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Diehl & Teichmuller [36] showed that ¹H-NMR is an essential tool for assessing the identity and quality of A. vera gel preparations. Acemannan has β1→4 linkages in the partially acetylated mannose residues at positions 2, 3 or 6, and features a characteristic signal (2.00–2.26 ppm) on ¹H-NMR spectra of acetyl groups which can be regarded as the fingerprint of A. vera. Thus, the structure and position of the functional groups of acemannan can be analyzed by ¹H-NMR spectroscopy, constituting an essential means of identifying and preventing falsification by checking for the presence of acetyl groups [14, 19, 36]. Chokboribal et al. [14] stated the data derived from ¹H-NMR and IR spectra, together with the ¹³C-NMR spectra, confirmed that the precipitate isolated from A. vera gel as acemannan. The ¹H-NMR results also indicate that approximately 95% of mannose residues were acetylated, that protons at C2–C6 (H_2-6) occurred at 3.1–4.0 ppm, whereas H_Ac protons occurred at around 1.9 ppm.

Davis & Goux [38] studied commercially available products and, comparing with alcohol-precipitated polysaccharide fractions of A. vera, showed high resonance of methyl acetyl protons at 2.0 and 2.2 ppm. Spectra also revealed signals of protons from the pyranose ring H₂–H₆ at 3.0–4.2 ppm and acetic acid methyl protons at 1.9 ppm.

According to Ray & Aswatha [24], the signals corresponding to acemannan and glucose are evident in the ¹H-NMR spectra. Peaks at 2.05 and 5.13 ppm suggest the characteristic presence of acemannan and glucose, respectively. In the present analysis, the malic acid peak at 3.08 ppm, and a high concentration of phenolics may have suppressed the malic acid peak at 4.3 ppm.

In an analysis of 21 commercial A. vera gel products, Kim et al. [32] found that 33% of the samples contained high levels (45–95%, w/w) of maltodextrin as an adulterant undeclared on labels. In another study, a sample exhibited a signal at 5.4 ppm on ¹H-NMR spectra, revealing significant amounts of maltodextrin, although in this case, the presence of the adulterant was declared [19].

A. vera gel contains three principal components: acetylated polysaccharides (acemannan), glucose, and malic acid. High levels of lactic acid and acetic acid in products are the result of bacterial degradation, hydrolyzes, or thermal degradation of the materials during production or storage [39].

Malic acid is the only organic acid present in fresh A. vera gel, constituting a natural component essential for the plant’s photosynthesis. By contrast, commercial products may contain high levels of other organic acids, such as citric acid, lactic acid, and succinic acids [19].

In the studies by Minjares-Fuentes et al. [27], the ¹H-NMR spectra exhibited signals corresponding to malic acid and acemannan polymer, two natural components found in A. vera gel, in all samples studied. Additionally, the quantitative analyses performed to determine the levels of acetylation of acemannan showed a 40–70% reduction in acetylation of the polymer depending on the drying process used. The deacetylation of acemannan was also observed on FT-IR analyses by other authors [28, 30].

Citric acid is a natural preservative added to foods as a flavor enhancer and to prevent oxidation that is widely used in the food industry. The pH of juice from A. vera gel is generally adjusted to 3.0–3.5 with citric acid before concentration and drying. However, some samples contained extremely high levels of citric acid [19]. Acemannan can be converted into acetic acid (2.08, 11.00 ppm), lactic acid (1.34; 2.00; 4.27; 11.00 ppm), and succinic acid (2.5; 11.00 ppm) by microbial contamination and subsequent degradation. Detection of these organic acids on ¹H-NMR spectra suggests the occurrence of degradation [24] and should be absent in quality A. vera products.

The results found by Minjares-Fuentes et al. [27, 28] showed that acemannan polymer was severely affected by the different drying methods employed, with acemannan deacetylation detected by ¹H-NMR and FT-IR techniques, having a potentially serious impact on the biological activities attributed to the plant. Acetylated polysaccharides have been identified as an authentic marker of A. vera gel, and good quality derivatives should contain high levels of these polysaccharides [39].