Proteins stability succinylation

Additives had substantial effects on the aeration properties of bromelain-modified succinylated fish protein (50). Foam volume was increased with up to 2% sodium chloride in the system however there was a decrease in foam stability when greater than 0.3% salt was used. Sucrose, at concentrations up to 50%, increased foam stability. When fat was added to treated fish protein dispersions... 

Fig. 18. Effects of acetylation or succinylation of iron ovotransferrin on stabilities of complexes in urea. Acetylated was40% modified succinylated was60—70% modified. General conditions are described in text. Reactions were performed withh 0.5% protein in 0.005 m NaHCOs, 0.001 m sodium citrate, 0.001 m FeNH4(S04)2 at pH 8.4, and 0—8 m urea. Optical densities were determined at 470 mp A — A. unmodified (control) iron ovotransferrin in 0—8 m urea for 1 hour —, acetylated or succinylated ovotransferrin in 0—8 m urea immediately after mixing (zero time) O—O. acetylated or succinylated ovotransferrin in 0—8 m urea for 1 hour. (Biochemistry 4, 998 [1965]).

Several workers have chemically modified milk proteins ( c-casein, casein) to determine the chemical basis for the stabilization of the casein micelle by c-casein and to elucidate the mechanism of rennin action (35,36). Creamer et al. (37) made several derivatives of sodium caseinate and showed their improved solubility. In preliminary feeding trials in which succinylated casein was the only protein source, supplementation with lysine was required for the normal growth of rats. 

Isolation of Proteins with a Reduced Nucleic Acid Level. The procedure is virtually identical to that described for succinylation of yeast proteins (87). In a typical experiment proteins, together with NA, were extracted from the disrupted yeast cells at pH 8.5-9.0 and centrifuged at 15,000 rpm for 30 min at 5°C. Citraconic anhydride then was added in small increments to the supernatant with constant stirring while the pH was maintained between 8.0-8.5 by adding 3.5IV NaOH. After the stabilization of the pH, the pH of the solution was decreased to 4.2 to precipitate the proteins. Protein then was separated by centrifugation, dissolved in water (pH adjusted 8.5), dialyzed extensively against water (pH 8.5) at 5°C, and lyophilized. 

Succinylation increased the emulsifying activity and emulsion stability of soy and cottonseed proteins (12,38). The pH emulsifying capacity profiles of succinylated protein paralleled those of the solubility curves and in all cases the succinylated protein had about double the emulsifying capacity of the unmodified... 

The viscosity of modified peanut protein increased with the extent of succinylation (Table V) and this was most pronounced at high concentrations of the protein (43,45). Despite the increased electronegativity of succinylated proteins the addition of calcium to dilute dispersions resulted in no apparent increase in viscosity (12,37). Melnychyn and Stapely (47) noted a reduced viscosity in succinylated vegetable proteins. They noted the thermal stability of these proteins when heated to 100°C and suggested their use for coffee whiteners. 

The emulsifying capacity of the yeast proteins was progressively improved with the extent of succinylation (Table IX) as measured by the turbidimetric technique (89). The modified yeast proteins had excellent emulsifying activities compared to several other common proteins. McElwain et al. (88) observed that succinylation of yeast protein increased emulsion viscosity but decreased emulsion stability. 

Grant (58), single-cell protein concentrates by McElwain et al. (59), and fish protein by Groninger and Miller (60) and Chen et al. (61). Succinylated fish myofibrillar protein had rapid rehydration and good dispersion characteristics at neutral pH (60). Succinylation of fish protein concentrate improved its emulsifying capacity and emulsion stability (61). 

Groninger and Miller (28) succinylated myofibrillar fish protein and then treated the succinylated proteins with bromelain to obtain an acylated mixture of polypeptides. Both the extents of succinylation and enzymic hydrolysis affected the volume of foam of the whipped protein. Optimum foam volume and stability occurred when 54% of the c-amino groups of lysine were acylated and the succinylated protein was mildly hydrolyzed at pH 7, 25°C for 10 min using a bromelain protein ratio of 1 100 (w/w). 

Table IV shows the effect of protein concentration on foam volume and stability compared with egg white and soy isolate. Foam volumes for the hydrolyzed, succinlyated fish protein were highest at 3 g protein/ 100 ml, but decreased at 4 g/100 ml. Compared with egg white and soy isolate, the hydrolyzed succinylated fish protein yielded a more stable, but less voluminous foam.

Table IV. Effect of Protein Concentration on Foam Stability and Comparison of the Stabilities of the Foam of Egg White and Soy with That of Hydrolyzed, Succinylated Protein (28)...

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... 

Multiple regression analysis performed for succinylated rapeseed protein isolates indicated that emulsification activity was related to protein solubility, hydrophobicity, zeta potential, and flow behavior of aqueous dispersions of the proteins. Emulsion stability was affected by protein solubility, zeta potential, apparent viscosity of protein dispersions, and difference in density between aqueous and oil phases [76],... 

Figure 6 Emulsifying activity (EA, ) and emulsion stability (ES, ) of native and succinylated faba bean protein isolates in dependence on the degree of /V-succinylation. (From Ref. 18.)...

While foaming is favored by increased viscosity, hydrophobicity, and solubility, the increase of net charge density caused by succinylation tends to decrease foam stability (FS), since it prevents optimum protein-protein interactions required in a continuous film around air bubbles. Therefore a number of succinylated proteins showed a drop of the FS with increasing degree of modification. This was reported for protein preparations from faba beans [86], peas [72], cottonseed [69], oat [66], and cheese whey protein concentrate [88] for instance. The unfavorable charge effect of succinylation can be overcome by foaming at sufficiently high protein concentration, as shown for faba bean protein isolates [86] and napin from rapeseed [84]. 

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