Drying Kinetics and Moisture Diffusion Behaviour of Selected Medicinal Leaves Under Electrically Controlled and Ambient Atmospheric Conditions

Drying remains one of the most important postharvest engineering operations required for the preservation of medicinal leaves through effective moisture reduction while maintaining product quality, storability, and process reliability. This study investigated the time–temperature dependent drying kinetics and moisture diffusion behaviour of guava (Psidium guajava), bitter (Vernonia amygdalina), and scent (Ocimum gratissimum) leaves under ambient sun drying and electrically controlled oven drying conditions. Emphasis was placed on moisture content reduction, moisture ratio (MR), drying rate, moisture retention capacity, and thin-layer kinetic modelling as influenced by leaf type and drying environment. Drying experiments were conducted over an 8-hour period with hourly measurements of mass, temperature, and relative humidity. Sun drying was carried out under fluctuating atmospheric conditions (32–37 °C; 59–80% RH), whereas oven drying was maintained at 60 ± 1 °C. Results showed that sun drying reduced moisture content to safe storage levels (<10%) but exhibited irregular drying patterns characterized by fluctuating MR profiles, lower drying constants, and unstable falling-rate behaviour. In contrast, oven drying achieved rapid and uniform moisture reduction within 6 hours, with smooth MR decay curves and higher drying constants, indicating enhanced internal moisture diffusivity. Among the leaves, bitter leaf exhibited the fastest drying response, while guava leaf showed greater resistance to moisture migration. Thin-layer model fitting revealed that the Page model provided the best predictive performance with coefficient of determination (R²) values up to 0.998. Overall, electrically controlled drying demonstrated superior efficiency, predictability, and engineering suitability for large-scale medicinal leaf preservation.

Thin-Layer Drying, Medicinal Leaves, Moisture Diffusivity, Postharvest Engineering, Drying Kinetics

1. Acar, B., Sadikoglu, H., and Doymaz, I. (2020). Drying kinetics and modeling of food materials: A review. Journal of Food Processing and Preservation, 44(3), e14376. https://doi.org/10.1111/jfpp.14376 [Google Scholar] [Crossref]

2. Akinmoladun, A. C., Ibukun, E. O., Afor, E., Akinrinlola, B. L., Onibon, T. R., Akinboboye, A. O., Obuotor, E. M., and Farombi, E. O. (2007). Chemical constituents and antioxidant activity of Alstonia boonei. Scientific Research and Essay, 2(5), 163–166. [Google Scholar] [Crossref]

3. Akinyemi, K. O., Oladapo, O., Okwara, C. E., Ibe, C. C., and Fasure, K. A. (2005). Screening of crude extracts of six medicinal plants used in south-west Nigerian folk medicine for antimicrobial activity. African Journal of Traditional, Complementary and Alternative Medicines, 2(2), 204–211. [Google Scholar] [Crossref]

4. Akpinar, E. K. (2006). Mathematical modelling of thin layer drying process under open sun of some aromatic plants. Journal of Food Engineering, 77(4), 864–870. [Google Scholar] [Crossref]

5. https://doi.org/10.1016/j.jfoodeng.2005.08.014 [Google Scholar] [Crossref]

6. Akpinar, E. K. (2021). Drying kinetics and modelling of selected medicinal plants. Heat and Mass Transfer, 57(2), 345–356. [Google Scholar] [Crossref]

7. Aktas, M., Ceylan, I., and Yilmaz, S. (2021). Determination of drying characteristics and effective moisture diffusivity of agricultural products. Thermal Science, 25(1), 245–256. [Google Scholar] [Crossref]

8. Almeida, R. L. J., Santos, N. C., and Silva, W. P. (2024). Thin-layer drying modeling of plant materials: Recent advances. Journal of Food Engineering, 350, 111002. [Google Scholar] [Crossref]

9. Arabi, M., Kaveh, M., Ghasemi, M., Hosseinpour, S., & Rezaei, M., (2025). Advances in drying kinetics modeling of agricultural materials. Drying Technology, 43(1), 1–15. [Google Scholar] [Crossref]

10. Aregbesola, O. A., Ogunsina, B. S., & Sofolahan, A. E. (2024). Drying kinetics and modeling of leafy vegetables under varying drying conditions. Journal of Food Process Engineering, 47(2), e14210. https://doi.org/10.1111/jfpe.14210 [Google Scholar] [Crossref]

11. Aregbesola, O. A., Ogunsina, B. S., and Sofolahan, A. E. (2015). Mathematical modeling of thin-layer drying characteristics of agricultural products. Agricultural Engineering International: CIGR Journal, 17(4), 233–241. [Google Scholar] [Crossref]

12. Arima, H., and Danno, G. (2002). Isolation of antimicrobial compounds from guava leaves. Bioscience, Biotechnology, and Biochemistry, 66(8), 1727–1730. [Google Scholar] [Crossref]

