A comprehensive review on the sources, biosynthesis, extraction, and characterization of β-glucans

Glucans are polysaccharides of D-glucose interconnected by glycosidic linkages. Glucans persist in alpha (α-) and beta (β-) forms. Alpha (α-) Glucans have alpha-glycosidic linkages whereas beta (β-) Glucans have beta-glycosidic linkages. In β-Glucans, D-glucose units linked with β-D-(1→3), β-D-(1→4), and β-D-(1→6). β-Glucans have more nutraceutical importance as compared to α-Glucans. The maximum concentration of β-Glucans is reported in the eukaryote, Euglena (90%). The biological synthetic mechanism of β-Glucans involves a cascade of enzymatic reactions and transporters. Numerous techniques are used for extraction of β-Glucans however some reports highlight that combined acidic and alkaline extraction methods are more significant. Various characterization techniques play a noteworthy role in identifying and characterizing β-Glucans. In the Ultraviolet-visible (UV/Vis) spectrophotometer, a peak at 260nm highlights the occurrence of a carbonyl group that confers β-Glucans presence. In Fourier Transform Infrared Spectroscopy (FTIR), the absorbance peak at 978.24cm^-1 suggests the existence of β-Glucans due to C1–H bond deformation. In Nuclear Magnetic Resonance (NMR), resonance peaks at 104ppm, 69ppm, and 62ppm highlight β- D-(1→3) and β-D-(1→6) linkages between the glucose molecules suggesting the presence of β-Glucans. In High-Performance Anion Exchange Chromatography (HPAEC), linkage ratios in the range of 2.27-2.39 specify glycosidic linkages suggesting β-Glucans presence. In High-Performance Liquid Chromatography (HPLC), the retention time of 9.024 minutes indicates the degree of branching, size, and linkages signifying β-Glucans occurrence. In Differential Scanning Calorimetry (DSC), the melting peak at 118°C, indicates variations in the physical state of the molecule with temperature that specifies β-Glucans appearance. In X-ray diffraction (XRD), the strongest absorption at 20°C, highlights its polymeric structure that represents the existence of β-Glucans. The present review gives a deep insight into β-Glucans sources available in prokaryotes and eukaryotes, their biosynthesis mechanism, extraction, and structural identification methods.