Kunduru M R, Pometto A L
Department of Food Science and Human Nutrition, Iowa State University, Ames 50011, USA.
J Ind Microbiol. 1996 Apr;16(4):249-56. doi: 10.1007/BF01570029.
Continuous ethanol fermentations were performed in duplicate for 60 days with Zymomonas mobilis ATCC 331821 or Saccharomyces cerevisiae ATCC 24859 in packed-bed reactors with polypropylene or plastic composite-supports. The plastic composite-supports used contained polypropylene (75%) with ground soybean-hulls (20%) and zein (5%) for Z. mobilis, or with ground soybean-hulls (20%) and soybean flour (5%) for S. cerevisiae. Maximum ethanol productivities of 536 g L-1 h-1 (39% yield) and 499 g L-1 h-1 (37% yield) were obtained with Z. mobilis on polypropylene and plastic composite-supports of soybean hull-zein, respectively. For Z. mobilis, an optimal yield of 50% was observed at a 1.92 h-1 dilution rate for soybean hull-zein plastic composite-supports with a productivity of 96 g L-1 h-1, whereas with polypropylene-supports the yield was 32% and the productivity was 60 g L-1 h-1. With a S. cerevisiae fermentation, the ethanol production was less, with a maximum productivity of 76 g L-1 h-1 on the plastic composite-support at a 2.88 h-1 dilution rate with a 45% yield. Polypropylene-support bioreactors were discontinued due to reactor plugging by the cell mass accumulation. Support shape (3-mm chips) was responsible for bioreactor plugging due to extensive biofilm development on the plastic composite-supports. With suspension-culture continuous fermentations in continuously-stirred benchtop fermentors, maximum productivities of 5 g L-1 h-1 were obtained with a yield of 24 and 26% with S. cerevisiae and Z. mobilis, respectively. Cell washout in suspension-culture continuous fermentations was observed at a 1.0 h-1 dilution rate. Therefore, for continuous ethanol fermentations, biofilm reactors out-performed suspension-culture reactors, with 15 to 100-fold higher productivities (g L-1 h-1) and with higher percentage yields for S. cerevisiae and Z. mobilis, respectively. Further research is needed with these novel supports to evaluate different support shapes and medium compositions that will permit medium flow, stimulate biofilm formation, reduce fermentation costs, and produce maximum yields and productivities.
使用运动发酵单胞菌ATCC 331821或酿酒酵母ATCC 24859，在装有聚丙烯或塑料复合载体的填充床反应器中进行了60天的重复连续乙醇发酵。所用的塑料复合载体，对于运动发酵单胞菌，含有聚丙烯（75%）、磨碎的大豆壳（20%）和玉米醇溶蛋白（5%）；对于酿酒酵母，则含有磨碎的大豆壳（20%）和大豆粉（5%）。运动发酵单胞菌在聚丙烯和大豆壳 - 玉米醇溶蛋白塑料复合载体上分别获得了536 g L-1 h-1（产率39%）和499 g L-1 h-1（产率37%）的最大乙醇生产率。对于运动发酵单胞菌，在大豆壳 - 玉米醇溶蛋白塑料复合载体上，稀释率为1.92 h-1时观察到最佳产率为50%，生产率为96 g L-1 h-1；而在聚丙烯载体上，产率为32%，生产率为60 g L-1 h-1。在酿酒酵母发酵中，乙醇产量较低，在塑料复合载体上，稀释率为2.88 h-1时最大生产率为76 g L-1 h-1，产率为45%。由于细胞团块积累导致反应器堵塞，聚丙烯载体生物反应器停止运行。载体形状（3毫米碎片）是导致生物反应器堵塞的原因，因为塑料复合载体上形成了大量生物膜。在连续搅拌台式发酵罐中进行悬浮培养连续发酵时，酿酒酵母和运动发酵单胞菌分别获得了5 g L-1 h-1的最大生产率，产率分别为24%和26%。在悬浮培养连续发酵中，稀释率为1.0 h-1时观察到细胞被冲出。因此，对于连续乙醇发酵，生物膜反应器的性能优于悬浮培养反应器，生产率（g L-1 h-1）分别高出15至100倍，酿酒酵母和运动发酵单胞菌的产率百分比也更高。需要对这些新型载体进行进一步研究，以评估不同的载体形状和培养基组成，从而实现培养基流动、刺激生物膜形成、降低发酵成本，并实现最大产率和生产率。
