Abstract
β-Glucans are biomacromolecules of industrial interest for its biological and technological properties, including ability to modify the rheology of food systems and different biological functionalities. In this study, lasiodiplodan an exocellular polysaccharide of the (1→6)-β-D-glucan type produced by the fungus Lasiodiplodia theobromae MMPI was obtained in a bench-scale bioreactor operated in discontinuous mode. Lasiodiplodan produced was derivatized by carboxymethylation and characterized by Fourier Transform Infrared spectroscopy (FT-IR), Thermogravimetry and Differential Thermal Analysis (TG-DTA), X-Ray Diffraction (XRD), scan electron microscopy (SEM) and their antioxidant and antimicrobial potential also was assessed. Two strong absorption bands in the regions of 1422 to 1598 cm-1, resulting from symmetric and asymmetric stretching vibrations of the -COO- group respectively, were observed in the FT-IR spectrum of the derivatized sample and indicated the carboxymethylation of the macromolecule. TG-DTA curves indicated that native (LAS-N) and carboxymethylated (LAS-C) lasiodiplodan did not suffer significant changes in relation to the heating rates. Native and carboxymethylated lasiodiplodan demonstrated high thermal stability considering the usual standards of the pharmaceutical industry. The final temperature of thermal decomposition increased when the heating rate was increased and less number of steps for thermal decomposition was observed when air was substituted for nitrogen. XRD analysis showed the LAS-N and LAS-C have no crystalline structure, but carboxymethylation led to the arising of regions with certain molecular orientation in biopolymer structure. SEM analysis showed that the carboxymethylation promoted changes in biopolymer macrostructure, including breaking of the polymeric structure and arising of bubbles on the surface area. Carboxymethylation contributed to improving the polysaccharide's antioxidant capacity and LAS-C demonstrated antimicrobial activity against Candida tropicalis.
Highlights
Several microorganisms, including seaweeds, bacteria and fungi are able to produce polysaccharides and some can secrete these outside the cell in soluble forms (Wang et al, 2008)
Fourier Transform Infrared spectroscopy (FT-IR) spectroscopic analysis allowed the characterization of the structure of lasiodiplodan by identifying specific absorption bands of chemical groups and bonds presents in the macromolecule
Chemical derivatization of lasiodiplodan by carboxymethylation was confirmed by the presence of two strong absorption bands in the regions of 1422 to 1598 cm−1, being attributable to carboxymethyl groups, whereas these were absent in LAS-N
Summary
Several microorganisms, including seaweeds, bacteria and fungi are able to produce polysaccharides and some can secrete these outside the cell in soluble forms (Wang et al, 2008). Microbial Exopolysaccharides (EPS) have been used by chemical, pharmaceutical and food sectors as bio-flocculants, bio-adsorbents, agents to remove heavy metals, for control-release of drugs and as gelling, stabilizer and food thickening agents (Wang et al, 2008; Schultheis et al, 2009) Some of these EPS’s and especially the fungal β-D-glucans, present biological activities, which have been demonstrated to possess antioxidant (Schultheis et al, 2009), antimutagenic (Cho et al, 2006), antiviral (Miranda et al, 2008), anticoagulant and antithrombotic (Yuan et al, 2009), hypoglycemic and hypocholesterolemic (Miranda-Nantes et al, 2011) properties, as well as exhibiting an anti-proliferative effect on breast cancercells (Cunha et al, 2012). They have attracted attention as bioactive substances that can promote human health benefits (Kivela et al, 2010)
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