Cross-Linking Activity of Ethanolic Coconut Husk Extract Toward Sardine (Sardinella albella) Muscle Proteins

Abstract

Effects of ethanolic coconut husk extract (ECHE) at various levels (0–0.03%, based on protein content) on the heat-induced aggregation of natural actomyosin (NAM), extracted from sardine (Sardinella albella) muscle, were studied. During heating from 20 to 90C, the NAM solution showed increased turbidity, surface hydrophobicity, and disulfide bond content. Aggregation was more pronounced as ECHE concentration increased (P < 0.05), while protein solubility and total sulfhydryl groups decreased (P < 0.05). Furthermore, the Ca2+-ATPase activity of NAM decreased in the presence of ECHE, during heating up to 40C. Zeta potential analysis revealed that NAM became less negatively charged with the increasing amount of ECHE added (P < 0.05). Cross-linking of protein strands during heating was enhanced by the presence of ECHE, as evidenced by increased G′, and particle size, and denser aggregates. Thus, ECHE could serve as a cross-linking agent for fish muscle proteins. Practical Applications Coconut husk is an underutilized product from coconut processing, and generally contains several phenolic compounds including tannic acid, which acts as a protein cross-linker. Coconut husk extract could therefore increase the cross-linking of proteins, thereby enhancing the strength of surimi gel. Alternatively, coconut husk extract could be used as a new natural protein cross-linker to improve the properties of surimi as well as other muscle foods.