Effect of alkali treatment time and extraction time on agar from Gracilaria vermiculophylla

The effects of alkali treatment time and extraction time of native agar and alkali treated agar obtained from Gracilaria vermiculophylla were studied. The response characteristics were mainly agar yield and gel strength. Alkali treatment was carried out at 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 h. Agar yield and gel strength decreased with the increase in the time of the alkali treatment. The highest yield (15.3%) and highest gel strength (1,064 g cm^-2) were obtained at 0.5 h, and therefore this time was used for the next experiment. The extraction of both native and alkali treated agars was carried out at 1.5, 2.0, 2.5, and 3.0 h. The best extraction time for alkali treated agar was 1.5 h, and for native agar 2.5 h. The alkali treated agar obtained with the different alkali treatment and extraction times showed higher melting (92.4-99.7°C) and gelling (35.7-39.6°C) temperatures. Native agar was lower in melting (60.2-64.1°C) and gelling (20.4-23.4°C) temperatures. The 3,6-anhydrogalactose content decreased with increasing alkali treatment time, with the opposite effect during the extraction of native and alkali treated agars.