The Effects Of Drying Methods On The Antioxidant Activity and The Accumulation Of Artemisinin and its Precursors in Artemisia Annua L. Leaves

The anti-parasitic, anti-cancer, and anti-viral sesquiterpene lactone artemisinin, commercially extracted from Artemisia annua, is in high demand worldwide.  However, limited information is available on how post-harvest drying procedures affect plant biochemistry leading to the biosynthesis of artemisinin and the phenolic antioxidants. This information is vital for optimization of the commercial production of artemisinin and other bioactive phytochemicals. The current study evaluates and compares the effect of four commonly deployed drying procedures (freeze, oven, shade, and sun) on the concentration of artemisinin, its precursors and the antioxidant activity of A. annua leaves.  The influence of drying time and light intensity on the sesquiterpene composition and antioxidant capacity was also quantified.  Artemisinin concentration was the lowest in freeze dried samples as compared to oven, shade, and sun dried samples.  However, opposite results were obtained for antioxidant activity using the FRAP (ferric reducing antioxidant power) assay, where freeze and oven dried samples showed similarly high antioxidant activity while antioxidant activity declined significantly after three weeks of drying plants under sun and shade. While drying samples for one, two, and three weeks showed no significant changes in artemisinin content, increasing drying time consistently decreased antioxidant activity of samples. Similarly, while there was no significant differences in artemisinin, when plants were dried under low and ambient light, ambient light tended to marginally decrease the antioxidant capacity.  Significant increase in artemisinin occurred at all drying procedures when compared to freeze dried subsamples with a simultaneous, and significant, decrease in dihydroartemisinic acid.  Our data reiterates the hypothesis that dihydroartemisinic acid, instead of artemisinic acid, might be the main biosynthetic precursor of artemisinin.  The data also indicates that oven drying for 24 hours at 45 ºC favored optimal recovery of both artemisinin and antioxidant capacity. These results on post-harvest processing are of considerable value for A. annua farmers to optimize artemisinin production at a commercial scale.  They are also useful for exploiting the antioxidant benefits of A. annua as a traditional anti-malarial, modern anti-cancer herb, and as a potential animal feed supplement.