Changes in the Physical Properties and Composition of Fish Bone during Cooking in an Acetic Acid Solution and Green Tea Infusion

Abstract

Changes in the physical properties and composition of fish bones were examined after cooking them in different solutions to render them edible. Bones of horse mackerel were cooked in either a 1% acetic acid solution, green tea infusion or deionized water at atmospheric pressure or under pressure. The breaking strength of the bones was measured with a rheometer, and the calcium and crude protein contents were measured by atomic absorption spectrometry and by the Kjeldahl method, respectively. Bone apatite was examined by an X-ray diffraction analysis. The breaking energy value of the bones decreased with increasing cooking time; the decrease was greatest in the 1% acetic acid solution. Crude protein and calcium were eluted from the bones into the 1% acetic acid solution during cooking. The apatite crystal of the cooked fish bones was different from that of the untreated fish bones, a long cooking time giving a crystal resembling that of pure hydroxyapatite. Softening of the fish bones during cooking can probably be explained by the elution of crude protein and by the consequent change in the bone structure.