Enhanced Phenolic Diterpenes Antioxidant Levels Through Non-transgenic Approaches

Abstract

Plant-derived antioxidants are essential in our diet, and antioxidant composition is a key determinant of the quality of plant extracts of interest to the pharmaceutical and food industries. By using carnosic acid as an example of a key antioxidant constituent of rosemary and sage extracts, we discuss the importance of studying non-transgenic approaches to enhancing antioxidant levels in plants and improving the antioxidant composition of plant extracts. In contrast to other terpenoids or phenolic compounds, carnosic acid has only been found in some Labiatae species, such as rosemary and sage. Carnosic acid has medicinal properties; it is a potent antioxidant and protects skin cells against UV-A radiation and cancer. Furthermore, it has been used as a preservative in food and non-food products, displaying important antimicrobial effects. However, the key steps involved in its biosynthesis remain largely unknown, and thus non-transgenic approaches are required to increase its level in plant extracts. Dried rosemary or sage leaves can contain between 0.1% and 7% carnosic acid, depending on the species and variety, but also on plant growth conditions, sample treatment and mode of extract preparation. Furthermore, leaf age, salinity and ionic interactions can also have a significant effect on biosynthesis and therefore have a strong impact on the total antioxidant potential of rosemary and sage extracts. Non-transgenic approaches, used in these or other species, can significantly increase antioxidant levels and therefore provide very significant improvements in the quality of several botanical extracts used in industry, and can be applied as either an alternative or a complement to transgenic approaches.

FIG. 1 Chemical structure of synthetic and natural plant-derived antioxidants. Note that the hydroxyl groups in the ortho-position at C₁₁ and C₁₂ of the carnosic acid molecule provide high antioxidant properties (color figure available online).

FIG. 2 Outline of the non-transgenic approaches presently available to enhance antioxidant levels in plant extracts (color figure available online).

Keywords:

• antioxidants
• botanical extracts
• phenolic diterpenes
• growth conditions
• non-transgenic approaches

ACKNOWLEDGMENTS

Support for the research of S.M.-B. laboratory was received through grants BFU2012-32057, BFU2009-07294 and BFU2009-06045 from the Spanish Ministry of Science and Innovation, and the ICREA Academia award funded by the Generalitat de Catalunya. The authors wish to thank Jon Falk (Carlsberg Research Center) for helpful discussions and a critical reading of the manuscript. We are also indebted to Toffa Evans (University of Barcelona) for English corrections of the manuscript.