DIRECT STRUCTURAL IDENTIFICATION OF POLYSACCHARIDES FROM RED ALGAE BYFTIR MICROSPECTROMETRY .2. IDENTIFICATION OF THE CONSTITUENTS OF GRACILARIA-VERRUCOSA

The use of the infrared microspectrometry analytical technique as a ne w tool for the identification of the polysaccharides contained in the red algae Gracilaria verrucosa has demonstrated that in addition to ag ar spectra, features of the other coexisting constituents can also be obtained. Indeed, the infrared spectra recorded previously, all exhibi t two important bands at about 1645 and 1530 cm-1. These two bands wer e not present in the infrared spectra of the extracted agars and they are expected to be due to the amide I and amide II protein vibrations. In order to confirm this supposition, we have applied some enzymatic treatments, firstly on the whole algae and secondly on the ground alga e (the algae has been previously depigmented and then dehydrated). Aga rase, xylanase and cellulase were successively carried out on the alga e. The last resulting spectrum, i.e. the spectrum obtained from the fr action which has undergone the three treatments, has been identified t o be characteristic of proteins. This spectrum contained, both the ami de I and II vibrations and in addition, weak absorption at 1230 cm-1 d ue probably to the amide III, was observed. Additional weak bands in t he 1400-1300 cm-1 due to the different skeletal modes of the proteins were also present in this spectrum. The infrared spectra also revealed that the use of the enzymatic treatments on the ground algae is more efficient than when it is carried out on the whole algae.