Chen C, Dale M C, Okos M R
Department of Agricultural Engineering, Purdue University, W. Lafayette, Indiana 47907, USA.
Biotechnol Bioeng. 1990 Dec 5;36(10):975-82. doi: 10.1002/bit.260361002.
The effects of ethanol on reactor performance were studied in a small, 5-cm packed height, "differential" type immobilized cell reactor. Lactose utilizing yeast cells, Kluyveromyces fragilis, were absorbed to a porous adsorbant sponge matrix in a gas continuous reactor. Step changes in the feed ethanol concentration to the column (10-130 g/L) were used to test the reactor response over extended periods of time (about 30-50 h per dosage level) followed by a return to basal zero inlet ethanol feed. Effluent cell density and effluent cell viability were measured at intervals. An inhibitory response in ethanol productivity to feed dosage ethanol levels above 20 g/L was detected almost immediately, with a near steady state response noted within 2.5 h of initiating the dosage. Feed ethanol levels above 50 g/L resulted in a subsequent gradual decrease in reactor productivity over time, which was associated with a decrease in the fraction of viable shed cells in the reactor effluent. The reactor response to a step removal of the ethanol inhibition was also monitored. Quick and complete rebounding of the fermentation rate to the original basal rate was noted following dosage concentrations of under 50 g/L ethanol. Recovery rates slowed following ethanol dosage levels above 50 g/L. Viable shed cell density improved overtime during the slow recovery periods. Growth rates (as determined by shed cell density) were more strongly inhibited than productivity. Growth responded more slowly to changes in ethanol environment as growth rates at 30 h fell to about 40% of the rates measured 7.5 h after initiation of a dosage level. It is concluded that ethanol contributions to cell injury and death (and consequent ICR performance degradation) may be more important than ethanol inhibition of productivity rates in the long-term operation of immobilized cell reactors at ethanol concentrations over 50 g/L.
在一个小型的、填充高度为5厘米的“微分”型固定化细胞反应器中研究了乙醇对反应器性能的影响。利用乳糖的酵母细胞脆壁克鲁维酵母被吸附到气体连续反应器中的多孔吸附剂海绵基质上。向柱中进料乙醇浓度进行阶跃变化（10 - 130克/升），以测试反应器在较长时间内（每个剂量水平约30 - 50小时）的响应，随后恢复到零乙醇进料的基础水平。定期测量流出物细胞密度和流出物细胞活力。几乎立即检测到乙醇生产率对进料剂量乙醇水平高于20克/升有抑制反应，在开始给药后2.5小时内观察到接近稳态的反应。进料乙醇水平高于50克/升导致反应器生产率随时间逐渐下降，这与反应器流出物中活的脱落细胞比例的下降有关。还监测了反应器对乙醇抑制作用逐步消除的响应。在乙醇剂量浓度低于50克/升后，观察到发酵速率迅速且完全反弹至原始基础速率。乙醇剂量水平高于50克/升后，恢复速率减慢。在缓慢恢复期间，活的脱落细胞密度随时间增加。生长速率（由脱落细胞密度确定）比生产率受到更强的抑制。生长对乙醇环境变化的反应更慢，因为在给药水平开始30小时后的生长速率降至给药7.5小时后测量速率的约40%。得出的结论是，在乙醇浓度超过50克/升的固定化细胞反应器长期运行中，乙醇对细胞损伤和死亡的影响（以及随之而来的ICR性能下降）可能比乙醇对生产率的抑制作用更重要。
