An international research coalition unravels the chemical mystery of saffron

A paper, published in the last issue of PNAS , reports a major breakthrough in our understanding of the sensory properties of one of the most expensive food ingredients: the saffron spice.

Saffron is composed of the dried stigmas of the flowers of Crocus sativus, which is cultivated in temperate areas, from Spain to Kashmir. The earliest archaeological evidence of its cultivation is found in Minoan frescoes dated 1,700-1,500 B.C. One kilogram of saffron spice requires the manual harvest of stigmas from over 100,000 flowers and costs 2,000 to 7,000 €. Because of its high price, fraudulent adulteration of saffron with other plant ingredients or chemicals is common.

Saffron stigmas owe their red colour to crocetin and crocin, natural molecules that derive from the cleavage of a carotenoid precursor molecule. The same cleavage reaction also gives rise to molecules involved in saffron flavour and aroma. An international group led by Prof. Giovanni Giuliano of the Italian National Agency for New technologies, Energy and Sustainable Economic Development (ENEA) and including researchers from King Abdullah University for Science and Technology (Saudi Arabia), University of Freiburg (Germany) and University of Castilla-La Mancha (Spain) have discovered the gene responsible the cleavage reaction, named CCD2 (Carotenoid Cleavage Dioxygenase 2).
The race to discover the gene began in 2003, when a group from the University of Strasbourg pointed to another gene, named ZCD, as the one responsible for the cleavage reaction. However, further research demonstrated that ZCD is expressed in mature stigmas, where crocin synthesis is no more active, and that it encodes a truncated protein. Prof. Giovanni Giuliano said: “We had to go back to immature stigmas, where crocin is actively made, to find the CCD2 gene. The expression in this tissue and the structure of the CCD2 protein were the “smoking gun” telling us that this was probably the right gene. Further experiments showed that the CCD2 protein was able to do the same cleavage reaction it does in saffron when transferred to the bacterium E. coli or to maize, and also in a test tube. In the same conditions, the ZCD protein was inactive. This was the final proof”.

The research, funded by the European Commission (METAPRO and DISCO projects) and by national funds, adds a fundamental new brick to our knowledge of how natural molecules are made. Prof. Giovanni Giuliano adds: “Our goal is not to achieve a biotechnological equivalent of saffron, because the natural one is still unsurpassed. However, crocin is a potent colorant and antioxidant, used as a natural dye and medicine ever since the Minoan civilization. Since it cannot be made through chemical synthesis, the only way to make large amounts of it is through biotechnology”.

Contact:
Prof. Giovanni Giuliano:
Email
Tel. +39 329 831 3627
http://utagri.enea.it/en/utagri-gen