Free radicals and oxidant molecules are very harmful to any living organism. In this study, biomolecules from Opuntia ficus-indica fruit peels were used as oxidant-scavengers. The work was conducted first by characterizing this waste matrix from the physicochemical side; Acidity, pH, brix and moisture were determined, then, the antioxidant molecules, mainly betaxanthins, were extracted by maceration in 70% ethanol (v/v). The quantification of betaxanthins, flavonoid, ascorbate and proanthicyanidins were performed spectrophotometrically. After that, the extract was tested on its Hydrogen donation and electron transfer potentials by several antioxidant and antiradical tests; DPPH° and ABTS° assays for synthetic radicals, anti-OH and anti-NO assays for the highly reactive biological species, reduction of phosphomolybdate, and ferrous ion chelating potential. These tests were compared to the appropriate standards for each activity.
The physicochemical results showed an important amount of water within the fresh matrix estimated at 83±0,50 %, a considerable amount of TSS (12±0,50 %), a less acidic pH (5,40±0,10) followed by a slight rate of acidity (0,05±0,003 %). For the biomolecules determination, 2309,59±10,33 mg of phenolics by 100g of Dry matter, 32.62 ± 3.64 mg of betaxanthins, 806,55 ± 8,78 mg of flavonoids and 254,75 ± 4,57 mg of ascorbate. The antioxidant activities showed a very interesting results; All the test performed showed an activity rate near to 100%. At low concentrations, the peel extract (CPE) showed an IC50 within DPPH and ABTS radicals tests at 94,63±4,92 µg/mL and 233,94±15,6 µg/mL, respectively, 94,62±2,4 µg/mL and 261,56±7,88 µg/mL against OH° and NO° biological radicals. Ferrous ions were quenched by 50% at 143,97±9,33 µg/mL and finally phosphomolybdate reduction power showed an EC50 of 203,44±7,77 µg/mL. Significant correlations were found between the two antioxidant tests and the content in betaxanthins comparing with the other parts of the plant. Our findings let us to conclude that cactus fruit peels are considered as an important source of pigments, flavonoids and ascorbate wich would be used in different industrial sectors.