Effect of drying methods and pretreatments on the physical and antioxidant properties of prickly pear (Opuntia stricta and Opuntia ficus-indica)

The invasive proliferation of prickly pear ( Opuntia stricta [OS] and Opuntia ficus - indica [OFI]) in arid regions offers an opportunity to source a wide array of valuable bioactive and nutraceutical compounds. This study aimed to identify optimal drying and pretreatment strategies to preserve the quality of these fruits for commercial applications. Physical properties analyzed included moisture content, water activity, rehydration characteristics, and color. Antioxidant retention was determined using UV–VIS spectrophotometry to quantify betalains, total phenols, total flavonoids, total carotenoids, β-carotene, and antioxidant activity (DPPH assay). Results showed that freeze drying (FD) best preserved structural integrity, yielding the highest rehydration ratios (OS: 3.68–3.70; OFI: 4.27–4.52) and minimal color change (ΔE = 7.48–23.18), while oven drying (OD) and solar drying (SD) achieved lower final moisture content (6.99%–9.65%) and water activity (0.346–0.484). For antioxidant retention, FD was superior, but the efficacy of citric acid pretreatment was compound-specific: it was crucial for preserving flavonoids and β-carotene, marginally beneficial for phenols, and ineffective for betalains. Blanching consistently reduced antioxidant content. OFI exhibited higher carotenoid levels, whereas OS retained more phenols. These findings demonstrate that the optimal processing strategy is goal-dependent. Although FD is ideal for premium quality, oven-drying combined with citric acid pretreatment represents the most practical approach for industrial-scale processing, effectively balancing bioactive retention with shelf-stability and cost-effectiveness. This approach facilitates the transformation of an ecological threat into a sustainable source of functional food ingredients.