Total Polyphenols, Antioxidant Activity and Antibacterial Effect of Nine Cultivars of Cactus Pear (Opuntia spp.) and Their By-products

Introduction: Nopal cactus (Opuntia spp.) is an important resource of semi-arid zones of the world, where fruits and stems are used as food or forage, depending on the variety or ripeness of the cladode. Opuntia genus has a good capacity of adaptation, and comprises a large number of species with variable phytochemical composition. About 20% of the cladodes are by-products (modified leaves or thorns) that are usually discarded. 

Purpose: To evaluate the antioxidant and antibacterial potential of 9 nopal cultivars and their by-products.

Methods: Cladodes and by-products from 9 nopal cultivars were washed, dried and macerated in ethanol, evaporated and the extract resuspended in water. The antimicrobial activity against V. cholerae and C. perfringens was determined. Preliminary analyses were conducted by the well diffusion method. Minimal bactericidal concentrations (MBCs) were determined using the broth microdilution method. Quantification of total phenols and flavonoids, and antioxidant capacity, as TEAC and inhibition percentage of DPPH radical, were performed by spectrophotometric methods.

Results: All extracts showed antioxidant and antibacterial activity. Extracts of cladodes and by-products showed similar MBC (around 7.5 mg/ml) for C. perfringens and (4.0 mg/ml) for V. cholerae. The cladode by-products showed higher antioxidant capacity (DPPH and TEAC tests) when compared with cladodes. High concentrations of phenols and flavonoids were also found in the by-products analyzed (ranges from 91.23 to 853.78 mg GAE/g DW and from 17.10 to 39.42 mg QE/g DW). 

Significance: This study demonstrated the antimicrobial activity of nopal cactus byproducts with a higher content of phenols and flavonoids, and an increased antioxidant activity compared with cladodes.