Mixed acid fermentation products, table

Some of the glucose is converted to D-lactic and to succinic acids (pathway/, Fig. 17-9) hence the name mixed acid fermentation. Table 17-1 gives typical yields of the mixed acid fermentation of E. coli. Among the four major products are acetate, ethanol, H2, and C02, as shown in Eq. 17-25. However, at high pH formate accumulated instead of C02. 

The multiple tube fermentation method requires the use of replicate tubes and dilutions of samples. The fermentation products of lactose include mixed acids and gas, which is usually detectable. Coliforms are reported in terms of MPN of organisms present. MPN tables are based on a random dispersion of coliforms (Poisson distribution). Failure to shake the samples very well will result in a nonrandom distribution that will underestimate the actual density of the bacteria. If testing drinking water, a single bottle containing 100 mL may be used or 5 replicate tubes with 20 mL each or 10 replicate tubes with 10 mL each. If testing nonpotable water such as salt water, brackish water, or sediments, multiples and subsamples of 10 mL (e.g., 0.1 1.0 10 mL) should be used. 

Summary 95% Ethanol can also be obtained on a lower yield by hydrolyzing table sugar with dilute acid, and then fermenting the resulting mixture with yeast to form an ethanol solution. The solution will be contaminated heavily with by-products so multiple distillations and treatments with baking soda will be needed in order to fulfill proper purification. Baking soda is mixed with the distilled liquid to absorb odors and the like. 

The current state of strain development for ethanol production via C. thermocellum and T. saccharolyticum is summarized in Table 10.3 with reference to key performance metrics. It may be noted that solubilization data and fermentation of high substrate concentrations have been summarized in Table 10.1. Volumetric productivities (g ethanol 1 h ) calculated from the data in Table 10.3 include 0.78gl h for T. saccharolyticum fermentation of mixed cellodextrins and 0.20 gl h for C. thermocellum fermentation of Avicel. Similarly to the wild type, C. thermocellum mutant strains still secrete amino acids into the culture medium, providing a target for further increasing ethanol yields and titers. 

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