Abstract:
Actomyosin, a myofibrillar complexed protein of fish muscle was isolated from whitefish (Coregonus clupeaformis) by solubilization in 0.04 M Na2HPO4 with 0.5 M NaCl, pH 7.2 and hydrophobic out precipitation. This protein could be formed into discrete fibers when pumped through a 0.8 mm orifice into a 95% ethanol coagulating bath, adjusted to pH 4.5 with acetic acid. Prior to fiber formation, the protein extract had to be adjusted to a pH of approximately 8.0 to facilitate coagulation. A modification of the basic surimi manufacturing process was used to prepare three intermediate protein mince bases, varying in the number of wash cycles employed. Mince bases subjected to either two, four or six wash cycles were frozen at -40oC and periodically tested over 48 weeks of storage. The standard protein extraction procedure was used to measure the possible change in the extractability of fish actomyosin with time. Changes in extract yield and protein recovery were determined by measuring the dry weight of the starting material and recovered extract along with their total nitrogen content. Significant changes in extract yield and protein recovery occurred throughout the 48 weeks of storage, but no major trends in insolubility were apparent. Frozen storage at -40oC seemed to retard freeze denaturation, however, a decrease in fiber forming capacity of the protein occurred with time. Step-wise modification of the major steps in the standard extraction procedure was carried out to maximize the recoverable protein and minimize the time of preparation, while producing a protein extract capable of forming strong fibers around pH 8.0. To optimize the standard isolation method, the parameters considered included the overall homogenization procedure, the reduction in the overall extraction time, the optimum buffer to fish ratio and dilution volume for protein precipitation. By omitting the 24 hour stirring period, the procedure time was reduced to one half, while the protein recovery (66.20%) and fiber forming capability of the extract were still satisfactory. The influence of pH on the conformational properties of actomyosin were monitored by the Bohlin VOR Rheometer and the Differential Scanning Calorimeter. The protein extract was adjusted to pH intervals of approximately 0.5 units from the original extract pH (approximately 7.2) to pH 9.0 with 1 N NaOH. Since preliminary studies revealed changes in the protein over a two day period, the study was conducted over two consecutive days, in order to monitor these potential changes. Intact samples were used to observe the rheological properties of the extract. For observing the thermal properties, the adjusted protein was first freeze dried then prepared as a 15% (w.w) slurry with saline buffer...
