A critical review on production and industrial applications of beta-glucans

β-Glucan is an important bioactive compound for human health, but its low solubility has led to the development of chemical modification technologies to improve bioavailability. Several methods to modify β-glucan are laid out to improve their functional and technological properties via physical and chemical cross-linking reactions (Ahmad, Mustafa, & Che Man, 2015). In this respect, β-glucans can be chemically modified to obtain various derivatives with potential industrial or medicinal importance (Synytsya & Novák, 2013). Because of the insoluble chemical nature of β-glucan, particulate β-glucans are not suitable for many medical applications (Zeković et al., 2005). Various approaches in changing or modifying the chemical structures of β-glucan and transforming it to a soluble form have been reported. Modifications will affect the bioactive properties of β-glucan either positively or negatively. Carboxymethyl glucan (CM glucan) (Fig. 1(c)) is a water soluble polysaccharide modified from the insoluble β-glucan by carboxymethylation. The structure of the CM glucans in the solution depends upon the degree of substitution and with the increase of the degrees of substitution, a transition from triple-helical structure through single helical to random structure takes place (Kogan, 2000). CM glucan has biological activities which are consistent with its insoluble form. The improvement of solubility enables its application as a biomaterial for pharmaceutical and cosmetic aspects (Kanlayavattanakul & Lourith, 2008). The soluble phosphorylated glucans derived from the yeast Saccharomyces cerevisiae were investigated. This glucan is useful for promoting the wound healing process (Williams, Browder, & DiLuzio, 1990) and for prophylactic and therapeutic applications against neoplastic, bacteria, viral, fungal and parasitic diseases (Williams, Browder, DiLuzio, & DiLuzio, 1989).

Owing to β-glucan derived from Poria cocos hardly exhibits bioactivities. To extend its use, Wang et al. (2014) synthesized three types of (1 → 3)-β–D-glucan derivatives, which were sulfated (1 → 3)-β–D-glucan (Fig. 1(d)), carboxymethyl (1 → 3)-β–D-glucan and carboxylmethyl (1 → 3)-β–D-glucan sulfate. These results showed that multiple modifications of polysaccharides may bring the derivatives with excellent properties and various applications. In the homogenous sulfating of β-glucan from Saccharomyces cerevisiae, the 125 kDa fraction of the sulfated material accounted for only 1% of the product, with 99% of molecular weight of sulfated glucan being 14.5 kDa. The 13C NMR confirmed the presence of (1 → 3)-β interchain linkage in the polysaccharide chain and in solution the chains were self-associated in a triple helix form (Williams et al., 1992). Some chemically modified β-glucans from Volvariella volvacea were obtained and the inhibitory activity on the growth of mouse-transplanted tumors was studied (Kishida, Sone, & Misaki, 1992). Conversion of the glucosyl groups substituted at O-6 atoms of the (1 → 3)-linked d-glucose residues into the corresponding polyhydroxyl groups gave significant enhancement of the original activities both on allogeneic and syngeneic tumors. Conversion of the epoxy groups to hydrophilic glycerol groups remarkably enhanced the antitumor activity (Kishida et al., 1992). In another study, Berdal et al. (2007) prepared an aminated β-glucan (Fig. 1(e)), a water-soluble derivative of curdlan. They found this aminated β–D-glucan could improve wound healing in an animal model with diabetes mellitus.

β-Glucans derived from oats were subjected to chemical modification, specifically 2, 2, 6, 6-tetramethyl-1-piperidine oxoammonium ion-mediated oxidation whereby C6 primary hydroxyl groups were selectively oxidized into carboxyl groups. The results showed that the oxidation increased water solubility of oat β-glucans. In this study, oxidized oat β-glucans have the potential as an active cholesterol-lowering ingredient (Park, Bae, Lee, & Lee, 2009).

Ding, Wang, Xiong, Zhao, and Huang (2013) optimized the carboxymethylation of β-glucan by a two-step alkalization and etherification with monochloroacetic acid. The effect of ball milling pretreatment on the original β-glucan and its carboxymethyl derivative were studied on the basis of optimized technology for the carboxymethylation of β-glucan from S. cerevisiae. As a result, the ball milling pretreatment was beneficial for original β-glucan to carboxymethylation. Therefore, the expanded use of modified β-glucans may be taken into account for better health improvement.

