EFFECTS OF THALLUS AGE AND ALKALI TREATMENT ON PYRUVIC-ACID CONTENTS OF AGARS FROM THE RED ALGA GRACILARIA-CHORDA

The pyruvic acid content of agars from Gracilaria chorda Holmes were analyzed in relation to thallus (agarophyte) age and alkali treatment. Its distribution in agar fractions obtained by sequential solvent extraction [cold water (22-degrees-C), boiling 99.5, 80, 60, 40, and 20% EtOH and water (100-degrees-C)] before and after alkali treatment of young, mature, and senescent thalli were compared Pyruvic acid content increased with thallus age (young, 0.11%; mature, 0.17%; and senescent, 0.33%) indicating increasing substitution of the agar repeating unit with pyruvic acid ketal groups as the agarophyte grows. This substitution increased the solubility of agar molecules particularly in cold water. Alkali treatment did not affect pyruvic acid concentration; however, its distribution among the fractions changed after alkali treatment. Pyruvic acid concentration in the agar fractions ranged from 0.05 to 0.76% and from 0.08 to 1.25% before and after alkali treatment, respectively. The agars from G. chorda had a relatively lower pyruvic acid content than most of the commercial agars examined.