Response surface methodology (RSM) was used to determine optimum extraction conditions for yield, gelling temperature, melting temperature and apparent viscosity of native agar from the red alga Hydropuntia cornea. Two independent variables were selected during extraction, temperature (80, 90 and 100 degrees C) and time (2, 3 and 4 h). The extraction procedure using 100 degrees C and 3 It produced the greatest yield (43.3%), the greatest gelling temperature (32 degrees C and the greatest melting temperature (78 degrees C). The extraction using 65 'C and 4 h produced the optimum statistical apparent viscosity (80.73 cPs), though agar yield under these conditions had low quality for industrial purposes. Temperature and time do not affect melting temperature, but do play an important role in gelling temperature. From the independent variables studied, extraction temperature is most important in producing an increase in yield, and time is the only variable that contributes significantly to increasing viscosity. Most of the physicochemical properties found in the native agar from H. cornea extracted at 100 degrees C/3 h were similar to commercial samples. These findings suggest the feasibility of using this colloid in spreads and soft-texture food products. (c) 2006 Elsevier Ltd. All rights reserved.