Background and Objectives: Caper (Capparis spinosa L.) is one of the most important medicinal plants of arid and semi-arid regions and has attracted considerable attention in the pharmaceutical, food, and cosmetic industries due to its wide range of bioactive compounds. Despite the importance of this species, information regarding the distribution of biochemical and phytochemical compounds among different plant organs and at various stages of fruit ripening remains limited in many natural habitats of Iran, including Beyza County. Therefore, the present study was conducted to compare the biochemical and phytochemical characteristics of leaves, flower buds, flowers, peduncles, and fruits at three developmental stages (unripe, semi-ripe, and fully ripe) in order to identify the most suitable plant organ for pharmaceutical and industrial applications.
Materials and Methods: Plant samples were collected from a natural population located in Beyza County, Fars Province, during the flowering and fruiting seasons. The experiment was conducted in a randomized complete block design (RCBD) with seven categories, including leaves, flower buds, fully opened flowers, peduncles, unripe fruits, semi-ripe fruits, and fully ripe fruits, with three replicates. After drying the samples and preparing 70% methanolic extracts, antioxidant activity was evaluated using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging assay. Total phenolic content was determined using the Folin–Ciocalteu reagent, and the results were expressed as milligrams of gallic acid equivalents per gram of dry weight (mg GAE g⁻¹ DW). Total flavonoids as well as flavones and flavonols were determined by the aluminum chloride colorimetric method using quercetin as the standard. Total tannin content was measured using the vanillin–hydrochloric acid colorimetric assay, and the results were expressed as milligrams of catechin equivalents per gram of dry weight (mg CE g⁻¹ DW). Total carbohydrate content was determined by the anthrone colorimetric method using glucose as the standard. After verification of the statistical assumptions, the data were subjected to analysis of variance (ANOVA), and treatment means were compared using Tukey’s test at the 1% probability level. Pearson's correlation analysis was performed to evaluate the relationships among the measured traits, while cluster analysis based on Euclidean distance and standardized data was used to determine the similarity among the investigated plant organs.
Results: Analysis of variance revealed significant differences among the investigated organs for all measured traits at the 1% probability level. The highest antioxidant activity (90.20%) was observed in flower buds, whereas leaves contained the highest total phenolic content (17.74 mg GAE g⁻¹ DW), total flavonoid content (23.97 mg QE g⁻¹ DW), and flavones and flavonols (5.95 mg QE g⁻¹ DW). The highest tannin content was recorded in flowers (1.19 mg CE g⁻¹ DW), leaves (1.15 mg CE g⁻¹ DW), and fully ripe fruits (1.10 mg CE g⁻¹ DW), with no significant differences among these organs. In contrast, fully ripe fruits exhibited the highest carbohydrate content (302.67 mg glucose g⁻¹ DW). During fruit ripening, carbohydrate content increased progressively, whereas most phenolic compounds showed a decreasing trend. Correlation analysis revealed significant positive relationships between antioxidant activity and total flavonoids, flavones and flavonols, and total phenolic content. Likewise, total phenolic content showed a very strong positive correlation with total flavonoids, and total flavonoids were strongly correlated with flavones and flavonols. In contrast, carbohydrate content exhibited significant negative correlations with both total phenolic content and total flavonoids. Cluster analysis classified the investigated organs into distinct groups according to their biochemical and phytochemical characteristics and clearly separated vegetative and reproductive organs from fruits at different ripening stages.
Conclusion: The results of this study demonstrated that plant organ and developmental stage play decisive roles in the accumulation of primary and secondary metabolites in caper. Flowers, leaves, and flower buds, owing to their high contents of phenolic compounds, flavonoids, and antioxidant activity, represent the most suitable organs for the extraction of bioactive compounds and their utilization in pharmaceutical, food, and cosmetic industries. In contrast, fully ripe fruits were superior in terms of carbohydrate accumulation. These findings provide a valuable scientific basis for selecting the appropriate plant organ and optimum harvesting stage to maximize the utilization of this valuable medicinal species.