Unraveling the chemical mystery of saffron

Following the scent of saffron: Prof. Dr. Peter Beyer from the Institute of Biology II of the University of Freiburg has discovered a key enzyme for the synthesis of crocetin/crocin, picrocrocin, and safranal in cooperation with Prof. Dr. Giovanni Giuliano from the Casaccia Research Centre in Rome, Italy, and researchers from Saudi Arabia and Spain. These chemicals are responsible for giving saffron its characteristic color and aroma. The enzyme, named carotenoid cleavage dioxygenase 2 (CCD2), synthesizes the taste of the world’s most expensive spice by cleaving a precursor molecule. “The improved understanding of the biosynthesis of saffron opens up possibilities for producing its ingredients through biotechnological methods,” explains Beyer, member of the Cluster of Excellence BIOSS Centre for Biological Signalling Studies of the University of Freiburg. The scientists published their results in the current issue of the journal Proceedings of the National Academy of Sciences.

Saffron consists of dried stigmas from Crocus sativus. The plant grows in temperate climatic zones ranging from Spain to Kashmir. A single kilogram of saffron threads costs between 2,000 and 7,000 euros and involves the harvesting of 100,000 flowers by hand. Previous attempts to synthesize the ingredients of the crocus have been unsuccessful. Researchers long assumed that another enzyme by the name of ZCD cleaves the precursor molecule of crocetin/crocin, but they were unable to provide evidence for its effect in biosynthesis.

Beyer and his team studied the pistil of the crocus at the developmental stage in which crocetin/crocin is produced. “We discovered that the gene CCD2 is particularly active during this stage,” says Beyer. The researchers then verified the effect of the enzyme CCD2 by introducing it to the bacterium E. coli and maize. The enzyme also caused the precursor carotenoid to split in these model organisms.

The team does not aim to reproduce saffron through biotechnological means. The natural spice is too complex for this. However, the ingredients of the spice are also used as a dye and in medicine. “It would be possible to produce large amounts of crocetin/crocinc, picrocrocin, and safranal inexpensively through biotechnology,” explains Beyer. The European Commission provided funding for the study as part of the projects “From DISCOvery to product” (DISCO) and “METAPRO.”

Original publication:

Novel carotenoid cleavage dioxygenase catalyzes the first dedicated step in saffron crocin biosynthesis. Frusciante S, Diretto G, Bruno M, Ferrante P, Pietrella M, Prado-Cabrero A, Rubio-Moraga A, Beyer P, Gomez-Gomez L, Al-Babili S, Giuliano G. Proc Natl Acad Sci U S A. 2014 Aug 19;111(33):12246-51.

http://www.pnas.org/content/early/2014/08/05/1404629111.long