These experiments were performed to acquire basic data for more efficient extraction of agar from seaweeds in which it probably occurs in a state similar to that in air dried agar material. Because the use of acid during the cooking process of seaweeds is a common procedure in the agar industry, the effect of acid treatment on the properties of air dried agar samples was saudied.
Short ribbons of refined air dried agar about 1 mm in thickness were prepared from powdered agar (alkali-treated Gracilaria agar with an average Total-SO3 content of 0.96%) by the procedure of dissolution, gel formation, quick freezing at -20°C, thawing in water and drying. The properties of the refined agars were: moisture, 23.0%; gel strength, 690 or 740; melthing point of 1.5% gel, 82.8 or 84.1°C.
Fist it was found that the air dried agar was stable to acid treatment at pH 1.0 when soaked in aqueous acid solutions of varying concentrations for 15 min at 15°C. Secondly, in the treatment with 1N hydrochloric acid for 15 min, the hydrolytic decomposition of agar accelerated logarithmically was increasing temperature. Complete decomposition of agar was observed at 65°C, as evaluated from the recovered solids through the freezing and drying process.