Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 2009
Publication Date: January 5, 2010
Citation: Ferreira, J.F., Luthria, D.L. 2010. DRYING AFFECTS ARTEMISININ, DIHYDROARTEMISINIC ACID, ARTEMISINIC ACID, AND THE ANTIOXIDANT CAPACITY OF ARTEMISIA ANNUA L. LEAVES. Journal of Agricultural and Food Chemistry. 58:1691-1698. Interpretive Summary: Artemisinin is widely known as a safe and natural antimalarial and is gaining momentum as an anti-cancer compound commercially extracted from the annual wormwood plant (Artemisia annua). However, very little is published on the effects of post-harvest processing of A. annua leaves on antioxidant capacity or on the accumulation of artemisinin. This work compared the effects of commonly deployed drying procedures namely oven, shade (low and ambient light), and sun drying, from one to three weeks, on artemisinin accumulation for three consecutive years (2005-2007) and on the plant antioxidant activity. In one of these years (2006), freeze-dried subsamples of each plant were used as controls to quantify the biochemical conversion of artemisinin-related molecules into artemisinin in the plant during the drying process, and to quantify the effects of post-harvest drying on the antioxidant activity of the leaves. While drying the plants from one to three weeks under sun or shade did not affect artemisinin levels in the plant for 2005-2007 compiled data, sun drying in 2006 did increase artemisinin significantly compared to shade and oven drying. Quantitative analysis of the artemisinin and its bioprecursor molecule indicated that sun drying plants favor the conversion of the precursor into artemisinin. Shade-drying plants under low and ambient light for three weeks also did not affect artemisinin concentrations. However, shade drying from one to three weeks consistently decreased the antioxidant activity of the leaves, and so did shade drying under ambient light, compared to low light. Freeze dried sub-samples had similar antioxidant activity as plants that were oven dried (at 45 deg C for 24 hours), and these two drying procedures produced significantly higher antioxidant activity when compared to shade and sun drying. Our data indicates that drying procedures should be determined depending on the intended use of the plant. Shade and sun drying for a week only can increase the final artemisinin production per cultivated area, but oven or freeze drying should be chosen to maximize the antioxidant activity of the leaves. Although oven drying was not as effective as shade and sun drying to increase artemisinin, it could be used as the sole drying procedure to obtain a fair artemisinin concentration without sacrificing antioxidant activity. This information is valuable for the commercial production of artemisinin by farmers who use the annual wormwood as a pharmaceutical crop, but intend to use the remaining byproduct as a source of antioxidants for animal feed. This information is also valuable to maintain the antioxidant activity when the crop is to be used as a traditional medicine as source of antimalarial and anti cancer natural compounds.
Technical Abstract: 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 drying) on the concentration of artemisinin, dihydroartemisinic acid, artemisinic acid, 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 FRAP (ferric reducing antioxidant power) assay, where freeze and oven dried samples showed similarly high antioxidant activity while the antioxidant activity declined significantly after drying plants under shade or sun. While drying samples for one, two, and three weeks under ambient or low light did not change artemisinin content, increasing drying time and light intensity significantly decreased antioxidant activity in the leaves. Increase in artemisinin content was observed with all drying procedures as compared to freeze-dried subsamples, with simultaneous significant decrease in dihydroartemisinic acid. Dihydroartemisinic acid decreased an average of 82% in oven, shade, and sun dried plants as compared to the freeze-dried sub-samples. The conversion of dihydroartemisinic acid into artemisinin was on average 43% for oven and shade-dried plants and 94% for sun dried plants. Our data reiterates the hypothesis that dihydroartemisinic acid, not artemisinic acid, is the main biosynthetic precursor of artemisinin and indicates that sun-drying might make the bioconversion from dihydroartemisinic acid to artemisinin more efficient. The data also indicates that oven drying for 24 hours at 45 deg C can provide good levels of both artemisinin and antioxidant compounds in leaves. This information on post-harvest processing is valuable for commercial production, and also provides new information on the best way to process the plants for maximizing extraction of bioactive phytochemicals from A. annua as a traditional anti-malarial, modern anti-cancer herb, and as a potential animal feed supplement.