Water agar-agar equilibrium: determination and correlation of sorption isotherms

Water activity in hygroscopic solids determines the behaviour of many mater ials in storage as well as in drying and freezing operations. Available dat a concerning phycocolloid gels, such as those of agar-agar and derivatives, ape scarce in spite of their interest for pharmacology and the food indust ry. Thus, we have determined the isotherms of adsorption and desorption of agar-water gels by means of a gravimetric procedure, at 25, 40, 60 and 80 d egrees C, determining the effect of temperature on the heat of desorption b y the isosteric heat method, using the Henderson model.