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.