Protein Flavor Interactions

T O Neill, JE Kinsella. Flavor protein interactions Characteristics of 2-nonanone binding to isolated soy protein fractions. J Food Sd 52 98-101,1987. K Sostmann, E Guichard. Immobilised beta-lactoglobulin on a HPLC-column A rapid way to determine protein/flavor interactions. Food Chem 62 509-513, 1998. 

The problem of developing desirable meat flavor in the presence of vegetable protein has been clearly demonstrated in the literature. Physical measurements after heating a meat model system with soy proteins have shown a dramatic reduction in the concentration of alkyl pyrazine compounds due to interaction with the soy proteins. These interactions have been defined in terms of stoichiometry and binding energies from measurements on pure standards of the methyl pyrazines. 

Flavor Interactions of Proteins with Volatile Compounds... 

The hurdles affecting the shelf life of foods also influence other food properties, including texture. The effects of several physical, chemical, and mechanical treatments should be carefully considered in developing new processes and products. It is not enough to describe the composition of a food product and to determine the conditions and types of unit operation necessary to achieve the required quality. How the major food components, such as water, salt, hydrocolloids, starches, lipids, proteins, flavors, and additives, interact with each other and affect the product quality with respect to microstructure, texture, and appearance should be examined. 

In this chapter we will provide a broad overview of the flavor interactions that may occur in foods considering how flavors interaction with nonvolatiles in foods [6]. Initially the interaction of flavorings with the major food constituents (e.g., lipid, carbohydrates, and proteins) will be discussed. The final section will include some discussion of interactions with minor constituents (e.g., melanoidins, polyphenolics, and high potency sweeteners) as literature permits. The reader is encouraged to go to more detailed reviews included in books edited by Taylor [ 1 ] or symposia proceedings such as Roberts and Taylor [3], Schieberle and Engel [4], Teranishi et al. [2], or Taylor and Mottram [5]. 

Of the food matrix flavor interactions, the effect of fat/oil on flavor release is most understandable and thus predictable. In the case of fat/flavor interactions, the overriding effect is the role fat plays as a flavor solvent. Unlike carbohydrates or proteins where numerous undeflnable chemical interactions come into play, fat has little true chemical interaction, and thus its effect on flavor release is largely quantifiable. (The discussion that follows will look very much like that provided in Chapter 3 where partition coefficients in solvent extraction [and headspace methods] were discussed.)... 

The issues of flavor interactions with proteins are similar to those discussed above for carbohydrateiflavor interactions, i.e., we expect to see chemical interactions and mass transfer effects. However, the effects may be more diverse since proteins offer a much wider range of chemical structures for interaction (e.g., amino acid side chains and terminal ends of proteins as well as hydrophobic pockets. Figure 6.9), and mass transfer must consider both the viscosity and gel structures often associated with proteins. 

In terms of chemical interactions, reversible weak hydrophobic interactions, as well as stronger ionic effects and irreversible covalent bonds, may be formed (e.g., the reaction of aldehydes with the NH2 and SH groups of proteins) between aroma compounds and proteins. The interactions one would expect are influenced by the type and amount of protein (amino acid composition), types of flavoring components. 

When we consider the other chemical interactions (e.g., flavor interactions with carbohydrates, proteins, and high potency sweeteners), we understand that interactions take place but they are so complex that we cannot model them to even attempt to make corrections in the flavorings. Thus, we know that a substitution of one protein for another or one hydrocolloid for another will affect the flavor of a product, but we cannot quantify these effects and therefore make changes in flavor formulations. At this time, we can only expect effects and attempt to deal with them in a less than scientific manner, i.e., empirical efforts. 

Virtual screening applications based on superposition or docking usually contain difficult-to-solve optimization problems with a mixed combinatorial and numerical flavor. The combinatorial aspect results from discrete models of conformational flexibility and molecular interactions. The numerical aspect results from describing the relative orientation of two objects, either two superimposed molecules or a ligand with respect to a protein in docking calculations. Problems of this kind are in most cases hard to solve optimally with reasonable compute resources. Sometimes, the combinatorial and the numerical part of such a problem can be separated and independently solved. For example, several virtual screening tools enumerate the conformational space of a molecule in order to address a major combinatorial part of the problem independently (see for example [199]). Alternatively, heuristic search techniques are used to tackle the problem as a whole. Some of them will be covered in this section. 

The perception of flavor is a fine balance between the sensory input of both desirable and undesirable flavors. It involves a complex series of biochemical and physiological reactions that occur at the cellular and subcellular level (see Chapters 1-3). Final sensory perception or response to the food is regulated by the action and interaction of flavor compounds and their products on two neur networks, the olfactory and gustatory systems or the smell and taste systems, respectively (Figure 1). The major food flavor components involved in the initiation and transduction of the flavor response are the food s lipids, carbohydrates, and proteins, as well as their reaction products. Since proteins and peptides of meat constitute the major chemical components of muscle foods, they will be the major focus of discussion in this chapter. 

Food flavor is governed by many factors, including lipid oxidation and protein degradation. Enzyme-catalyzed oxidation ( ) and autoxidation (2) can substantially alter the flavor q ality of foods. In "addition, protein degradation, whether caused by enzymes, heat, or interactions with other compounds, can also affect flavor characteristics of certain foods (3, 4, ... 

The importance of direct gas chromatography and combined direct GC/MS to the food industry is demonstrated by the analysis of volatile flavor components and contaminants in experimental samples of rice, food blends, and raw and roasted peanuts. By examining these samples, we are able to investigate flavor systems that are probably associated with lipid oxidation, thermal degradation of protein, or protein interactions with other compounds. 

This unconventional approach provides a practical means of eluting, resolving, and identifying volatiles that might impart off-flavors (e.g, volatile components contributed by protein interactions, and external contaminants) in edible protein ingredients. It also provides information to resolve complex flavor problems for processors and plant breeders. 

The major cause of deterioration of food products is lipid oxidation, from which low-molecular-weight, off-flavor compounds are formed. This deterioration is often caused by the oxidation of the unsaturated lipids present in foods. Off-flavor compounds are created when the hydroperoxides, formed during the initial oxidation, are degraded into secondary reaction compounds. Free radicals are also formed which can participate in reactions with secondary products and with proteins. Interactions with the latter can result in carbonyl amino... 

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. 

Proteins are important from the nutritional and technological points of view. Proteins affect every property that characterizes a living organism, and they play different roles in the human body. Proteins are also very important in food technology and are responsible for many food properties. The physical properties of proteins and their interactions with other components contribute significantly to the functional behavior and quality of several food products, such as cheese, bread, and meat products (9). An overview of the functional roles of proteins in different food systems is presented in Table 2. Food preferences by human beings are based not on nutritional quality but on sensory attributes to the food, such as appearance, color, flavor, texture, and... 

During AEDA, interactions between the odorants are not taken into consideration, since every odorant is evaluated individually. Therefore, it may be possible that odorants are recognized which are possibly masked in the food flavor by more potent odorants. Furthermore, the odor activity values only partially reflect the situation in the food, since OAVs are mostly calculated on the basis of odor thresholds of single odorants in pure solvents. However, in the food system, the threshold values may be influenced by nonvolatile components such as lipids, sugars or proteins. The following examples will indicate that systematic sensory model studies are important further steps in evaluating the contribution of single odorants to the overall food aroma. 

Phenolic compounds also contribute directly to the flavor due to their astrin-gency and bitter taste characteristics [11]. In fact, astringency is believed to be due to the interaction between tannins and salivary proteins, resulting in the formation of protein-tannin aggregates in the mouth, as discussed in more detail below [12-15],... 

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