How to prepare flavors and fragrances by enzymes

Brunette woman smelling a dandelion.

Flavors and fragrances are constant companions in our daily life. We find them in food and in cosmetics, and of course, the demand for natural ingredients instead of chemicals is increasing. A special group of enzymes allows us to produce these valuable compounds from raw materials.

Flavors and fragrances play a big role in our daily lives. We wake up, loving the smell of hot coffee or tea. We enjoy a fruit juice, our cereals or some of us prefer the joy of smoky bacon and eggs. We then switch to brushing our teeth with toothpaste filling our mouths with freshness. We get a shower with musk shower cream and almond shampoo, we dry ourselves with towels with a scent of lavender. Finally, when properly dressed, we decorate ourselves with a puff of perfume. Many of us wish that the products, we consume on the daily basis are flavored with natural ingredients rather than chemicals and xenobiotics. And this is, where biocatalysis can kick in: instead of chemical steps, we let natural enzymes catalyze reactions in the transformation of raw materials to valuable compounds.

Most smells are based on an aldehyde

Many compounds we know from their pleasant smell contain an aldehyde group. Some examples are vanillin, the typical smell of vanilla, or cinnamaldehyde, a constituent of cinnamon smell. A totally different aldehyde compound has the smell of grass and there are many, many more. Scientists from acib recently searched for enzymes which are able to produce aldehyde compounds in a very selective manner. The team of Margit Winkler built on the work of researchers from the late 1960s: they had described a promising enzyme, which was isolated from the fungus Neurospora crassa. To be able to use this enzyme in modern processes, the first essential step was to filter the amino acid sequence from the myriad of sequences in today’s database jungle.

CAR – the tool for aldehyde production

The next step was to find a good method to produce this enzyme, which is called by its nick-name CAR for simplicity to avoid the lengthy full name carboxylate reductase. The trick for the rather complicated 120 kDa three-domain protein was its heterologous expression in E. coli using autoinduction conditions at 20°C. Once the CAR was accessible in satisfying amounts, the team challenged the CAR with many different substrates and conditions to understand it in depth and to learn how to use it in the best possible way. The new concept using an engineered E. coli strain allows the preparation of aldehyde in high amounts and almost without the formation of undesired impurities, which is the achievement of a collaboration with the Massachussetts Institute of Technology (MIT), Boston, USA. With this strategy, the team filled their laboratory in Graz with the overly pleasant smell of piperonal: a mixture of vanilla, almond and cherry, which is also known as heliotropin from the tropical flower heliotrope.

This work is based on:
D. Schwendenwein, G. Fiume, H. Weber, F. Rudroff, M. Winkler: Selective Enzymatic Transformation to Aldehydes in vivo by Fungal Carboxylate Reductase from Neurospora crassa. 2016 Advanced Synthesis and Catalysis, 358 (21), p. 3414 – 3421, DOI: 10.1002/adsc.201600914

Picture credits: Pixabay