Proteins flavor, undesirable

Soybean concentrate production involves the removal of soluble carbohydrates, peptides, phytates, ash, and substances contributing undesirable flavors from defatted flakes after solvent extraction of the oil. Typical concentrate production processes include moist heat treatment to insolubilize proteins, followed by aqueous extraction of soluble constituents aqueous alcohol extraction and dilute aqueous acid extraction at pH 4.5. 

Soy proteins are used extensively in meat and meat products by the military, the school lunch program and consumers to save money. Their ultimate acceptability is equally dependent upon the nutritional, chemical, sensory and shelf life changes which occur when they are added. Soy proteins in meat products such as ground beef inhibit rancidity, improve tenderness, increase moisture retention, decrease cooking shrink, fat dispersion during cooking and have no important effect on microbiological condition. Concomittantly, inordinate amounts of added soy protein may cause the meat product to be too soft, exhibit an undesirable flavor and may lead to a decreased PER and a deficiency in B-vitamins and trace minerals. In emulsified meat products, soy protein effectively binds water but does not emulsify fat as well as salt soluble muscle protein. Prudent incorporation of plant proteins can result in an improvement of the quality of the meat product with inconsequential adverse effects. 

When structured soy protein fiber was added to fermented salami at 15 or 30% levels, trained sensory panels found the flavor to be undesirable, whereas a 116-member untrained panel found the product containing 30% soy flour to be undesirable in flavor, tenderness and overall desirability (26). The flavor of beef patties containing 20% soy protein flour or concentrate was rated about equal to all beef patties by a 52-member panel, whereas patties containing 30% were scored lower by the panel (6). Berry et al. (7) found the characteristic "soy-like" flavor to be more... 

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. 

WOF is a problem associated with the use of precooked meat products such as roasts and steaks. The term WOF was first used by Tims and Watts (2) to describe the rapid development of oxidized flavors in refiigerated cooked meats. Published evidence indicates that the predominant oxidation catalyst is iron from ntyoglobin and hemoglobin, which becomes available following heat denaturation of the protein moiety of these complexes. The oxidation of the lipids results in the formation of low molecular weight components such as aldehydes, adds, ketones and hydrocarbons which may contribute to undesirable flavor. 

When texturized soy protein was used to replace some of the meat in patties, undesirable off-flavors were released during preparation and consumption of the meat-soy mix (3). The source of these were identified as oxidation products of unsaturated fatty acids. High protein content soy ingredients have mitigated this problem (4j. 

Four major objectives in the chemical modification of food proteins are (a) the blocking of deteriorative reactions (b) improvement of physical properties (c) improvement of properties related to acceptability, such as flavor and color and (d) improvement of nutritional properties. Modifications also may aid the physical separation from crude animal, plant, or microbial material and may inactivate or remove relatively small amounts of undesirable substances. There is considerable interest among food technologists in chemical modification as a means of changing the physical characteristics of proteins to give, e.g., better solu-... 

The present paper reviews some of the undesirable effects resulting from the interaction of flavor constituents, lipids and pigments with proteins. Our laboratory as well as others have contributed to this knowledge. 

The water-extractability of both the 7S and 11S proteins decreases with aging of the soy meal (4). During isoelectric precipitation 15-30% of the globular fraction is denatured and fails to redissolve in neutral buffer (4, 5). As the pH is lowered to 2-3 the 11S component becomes increasingly sensitive to irreversible denaturation. This acid-sensitive fraction not only limits the solubility of such isoelectric protein isolates, and therefore their functional uses, but this fraction may also be responsible for retention of undesirable flavors (5). 

Reactions in proteins and other nitrogenous compounds catalyzed by endogenous enzymes are responsible for desirable and undesirable sensory attributes of foods — color, flavor, and texture — as well as for the development of compounds that are nutritionally beneficial or have detrimental effects on human health. The use of added enzymes or enzyme sources is also an essential part of many traditional methods of food processing. Since the conditions of enzymatic reactions are much milder than those applied in chemical treatments, different added enzymes are being used to an increasing extent to modify the functional properties of food proteins. 

Partial proteolysis of soybean proteins with endopeptidases has been used to remove flavor compounds and related fatty materials from soybean curd and defatted soybean flour (21). Certain soybean protein concentrates possess an undesirable beany and oxidized flavor. Treatment of soybean curd and defatted soybean flour with endopeptidases such as aspergillopeptidase A released off-flavor compounds such as 1-hexanal and 1-hexanol which could be removed from the hydrolysate by solvent extraction. The enzymically digested products had less odor, taste, and color than the starting material and were more stable to oxidative deterioration. 

In enzymic digestions, the structures of the released peptides will, of course, depend upon the specificity of the particular protease. Often the peptides exhibit a very undesirable bitter flavor. For example, Fujimaki et al. (22) have characterized seven bitter peptides in peptic hydrolysates of soybean proteins. Almost all the bitter peptides had leucine at the N or C termini, and the bitterness of the peptides could be reduced by treatment with exopeptidases such as carboxypeptidase A. 

Food proteins, especially those of plant origin, often require modification to achieve desirable functional properties for use as food ingredients. For instance, soy protein has limited water solubility at acid pH, which restricts its use in acidic foods such as coffee whitener and acidic beverages. Improved solubility at acid pH for commercial soy protein isolate can generally be achieved by hydrolysis. However, the hydrolysis has to be carefully controlled, because excessive peptide bond hydrolysis may release bitter peptides, resulting in undesirable off-flavors. Scientists are constantly looking for better and safer methods to improve the functional properties of protein to meet the needs of the food industry. 

As an example of the case where deactivation is advantageous, moist carbon dioxide at conditions of 600 atm, 80°C was found to improve the flavor of soy bean protein and to deactivate peroxidase enzymes that can result in subsequent undesirable oxidation of residual lipids in the protein meal (48) the deactivation of the peroxidase was, thus, beneficial since a better soy bean protein meal product resulted. 

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