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Fourier-transform infrared spectroscopy (FT-IR) spectra have been widely used for comparisons in the distribution of functional groups of A. vera products. Absorption bands at 1,247 cm⁻¹ indicate bands of C–O–C of acetyl groups, cited by many authors as the component that promotes biological activity [2]. The FT-IR profiles of different samples of A. vera studied typically indicate the presence of groups –OH (3,420 cm⁻¹), stretching of –CH (2,923 cm⁻¹), C=O stretching of acetyl (1,760–1740 cm⁻¹), C=O (1,650–1,578 cm⁻¹), COO– asymmetric stretching (1,598 cm⁻¹), CH₃ and COO– symmetric stretch (1,428 cm⁻¹), C–O–C stretching of acetyl groups (1,248 cm⁻¹), C–O–C ether in sugar (1,091–1,030 cm⁻¹) and glucan bands (1,031 cm⁻¹) [22, 28]. High-intensity peaks at 3,420 cm⁻¹ also confirm the presence of hydroxyl groups, indicating the presence of a mixture, as reported by some authors. A great band in the 1,078–1,036 cm⁻¹ range also shows the presence of polysaccharide sugars such as mannose, galactose, and units of glucans [22, 79].

Using the polysaccharide fraction Kiran & Rao [22, 37] showed the presence of peaks at 3,420, 1,740, 1,598 and 1,248 cm⁻¹ indicating the presence of –OH, C=O, COO– and C–O–C stretching of acetyl groups, suggesting that the powder of the polysaccharide fraction consists of high levels of storage polysaccharides, such as acemannan. These results have been confirmed in other recent observations of bioactive acetylated polysaccharide [5, 7, 24, 80]. The profile reported by Ray & Aswatha [24] in their study of freeze dried mucilaginous gel indicated the presence of absorption bands at 1,635 cm⁻¹ and 1,078.53 cm⁻¹. It was more marked in the gel obtained from 3-year-old plants, indicating a high level of acemannan in the sample relative to gel from 2 to 4-year-old plants.

The profile of the IR spectra of fractions obtained from A. vera skin and gel fraction was similar, indicating similar macromolecular structures. The signals for the hydroxyl group and ether (C–O–C) in sugar units were strongly absorbed at 3,420 cm⁻¹ and 1,050 cm⁻¹, respectively. A band at 1,066 cm⁻¹ in polysaccharides from the skin and gel represents the presence of mannopyranose components. More specifically, peaks at regions in the 1,736–1,740 cm⁻¹ and 1,246–1,252 cm⁻¹ range confirm the presence of O-acetyl ester [34]. Sriariyakul et al. [30] examined dehydrated samples using FT-IR spectroscopy and confirmed the presence of bands of C=O of acetyl groups at the 1,740 cm⁻¹ wavelength. The authors reported a marked decrease in these bands and that this decrease might be attributed to the deacetylation of acemannan during the hot-air drying process combined with FIR radiation and HVEF.

The samples submitted to the pasteurization processes in the studies of Rodríguez-González et al. [7] underwent partial deacetylation of the acemannan polymer, evidenced by a decrease in the 1,740 and 1,250 cm⁻¹ bands, which correspond to C=O and C–O–C stretching of acetyl groups. Chokboribal et al. [14] reported that complete acemannan deacetylation led to the disappearance of the absorption of the carbonyl at 1,740 cm⁻¹.