2.5 Conclusions
In recent decades, many different bacterial and enzymatic processes for
the synthesis of natural fragrances and flavors have been described in
literature. Few of these processes have made it into industrial
large-scale production, due to high barriers in the strongly cost-driven
beverage and food industry.
In the case of alkyl pyrazines, the increasing demand can no longer be
supplied economically from natural sources.
As discussed above, the consumer can no longer be satisfied by
commercial chemical synthesis and the dependency on fossil oil chemicals
is becoming a crucial negative factor. Production in engineered
microorganisms such as Pseudomonas sp., Bacillus sp.,Chondromyces sp. and Streptomyces sp. opens possibilities
for the future of small in vivo factories. Up to now, pyrazine
producing strains were identified and modified by gene knockouts or
transfer of genes into other organisms to produce several types of
pyrazines. However, these systems are far too unspecific and produce
many different products. Cell factories are more difficult to optimize
compared to conventional chemistry, where typically one main product and
few by-products are obtained. Recently, optimized in vivofactories of heterologous genes for pyrazine synthesis in E. colihave been thoroughly described. However, the product range has been very
limited so far and has little to do with the 7 most required
alkylpyrazines. For these 7 compounds, smart routes yet need to be
designed. While industry will continue to improve running processes,
academic developments in technological science will expand the
complementary fields of chemistry and microbiology to deliver
commercially affordable and sustainable products in the next decades.