# Insight on Extraction and Preservation of Biological Activity of Cereal \(\beta\)-D-Glucans
## 1 Introduction  
\(\beta\)-D-glucans is a predominant nonstarchy polysaccharide composed of linear chains of \(\beta\)-D-glucose linked by 1,3-, 1,4-, or 1,6-\(\beta\)-glycosidic linkages either in branched or unbranched form. The major sources of \(\beta\)-D-glucan are cereals, microorganisms, mushrooms, and seaweeds. The glycosidic linkages in cereal and lichen \(\beta\)-D-glucans are a combination of 1,3 and 1,4-\(\beta\)-glycosidic linkages; hence, it is called (1\(\rightarrow\)3) (1\(\rightarrow\)4)-\(\beta\)-D-glucan. Lichenan is a linear polymer of predominantly 1,3-\(\beta\)-glycosidic-linked cellotrirosyl units. The proportion of cellotrirosyl units is higher than in the cereal \(\beta\)-D-glucans. 1,3-\(\beta\)-glycosidic-linked cellotrirosyl units are the second most prevalent feature, unlike the cereal \(\beta\)-D-glucans, where the cellottarosyl units are the second most common component. There are also regions of 1,3-\(\beta\)-glycosidic-linked cellodextrins with a higher degree of polymerization (DP), similar to the cereal \(\beta\)-D-glucans [1]. Mushroom \(\beta\)-D-glucans consist of a linear 1,3-\(\beta\)-glucan chain with single 1,6-\(\beta\)-glycosidic-linked glucose units attached to the backbone. Yeast \(\beta\)-D-glucans, extracted as large molecules, show a highly branched structure. They contain only side chains linked with 1,6-\(\beta\)-glycosidic linkages to the backbone consisting of 1,3-\(\beta\)-glycosidic linkages. Seaweed \(\beta\)-D-glucans are composed of \(\beta\)-1,3-glucan chains with the presence of \(\beta\)-1,6 branching. Some seaweed \(\beta\)-D-glucans are characterized by the presence of mannitol at the end of the \(\beta\)-1,3-glucan chain. Finally, \(\beta\)-D-glucans extracted from bacteria and _Euglena gracilis_ (a single-cell microalgae) consist of linear \(\beta\)-D-1,3-glucan chains without branching [2]. Based on the above molecular structure, \(\beta\)-D-glucan has a high water-binding capacity, resulting in its physicochemical properties, such as solubility, viscosity, and gelation [3]. 1,3-\(\beta\)-bonds interrupt the system of interunit hydrogen bonds in a cellulose-like chain that permits water to solvate glucan macromolecules [4]. For this reason, \(\beta\)-D-glucans are often used as thickeners, stabilizers, and fat substitutes in foods [5]. The constitution of a viscous gel is also an essential aspect at the digestive level, as it incorporates part of thedigestible sugars and fats taken, reducing their assimilation and making nutrients less accessible to human digestive enzymes [6; 7]. The \(\beta\)-D-glucans from these different sources are recognized as functional and bioactive food ingredients due to their biological activities, such as, hypocholesterolem properties, immunomododulation, hypoglycaemic activity, prebiotic properties, antioxidation, and anti-inflammation [8]. The content of \(\beta\)-D-glucans differs greatly between different sources. The \(\beta\)-D-glucans content is higher in barley than in any other cereal, ranging from 5.0 to 11.0%, and it is present in the endosperm and aleuronic layers. The percentage of \(\beta\)-D-glucans in oats varies between 4.5% and 5.5% and is predominantly present in the aleuronic and subaleuronic layers. \(\beta\)-D-glucans content is relatively low in wheat and ranges between 0.2% and 1.2%. Most of the \(\beta\)-D-glucans in cereals are present in cereal brans; so, the byproducts of cereal milling are mainly used as the main source of \(\beta\)-D-glucan extraction [7; 9]. The \(\beta\)-D-glucans found in cereal brans, such as barley and oats, are usually produced as an agricultural byproduct. Their extraction and isolation allow to obtain a value-added product [10]. Among other sources, cereal \(\beta\)-D-glucans have been shown to be the most effective for preventing type 2 diabetes and cardiovascular disease.