Hydration of muscle proteins of Bombay duck (Harpodon nehereus) during acetic acid-induced gelation and characteristics of the gel dispersion

Washed fillets of Bombay duck (Harpodon nehereus), a fish having unusually high moisture content (above 90%), were held overnight in cold, 2% (v/w) aqueous acetic acid, which resulted in gelation associated with a 33% increase in weight due to water uptake by the proteins. Gamma irradiation at 3 kGy or repeated freezing and thawing did not affect protein hydration. The presence of sodium chloride in the acid adversely affected protein hydration. The effects of urea, dithiothreitol and o-phenanthroline on water uptake suggested that the imbibed water was held by non-covalent interactions with the fish proteins. Water homogenates of the gel had higher apparent viscosities than native muscle. Temperature significantly influenced the apparent viscosity of the gel. Unlike water homogenates of washed fish, heating of the gel dispersion at 100 °C did not cause precipitation of the proteins. However, the stability of the proteins in the dispersion was adversely affected by sodium chloride or by increase in pH above 5.0. The acid-induced gel was very weak; its hardness could be enhanced by incorporation of certain food additives.