Characterization of Bioactive Composition and Structural Properties of Epidermis and Cortex Tissues in Edible Cactus [Opuntia ficus-indica (L.) Mill.] Cladodes at Different Maturity Stages

Opuntia ficus-indica (L.) Mill., an edible cactus, has gained increasing attention as a potential food resource due to its adaptability and nutritional value. This study aimed to characterize the bioactive compound profiles and structural characteristics of the epidermis and cortex of cladodes across different maturity stages. Numerically higher levels of bioactive compounds were generally observed in the epidermis than in the cortex, particularly gentisic acid (384.58–668.23 µg/g DW in the epidermis vs. 191.11–426.69 µg/g DW in the cortex) and protocatechuic acid (154.04–234.45 µg/g DW in the epidermis vs. 40.78–118.44 µg/g DW in the cortex). The epidermis and cortex also exhibited distinct organic acid profiles, with oxalic and malic acids being the predominant organic acids detected in both tissues. FTIR analysis further revealed a more pronounced O–H absorption band associated with water molecules in the cortex than in the epidermis. Furthermore, stage-dependent variations were observed in both bioactive composition and structural characteristics. Organic acids exhibited stage-dependent variations in both tissues. Oxalic, malic, and succinic acids generally occurred at higher levels during the later maturity stages, whereas fumaric acid was more abundant at the earliest maturity stages. Their concentrations ranged from 13.61–47.20, 10.74–16.27, 7.56–14.47, and 0.51–20.46 mg/g DW in the epidermis, and 8.19–46.82, 9.67–52.26, 2.76–14.72, and 0.27–34.41 mg/g DW in the cortex, respectively. These findings provide baseline information on the compositional and structural characteristics of edible cactus cladodes and may support future studies on their potential food-related applications.