Abstract

A fundamental study on quantitative extraction of actomyosin from frozen ‘surimi’ (fish paste) was made. A determination was achieved by measuring Ca2+-ATPase specific activity and protein content after exhaustively extracting actomyosin from frozen surimi. The quantitative method finally used was as follows: 10g of mined frozen surimi was washed twice with cold 0.05 μ phosphate buffer, pH 7.5. The residue was then homogenized for 3min in 30ml of cold 0.8 M KCI, pH 7.0 at about 6, 000 rpm by homogenizer (Nihon Seiki K. K. type HB). Extraction was carried out for 2 hr after washing out homogenate by adding another 20ml of cold 0.8 M KCI, pH 7.0. Extracted protein was collected by centrifugation at 7, 000×g for 20 min and diluted by the addition of 10 volumes of cold water. The precipitated protein was collected, dissolved into 0.6 M KCI, pH 6.8, and dialyzed against the same solution. The precipitated protein which separated by centrifugation at 15, 000×g for 60min, was redissolved into 0.6 M KCI, pH 6.8 by grinding up with a magnetic stirrer (‘precipitated protein’ fraction). The content of protein and Ca2+-ATPase specific activity in the supernatant and precipitated protein fractions were measured and the amount of actomyosin in frozen surimi could be determined as the sum of Ca2+-ATPase total activity (μ moles Pi liberated/min/10g of surimi) in both fractions. It was suggested that the precipitated protein fraction could contain denatured forms (modified molecules) of actomyosin, since the properties of ATPase activity in the fraction were very similar to those of native actomyosin.

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