Flavor Technology. Physical Chemistry, Modification, and Process
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In beverages, oils and fats may be dispersed as droplets 91 that are thermodynamically unstable; therefore, surfactants emulsifiers such as proteins are added to protect oil drops from coalescence. Roberts et al. Investigations at various temperatures showed lower flavor release at higher solid fat content for practically all systems with the exception of 2-pentylfuran and limonene in milk fat, which may be due to crystal exclusion effects.
Protein-containing beverages cover a broad spectrum, including dairy, soft drinks, sports drinks, and fermented beverages, and may contain proteins from animal and plant origin. Even though proteins do not contribute to the flavor of products directly, 97 they can interact with flavors either reversibly 22 , 27 or irreversibly 98 , 99 if hydrolyzed, proteins are known to form peptides that can be extremely bitter depending on their size and hydrophobicity Covalent chemical linkage such as amide and ester formation and condensation of aldehydes with sulfhydryl SH groups are irreversible, and noncovalent hydrophobic and electrostatic interactions, hydrogen bonds, and van der Waals interactions are reversible.
Proteins may also convey undesirable off-flavors to foods, soy protein in particular is known for this. BLG, of which the characteristics and structure are well-known, 9 , is also known to bind various flavors such as alkanones, 22 esters, 29 methyl ketones, alcohols, 61 and lactones 9 reversibly through hydrophobic interactions. Caseins are less ordered and more flexible than the globular whey proteins that have secondary and tertiary structure.
Flavor retention depends on aroma compounds and the protein content, as was the case for the other proteins. For a homologous series of ethyl esters ethyl acetate, butanoate, and hexanoate , Landy et al. Fares et al. The binding behavior of diacetyl is in agreement with findings of Landy et al. In another study performed by Le Thanh et al. Soy protein consists of four protein fractions, 2S, 7S, 11S, and 15S, according to their Svedberg units.
Gremli and co-workers used the headspace sampling method along with what they named high vacuum transfer method and investigated flavor interactions with soy protein; unsaturated aldehydes strongly interact a percentage is permanently bound due to irreversible bonds compared to that of saturated ones.
By using the micropartitioning method, Li et al. In food products such as ice cream, beverages, jellies, and sauces, carbohydrates are used as sweeteners, thickeners, stabilizers, and gelling agents. The impact of carbohydrates on aroma compounds is quite diverse and difficult to predict because they are able to induce both retention and release effects depending on the conditions used and on the actual flavor molecules.
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In expresso coffee beverages, the addition of sucrose, fructose, or lactose was shown to lead to a significant release of some furan compounds and a lower release of pyrazines, whereas in ready-to-drink coffee, the presence of sugars induced either no change or a retention effect depending on the sugar type. Even though salting-out should not be excluded, Paravisini and Guichard believe that retention can be a result of interactions between other nonvolatile compounds and aroma compounds. Bredie et al.
The activity of flavors with low solubility is much more affected by the addition of sugars.
Ethanol odor is described as sweet, 14 and the concentration ranges from 2. Bakker et al. Although most foods do not contain large amounts of salt, it can still also be relevant as some salts have much greater effects than others e. We mention here a number of effects that were reported to be complete. They found that NaCl and Na 2 So 4 increased the activity coefficient of 2-nonanone, leading to its removal from the protein phase to the salt solution.
From the above it is clear that salts can have various effects starting from a direct effect on the activity of flavor components present in the water phase depending on their solubility to indirect effects, mostly on proteins. Salt can influence charges of binding sites for flavors, lead to exposure of more hydrophobic patches, and even lead to aggregation of proteins.
All these effects can influence the release and retention of flavors, and what we see in the literature is that often the more complex explanations are preferred while overlooking the direct thermodynamic effects on activity, which is a true omission. Viscosity is an internal friction of a fluid and acts on molecular diffusion as suggested by the Stokes—Einstein and Wilke—Chang equations. In general, highly volatile flavors are most affected by viscosity compared to that of less volatile ones, 70 which is logical because highly volatile compounds hardly experience resistance from the gas phase, and the movement across the liquid phase is rate-limiting for mass transfer.
