Alginic acids in Lessonia trabeculata: characterization by formic acid hydrolysis and FT-IR spectroscopy

The ratio of mannuronic acid to guluronic acid (M/G) in alginic acids from blade, stipe and holdfast of Lessonia trabeculata collected in three locati ons of the Chilean coast was determined by total hydrolysis with formic aci d. It was found that the reaction of alginic acids with 90% formic acid for 6 h at 100 degreesC, followed by treatment with 1.5 N formic acid for 2 h at 100 degreesC produced the total hydrolysis. The values of M/G ratio, det ermined by HPLC, were slightly lower than those obtained by the traditional hydrolysis method employing 80% sulphuric acid. No systematic tissue-to-ti ssue variations in the M/G ratio were observed. FT-IR spectroscopy, especially in the second-derivative mode, was applied f or characterizing alginates and partial hydrolysis fractions. The alginate fraction enriched in polymannuronic acid presented two bands at similar to 893 and similar to 822 cm(-1) while the polyguluronic acid enriched fractio ns showed four characteristic absorption bands at around 947, 903, 813 and 780 cm(-1). (C) 2001 Elsevier Science Ltd. All rights reserved.