Some Functional Properties of Succinylated Proteins from Fish Protein Concentrate

Abstract

Fish protein concentrate (FPC) prepared from hake extracted with hot isopropanol was partially solubilized by succinylation with succinic anhydride followed by heating at pH 9 for 30 min. The yield was 73% of the FPC, and the degree of succinylation of this protein isolate was 90%. FPC was also extracted at a high pH of 11.5; the yield was approximately 50%. Racemization was not detected in either the succinylated protein or the protein extracted at high pH. Pancreatin digestion of protein isolates resulted in release of 4.1 and 41.5% of the total lysine from succinylated fish protein and fish protein extracted at high pH, respectively, indicating a low apparent digestibility for the succinylated protein. The isoelectric point of succinylated fish protein was about 4, whereas that of fish protein extracted at high pH was about 5. Furthermore, fish protein extracted at high pH was relatively soluble below pH 4. Succinylated fish protein generally had a greater emulsion capacity and stability than did fish protein extracted at high pH which in turn had a greater emulsion capacity and stability than did gelatin. Addition of carboxymethyl cellulose decreased stability of the emulsion, but increased the emulsion activity. Succinylated fish protein formed a strong cheese-like curd upon quiescent acidification, whereas fish protein extracted at a high pH formed a very fragile curd. With addition of calcium ion, the curd tension of succinylated fish protein decreased, and the texture of the curd was smoother. Calcium ion precipitated the fish protein extract at high pH.