固定化嗜热脂肪芽孢杆菌合成低聚半乳糖

利用海藻酸钙、明胶和壳聚糖为固定化载体包埋嗜热脂肪芽孢杆菌细胞合成低聚半乳糖 (GOS)。通过比较三种方法的酶活力回收、最适反应条件、GOS的得率和和载体机械强度 ,选择明胶作为固定化细胞的载体。反应体系的温度、pH、乳糖浓度、乳糖的转化率和载体的传质阻力对GOS合成有明显影响。在CSTR反应器中水解 60 %乳糖 ,GOS最大得率为31 2 % ,经过 96h( 8批反应 ) ,产物得率为原来的 88%。在空速 0 0 9h- 1条件下 ,利用填充床反应器连续水解乳糖 ,GOS的得率和反应器生产能力分别为 31 5%和 1 7 4g (L·h) ,连续反应1 40h,GOS得率下降 2 0 %。产物经过活性炭柱层柱分离纯化 ,通过13C NMR鉴定四糖的化学结构为 β D Gal ( 1→ 3) D Gal ( 1→ 6) D G ( 1→ 4) D Glu。

SYNTHESIS OF GALACTO-OLIGOSACCHARIDES BY IMMOBILIZED BACILLUS STEAROTHERMOPHILUS

Bacillus stearothermophilus was embedded in sodium alginate, chitosan, gelatin respectively and utilized for galacto-oligosaccharides (GOS) production. By comparing with each other in the enzyme recovery, optimal reaction conditions, yields of GOS and mechanical strength of the carriers, the gelatin was selected as better carrier for immobilization. pH, temperature, lactose concentration, lactose conversion and mass transfer resistance of carrier significantly influenced the Yield of GOS. The maximum yield of GOS was 31.2% in a stirred reactor with lactose concentration at 60%. It remained about 88% after 96 h (8 batches) reaction. A packed bed was employed for a continuous reaction at space velocity 0.09 h-1, where GOS yield and reactor productivity was 31.5% and 17.4% respectively. It lost about 20% of its original yield of GOS after 140 h reaction. Products were separated by active charcoal columm. The chemical structure of tetrasaccharide identified by 13C-NMR was beta-D-Gal-(1-->3)-D-Gal-(1-->6)-Dal-(1-->4)-D-Glu.