# Insight on Extraction and Preservation of Biological Activity of Cereal \(\beta\)-D-Glucans
## 4 Methods of Extraction and Purification of Cereal \(\beta\)-D-Glucans
### Emerging Extraction Methods  
In addition to conventional extraction methods, some new extraction techniques reported in the literature are ultrasonically assisted extraction (UAE), microwave-assisted extraction (MAE), and accelerated solvent extraction (ASE). In the UAE technique, ultrasound can induce specific actions such as fragmentation, erosion, sono-capillary effect, sono-poration, and stress or local detexturation (or combined actions of the above) within the raw material, thus improving the efficiency and yield of extraction [40; 41]. Reports on MAE technology, used for the extraction of phytochemicals, reveal that this technique requires a lower volume of solvent and offers a higher yield in shorter extraction times than conventional methods [42]. The ASE technique involves extraction with a pressurized solvent at high temperature. While high-temperature extraction speeds up the process, high pressure helps keep the solvent in a liquid state, thus promising safe and fast extraction with less solvent and less extraction time [40; 43]. Among the methods reported, the ASE is configured as the best in the ratio between speed and yield. The conventional solvent extraction method has several drawbacks, such as time- and labor-intensive operations, as well as extended concentration steps that can result in loss and degradation of target analytes. ASE can potentially be used as a cereal \(\beta\)-D-glucan extraction technique at the industrial level. ASE has a wide range of advantages. It uses an eco-friendly extraction system and solvent (water), extraction times are shorter than most other techniques, and extraction discrimination, compared with conventional methods, is reduced [45]. However, further optimization of the \(\beta\)-D-glucans is needed before ASE is established on an industrial scale to extract \(\beta\)-D-glucans in the food and pharmaceutical sectors. Especially, it is of paramount importance to accurately control the extraction time to prevent excessive depolymerization and consequent loss of the functional properties of the polymer [46]. Considerations on Different Extraction Methods and Purification of \(\beta\)-D-Glucans in Cereals  
The methods of wet extraction of cereal \(\beta\)-D-glucans differ mainly in the raw materials used, the ratio of \(\beta\)-D-glucans in the raw material to the solvent used, and the type of solvent used. All these factors affect the contamination of the extract with unwanted residues of starch and protein. After \(\beta\)-D-glucan is extracted, purification processes to remove starch and proteins are not always carried out. In any case, these contaminants in the extract can prevent adequate characterization and create considerable difficulties in applying the application of this polysaccharide to food [47]. Among the different types of wet extraction, those that use alkaline aqueous solutions can provide the highest yield of cereal \(\beta\)-D-glucans extracted [48]. As known, the functionality of soluble fiber lies mainly in its ability to absorb large amounts of water forming viscous solutions at the gastrointestinal level that make it more difficult for nutrients to pass from the lumen to the intestinal mucosa. The viscosity is conditioned by the MW and the concentration (c) of \(\beta\)-D-glucan in the solution. Thus, the parameter MW \(\times\) c is a key indicator of the potential health-promoting effect of \(\beta\)-D-glucan extract [7; 49]. Just as endogenous \(\beta\)-D-glucanases can reduce polymer MW following enzymatic depolymerization, a low pH can also compromise the primary structure of the molecule. A pH 4 can lead to acid hydrolysis of \(\beta\)-glycosidic bonds, thus decreasing the MW and viscosity of the solution [10]. Primary solvent extraction is effective at pH 8, endogenous \(\beta\)-D-glucanases are inactivated, MW is high, and consequently, viscosity is high [20]. Removal of contaminants (proteins and starch) is generally performed using hydrolytic enzymes or selective adsorption.