Improvement of yield and quality of agar from Gracilaria edulis (Gmelin) Silva

Optimum levels of alkali/acid and thermal manipulations during extraction of agar were determined to increase the yield and quality of agar from red seaweed Gracilaria edulis (Gmelin) Silva. Pre-soaking of dry weeds in water for 2 h increased the yield by 11.44%, but did not improve the gel strength. Pre-soaking for 12 h increased gel strength and melting temperature considerably, but not the yield. Pre-soaking of dry weeds in 1.ON NaOH resulted in gel strength of 135 g.cm ^-2. Pre-soaking of dried weeds with 0.5N and 1.ON HCl even at higher temperature showed improvement neither in yield nor in the quality of agar and also resulted in hydrolysis of agar. Pretreatment at 2.0 - 3.0 N NaOH at 80°C for 1 hour to pre-soaked G.edulis for 11 h in water proved to be the most ideal and optimum extraction procedure to obtain higher yield (14.16%), maximum gel strength (291g.cm ^-2 ), lowest sulphate (0.732%) and highest melting point (99°C) of agar.