the hydrocolloid mixtures was theorized to correlate with interactions involving the hydrophobic ester and hydrocolloids. Diacetyl release was not affected by increasing viscosity in sodium alginate and guar gum solutions. The release rate of both compounds was found to differ—depending on the hydrocolloid variety and concentration—and was independent of viscosity. The research suggests that a fundamental understanding of hydrocolloid ingredients themselves is more valuable to maximize flavor retention rather than increasing physical thickness of the product.
Abstract: “Determination of specific interactions between aroma compounds and xanthan/galactomannan mixtures,” C. Jouquand, C. Malhaic and M. Grisel.
[The gas/liquid partition coefficient (K) of aroma compounds was measured in pure polysaccharide solutions and in polysaccharide mixtures using the Phase Ratio Variation method. With this method, the retention in 0.1% and 0.02% polysaccharide concentrations was determined. The results showed that in semi-dilute regime (0.1%), all solutions and mixtures induced a high retention of limonene and hydrophobic esters, thus confirming hydrophobic interactions between these compounds and the polymer chains. In dilute pure polysaccharide solutions (0.02%), a decrease in retention was noticed for the esters and a “salting out” effect for limonene. Inversely, at 0.02%, mixtures of polysaccharides showed a good retention of aroma compounds explained by the well-known synergistic interactions between xanthan and carob gums.]
Some 60% or more of limonene was retained by all the variables with 0.1% xanthan (see chart “Polysaccharides and Flavor Retention”). In more dilute concentrations of 0.02%, there was a “salting out” effect with release of limonene exhibited by the polyelectrolytic behavior in xanthan solutions. Some ingredients that are shown to increase flavor retention may effectively mask off-flavors, which become apparent due to flavor migration into the product atmosphere.

Protein Perseverance

Abstract: “How can protein ratio affect aroma release, physical properties and perceptions of yoghurt?” A. Saint-Eve, N. Martin, C. Levy and I. Souchon.
[Among yoghurt dairy components, the type of proteins is known to influence the behavior of odorous volatile organic compounds (VOC). The aim of this study is to focus on the impact of the proteins on the physicochemical (rheological properties, microstructure, VOC release) and sensory (texture and flavor) properties of 4% fat flavored stirred yoghurts. Yoghurts varied according to the ratio of milk proteins used. Large differences were highlighted concerning the structures of the different yoghurts observed by scanning electron microscopy. Yoghurts differed largely in viscosity and in texture perception. Different effects on retention of VOC and the intensity of most olfactory attributes of the strawberry flavor were observed in yoghurts.]
In order to retain “fresh” flavor in fruit-flavored dairy products, manufacturers may add green note aromas (for example, hexanal), which are found naturally in fruits and vegetables. In this study, researchers experimented with 17 volatile flavors that are typically used to maximize quality in yogurt. The study assessed flavor intensity in yogurt thickened with caseinates, whey protein and milk powder. The thickest yogurt using caseinates resulted in the least homogenous density. In contrast, the yogurt using whey protein was the least viscous, but the densest. Yogurt using milk powder was in between the two. The sensory descriptive analysis indicated that the thinner yogurts made with whey protein and milk powder showed more mouth coating. Release of ethyl butyrate and methyl cinnamate were highest with milk powder, but sensory results did not show any loss of intensity. Although caseinate-containing samples retained the most volatile organic compounds, the actual flavor intensity by olfactory description was the lowest of the three. The flavor profile in yogurt thickened with whey protein was characterized as the most intense, especially in green note flavors. The study supports that volatile retention cannot predict flavor intensity of a product. Perception is influenced by viscosity, protein structure and texture interactions.

Fat Bursters

Abstract: “The role of lipids in aroma/food matrix interactions in complex liquid model systems,” C. Riera, E. Gouezec, W. Matthey-Doret, F. Robert and I. Blank.
[The release of nine aroma compounds was investigated in complex liquid bouillon-type model systems containing various non-volatile constituents. The relative release was determined by static headspace GC-MS as a function of the bulk composition. Among the non-volatile food constituents studied, fat appeared to be very efficient in binding volatile aroma molecules. This retention by the fat was directly correlated with the intrinsic physical properties of the aroma compounds, such as the water/octanol partition coefficient. The individual effect of the major fat constituents was studied as well, indicating that, for example, even small amounts of phospholipids may effectively retain volatile compounds.]
Protein and hydrocolloids are typically successful in retaining aroma compounds in thick yogurt and dressing applications. However, in more fluid applications, as illustrated in this study, fat is more effective at retaining aroma compounds. The effectiveness not only varies based on the flavor chemical structure, but fatty acid chain length, saturation level and fatty acid sequence also influence retention.
More variables are involved when other ingredients are added, as with any complex food system. None of the non-lipid ingredients, such as chitin, collagen and cellulose, bound aroma compounds as effectively as fat. Chitin was the most effective at releasing aromas. Collagen retained 20% and 70% of aliphatic aldehydes and 1-octen-3-one, respectively. Cellulose retained 60% and 15%, respectively, of apolar compounds α-pinene and nonanal. On the contrary, fat released polar compounds including 1-hexanol and 3-methyl butanal. Previous studies support that very high concentrations of hydrocolloids and proteins are required to retain flavors, in contrast to fat. (See chart “Macromolecule Impact on Flavor.”)

Cultivated Palates

Abstract: “Effect of physiology and physical chemistry on aroma delivery and perception,” A.J. Taylor, K.S.-K. Pearson, M.D. Hodgson, J.P. Langridge and R.S.T. Linforth.

[To perceive aroma compounds, they must be delivered to the olfactory receptors—a process that depends on physical chemistry and physiology. The role of these two factors was studied using a variety of delivery mech-anisms, ranging from gas phase delivery to the location and form of the aroma compounds in the food matrix. The effect of mouth loading and body position was also investigated. Delivery to the olfactory receptors was monitored in vivo using atmospheric pressure chemical ionization-mass spectrometry (APCI-MS), and physiological responses were monitored simultaneously. It was found that body position and mouth loading affected the opening of the velum, while common aroma solvents had a significant effect on the delivery of hydrophobic compounds. Aroma delivery from droplets of pure compounds suspended in the food matrix was very intense and could not be explained by conventional partition mechanisms. A delivery mechanism based on direct volatilisation from the air-liquid interface was proposed to explain this intense release, which is also seen from some commercial materials.]

When the velum, located between the mouth and throat, is closed, less aroma transfer can occur from the mouth to nose than if an individual swallows. Human velum behavior of opening and closing varies based on individual physiology and consumption behavior. This suggests one reason that “tasting” may yield different evaluations than “consumption.”

Release of hydrophilic aroma compounds was not affected by the common flavor solvents ethanol and propylene glycol. However, hydrophobic compounds were affected. Results suggest that solubilized aromas encapsulated in glass-like materials demonstrated an intense “burst” of aroma release and are not partition-driven. Controlled release is used in many confectioneries. An efficient hydrocolloid can control the rate of flavor release ranging from instant to extended. Developers seek polymers that can entrap volatile aroma molecules and release them at the appropriate time.

Researchers continue to expose intriguing new aspects to the complex mechanisms surrounding flavor release and experience. Whether the flavored system is optimized with hydrocolloids, protein or fat, it is clear from these studies that viscosity and flavor retention alone are not accurate predictive measures for flavor perception. Developers must also have a thorough understanding of the chemical structures, consumption behavior, concentrations used and synergies with other materials. Human anatomy and eating and drinking behavior vary, making comprehension of flavor perception more complicated. Scientists will continue to optimize tools to accurately measure flavor intensity and perception to support product launch and success.