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Evaluation of quantitative changes in phenolic, flavonoid and saponins compounds of caltrop (Tribulus terrestris L.) fruit as affected by drying methods

Document Type : Research Paper - Medicinal Aromatic Plants

Authors
Yasamin Dabaghkar 1
Ghasem Eghlima 2
Fateme Aghamir 2
Mohammad Hossein Mirjalili 3
1 M.Sc. Student, Department of Agriculture, Medicinal Plants and Drugs Research Institute, Shahid Beheshti University, Tehran, Iran
2 Assistant Professor, Department of Agriculture, Medicinal Plants and Drugs Research Institute, Shahid Beheshti University, Tehran, Iran
3 Professor, Department of Agriculture, Medicinal Plants and Drugs Research Institute, Shahid Beheshti University, Tehran, Iran
10.22055/ppd.2025.48143.2215
Abstract
Introduction
 Caltrop (Tribulus terrestris L.) from the family of Zygophyllaceae, which is rich in saponins compounds, especially diosgenin, has various biological properties, such as anti-inflammation, anti-Alzheimer, anti-obesity, anti-diabetes, anti-leukemia, and anti-cancer activities, due to these compounds and many medicines are produced from it. Drying is one of the main steps in the post-harvest process of medicinal plants, which plays an important role in the quantity and quality of their effective ingredients. The results of studies have shown that the method used for drying has a significant effect on the performance and content of secondary metabolites of medicinal plants. Considering the wide use of the caltrop in the pharmaceutical industry, as well as the importance of the drying process in medicinal plants, this research aims to investigate the effect of different drying methods on the drying time and some phytochemical traits (including diosgenin content) of the fruits of caltrop was executed.
 Materials and Methods
 In order to investigate the effect of different drying methods on the fruit of the caltrop, an experiment based on a completely randomized design with eight treatments and three repetitions was carried out in 2023 in the Ecophysiology Laboratory of Plants and Medicinal Plant and Drug Research Institute of Shahid Beheshti University, Tehran. In this study, the fruit of caltrop plant was used, which was collected from the collection of medicinal plants of Shahid Beheshti University, which was harvested at the fruiting stage. The tested treatments included natural drying (drying in the sun and shade), drying in the oven (40, 50 and 60 °C) and drying in the microwave (power 500, 700 and 900 W). In different methods, drying was continued until the moisture content reached 10% (based on plant-wet weight). The dried samples were used to extract the methanolic extract in order to measure some secondary metabolites, including total phenol content, total flavonoid content, antioxidant activity, total saponins and diosgenin content. The content of total phenol, total flavonoid and antioxidant activity were measured by Folin–Ciocalteu, aluminum chloride and DPPH methods, respectively. High-performance liquid chromatography (HPLC) analysis was used to measure diosgenin content.
 Results and Discussion
According to the results obtained, increasing microwave powers resulted in a significant reduction in the time required to reach a moisture content of 10% on a wet weight basis. Also, the drying time in the microwave method, especially at 900 W power, was shorter compared to the oven method (with a duration of 9, 12 and 16 hours). In the oven-drying method, the drying process varied from nine to 16 hours depending on the different temperatures, and increasing the oven temperature increased the slope of the moisture content reduction curve. In addition, with increasing temperature, the drying time decreased significantly. The drying process in the natural method was 45 and 70 hours in the sun and shade methods, respectively. The highest content of total phenol (12.6 mg GAE. g-1 DW), total flavonoid (7.38 mg RE g-1 DW) and antioxidant activity (IC50 = 16.70 μg.ml-1) in shade drying treatment was achieved.  The highest content of total saponins (9.75 μg oleanolic acid g-1 DW) and diosgenin (7.75 mg. g-1 DW) was observed in oven treatment with a temperature of 40 °C. With the increase of oven temperature and microwave power, the amount of secondary metabolites in caltrop fruit extract decreased.
 Conclusion
Overall, shade drying and oven drying at low temperature (40°C) were the most effective methods for preserving bioactive compounds, while microwave drying provided a rapid alternative with little loss of quality. These findings provide practical insights for optimizing post-harvest processing to enhance the medicinal value of caltrop.
Keywords
Antioxidant activity
Diosgenin
Processing
Total saponins
Subjects
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Plant Productions
Volume 48, Issue 4
Winter 2026
Pages 685-698