Marin et al. Hansson et al. Starting from the penetration theory, it is clear that the diffusion coefficient is influenced by viscosity, 7 and this is the case for both molecular and eddy diffusion, which is a complex matter because diffusion of small molecules does not obey the Stokes—Einstein relation. The macroscopic viscosity of the xanthan solutions measured at low shear rates is much higher than that of water, but the sugar molecules can pass through the pores rather unhindered. Temperature affects retention of aroma compounds either directly or indirectly. At higher temperature, more flavor will be found in the headspace, which is a direct effect.
Binding of hydrocarbons by proteins was investigated by Mohammadzadeh et al. A flavor will partition between liquid and gas 2nd panel , and this partitioning can be influenced by the presence of small components 1st panel that affect the chemical activity of the flavor. When introducing a binder such as protein, depending on its state native or denatured , the flavor will bind more or less to it while obeying sorption relations 3rd panel , whereas introduction of an additional phase 4th panel such as oil will lead to redistribution of the flavor over all available phases depending on the partitioning coefficients.
Schematic representation of the effect of different beverage ingredients on the partition coefficient of flavors. Although many investigations have been done on flavors, application of models in food design is still a step to take.
Flavour Matrix Interactions
We have shown that there are ample methods, thermodynamic insights, and kinetic models. We think that the theoretical background is not used that often due to the peculiarities of the components: they are mostly present at a very low concentration, and the models are validated for conditions in which the ratio of components is not that extreme. This is also linked to the analysis threshold that can induce a relatively large measurement error at the low flavor concentrations in foods.
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To that needs to be added that, even the smallest loss of flavor to, e. We want to stress that the methods that are standardly used to derive parameter values as described in that section , either through linearization in a log plot or taking reciprocal values, are very prone to small differences in concentration. For example, in a reciprocal plot, those measurements that are done at low concentration give a lot of weight to the parameter values that are derived from, for example, the slope because they would be positioned at the high end of the x -axis.
Because these concentrations are also prone to the highest experimental error often in the range as the measured values , this can very rapidly lead to misinterpretation. Because of these aspects, we recommend the use of fitting procedures that are nonlinear and are directly applied to measured data. This is a well-established fact in, for example, enzyme kinetics research in which linearization was traditionally used in the Lineweaver—Burke approach, which leads to over- and underestimation of parameters, whereas this does not occur using a nonlinear approach.
We already mentioned the analysis threshold, and we think that this is an undervalued aspect of flavor research, especially in combination with interaction analysis that makes the situation as described above even more complex. The concentrations that are to be measured will in most cases be lower than in a system that contains liquids and flavor, which puts even more relevance to the measurement method.
It cannot be ignored that this may also have led to misinterpretation of parameter values and consequently models that are unable to capture the observed release behavior.
We thoroughly believe that more attention needs to be paid to how concentrations are measured and their influence on parameter values and model predictions. National Center for Biotechnology Information , U. Journal of Agricultural and Food Chemistry. J Agric Food Chem. Published online Sep 6. Author information Article notes Copyright and License information Disclaimer. Open in a separate window. Keywords: aqueous food, experimental method, flavor release, modeling. Introduction Aroma, taste, texture, and mouthfeel all contribute to the perception of flavors.
Methods to Determine Flavor Retention Thermodynamics and transport phenomena can be investigated experimentally or mathematically to predict equilibrium and kinetics of flavor—matrix interactions.
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Experimental Approach Flavor behavior can be assessed by sensory or instrumental analysis. Dynamic Headspace DHS In this method, volatiles are continuously removed from the headspace by sweeping with an inert gas or taking multiple samples in time, leading to depletion of the matrix. Batch Stripping This method is used if direct gas-phase analysis is not possible. Figure 1. Equilibrium Dialysis This is one of the oldest methods; 40 two cells of equal volume separated by a membrane are filled with, e.
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Data Analysis In most methods mentioned earlier, gas chromatography is used to measure headspace composition. Predictive Approach Various modeling approaches have been successfully applied; here, we focus on phase equilibria and mass transfer starting with the partition coefficient that underlies both. Phase Equilibrium Buttery et al. Temperature, Pressure, and Phase Composition We discuss these factors together because they are linked: equilibrium is established when the chemical potential of a component in the two phases is equal.
Interfacial Mass Transfer Transfer of flavors from the aqueous phase to either air or another liquid phase such as saliva can be described using theoretical concepts from chemical engineering. Figure 2. The Two-Film Theory In this theory, it is assumed that turbulence creates concentration uniformity in gas and product while bringing molecules close to the interface where eddies die out and form a laminar stagnant region where the resistance to transfer is located.