Artemisia: sun, shade or oven drying

Sun, shade or oven drying It has traditionally been accepted that drying of Artemisia annua should take place in the shade because drying in the sun would destroy many useful molecules. But recent papers have questioned this belief and have studied the effect of ultraviolet radiation on the accumulation or decrease of medicinal compounds in plants. Zhang WJ, Björn LO. The effect of ultraviolet radiation on the accumulation of medicinal compounds in plants. Fitoterapia. 2009 Jun;80(4):207-18. doi: 10.1016/j.fitote.2009.02.006. Concerning essentials oils: Supposedly it should be preferable to dry at temperatures below 60°C because volatile components might evaporate. But this is not confirmed in the scientific literature. The decrease was even lower for sun drying than for shade or oven drying in the case of Ocimum basilicum. However, at temperatures of 60°C the composition of the oils changes. M B Hassanpouraghdam , A Hassani ,. Drying Method Affects Essential Oil Content and Composition of Basil (Ocimum basilicum). J Essential Oil Bearing Plants, 2010, 13, 759-766. In the range 15°C to 45°C the impact on essential oil content is negligeable, some decrease, some slightly increase, especially the heavier ones. S Khangoli, A Rezaeinodehi. Effect of drying temperature on essential oil content and composition of Artemisia annua growing wild in Iran. Pakist J Biol Sc 2008, 11(6) 934-937 The USDA evaluated the effect of freeze, oven, shade, and sun drying on the leaf concentration of artemisinin, dihydroartemisinic acid, artemisinic acid and on the leaf antioxidant capacity. Ferreira JF, Luthria DL. Drying affects artemisinin, dihydroartemisinic acid, artemisinic acid, and the antioxidant capacity of Artemisia annua L. leaves. Agric Food Chem. 2010 Feb 10;58(3):1691-8. doi: 10.1021/jf903222j. Freeze-dried samples had the lowest artemisinin concentrations as compared to the other drying methods. A significant decrease (82% average) in dihydroartemisinic acid was observed for all drying procedures, with a simultaneous, significant increase in artemisinin. The average bioconversion was 43% for oven- and shade-dried plants and 94% for sun-dried plants, reiterating the hypothesis that dihydroartemisinic acid, not artemisinic acid, is the main biosynthetic precursor of artemisinin and suggesting that sun drying improves this bioconversion. Similar results had been found in Tasmania J.C. Laughlin. Post-harvest Drying Treatment Effects on Amtimalarial Constituents of Artemiasia annua L.. ISHS Acta Horticulturae 576: International Conference on Medicinal and Aromatic Plants. Artemisinin increased in the plants 21 days after harvest, either in the sun or the shade, more than in oven dried samples. Ripening of loquat fruits or postharvest ripenin of mango fruit increases chlorogenic acid content. CK Ding, K Chachuo : Metabolism of phenolic compounds during loquat fruit development. J Agric Food Chem 2001, 49, 2883-2888 MDK Vithana, Z Singh, Dynamics in the concentration ot health-promoting compounds during post harvest ripening of mango fruit, J Sci Food Agric, 2017, Aug 8 doi 10.1002/jsfa.8614 PM Mehta, Effect of light on the phenols in the development of fruit in brinjal. Proc Indian Acad Sci 1980, 89.2, 139-142 Phytosterols, saponins and fatty acids are not much affected by high drying temperatures. Only above 80 °C noticeable decreases are found Hong Ngoc Thuy Pham , Van Tang Nguyen, t. Effect of Extraction Solvents and Drying Methods on the Physicochemical and Antioxidant Properties of Helicteres hirsuta Lour. Leaves. Technologies 2015, 3(4), 285-301; doi:10.3390/technologies3040285 In green tea catechins, particularly EGCG, are increased by UV-B irradiation. XG Zheng, J Jin, YR Liang, Effect of ultraviolet-B irradiation on accumulation of catechins in Camellia sinensis. Afr J Biotechnol. 