Harness the power of saffron color for foo

image: A KAUST team has developed a method to produce the active ingredient in saffron from the fruit of a popular ornamental plant in China, Gardenia jasminoides, pictured here at left. On the right, saffron, the most expensive spice in the world.
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Credit: © 2022 KAUST.

Saffron is the most expensive spice in the world. Usually obtained from the stigma of Crocus sativa flowers, it takes 150,000 to 200,000 flowers to produce one kilogram of saffron. Now, KAUST researchers have found a way to use a common garden plant to produce the active ingredient in saffron, a compound with important therapeutic and dietary applications.

The color of saffron comes from crocins: water-soluble pigments derived from carotenoids by a process catalyzed by enzymes called carotenoid-cleaving dioxygenases (CCDs). Crocins are also present, although in much lower quantities, in the fruits of Gardenia jasminoidesan ornamental plant used in traditional Chinese medicine.

Crocins have high therapeutic potential, including their role in protecting neural cells from degradation, as well as their antidepressant, sedative, and antioxidant properties. They also have an important role as natural food colorants.

Harvesting and processing hand-picked saffron stigmas is labor intensive. Additionally, saffron is only grown in limited areas of the Mediterranean and Asia. Thus, new biotechnological approaches to produce these compounds in large quantities are in great demand.

KAUST researchers have identified a highly efficient carotenoid-cleaving dioxygenase enzyme from Gardenia jasminoides which produces crocetin dialdehyde, a precursor to crocin. They have now established a system to study CCD enzyme activity in plants and developed a multi-gene engineering approach for the sustainable biotechnological production of crocins in plant tissues.

“The enzyme we identified and the multigene engineering strategy could be used to establish a sustainable plant cell factory for the production of crocin in the tissue culture of different plant species,” says the study’s lead author. Xiongie Zheng.

“Our biotech approach can also be used on crops, such as rice, to develop crocin-rich functional foods.”

According to team leader Salim Al-Babili, the study paves the way for efficient biotechnological production of crocins and other high-value carotenoid-derived compounds (apocarotenoids) as pharmaceuticals in green tissue as well as in other starch-rich plant organs. It also highlights the contribution of functional diversification of CCD genes to the independent evolution of alternative apocarotenoid biosynthetic pathways in different plants.

“Most of our knowledge of CCD enzyme activity and substrate specificity comes from experiments using E.coli engineered to produce different carotenoids,” he says.

“Functional characterization in plants, for example using a transgenic approach like the one we have here, is important to infer the role of CCDs in carotenoid metabolism and unravel their actual contribution to the carotenoid/apocarotenoid model.”

The platform’s technology could be used to produce other important carotenoid-derived compounds, including widely used fragrances and colorants.

“It could be used to produce safranal and picrocrocin, for example, which give the characteristic taste and aroma of saffron. These could be used as flavor additives and they also have bioactive potential awaiting exploration,” adds Zheng.

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