Chemical composition of agars from a newly reported Japanese agarophyte,Gracilariopsis lemaneiformis

The chemical composition of agars from Gracilariopsis lemaneiformis, newly reported from Japan, was investigated. Native agars were isolated by a sequential extraction of plants in water at 22 °C and 100 °C, and in boiling 20, 40 and 60° ethanol. Agars in each extract were analyzed by chemical methods, ¹H, ¹³C NMR; and IR spectroscopy. The highest yield of agar (total carbohydrate) was obtained from the 40° ethanol extract (55°). Highest sulfate content was attained in non-alkali treated agars extracted with hot water (4.81°, DS 0.2). The 3,6-anhydrogalactose content was highest in the 40° ethanol extract (36.1° in non-alkali treatment, 40.3° in alkali treatment). The highest methoxyl content (6.51°, DS 0.66) was obtained in the 60° ethanol extract. The G. lemaneiformis agar is composed of the biological precursor to agarobiose repeating units and agarobiose containing 6-O-methyl agarobiose and a small amount of 2-O-methyl-α-l-galactopyranose residues. Alkali treatment improved the chemical quality of the agar fractions, which was comparable with Japanese commercial agar and agarose.