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

Abstract

The effect 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 done for 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 (1064 g cm-2) were obtained at 0.5 h, therefore this time was used for the next experiment. The extraction of both native agar and alkali-treated agar was done for 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 was 2.5 h. The alkali-treated agar obtained with the different alkali-treatment times and extraction times showed a high melting temperature (92.4 to 99.7 ºC) and gelling temperature (35.7 to 39.6 ºC). Native agar was lower in melting temperature (60.2 to 64.1 ºC) and gelling temperature (20.4 to 23.4 ºC). The 3,6-anhydrogalactose content decreased with increasing alkali-treatment time, with the opposite effect during the extraction of native agar and alkali-treated agar.