摘要
前期有关高浓度乙醇重复批次发酵的研究工作中发现,随着发酵批次的增多,SPSC01菌株的絮凝特性出现退化的现象,导致发酵时间延长,细胞沉降速率变慢,发酵系统变得不稳定。对影响SPSC01絮凝性能的因素进行了研究,并评估了这些因素对絮凝退化的影响程度。实验表明,细胞表面疏水性、乙醇浓度、细胞线粒体功能的改变,这些理化因素的影响均不足以导致酵母絮凝性能下降。而在重复批次发酵结束时SPSC01的絮凝基因FLO1的转录水平较发酵初始阶段下降了76.9%,这一改变是导致絮凝性能衰退的真正原因。研究亦发现,絮凝性能衰退的SPSC01菌体经过重新摇瓶培养后,可恢复较好的絮凝特性,表明重复批次发酵过程乙醇浓度及其变化速率对FLO1的转录有负面影响。据此依据,对高浓度重复批次发酵实验进行了优化,在每批次发酵终点泵出一部分酵母菌悬液以维持生物量在适当浓度,通过降低发酵速率来刺激酵母增殖,以维持絮凝性能。在这一操作下,发酵生产强度降低至3.9g/(L·h),每批次发酵时间控制在24h左右,菌体的絮凝特性及沉降性能在12批次后趋于稳定,并持续稳定地进行了后续13个批次的发酵。
Previous work on consecutive batch fermentation for very high gravity(VHG) ethanol production has shown that the flocculation capacity of the flocculating yeast strain SPSC01 degenerated with prolonged fermentation,resulting in slower cell settling and system instability.In this study,factors affecting flocculating capacity were investigated and their contributions to flocculation deterioration of SPSC01 were evaluated.The physicochemical effect from cell surface hydrophobicity and ethanol concentration was insufficient to trigger flocculation deterioration,and the effect from change in mitochondrial function was also insignificant.The transcription level of FLO1 in SPSC01 was down regulated by 76.9% at the end of fermentation,which was the primary reason for the deterioration of flocculation.The flocculating capacity of SPSC01 could be restored by re-cultivation of the yeast cells harvested at the end of fermentation,indicating that the concentration of ethanol and the rate of ethanol concentration change had adverse impact on FLO1 transcription.The fermentation was thus optimized by purging a portion(~40%) of yeast suspension at the end of each batch to lower the fermentation rate and to stimulate yeast propagation.Under these conditions the productivity was reduced to 3.9g/(L·h) with batch fermentation time of 24h,the flocculation and settling performance were stabilized after 12 batches,and the fermentation system could be operated with good repeatability for another 13 batches.
出处
《中国酿造》
CAS
2013年第S1期9-16,共8页
China Brewing
基金
国家863计划课题(2007AA10Z358
2012AA022205)
关键词
重复批次发酵
SPSC01
理化因素
转录水平
consecutive batch fermentation
SPSC01
physicochemical factors
transcription level
