Substrate feeding product removal

A quantitative jump was finally brought by a two-in-one resin-based in situ substrate feeding product removal method (SFPR) [104]. An adsorbent polymeric resin acts simultaneously as a reservoir for the substrate and as a trap for the product (Figure 21.5). The substrate, preloaded onto the resin, slowly diffuses into the broth and is hansformed by cells while the formed product is readsorbed onto the soUd. The system is conveniently tuned by a simple choice of substrate resin ratio. Thus, both the substrate and product concentrations are controlled in order to maintain them below their inhibitory or toxic levels and allow a higher productivity. Additional benefits are also to be considered for prachcal large-scale applica-... 

Brenna, E., Gatti, F.G., Monti, D., Parmeggiani, F., and Sacchetti, A. (2012) Productivity enhancement of C=C bioreductions by coupling the in situ substrate feeding product removal technology with isolated enzymes. Chem. Commun., 48, 79-81. 

Figure 13.17 Cram-scale enzymatic production of ethyl (S)-2-ethoxy-3-(4-methoxyphenyl) propanoate using in situ substrate feeding product removal technology.

In many cases, problems cannot be overcome by biological means. This is especially true for those related to inhibition by substrate or product. There may, however, be technical solutions to these problems. Nowadays, complicated feed strategies with different substrates can be achieved through the use of flow injection analysis, on-line sensors, mass flow meters and sophisticated computer control. Such control coupled to a fed-batch mode of operation (Figure 2.5) can often eleviate problems caused by substrate inhibition. For some processes, continuous product removal can avoid the problems associated with product inhibition the various options include ... 

The batch experiment had neither incoming fresh media nor any product stream leaving the fermentation vessel. A complete experimental set up with a B. Braun Biostat, is shown in the above laboratory experimental set up. The continuous flow of media requires a feed tank and product reservoir. The batch process has many disadvantages such as substrate and product inhibition, whereas in the continuous process the fresh nutrients may remove any toxic by-product formed. 

Substrate utilization (neglect maintenance energy and substrate removal) Substrate accumulation equals Substrate Feed minus Growth minus Enzyme Production... 

Fig. 7 Resin-based in situ substrate feeding and product removal concept (Hilker et al. 2004)...

The bottleneck of substrate and product toxidty to the microbial cells used for the reduction has been overcome by the use of a polymeric resin to both supply substrate to and remove the product from the reaction mixture and therefore the microbial cells in the biocatalytic reduction of 3,4-methylene-dioxyphenyl acetone by Zygosacchar-omyces rouxii to the corresponding (S)-3,4-methylene-dioxyphenyl isopropanol in >95% isolated yield and with >99.9% enantiomeric excess [134]. This substrate feed and product recovery (SFPR) design made it possible to increase concentration from 6 to 40 g/1 and to achieve the reaction, product isolation, and resin recycling within a single piece of equipment at an overall reactor productivity of 75 g/l/day. 

Figure 4.19 Continuous feed of substrate and removal of products synthesis of 3-phenylcatechol from 2-phenylphenol applying a fed batch process with fluidized bed adsorption followed recrystallization...

CSTR Substrate and nutrients including oxygen are continuously fed so as to achieve the desired steady state. The beer containing ethanol, biomass and unconsumed nutrients is removed continuously. The productivity can reach 6g/l h, about three times of a batch reactor. The yield of ethanol is limited by the inhibition effect Total productivity is also limited by low biomass concentration (10-12g/l). A sugar concentration of 10% in the feed gives the highest productivity. Two or more CSTR in series can be used. 

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