Abstract:The yield and molecular weight of water-soluble glucan obtained by degradation at different temperatures under a pressure of 0.1 MPa were analyzed by phenol sulphate method and high-performance gel exclusion chromatography，with brewer's yeast powder as raw material. The structural changes of water-soluble yeast glucan under different degradation conditions were also observed by Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy.The results showed that the yield of water-soluble yeast glucan was less than 20% at 120 ℃. When the temperature was increased to 135 ℃，and the pH value was between 3 and 5，the yield of water-soluble yeast glucan can be increased to 60%-80%.Lower pH indicated longer hydrolysis time and higher yield of water-soluble yeast glucan and gluco-oligosaccharides. When pH3 degraded at 135 ℃for 3.0-6.0 h，the yield of gluco-oligosaccharides as the main product was 79.89%；when pH4 degraded for 4.0-6.0 h，and pH5 degraded for 6.0 h，water-soluble yeast glucan of 12-100 kDa was mainly obtained. The results of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy showed that the glucans still had β-（1，3）as the main chain and β-（1，6）as the branched chain after hightemperature and high-pressure degradation. However，lower pH indicated lower β-（1，6）content in the branched chain，and the lowest integral of β-（1，6）/β-（1，3）was 0.61 at pH3.Therefore，by controlling the pH，temperature，and time of degradation，the high-temperature and high-pressure degradation method can effectively prepare water-soluble yeast glucans and gluco-oligosaccharides with different molecular weights.