树干毕赤酵母固定化细胞的酒精发酵

Fermentation of Ethanol by Immobilized Cells of Pichia stipitis

利用海藻酸铝凝胶包埋 ,将低浓度的树干毕赤酵母 (Pichiastipitis)细胞固定 ,其凝胶粒直径约 2～ 3mm ,经增殖培养 ,使凝胶珠表面的细胞密集 ,极大地减少了传递阻力 ,有利于该酵母细胞的“半好气”酒精发酵。结果表明 ,固定化细胞戊糖、己糖同步酒精发酵糖液初始 pH5 .0～ 5 .5较适宜 ;混合糖 60 g/L( 5 0 %葡萄糖、5 0 %木糖 )的固定化细胞酒精发酵 ,发酵前 1 2h主要利用葡萄糖 ,1 2h以后木糖利用占主导地位 ;以低pH( 2 .8,2 .4,2 .0 )无菌水处理酵母细胞海藻酸铝凝胶珠 ,2～ 3h后又恢复正常 pH( 5 .0 )。用pH 2 .8无菌水处理固定化细胞2～ 3h ,细菌基本上被杀死 ,而酵母细胞功能不受影响 ;当pH 2 .4时 ,对酵母细胞影响较大 ;而 pH 2 .0时 ,酵母细胞严重受损 ,大部分死亡。

Pichia stipitis yeast cells were immobilized by entrapment in marine alga aluminum gel,the resulted gel beads with a diameter of 2～3 mm were further incubated.Yeast cells were densely immobilized on the surface of the gel beads,therefore decreased the resistance to mass transfer and benefited the semiaerobic fermentation.The proper initial pH value of sugar solution for ethanol fermentation with immobilized cells was 5.0～5.5.In the fermentation of 60 g/L glucose xylose mixture,glucose was mainly consumed in the first 12 h,followed by xylose utilization in the next 12 h.In order to reduce bacterium contamination after several cycles of fermentation,the yeast cell immobilized gel beads were treated at pH 2.8 for 2～3 h,followed by normal pH fermentation.Most bacteria were killed after such a treatment,while the fermentability of the immobilized cells was not affected significantly.When treated at pH 2.4 or bellow,however,the immobilized cells were injured and it was difficult to recover the fermentability.