Preparation of hydroxypropyl agars and their properties.

A series of hydroxypropyl agars (HPAs) with different hydroxypropyl molar substitution (MS) were prepared and their physicochemical properties were characterized. After hydroxypropylation, the dissolving temperature, the gelling temperature, the gel melting temperature, the gel strength, and the thermal stability of agar all decreased except that its hygroscopicity increased. The gel skeleton structures of raw agar and HPAs were all of the porous network structures, but the pores of gel skeleton structure of HPAs became smaller and denser.