Chemical structure and physical-chemical properties of mucilage from the leaves of Pereskia aculeata
2017
Martin, Andressa Amado | de Freitas, Rilton Alves | Sassaki, Guilherme Lanzi | Evangelista, Paulo Henrique Labiak | Sierakowski, Maria Rita
Mucilage extracted from leaves of Pereskia aculeata, popularly called Barbados gooseberry (or ora-pro-nobis in Brazil), was investigated in terms of structural, chemical and physical-chemical properties. The mucilage was obtained with a new method using water at room temperature. Analysis of polysaccharide by GC-MS and NMR techniques showed the presence of galactose, arabinose, rhamnose, fucose and partially esterified galacturonic acid, whose main chain consisted of β-d-galactose linked (1 → 4), partially substituted at C-3 by arabinose, making it possible to characterize an arabinogalactan type I, highlighting the presence of fucose units. In water saline solution, the material is highly heterogeneous, as observed by size exclusion chromatography, where the main fraction is dispersed (Đ = 1.3) with weight average molar mass (Mw) of 7.9 × 105 g/mol. In addition, the intrinsic viscosity [η] (26 dL/g), by the Mark-Houwink equation, and the [η] dependence of Mw indicate that the mucilage has random conformation and flexible chains in sodium nitrate solution, with a radius of gyration of 41 nm and critical concentration (c*) of 4.6 mg/mL. Tensiometry allowed determining the critical adsorption concentration (CCA) and the critical self-association concentration (CSAC), as 1 and 6 mg/mL, respectively, and the sample showed mild surfactant characteristics. In aqueous dispersion (30 g/L), the rheological measurement showed pseudoplastic behavior of the mucilage, with polyelectrolyte characteristics. Finally, the pre-heating of the mucilage at 70 °C for 10 min caused an increase in viscosity and improved pseudoplasticity, for better interaction and molecular solubilization after cooling.
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