5.3.3. Enzymatic Extraction

To avoid alkaline-acid methods considered to be degrading to β-glucans, some researchers introduced enzymatic extraction as an alternative to treatments with strong chemical solvents. Thus, if the enzymes used in the above-mentioned lytic process are left in the system, they lead to a cell rupture until glucan residues are obtained. The enzymes mainly used in the extraction and purification of β-glucans presented in the literature are proteases [120,152]. Concerning proteases, after a treatment to the cell walls for 5 h at pH = 10.5 and 45 °C followed by successive washes of the sediment with acetone or ethanol, maximum values of β-glucans of 26% and 25% are reached (with a purity yield of 85% and 83%, respectively) [152]. The combination of enzymes in the extraction process is also discussed so that proteases (Savinase) and lipases (Lipolases) that are used after hot water treatment (125 °C/5 h) are described as soft treatments [153].

It should be mentioned that in these two articles presented by Freimund et al. and Borchani et al., the extraction of β-glucans started from S. cerevisiae procured in the form of cell walls; in the last article a yield of 18% and a purity of the glucan content of 79% was achieved. Tam et al., by using Alcalase^® 2.4 LFG (another type of endopeptidase used for protein hydrolysis) and combining the enzymatic treatment with ultrasounds on a spent yeast suspension adjusted to 15% (w/w), reached a purity of 72.06% from the glucanic compound (no reference was made to the yield of β-glucans) [131].