Method 5
This method[25] is similar with the method 3[23] based on yeast cell lysis with the use of cell autolysis and hot water and then further cell disruption with homogenization instead of sonication. The method is applied in brewer's spent yeast, a brewery by-product. Also a protease enzyme is used for the removal of cell wall proteins and organic solvents for the removal of lipids. The conditions for the use of the enzyme are not optimized. The final product is insoluble β-glucan. In the beginning, yeast slurry cells are passed through a sieve (125 µm) for a first purification and then centrifuged (4500g / 10 min) for 5–6 times until the supernatant is clear. The yeast cells are taken as a sediment after discarding the supernatant. Next, cell autolysis is induced: 15% (w/w) cell material / pH 5.0 / 3% NaCl / 55°C / 24 h / agitation (120 rpm). Then, autolyzed cells are heated (80°C / 15 min) for deactivating the endolytic cell enzymes. The autolyzed cells are separated by centrifugation (4500g / 10 min) as sediment and treated with hot water: 250 mL suspension of autolyzed cells / 10% (w/w) solids content / 0.02 M sodium phosphate buffer / pH 7.5 / 50 g glass beads (0.3–0.4 mm diameter) / 121°C / 4 h. Then, the cell material is washed twice with distilled water and separated as a sediment by centrifugation. In a next step, cells are disrupted with homogenization with a pressure between 70 and 80 MPa and three passes (other parameters are not shown). The received cell walls are treated with organic solvents for the removal of lipids. Isopropanol is proposed as the most appropriate: cell walls are suspended in organic solvent in a ratio of 1:4 (w/v), heated under reflux for 2 h, centrifuged for the separation of the residue from the supernatant (5000g / 10 min) and washed three times with acetone 1:1 (w/v). The defatted cells are obtained as a sediment after centrifugation. In the final step, proteins are removed enzymatically with the use of a protease. Protamex (Novozymes Co., Denmark) is suggested as the most efficient: 15% (w/w) solid content / pH 7.5 / 55°C / 5 h (the amount of the proposed enzyme is not shown), then heating of suspension (80o C / 15 min) for inactivation of protease and centrifugation (5000g / 10 min / wash several times). Wet β-glucans (sediment) are spray dried for the preparation of the final β-glucan: 8% (w/w) solids content / inlet temperature 180o C / outlet air temperature 85o C.[25]