2008, 18, no 7 The medicinal value of plants depends on phenolics and volatiles. Exposure of plants to UV‐B causes flavonoid productIon. The higher temperatures in sun drying may also inhibit the enzymatic degradadation of flavonoids and other constituents due to the longer period it takes to dry in the shade. E Goto. K Hayashi, Effect of UV light on phytochemical accumulationof anthocyanin biosynthesis genes in red leaf lettuce. ISHS, doi 10.17660/Acta Hortic.2016.1134.24. A Arakawa, Effect of UV light on anthocyanin synthesis in sweet cherry. J Japan Hort Sci, 1993, 62-3 543-546. A large study on Mediterranean herbs show that air dried herbs contain more flavonoids and polyphenols. This was also noticed for Ginkgo biloba leaves. M Sun, X Gu J Tian, Change of secondary metabolites in leaves of Ginkgo biloba in response to UV-B irradiation. Innov Food Sci and Emerging Technologies 2010 11, 672-676 This increase was also noticed for phenolic compounds in blueberries I Eichholz, S Huyskens-Keil, A Keller. UV-B induced metabolites and phenolic compounds in blueberries (Vaccinium corymbosum). Food Chemistry 2011, 126 60-64. and in carrots. 5-caffeoylquinic (chlorogenic) acid more than 4,5-dicaffeoylquinic acid. B Surjanidata, Luis Cisneros-Zevallos. UVA, UVB and UVC light enhances the biosynthesis of phenolic antioxidants in fresh-cut carrot. Molecules 2017,22, 668 and in cherries. UV light has more effect than white or red light. AR Vicente, C Pineda, L Lemoine. UC-C treatments reduce decay, retain quality and alleviate chilling injury in pepper. Postharvest Biol and Technol 2005, 35, 69-78 Photoregulation of anthocyanin synthesis in apple fruit under UV-B and red light. Thesis Leclercq, 1992, Wageningen CS Lewinski, IL Goncalves Effects of UV light on the physico-chemical properties of yerba-mate. Nutrition and Food Science 2015, 48,2, 221-2228. Flavonoids are the main sunscreen chemicals of plants. Flavonoids are even used as natural antioxidants and UV light stabilizers for plastics like polypropylene. MD Samper, E Fages, The potential of flavonoids as natural antioxidants and UV light stabilizers for polypropylene. J Appl Polym Sc. 2013, 129, 1707-1716 DOI: 10.1002/app.38871. A study in Turkey showed that UV-C radiation had remarkable promoting effects on the accumulation of secondary metabolites in the calli of a grape cultivar. Emine Sema Cetin. Induction of secondary metabolite production by UV-C radiation in Vitis vinifera L. Öküzgözü callus cultures. Biological Research201447:37. DOI: 10.1186/0717-6287-47-37 Drying leads to polymerization and oxidation of proanthocyanidins resulting in insoluble reddish compounds. The final color after drying is affected by several factors, like ambient humidity, drying time, drying temperature. A Arabhosseini, S Padhye, J Müller. Effect of Drying on the Color of Tarragon (Artemisia dracunculus L.) Leaves. Food and Bioprocess Technology. October 2011, 4, 7, 1281–1287 K Luostarinen, V Möttönen. Effects of log storage and drying on birch (Betula pendula) wood proanthocyanidin concentration and discoloration. J Wood Science. 2004, 50, 2, 151–156 Sun drying decreases Vitamin C. A sharp decrease in Vitamin C was noticed for sun drying of apricots. Madrau, M.A., Piscopo, A., Sanguinetti, A.M. Effect of drying temperature on polyphenolic content and antioxidant activity of apricots. Eur Food Res Technol (2009) 228: 441. doi:10.1007/s00217-008-0951-6 This may be considered as a beneficial effect as Vitamin C is antagonistic with most antimalarial treatments. Air-drying at low temperatures increases the content of proanthocyanidins in sorghum. But their methanol solubility decreases with storage time, probably due to an increase in the degree of polymerization. Sedghi M; Golian A; Soleimani-Roodi P; Ahmadi A; Aami-Azghadi M. Relationship between color and tannin content in sorghum grain: application of image analysis and artificial neural network. Revista