Soy protein solubility

Taste Evaluation. The four hydrolysates produced in pilot plant were evaluated for bitter taste by the laboratory s taste panel. Tasting took place in the taste panel room which is equipped with separate booths, and the panel has been selected and trained specially for discrimination of bitterness. The panel was instructed to rank two samples and four bitter-tasting standards, containing 20, 40, 80, and 160 ppm quinine hydrochloride dissolved in non-bitter iso-electric soluble soy protein hydrolysate (5, 6). 20 ppm quinine hydrochloride in this solvent had in previous experiments been established as the panel s threshold value. The protein (N x 6.25) concentration in the samples and standards was 4.0% and pH was adjusted to 6.5 with 4 N NaOH or 6 N HC1. 

An industrial process has been developed for production of isoelectric soluble soy protein hydrolysate with no bitterness and a bland taste (13). The raw material may be acid washed soy white flakes, soy protein concentrate or soy protein isolate. The raw material is hydrolyzed by the alkaline protease ALCALASE to a specified degree of hydrolysis using the pH-stat at pH 8.0... 

Figure 8. Flow sheet production of a nonbitter, soluble soy protein hydrolysate suitable for incorporation into soft drinks and other low pH foods.

As described previously in the present publication, we have developed a batch process for producing isoelectric soluble soy protein hydrolysate (ISSPH) with a bland taste. From studies of the kinetics of the hydrolysis reaction, which takes place in this process, we have come to the conclusion that the reaction is adequately controlled by keeping pH constant and monitoring DH. Termination of the reaction at a preset value of DH ensures a reproducible, optimal organoleptic quality of the product. 

Watanabe and Arai wrote an excellent review on the properties of enzymatically modified proteins and compared the chemical and enzymatic processes of various proteins [135]. Enzymatic processes can normally be carried out under milder and therefore safer experimental conditions than conventional chemical processes. Proteolytic enzymes have been used on proteins to improve their solubility soy protein, leaf protein concentrates, fish protein concentrates, meat proteins, egg proteins, milk proteins, and blood proteins. Special attention was given to caseins, gelatins, egg proteins, and cereals. Partial hydrolysis of these proteins under well-controlled conditions can produce emulsifying and whipping agents... 

Commercial soy protein concentrates typically contain 70 to 72% cmde protein, ie, nitrogen x 6.25, dry wt basis. Soy protein isolates are prepared from desolventhed, defatted flakes. A three-stage aqueous countercurrent extraction at pH 8.5 is used to disperse proteins and dissolve water-soluble constituents. Centrifugation then removes the extracted flakes, and the protein is precipitated from the aqueous phase by acidifying with HCl at pH 4.5. 

Figure 2. Relationship between calcium solubility and pH after complete digestion for four soy products. Key solid line, full-fat soy flour long-dashed line, soy protein isolate short-dashed line, soy protein concentrate and dotted line, defatted soy flour...

Table I. Effects of 17o Orthophosphate, Tripolyphosphate, and Hexametaphosphate on Calcium Solubility from Ground Beef or Soy Protein Concentrate Subjected to In Vitro Gastric and Gastrointestinal Digestions...

The binders vary quite widely—the most common being starch, soy protein and latexes in conjunction with other soluble polymers. Styrene-butadiene latexes have been the most popular but ethylene-vinyl acetate binders are also used. The method of polymer synthesis provides a way of modifying the properties of the latex. For example, adjustment of the ratio of styrene butadiene in the co-polymer gives rise to different degrees of softness or hardness. This property has a profound influence on the quality of the coating. It is also possible to co-polymerise monomers so as to introduce, for example, carboxy groups on to the surface of the latex particle which in turn assist in... 

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. 

Advances in soy protein processing technology have allowed extensive diversification of protein product applications. More sophisticated soy protein products now manufactured have more functionality, better performance, more consistency and better flavor than commercially available defatted soy flour and grits (50% protein dry basis). Among these products are improved textured soy flours, concentrates, and isolates (50%, 70% and 90% protein dry basis, respectfully), functional and non-functional soy protein concentrates (70% protein dry basis) and highly soluble, highly functional isolated soy proteins (90% protein dry basis) (6-8 14-18). 

Textured Soy Proteins. Textured vegetable proteins, primarily textured flours and concentrates (50% protein and 70% protein, dry basis, respectfully) are widely used in the processed meat industry to provide meat-like structure and reduce ingredient costs (3-6, 9-10). Available in a variety of sizes, shapes, colored or uncolored, flavored or unflavored, fortified or unfortified, textured soy proteins can resemble any basic meat ingredient. Beef, pork, seafood and poultry applications are possible 03, 4-7, 15, 19) Proper protein selection and hydration is critical to achieving superior finished product quality. Textured proteins have virtually no solubility and, thus, no ability to penetrate into whole muscle tissue Therefore, textured soy proteins are inherently restricted to coarse ground (e.g. sausage) or fine emulsion (e.g. weiners and bologna) products, and comminuted and reformed (i.e. restructured) meat products. None are used in whole muscle absorption or injection applications (2-4, 6, 11). 