Studies have been conducted to investigate the physical properties of β-glucans. Temelli (1997) investigated the physical properties, such as viscosity, whippability, foam stability and emulsion stabilizing capacity of the barley β-glucan gum to assess potential food applications. The results showed that maximum emulsion stability and viscosity were achieved at pH 7.0 and 55 °C. Viscosity increased with pH at constant temperature. Barley β-glucan gum shows a great potential as a thickener or stabilizer in products such as soups, sauces, desserts and salad dressings. Ahmad (2014) assessed the role of particle size of barley β-glucan concentrate (BGC) on two fundamental rheological properties namely oscillatory rheology and creep in a dough system. The results showed that all those information could be helpful to identify the particle size range of BGC that could be useful to produce a β-glucan enriched designed food. Moreover, Brummer et al. (2014) investigated that the textural and rheological properties of oat β-glucan gels with varying molecular weight compositions. The obtained results showed that the textural properties and melting profiles of β-glucan gels can be manipulated by adjusting the ratios of molecular weight fractions or addition of sugar for different applications. Liu (2010) evaluated the effects molecular weight and structure of β-glucan on viscosities of oat-flour slurries, the impacts of processing (steaming and flaking) on the viscosities and in vitro bile acid binding of oat-flour pastes were also discussed. The results showed that the greater bile acid binding capacity might have been caused by the β-glucan structural-molecular changes and/or the improved capacity of β-glucans through increasing availability during processing. The viscosity of the β-glucan solutions depends on their concentration, molecular weight, and structural features (Wood et al., 1994). For the structural characteristics of β-glucans, it was suggested that the amount of DP ≥ 5, ratio of DP3/DP4, and ratio of β-(1 → 3)/–(1 → 4) linkages are the important determinants of viscosity and solubility (Skendi et al., 2003). Irakli et al. (2004) explored the rheological behaviors of aqueous dispersions of β-glucans, particularly as it pertains to their gelation potential and the effect of added polyols on the textural properties of mixed gels made with these polysaccharides. These findings showed that β-glucans exhibited large differences in their flow behavior, shear thinning ability and gelling capacity.

The extraction needs careful attention as extraction process may affect the physiochemical properties of extracted β-glucan. Generally, extracted pellets had good water retention and foaming capacity (Ahmad, Anjum, Zahoor, Nawaz, & Din, 2009). Some authors reported the various physicochemical properties of barley β-glucan as affected by different extraction procedures. A significant variation in extraction methods was observed with respect to water binding capacity and foaming capacity. A significant impact of extraction methods was also observed on color parameters of β-glucan. A negative correlation exists between foaming capacity and viscosity, whereas a positive correlation observed between soluble fiber and viscosity. Thammakiti et al. (2004) investigated the effects of the homogenization on the chemical composition, rheological properties and functional properties of β-glucan from baker’s yeast. Homogenized yeast cell walls exhibited higher β-glucan content and apparent viscosity than those which had not been homogenized because of fragmentation of the cell walls and higher release of β-glucan. When compared with commercial β-glucan from baker’s yeast, it was found that the β-glucan obtained through homogenization had higher apparent viscosity, water-holding capacity and emulsion stabilizing capacity, but very similar oil-binding capacity.

The molecular weight values of β-glucans in oats ranged from 0.35 × 105 to 29.6 × 105 (Yao, Jannink, & White, 2007). Moreover, based on NMR data and methylation analysis, the calculated ratios of β-(1 → 4)/–(1 → 3) linkages in oat β-glucans were within the range of 1.9–2.8 (Lazaridou, Biliaderis, & Izydorczyk, 2003).

The fine structure, molecular weight, conformation and solubility of β-glucan have been shown to influence biological activities (Bohn and BeMiller, 1995, Leung et al., 2006, Soltanian et al., 2009). β-Glucan molecular weight and fine structure, such as 1 → 3 to 1 → 6 linkage ratio, lengths, number and distribution of cellulosic oligosaccharides will together with amount and nature of co-extracted compounds in a β-glucan preparation influence solubility, aggregate formation and polymer conformation (Rieder & Samuelsen, 2012).

In general, this review provides the consumer with a higher diversity of glucans; allow farmers an efficient and profitable use of the mushroom biomass. Advancement in the production process and functional properties of β-glucan will greatly enhance our ability to evaluate present and future β-glucan products. Taken together, screening and modification for the most potent and cost-effective β-glucans could then be made efficient. Promising results of clinical experiment in wound healing suggest that further in vivo experiments should be performed. The study also has been an attractive focus of developing β-glucan products that can aid in cancer treatment and has also performed research on the ability of β-glucans to assist in anti-inflammatory activity. Additionally, cereal β-glucan showed a great potential as a thickener or stabilizer in food products. However, further research will focus on its performance in food systems. It is hard to maintain consistency, reproducibility and reliability of different β-glucans due to the variable activities of raw material sources and the structure of β-glucan. Hence, it is necessary to establish the standard protocols for collection of the sources and for the extraction, isolation, purification and preparation of β-glucan. These will be useful for β-glucan applications in food, medicine and cosmetic products. To make better use of β-glucan, food manufacturers and processors must bring attention not only to ensure sufficient concentration of β-glucan in the raw material but also to the processing methods and physicochemical properties of β-glucan, decreasing mechanical and enzymatic breakdown of the β-glucans in end-product and optimizing processing conditions. Additionally, it is important for food scientists to develop alternative polysaccharide sources and the best use of polysaccharide to increase their digestibility and bioavailability.