This article appears in the January 2017 issue of Potato Grower.
Solanesol is a member of the terpene group of chemicals, which in pure form exists as a white crystalline powder. Solanesol was first isolated from flue-cured tobacco and subsequently found in the foliage of other solanaceous crops, including potatoes, tomatoes, eggplants and peppers. Researchers do not currently understand why the plant makes solanesol, though some recent research may offer clues.
Solanesol levels increase dramatically when potato plants are exposed to moderately elevated temperature. Even higher levels occur when heat and drought stress are applied together. This may imply that solanesol plays a role in the response to these stresses. However, irrespective of the function of solanesol in the plant, the chemical industry may have found some important uses of the chemical. Solanesol is used by the pharmaceutical industry as an intermediate in the synthesis—both chemically and biotechnologically—of metabolically active organic compounds such as coenzyme Q10 (which may help relieve sufferers of migraine headaches and Parkinson’s disease) and vitamin K analogues. The market for coenzyme Q10 was valued at over $400 million in 2015 and is growing rapidly due to its use in cosmetics, pharmaceuticals and as a dietary supplement.
There is also a growing awareness that solanesol may have useful properties in its own right with reports of anti-bacterial, anti-inflammation and anti-ulcerative activities. Reports about the mechanism of action of solanesol are starting to surface, and its potential in this arena is considerable.
As the foliage of many solanaceous crops such as potato and tomato is essentially regarded as a waste product, there is considerable potential to explore the extraction of solanesol from these sources as a valuable byproduct. However, as stated earlier, the factors that determine the level of solanesol accumulation in a plant are not yet well understood. In potato, for example, there is considerable variation in the level of extractable solanesol. This depends not only on environmental conditions during the season, but also on the genetic properties of a particular potato variety. Some genetic and environmental factors have been clarified in recent research. The maximum level of solanesol that could be extracted from potato foliage in studies approached 2 percent of dry weight.
Foliar dry matter content in potato has been reported to be just over 2 tons per acre. Assuming a 2 percent dry matter level can be achieved, this equates to a potential yield of about 90 pounds per acre. Of course, to achieve this yield, significant changes in potato production methods would be required. Currently, following chemical desiccation, potato foliage is not harvested and is generally plowed into the field. However, mechanical foliage destruction methods such as flailing can be developed, which may allow foliage to be harvested. Using mechanical rather than chemical means to kill vines may be then be possible and may also add green credentials to potato production.
Efforts to extract solanesol cheaply and efficiently would also be a requirement. Research to develop these methods is ongoing. Additional benefits may accrue by developing potato stems and leaves as a source of fiber and protein, as previous work has demonstrated yields of extractable protein of up to 530 pounds per acre. The potential of potato foliage as a commercial source of solanesol could add to the argument for using a bio-refinery approach to potato production.
This research work was supported through the European Union Framework Program 7 DISCO grant 613153.