# Insight on Extraction and Preservation of Biological Activity of Cereal \(\beta\)-D-Glucans
## 4 Methods of Extraction and Purification of Cereal \(\beta\)-D-Glucans
### Dry Technologies  
Pearling is a dry fractionation process in which the outer layers of the granular tissue are gradually removed through abrasion, without breaking the grain. This technology allows to obtain fractions enriched in \(\beta\)-D-glucans up to a concentration of 25% [34]. Pearl barley and pearl barley flour are commercially available, while the pearling of oat  
Figure 2: Technologies for the concentration of cereal \(\beta\)-D-glucans, adapted from [33]. grains has not been successful due to extensive caryopsis breakdown attributed to oats' relatively high lipid content [33]. In dry grinding and sieving, the separation of \(\beta\)-D-glucans is based on postgrinding particle size. Raw flour is a complex particulate, where each particle, depending on the extent of the size reduction, varies in its chemical composition (starch, proteins, \(\beta\)-D-glucan, hemicellulose, cellulose, lipids, and minerals) and physical characteristics (size, shape, and density). This practice is generally employed in barley; in oats, it is not feasible due to the high lipid content compared with barley, which entails an obstruction of the sieve meshes [33]. Generally, before dry extraction, it is necessary to carry out a degreasing of the sample; in fact, the removal of lipid content from plant material improves the extraction of cereal \(\beta\)-D-glucans [35]. Following various destructive grinding and selective sifting processes, concentrations of \(\beta\)-D-glucans of about 12% from barley and 17% from oats can be obtained. Although researchers have also obtained \(\beta\)-D-glucans from the cell walls of the amyliferous endosperm, these approaches are much less widespread. Generally, \(\beta\)-D-glucans are obtained from bran fractionation, a fraction normally removed to avoid interference during processing and used as animal feed [7]. Separation occurs in dry grinding and air classification based on particle density. Through the optimization of the parameters, it is possible to obtain a concentrate of fibers containing up to 30% \(\beta\)-D-glucan [33]. The principle of operation of the various air classifiers is based on the Stokes equation, thanks to which it is possible to obtain the different speeds of fall of the particles depending on their density compared with that of the medium (i.e., the air), as well as consider their diameter. As reported by [PERSON] et al. (2015), air classification can be considered a green technology to produce barley coarse fraction with high amounts of \(\beta\)-D-glucans from the whole grain [36]. To date, milling and subsequent sifting are commonly used in combination with wet extraction techniques to obtain sufficiently concentrated and pure \(\beta\)-D-glucan extracts [37]. The industrial relevance of dry extraction is very limited, mainly due to the intensity of the process's costs, low yields, and the need to degrease the sample before extraction. To increase the concentration of \(\beta\)-D-glucans in the extracts produced by dry methods, the possibility of implementing a combined effect of ultrafine grinding and electrostatic separation in defatted oat bran fractions was evaluated, obtaining a concentration in \(\beta\)-D-glucans of 48.4%. This portion, further fractionated by a combination of jet-milling and air classifier, allowed to reach concentrations of \(\beta\)-D-glucan up to 56.2% in the final product. Electrostatic separation, as an emerging technology, could become a much more feasible process, offering an interesting alternative for the extraction of \(\beta\)-D-glucans [35]. Anyway, to date, the most common way to fortify starch foods products with cereal \(\beta\)-D-glucans is the addition of bran obtained by selective milling.