Abstract
A (1→3)-β-d-Glucan produced by Lactobacillus suebicus CUPV221 strain was investigated by tapping mode atomic force microscopy (TM-AFM), to compare its supramolecular structure and conformation with two commercial polysaccharides: curdlan and scleroglucan. It was found that the β-d-Glucan was a (1→3)(1→2)-β-d-Glucan and at room temperature formed three-dimensional networks by entanglements between strands, as does scleroglucan. However, (1→3)(1→2)-β-d-Glucan strands seemed to be more stiff than those of scleroglucan. It was also observed that curdlan samples deposited from 5 mM NaOH aqueous solution showed supermolecular assemblies, recognized in the literature as micelles, which are controlled by hydrophobic hydration. The (1→3)(1→2)-β-d-Glucan in alkaline aqueous solutions produced different supramolecular structures depending on pH, and at 0.4 M NaOH (pH 13.16), denaturation took place. After neutralizing the alkaline solution with HCl, the formation of short linear, circular, and hairpin structures was observed.
Highlights
(1→3)-β-D-Glucan is produced by a lactic acid bacterium, Lactobacillus suebicus CUPV221 [15]
(1→2)-β-D-Glucopyranosyl pendant unit attached to every two units of the main chain, as shown in Figure 1 [16]. This (1→3)(1→2)-β-D-Glucan forms a gel network structure, that we probed by tapping mode atomic force microscopy (TM-AFM), Figure 2a
The image shows a three-dimensional network formed by entanglements between strands like that of the (1→3)(1→2)-β-D-Glucan and scleroglucan (Figure 2a)
Summary
(1→3)-β-D-Glucans from several bacteria and fungi constitute a group of natural polysaccharides with a main chain of (1→3)-linked β-glucopyranosyl units They can be linear or branched with either (1→6) or (1→2)-linked side chains of varying length and distribution. A better understanding of the structure-function relationship of these biopolymers remains a challenge to further improve applications and to better satisfy the consumer demand for appealing, tasty and even healthier products [3] These polysaccharides have been extensively studied in the last decade because they have potential as biological response modifiers. With respect to the industrial uses of (1→3)-β-D-Glucans, the strictly linear polysaccharide curdlan is the most studied [6], due to its unique rheological and thermal gelling properties [7] and its ability to form an elastic gel with strong bioactivity [8].
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