Functional properties of saponins from sisal (Agave sisalana) and juá (Ziziphus joazeiro): Critical micellar concentration, antioxidant and antimicrobial activities

• Juá and sisal saponins have CMCs around 0.08–0.15 g/L in the presence of NaCl.
• Antioxidant activity of juá and sisal extracts was higher than their isolated saponins.
• Juá saponins presented antimicrobial activity against Candida albicans and Aspergillus niger.

Saponins are triterpenic or steroidal glycosides largely distributed in plant kingdom, which have many physicochemical (foaming, emulsification, solubilization, sweetness, bitterness) and biological properties (haemolytic, antimicrobial, antioxidant, moluscacide, insecticide, ichthyocide), which are exploited in many applications in food, cosmetics and pharmaceuticals industries, and also in soil bioremediation. Among the saponins properties, critical micellar concentration (CMC), maximum surface density and aggregation number (number of monomers in a micelle) are of great importance for application as surfactants and foaming agents. These are influenced by variables such as temperature, salt concentration, aqueous phase pH, solvent concentration and type (ethanol, methanol). The objective of this work was to evaluate some functional properties as critical micellar concentration (CMC), antimicrobial and antioxidant activities of two different saponins originated from Brazilian agrobiodiversity: sisal (Agave sisalana), with steroidal aglycone, and juá (Ziziphus joazeiro), a triterpenic aglycone. The variation of CMC from juá and sisal saponins was measured against parameters as temperature, pH and NaCl (%m/v) concentration, using turbidimetric titration (spectrophotometry), and for each CMC, it was detected the respective surface tension. The highest reduction on CMC values from juá saponins can be observed in neutral pH, near room temperature (25–30 °C) and saline concentrations among 2 and 4% m/v, while for sisal saponins, the conditions were pH between 3 and 4 with near room temperature; or pH among 10–11 with temperatures around 55–60 °C; and saline concentration from 2 to 6% m/v. Antioxidant activity of isolated saponins from juá and sisal was very low, represented only 25% of the antioxidant activity reached by its corresponding raw extracts (saponins and phenolics). Juá saponins presented antifungal activity against Candida albicans (156 μg/mL) and Aspergillus niger (312.5 μg/mL), while sisal saponins possessed no antimicrobial activity.

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