Preparation Of Alkali-insoluble β-D-glucan From Waste Brewing Yeast’s Cell Wall

China annually generates a large amount of spent brewer’s yeast as a byproduct because of the continuously growing brewing industry. However, spent yeast is usually sold as a cheap animal feed. As an important constituent of the cell wall of spent yeast, β-D-glucan, shows a certain bioactivity and potential physiological values. Therefore, this study developed an innovative method of β-D-glucan extraction from spent yeast cells to improve the added value of spent yeast. It included comparison and analysis of assay methods for β-D-glucan, preparation of cell wall, extraction and purification of P-D-glucan, and preliminary analysis of structure. The main research contents and results were as follows:(1) The assay methods for β-D-glucan from yeast were compared and analyzed. It concluded that determination result after acid-enzyme hydrolysis was more precise. In the different glucose test methods, biosensor method was simpler, faster and more suitble for the production and test requirements. Besides, we found that a-glucan had a significant effect on determination results. Subtraction from total glucose of the glucose obtained from a-glucan was more reasonable.(2) Owing to poor cell disruption efficiency and long processing time of classic autolysis, a highly efficient cell disruption method, synergistic effect of enzymatic hydrolysis and homogenization, was developed in this study. The effects of compound enzymes, cell concentration, outlet temperature, operating pressure and passes on the ratio of broken cells were investigated. Optimum conditions could be summarized as a cell concentration of 50%(w/v), an outlet temperature of 30-35 ℃, an operating pressure of 1200 bar, a homogenization passes of two passes, and a kind of compound enzymes of papain (0.06%) and cellulase (0.04%). Under these conditions, the ratio of broken cells could exceed 95%. Compared with autolysis (the ratio of broken cells,50%), our method markedly increased the ratio of broken cells and reduced the processing time.(3) The classic preparation of P-D-glucan, alkali extraction at ordinary pressure, is limited by its long processing time and by the serious environmental problems caused by high alkali dosage. Hence, this study developed a new method of alkali extraction at high pressure. The optimal conditions of 0.85% alkali concentration,6.5:1 liquid-solid ratio,108 ℃ temperature (pressure,0.039 MPa), and 5 min processing time were obtained by using single-factor experiments and response surface methodology. Compared with alkali extraction at ordinary pressure, the new extraction method significantly reduced the alkali dosage and shortened the processing time.20 L experiment proved the feasibility of our method on a pilot scale. Then, Multifect Neutral, a kind of neutral protease, was select to remove residual protein and the purity of β-1,3-D-glucan increased to 80.12%.(4) The FTIR and NMR spectra confirmed that our glucan is a polymer of β-(1,3) linked glucose with β-(1,6) branches.