13. Basso A. N. S., ErdemT., and Öztekin S. (2025). Analysis of drying kinetics and mathematical modelling of peanut pods using sunlight, hot air, and microwaves drying processes. Turk. J. Agric. - Food Sci. Technol.13 (2), 368–375. 10.24925/turjaf.v13i2.368-375.7192 [Google Scholar] [Crossref]

14. Doymaz, I. (2011). Drying of green leafy vegetables: A review. Food Science and Biotechnology, 20(4), 965–972. [Google Scholar] [Crossref]

15. Ekor, M. (2014). The growing use of herbal medicines: Issues relating to adverse reactions and challenges in monitoring safety. Frontiers in Pharmacology, 4, 177. [Google Scholar] [Crossref]

16. Eleyinmi, A. F. (2007). Chemical composition and antioxidant activity of leafy vegetables. African Journal of Food Science, 1(2), 25–30. [Google Scholar] [Crossref]

17. Erbay, Z., and Icier, F. (2010). A review of thin layer drying of foods: Theory, modeling, and experimental results. Critical Reviews in Food Science and Nutrition, 50(5), 441–464. [Google Scholar] [Crossref]

18. Erukainure, O. L., Oke, O. V., Ajiboye, A. J., and Okafor, O. Y. (2011). Nutritional qualities and phytochemical constituents of Vernonia amygdalina. African Journal of Food Science, 5(4), 213–217. [Google Scholar] [Crossref]

19. Falade, K. O., Adenekan, M. K., Olatunde, S. O., Awolu, O. O., and Alamu, A. E., (2024). Modeling and simulation of drying processes in food engineering. Journal of Food Engineering, 340, 110998. [Google Scholar] [Crossref]

20. Farombi, E. O., and Owoeye, O. (2011). Antioxidative and chemopreventive properties of Vernonia amygdalina. International Journal of Environmental Research and Public Health, 8(6), 2533–2555. [Google Scholar] [Crossref]

21. Fellows, P. (2009). Food processing technology: Principles and practice (3rd ed.). Woodhead Publishing. [Google Scholar] [Crossref]

22. Food Chemistry Advances, (2023). Effect of thin-layer drying conditions on Malabar spinach leaves. [Google Scholar] [Crossref]

23. Fufa D. D., Bekele T., Tamene A., and Bultosa G. (2025). Drying kinetic models, thermodynamics, physicochemical qualities, and bioactive compounds of avocado (Persea americana mill. Hass variety) seeds dried using various drying methods. Heliyon11 (1), e41058. 10.1016/j.heliyon.2024.e41058 [Google Scholar] [Crossref]

24. Gutierrez, R. M. P., Mitchell, S., and Solis, R. V. (2008). Psidium guajava: A review of its traditional uses, phytochemistry, and pharmacology. Journal of Ethnopharmacology, 117(1), 1–27. [Google Scholar] [Crossref]

25. Igile, G. O., Oleszek, W., Jurzysta, M., Burda, S., Fanfunso, M., and Fasanmade, A. A. (1994). Flavonoids from Vernonia amygdalina and their antioxidant activities. Journal of Agricultural and Food Chemistry, 42(11), 2445–2448. [Google Scholar] [Crossref]

26. Ijeh, I. I., and Ejike, C. E. (2011). Current perspectives on the medicinal potential of Vernonia amygdalina. Journal of Medicinal Plants Research, 5(7), 1051–1061. [Google Scholar] [Crossref]

27. Journal of Agriculture and Food Research, (2024). Thin layer drying and temperature effect on bushbuck leaves. [Google Scholar] [Crossref]

28. Kaveh, M., Amiri Chayjan, R., and Taghinezhad, E. (2022). Thin-layer drying modeling of medicinal plants. Drying Technology, 40(8), 1605–1620. https://doi.org/10.1080/07373937.2021.1900972 [Google Scholar] [Crossref]

29. Khater, E. S. G., Shalaby, S. M., and El-Sebaii, A. A. (2024). Drying kinetics and modeling of aromatic leaves under different drying conditions. Journal of Food Process Engineering, 47(3), e14300. https://doi.org/10.1111/jfpe.14300 [Google Scholar] [Crossref]

30. Krokida, M. K., Maroulis, Z. B., and Saravacos, G. D. (2000). The effect of the drying method on the colour of dehydrated products. International Journal of Food Science & Technology, 35(2), 183–190. [Google Scholar] [Crossref]

31. Man X., Li L., Fan X., Zhang H., Lan H., and TangY. (2024a). Drying kinetics and mass transfer characteristics of walnut under hot air drying. Agric. Switz.14 (2), 182. 10.3390/agriculture14020182 [Google Scholar] [Crossref]

