Method 4
In this method[24] the cell disruption and the yeast cell wall preparation is achieved with sonication. Another point of this method is that the cell walls and β-glucan are obtained as a supernatant by centrifuging at low gs (500g). Saccharomyces cerevisiae yeast cells are obtained after their growth in Sabouraud dextrose agar containing chloramphenicol (0.005%) / 30°C / 3 days. The preparation of yeast suspension is conducted with 500 mL YPG broth (yeast extract 1% / peptone 2% / glucose 2%) with mild agitation (150 rpm) / 30°C / 48 h. The yeast cells are harvested by centrifugation 4500g / 5 min / 4°C, washed three times and freeze-dried. The cell disruption is conducted by sonication (ice bath / 60% amplitude / 48 min: 2/4 min pulse on/off basis) after preparation of yeast cells in chilled 0.1 M sodium phosphate buffer / pH 7.2. The cell walls are obtained with centrifugation (500g / 2 min) as a supernatant and separated by this way from the intact cells. Then, the cell walls are diluted to 10 mL of sterile distilled water and centrifuged (1000g / 4°C / 20 min), washed three times with sterile distilled water, suspended in the same buffer and then heated for 2.5 min in boiling water for the inactivation of cell endolytic enzymes. The extraction of β-glucan is achieved with NaOH (2% / 90°C / 5 h). The obtained supernatant after centrifugation (3000g / 10 min) is neutralized with 2 M acetic acid and treated with 3 volumes of ethanol for β-glucan precipitation. In a next step, the ethanol-β-glucan complex is dissolved in 3% acetic acid and centrifuged for the removal of proteins. β-Glucan is obtained as a supernatant, neutralized with 2 M NaOH and free-dried. In further steps for more purified fractions of β-glucans, proteins are removed with DEAE chromatography and mannans are removed with affinity chromatography.[24]