Chain length distribution and aggregation of branched (1→3)-β-d-glucans from Saccharomyces cerevisae

Transglycosylation of Stevioside by a Commercial β-Glucanase with Fungal Extracted β-Glucans as Donors

Abstract

Alternative sweeteners, such as steviol glucosides from the plant Stevia rebaudiana Bertoni, are becoming increasingly popular for the design of next-generation foodstuffs. However, the bitter aftertaste of native steviol glucosides is one of the main reasons behind consumer reluctance towards stevia-containing products. Biocatalysis could be a sustainable solution to this problem, through addition of glucosyl moieties to the molecule. Glycoside hydrolases are enzymes performing transglycosylation reactions, and they can be exploited for such modifications. In the present work, the commercial β-glucanase Finizym 250L® was employed for the transglycosylation of stevioside. After optimization of several reaction parameters, the maximal reaction yield obtained was 19%, with barley β-glucan as the glycosyl donor. With the aim to develop a sustainable process, β-glucan extracts from different fungal sources were prepared. Pulsed Electric Field pretreatment of mycelial biomass resulted in extracts with higher β-glucan content. The extracts were tested as alternative glucosyl donors, reaching up to 15.5% conversion yield, from Pleurotus-extracted β-glucan. Overall, in the present work a novel enzymatic process for the modification of stevioside is proposed, with concomitant valorization of β-glucans extracted from fungal biomass, potentially generated as a byproduct from other applications, in concert with the principles of circular economy.

Graphical Abstract

Yeast carboxymethyl-glucan improves endothelial function and inhibits platelet aggregation in spontaneously hypertensive rats

Carboxymethyl-glucan is a semi-synthetic derivative of β-D-glucan, a polysaccharide widely found in several natural sources, such as yeast, fungi, and cereals. This compound has beneficial effects on health and is considered an important immunomodulator. However, studies exploring carboxymethyl-glucan bioactivity in cardiovascular health remain lacking, mainly in hypertension. Thus, this study sought to expand understanding of the effects of carboxymethyl-glucan on vascular and platelet functions in a hypertensive animal model. Spontaneously hypertensive rats and their normotensive Wistar-Kyoto controls were assigned to five groups: control, carboxymethyl-glucan (60 mg kg^-1), control spontaneously hypertensive rats, spontaneously hypertensive rats carboxymethyl-glucan (20 mg kg^-1), and spontaneously hypertensive rats carboxymethyl-glucan (60 mg kg^-1). Animals were treated for four weeks with carboxymethyl-glucan at doses of 20 and 60 mg kg^-1 orally, and control rats received saline as a placebo. Vascular reactivity, platelet aggregation, and reactive oxygen species production were evaluated at the end of treatment. The results showed that carboxymethyl-glucan improved vascular function and reduced platelet aggregation, mainly at a 60 mg kg^-1 dose. However, despite these effects, there was no reduction in levels of reactive oxygen species. These findings suggested that carboxymethyl-glucan modulates endothelial function. It also acts as a platelet antiaggregant, which is an interesting resource for managing hypertension and its thrombotic complications.

Development of a novel beta-glucan supplemented hydrogel spray formulation and wound healing efficacy in a db/db diabetic mouse model

To relief the severe economic and social burdens and patient suffering caused by the increasing incidence of chronic wounds, more effective treatments are urgently needed. In this study, we focused on developing a novel sprayable wound dressing with the active ingredient β-1,3/1,6-glucan (βG). Since βG is already available as the active ingredient in a commercial wound healing product provided as a hydrogel in a tube (βG-Gel), the sprayable format should bring clinical benefit by being easily sprayed onto wounds; whilst retaining βG-Gel's physical stability, biological safety and wound healing efficacy. Potentially sprayable βG hydrogels were therefore formulated, based on an experimental design setup. One spray formulation, named βG-Spray, was selected for further investigation, as it showed favorable rheological and spraying properties. The βG-Spray was furthermore found to be stable at room temperature for more than a year, retaining its rheological properties and sprayability. The cytotoxicity of βG-Spray in keratinocytes in vitro, was shown to be promising even at the highest tested concentration of 100 μg/ml. The βG-Spray also displayed favorable fluid affinity characteristics, with a capacity to both donate and absorb close to 10% fluid relative to its own weight. Finally, the βG-Spray was proven comparably effective to the commercial product, βG-Gel, and superior to both the water and the carrier controls (NoβG-Spray), in terms of its ability to promote wound healing in healing-impaired animals. Contraction was found to be the main wound closure mechanism responsible for the improvement seen in the βG-treatment groups (βG-Spray and βG-Gel). In conclusion, the novel sprayable βG formulation, confirmed its potential to expand the clinical use of βG as wound dressing.

Mechanochemical phosphorylation and solubilisation of β-D-glucan from yeast Saccharomyces cerevisiae and its biological activities

To obtain a water-soluble β-D-glucan derivative cleanly and conveniently, a highly efficient mechanochemical method, planetary ball milling, was used to phosphorylate β-D-glucan isolated from yeast Saccharomyces cerevisiae in solid state. Soluble β-D-glucan phosphate (GP) with a high degree of substitution (0.77-2.09) and an apparent PEAK molecular weight of 6.6-10.0 kDa was produced when β-D-glucan was co-milled with sodium hexametaphosphate at 139.5-186.0 rad/s for 12-20 min. The energy transferred was 3.03-11.98 KJ/g. The phosphorylation of GPs was demonstrated by Fourier transform infrared spectroscopy and 13C and 31P Nuclear magnetic resonance spectroscopy. Three GP products with different degree of substitution (DS) and degree of polymerisation (DP) were able to upregulate the functional events mediated by activated murine macrophage RAW264.7 cells, among which GP-2 with a DS of 1.24 and DP of 30.5 exerted the highest immunostimulating activity. Our results indicate that mechanochemical processing is an efficient method for preparing water-soluble and biologically active GP with high DS.