# \(\beta\)-Glucans from Yeast--Immunomodulators from Novel Waste Resources
## 9 Extraction and Characterisation of \(\beta\)-Glucans
Additionally, combining ultrasonic waves with microwave-assisted extraction (MAE) for the separation of molecules of interest might yield even more significant advantages [135]. MAE uses microwave energy to heat the extraction solvent directly. The increased pressure and temperature that microwave extraction provides keep the water in a liquid state and above the boiling point. In addition to reduced CO\({}_{2}\) emissions and reduced usage of polluting solvents, this technique is deemed environmentally friendly becauseof its improved efficiency and lower energy use. In addition to being more effective and selective, this non-contact heat source may also speed up energy transfer, start-up, and reaction to heating control, and eliminate temperature gradients [138]. Studies have shown that the highest yield of \(\beta\)-glucans from mushrooms using MAE was obtained at 180 \({}^{\circ}\)C and 30 min [139]. Other studies have demonstrated that MAE had high reproducibility and was efficient and fast at \(\beta\)-glucan extraction from mushrooms [138]. MAE can be used alone as an extraction technique or combined with other methods such as UAE. A study characterised four proprietary yeast 1,3/1,6 \(\beta\)-glucan sources. The number of \(\beta\)-glucans and glycogen in each sample established its purity. Each sample's side chain length distribution was determined using an alkaline degradation test followed by ion chromatography. In addition, the purity profile, branching, and linking patterns of each proprietary source of yeast-glucan varied [140]. Glycogen, a 1,4-glucan comparable to starch, is a frequent component co-isolated with yeast \(\beta\)-glucans and downstream purification processes find it challenging to eliminate. It negates the \(\beta\)-glucans' intended health benefit. \(\beta\)-glucan samples from various sources have varying amounts of glycogen. Extraction methods must therefore remove any additional resides which can also affect activity. For example, mannoproteins inside the cell wall are coupled indirectly by 1,6 \(\beta\)-glucans via a glycosylphosphatidylinositol (GPI) anchor and directly by 1,3 \(\beta\)-glucans via linkages that can be broken in alkalis [141]. The manufacturing method can influence the formation structure. It is widely accepted that processing alters the physicochemical properties of \(\beta\)-glucans. Following extraction, linkage analysis is a widely used technique for establishing the relative percentages of each form of linkage in a sample from which % branching may be determined [142; 143]. Cell wall \(\beta\)-glucans are insoluble in hot alkaline solutions because they are covalently linked to chitin and other polysaccharides, for example, hydrogen bonds between hydroxyl glucose groups in the main chain. The 1,3 \(\beta\)-glucans solubility is affected by chain length or polymerisation. However, the degree of branching of 1,6 reduces the solubility [125; 144]. Together, these factors can enable \(\beta\)-glucans isolated from the same source to take on significantly differing immune-modulating properties [145; 13]. Extraction techniques can also have huge effects on \(\beta\)-glucans. Many investigators' uses of high or low pH and temperature settings in extraction procedures also results in molecules altered from their original conformation, changing their immune-stimulatory capabilities [146; 147]. There are numerous extraction methods widely available. Brewer's yeast has not been fully utilised as a source of \(\beta\)-glucan because of its low water solubility [148]. [PERSON] et al. (2015) analysed the effects of air-drying on the immunologic activity of \(\beta\)-glucan from spent brewers' yeast. Results showed that \(\beta\)-glucan content was not reduced after desiccation, positively impacting the quality of \(\beta\)-glucan extracted. This study also demonstrated that drying improved the immunogenic properties of spent brewers' yeast compared to new biomass \(\beta\)-glucan [148]. A study by [PERSON] et al.