Protein with emulsifiers

Deamidation of soy and other seed meal proteins by hydrolysis of the amide bond, and minimization of the hydrolysis of peptide bonds, improves functional properties of these products. For example, treatment of soy protein with dilute (0.05 A/) HCl, with or without a cation-exchange resin (Dowex 50) as a catalyst (133), with anions such as bicarbonate, phosphate, or chloride at pH 8.0 (134), or with peptide glutaminase at pH 7.0 (135), improved solubiHty, whipabiHty, water binding, and emulsifying properties. 

While partial substitution of egg with emulsifiers is possible there is no viable complete replacement. The most promising egg replacers are enzyme-modified soy proteins. 

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. 

Emulsifying activity index (EAI) is a measure of the ability of protein to emulsify oil, which depends on solubility, size, charge, and surface activity of the protein molecules. The effect of proteolysis with pronase E on EAI of the modified protein was relatively insignificant (Figure 6) However, deamidation appeared to enhance EAI, especially at pH values more basic than the isoelectric point (pH 4.7). 

Kuehler and Stine (43) studied the functional properties of whey protein with respect to emulsifying capacity as affected by treatment with three proteolytic enzymes. Two microbial proteases and pepsin were examined. The emulsion capacity decreased as proteolysis continued, suggesting that there is an optimum mean molecular size of the whey proteins contributing to emulsification. 

Advantages Surface hydrophobicity is often positively correlated with emulsifying and foaming properties of a protein. 

Figure 8 Air bubbles in ice cream (a). Interface (arrows) between a large air bubble (A) and water phase (W) in an ice cream sample without emulsifier. There is very little adsorption of fat globules to the air-water interface, which is stabilized by a thin protein film only, (b) Corresponding structures in an ice cream with emulsifier (saturated mono-diglycerides). Fat globules interact strongly with the air-water interface. Reprinted from reference 23, p 242, courtesy of Marcel Dekker Inc.

Figure 18 Interfaciai tension of sunflower oil/water with and without protein (0.25% skimmed milk) in the water phase, and with and without 0.1% emulsifier (saturated monodiglyceride) in the oil phase. The two-phase systems were heated to 40°C for 1 hour, cooled to 5°C and reheated again to 40°C. Symbols O = Oil W = Water P = Protein E = Emulsifier. Reproduced from reference44, courtesy of The American Institute of Chemical Engineers 1990 AlChE. All rights reserved.

Monoglycerides and mono-diglycerides have low HLB values and cannot form micelles. They build up a multi-layer at the surface, resulting in a constantly decreasing surface tension as their concentration increases. However, in systems with proteins such as fat-free ice cream mixes, these emulsifiers behave as if they have a CMC. A possible explanation for this observation is that the unbound emulsifier in the fat-free mix is in equilibrium with the protein-bound emulsifier. Above a certain concentration of emulsifier in the mix, any surplus of emulsifier will adhere to the protein in the water phase after the surface has been saturated. The unadsorbed emulsifier is seen as very small crystals less than 200 nm by electron microscopy analysis4. ... 

The Alkylglycosides (AGs) and Sucrose esters of fatty acids (SEFAs) are families of nonionic glycosurfactants that have been used for their ability to gently extract membrane proteins with a minimal loss of functionality. These compounds can be synthesized and purified economically, with a worldwide production of thousands of tons per year. Chemically, AGs and SEFAs are a group of uncharged amphipathic compounds that consist of an aliphatic hydrocarbon chain attached to a sugar moiety. Certain AGs and SEFAs such as dodecanoyl sucrose have enjoyed widespread use as food-grade emulsifiers and in cosmetic preparations. 

Hydrolysis of proteins has marked effects on their emulsifying properties. Hydrolyzed whey protein with a degree of hydrolysis of between 10% and 20% had good emulsifying properties (Dalgleish and Singh,... 

Generally, all soluble immunogens or protein-hapten conjugates are mixed with, emulsified in or adsorbed onto adjuvants. The most widespread adjuvants are (i) Freund s adjuvants (ii) aluminum salts and bentonite (iii) methylated bovine serum albumin and, (iv) heat-inactivated Bordetella pertussis. 

Introduction of additional negative charge into proteins by reaction with dicarboxylic anhydrides resulted in an increased solubility in neutral and weak alkaline aqueous solutions [11-13], A positive correlation between solubility and the ability of a protein to emulsify has been documented by some authors [59-62], An increase in protein solubility would encourage a rapid migration to and adsorption of the protein at the water-oil interface. The adsorption would, in turn, lower the interfacial tension between the water and the oil and stabilize the emulsion [63 J. In fact, improved emulsifying properties have been found after succinylation or citraconylation of a large number of food proteins such as myofibrillar fish proteins [10, fish protein... 

Kato et al. [54,55] reported using the proteases papain, pronase E, and chymotrypsin for the deamidation of food proteins, and Kato et al. [56] later reported deamidation of selected plant and animal proteins with chymotrypsin immobilized on controlled pore glass. The reactions were carried out at alkaline pH (pH 10) and 20°C and resulted in 5 to 20% deamidation with up to 8% peptide bond hydrolysis. Functional properties of proteins thus deamidated showed increased solubility and emulsifying and foaming properties. Enzymatic... 

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