Soy Protein Concentrates. Both non-functional (low or no solubility) and functional (good solubility, emulsification capacity, and dispersibility) soy protein concentrates (70% protein, dry basis) are commercially available for use in meat products (2-4, 6, j), 15) Normally, a highly functional product with no harsh or bitter flavors is desirable. When used to replace lean meat, non-hydrated concentrate can be used at levels up to 6-7% in finished nonspecific emulsion meats Higher replacement levels or formulas with specific cost/nutrition requirements may use soy protein concentrate with a judicious amount of textured soy protein (6). Excellent yields, cost savings, texture, flavor and nutrient profiles are possible. However, most soy protein concentrates lack sufficient solubility or sufficiently low viscosities to be used in brines for absorption or injection into whole muscle tissue. When legal standards for protein content exist (13), more concentrate must be used to achieve legal minimums. Brine viscosities increase and uniform distribution of brine components throughout the specific whole muscle piece is restricted. Finished product appearance and flavor are easily compromised. Thus, use of soy protein concentrates in whole muscle applications is limited. 

Isolated Soy Proteins. Isolated soy proteins (90% protein dry basis) are highly dispersible, highly soluble, highly functional soy products (8 9, H > 17, 18) Designed to replace a portion of... 

Furthermore, addition of lysine to soy protein markedly increased the rate of lipid absorption and addition of arginine to casein slowed lipid absorption. The slowed absorption of lipids in animals fed soy protein is similar to that reported for soluble fibers such as pectin and guar gum that act to lower serum cholesterol concentrations in a number of animal species, including humans. 

The present study was conducted to obtain additional information on changes in soy protein subunits during limited proteolysis. Enzymatic soy protein deamidation that occurred, in addition to limited proteolysis, during germination of soybean seeds was investigated. The effects of proteolysis and deamidation on solubility and emulsifying activity were compared. Phosphorylation of soy protein with a commercially available protein kinase and its effects on subsequent changes in functional properties of the protein were also studied. 

Effects of Protein Modifioation on Functionality. Figure 5 shows the solubility-pH profiles of soy proteins modified by pronase E. Solubility in the pH range of 3 to 8 increased initially with increased proteolysis. 

The effect of phosphorylation at 13 /xmoles/g protein on functional properties was minimal. Both solubility and EAI of the phosphorylated protein were slightly higher, compared to those of intact protein (not shown). Phosphorylation with protein kinase from bovine cardiac muscle is restricted by the limited number of potential phosphorylation sites in soy proteins. Experiments are... 

Figure 5. Solubility of soy proteins as a function of pH. Intact soy protein (O) soy protein proteolyzed with pronase E for 1 h ( ), 2 h (V), and 3 h (A) deamidated soy protein ( ).

In limited proteolysis, proteases such as pronase E hydrolyzed the 7S subunits of soy proteins more than the IIS subunits, resulting in enhanced protein solubility. Deamidation with relatively insignificant peptide bond hydrolysis that occurred during the germination of soybeans imparted to the storage protein improved solubility and emulsifying activity. On the other hand, the incorporation of phosphorus in soy proteins by the protein kinase cAMPdPK was too low to effect significant... 

In line with the general increase in thermodynamic affinity of surfactant-protein particles for the aqueous medium, a marked increase in the solubility of soy protein has been observed in response to interactions with SDS (Malhotra and Coupland, 2004). In contrast, however, the self-assembly of the globular protein legumin, as modified by the anionic... 

Malhotra, A., Coupland, J.N. (2004). The effect of surfactants on the solubility, zeta potential, and viscosity of soy protein isolates. Food Hydrocolloids, 18, 101-108. 

Modification of Raw Materials. In order to vary the protein and soluble sugar contents, portions of soy flour (Extra Acted Soy Flour 200-1) were replaced with various amounts of sucrose and soy protein isolate (Promine F). Levels of... 

Microscopic structure of texturized water-extracted soy flour and texturized soy concentrate were quite similar to that of texturized soy flour. Scanning electron microgrpahs showed that water extraction of soy flours had little effect on morphological characteristics of texturized soy products (Figure 10). Solubility of soluble sugars was not affected by texturization, whereas solubility of proteins decreased sharply when soy flour was texturized (Table VII). It appears that soluble sugars did not interact with proteins during texturization. Based upon results of microscopy and solubility studies, it is reasonable to speculate that natural soluble carbohydrates are not required (do not play an important role) in development of texture or stabilization of structure. 

Figure 19. SDS—PAGE patterns (without 2-mE) of various temperature-extruded soy proteins soluble in pH 7.2, 0.01 M phosphate buffer without (1) or with (2) 1% SDS. 7S PSU, 7S protein subunits IIS PSU, IIS protein subunits C, control (unheated soy protein).

Solubility and viscosity are two experimentally measurable properties that can yield information about the functional behavior as well as the physicochemical nature of the proteins. In this chapter, the application of these two measurements to isolated soy proteins and how these measurements can explain the basic physicochemical nature of isolated soy proteins are discussed. 

This observed behavior of soy proteins complicates the definition of soy protein solubility, the comparison of solubility data, and the interpretation of solubility experiments. Because the thermodynamic criteria are not met, protein solubility becomes an operationally defined quantity that depends upon the experimental methods of measurement. A number of different operational definitions have been used to measure protein solubility. Each has its own advantages and disadvantages, and limited utility. This plurality, though often desirable, makes it difficult to compare experimental results. 

Interpretation of solubility data in terms of the forces and the interactions at the molecular level is an even more difficult problem. Because thermodynamic criteria are not met, straightforward, thermodynamic analyses cannot be applied. Further, strict comparison of the results for soy proteins with the results of systems that meet the thermodynamic criteria cannot be justified. However, it may be valid to draw some qualitative insights into the nature of soy protein by making comparisons under favorable circumstances. One such favorable case would be the following hypothetical mechanism... 

Figure 3. The effect of blending on solubility (I). Samples A, B, D, and E are soy protein isolates. Sample C is a commercial sodium caseinate. T is the temperature of the slurry after blending.

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