Brasileira de Ciência Avícola. vol.14 no.1 Campinas Jan./Mar. 2012 Scopoletin and coumarins significantly increases after sundrying. Hashim K. Mohammed Al-oubaidi*, Baan Munim Abdulrazzaq Twaij*, Aseel Salih Mohammed-Amee. Effect of (UV) light on production of medicinal compounds of Althaea officinalis L. in vitro. World Journal of Pharmaceutical Sciences ISSN (Print): 2321-3310; ISSN (Online): 2321-3086 Sun drying is used in Africa for cassava chips. In Benin, cassava is one of the most important plants grown. The conservation of fresh cassava roots is very difficult because they are highly perishable products subject to contamination by fungi, bacteria and other germs Rafiatou Ba, Fernand Gbaguidi, Gouton Alban Houngbeme, Justin Kohoude, Influence on the drying on the scopoletin induction of cassava chips roduced in Benin. Int J Appl Biol and Pharmac Technol. 20167, ISSN 0976-45550 W Yi, H Wetzstein. HortScience,2011, 4, 70-73 The study showed that sun drying is a major factor promoting the accumulation of scopoletin. Scopoletin inhibits the growth of Aspergillus flavus and the production of aflatoxin in dried cassava roots Gnonlonfin, GJB, Adjovi, Y, Gbaguidi, F, Gbenou, J, Katerere, D, Brimer, L & Sanni, A 2011, 'Scopoletin in cassava products as an inhibitor of aflatoxin production' Journal of Food Safety, vol 31, no. 4, pp. 553-558. DOI: 10.1111/j.1745-4565.2011.00334.x More important even, in sun dried chips the scopoletin content stays high after 3 months of storage. UV-C irradiation also is used to induce scopoletin accumulation in oranges to avoid postharvest decay. Guy D’hallewin, Mario Schirra, and Enzo Manueddu. Scoparone and Scopoletin Accumulation and Ultraviolet-C Induced Resistance to Postharvest Decay in Oranges as Influenced by Harvest Date, J Amer Soc Hort Sci 1999, 124, 702-707 Alternaria alternata a tobacco pathotype is inhibited by the fluorescent scopoletin. Huanhuan Sun Lei Wang Baoqin Zhang Junhong Ma, Christian Hettenhausen. Scopoletin is a phytoalexin against Alternaria alternata in wild tobacco dependent on jasmonate signalling. J Exper Botany, 2014, doi :10.1093/jxb/en Scopoletin also acts as insect feeding deterrent and is present in Artemisia annua. Insect feeding deterrent and growth inhibitory activities of scopoletin isolated from Artemisia annua against Spilarctia obliqua. Insect Science,2011, 18, 189-194 US patent 6337095 finds a concentration of 0.3 % of scopoletin in the stems and only 0.2 % in the leaves and uses the stems for commercial scopoletin extraction. But the most important benefit of sun drying could be the killing effect of UV light for bacteria and molds. In other drying techniques, especially at room temperature, they might have ample time to develop. The thresholds of microbial count of medicinal plant material according to the European Pharmacopeia 2005 are - For herbal medicinal products to which boiling water is added before use are 10⁷ for aerobic bacteria, 10⁵ for molds and 10² for E.coli. - For preparations for oral and rectal administration 10⁴ for anaerobic bacteria, 10² for molds and nil for E.coli. Post-harvest processes such as collection of plant material in the field, transport to the farm are often suspected to increase mibrobial contamination of medicinal plants. When the bulk of harvested material is not ventilated, auto-heating provides favourable conditions for micro-organism growth. It is important to reach as soon as possible a moisture content < 10%. in the plants Rocha RP, Melo EC, Radunz LL. 2011. Influence of drying process on the quality of medicinal plants: A review. J med plants Res 5(33):7076-7084 Immediate drying of the harvested plants in the sun could prevent these problems. The exposure however should be moderate, hours and not days. It is important to cover the drying plants during the night, with a mosquito net for example, to avoid absorption of dew or moisture.