32. Martins, F. P., Bosch Neto, J. C., Silva, A. J. O., and Siqueira, A. M. O. (2020). Drying: A review. Journal of Engineering and Exact Sciences, 6(4), 600–607. [Google Scholar] [Crossref]

33. Matasyoh, J. C., Maiyo, Z. C., Ngure, R. M., and Chepkorir, R. (2007). Chemical composition and antimicrobial activity of the essential oil of Ocimum gratissimum. African Journal of Biotechnology, 6(6), 760–765. [Google Scholar] [Crossref]

34. Midilli, A., Küçük, H., and Yapar, Z. (2002). A new model for single-layer drying. Drying Technology, 20(7), 1503–1513. [Google Scholar] [Crossref]

35. Mujumdar, A. S. (2014). Handbook of industrial drying (4th ed.). CRC Press. [Google Scholar] [Crossref]

36. Oboh, G. (2006). Antioxidant properties of tropical green leafy vegetables. Journal of Food Composition and Analysis, 19(6–7), 629–634. [Google Scholar] [Crossref]

37. Okwu, D. E. (2004). Phytochemicals and vitamin content of indigenous species. Journal of Sustainable Agriculture and Environment, 6(1), 30–34. [Google Scholar] [Crossref]

38. Onwude, D. I., Hashim, N., Janius, R. B., Nawi, N. M., and Abdan, K. (2020). Modelling of thin-layer drying of fruits and vegetables: A review. Comprehensive Reviews in Food Science and Food Safety, 19(3), 928–954. [Google Scholar] [Crossref]

39. Pessoa, L. M., Morais, S. M., Bevilaqua, C. M. L., and Luciano, J. H. S. (2002). Anthelmintic activity of essential oil of Ocimum gratissimum. Memórias do Instituto Oswaldo Cruz, 97(8), 117–120. [Google Scholar] [Crossref]

40. Prakash, A., and Gupta, S. (2005). Antioxidant phytochemicals in plant foods. Journal of Food Science and Nutrition, 45(3), 123–130. [Google Scholar] [Crossref]

41. Processes, (2023). Drying Kinetics and Quality Analysis of Coriander Leaves. 11, 1596. [Google Scholar] [Crossref]

42. Rashid, M. T., Ngadi, M. O., & Hashim, N. (2022). Advances in drying kinetics modeling: A review of recent developments and applications. Food Engineering Reviews, 14(4), 655–678. https://doi.org/10.1007/s12393-021-09288-7 [Google Scholar] [Crossref]

43. Sacilik, K., and Unal, G. (2005). Dehydration characteristics of Kastamonu garlic. Journal of Food Engineering, 68(2), 159–166. [Google Scholar] [Crossref]

44. Simić, V., Pavlović, V., and Filipović, V. (2023). Open-air drying kinetics of plant materials. Processes, 11(4), 1120. https://doi.org/10.3390/pr11041120 [Google Scholar] [Crossref]

45. Sofowora, A. (2008). Medicinal plants and traditional medicine in Africa (3rd ed.). Spectrum Books. [Google Scholar] [Crossref]

46. Tezcan, D., Sabancı, S., Cevik, M., Cokgezme, O. F., & Icier, F. (2020). Determination of effective moisture diffusivity in drying processes. Journal of Food Engineering, 280, 109964. https://doi.org/10.1016/j.jfoodeng.2020.109964 [Google Scholar] [Crossref]

47. Togrul, I. T., and Pehlivan, D. (2002). Mathematical modeling of solar drying. Journal of Food Engineering, 55(3), 209–216. [Google Scholar] [Crossref]

48. Trease, G. E., and Evans, W. C. (2002). Pharmacognosy (15th ed.). Saunders. [Google Scholar] [Crossref]

49. Tzempelikos, D. A., Mitrakos, D., Vouros, A. P., & Bardakas, A. V. (2023). Thin-layer drying modeling of herbs. Drying Technology, 41(6), 987–1002. https://doi.org/10.1080/07373937.2022.2041234 [Google Scholar] [Crossref]

50. Vega-Gálvez, A., Ah-Hen, K., Chacana, M., Vergara, J., Martínez-Monzó, J., García-Segovia, P., and Lemus-Mondaca, R. (2012). Effect of temperature and air velocity on drying kinetics and quality of red pepper. Food Research International, 45(1), 333–340. [Google Scholar] [Crossref]

51. World Health Organization (WHO). (2013). WHO traditional medicine strategy 2014–2023. WHO Press. [Google Scholar] [Crossref]

52. Xie, M., Zhang, Y., Liu, H., Chen, X., and Wang, L. (2023). Drying kinetics and quality characteristics of medicinal herbs during hot-air drying. Molecules, 28(9), 3898. https://doi.org/10.3390/molecules28093898. [Google Scholar] [Crossref]

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