Anthocyanins from Red Cabbage Sorption Assessment on Bentonites from Patagonia (Argentina)

In the northern Patagonian region of Argentina, there exist some of the largest bentonite deposits. Four bentonite samples (B1, B2, B3, and B4) from two deposits were thoroughly characterized and evaluated as potential adsorbents of anthocyanins extracted from red cabbage. Anthocyanins (ACy) are natural colourants obtained from fruits and plants and have shown excellent antioxidant properties that have promising applications in health. The adsorption of ACy onto bentonites enhances their stability relative to that observed in aqueous solutions. Material characterization showed that three of the samples are sodium bentonites (Na-bentonites: B2, B3, and B4), while the fourth exhibits a large quantity of magnesium and calcium in its interlayer, classifying it as a Mg-Ca-Na-bentonite (B1). Na-bentonites demonstrated higher ACy adsorption capacities, occurring through cation exchange while Mg-Ca-Na-bentonite adsorption occurs by another kind of interaction and a cooperative adsorption mechanism, resulting in the lowest ACy adsorption. The highest adsorption capacity was for B3, characterized by the highest smectite content, cation exchange capacity, and proportion of monovalent cations in its interlayer. Under the conditions studied, sodium smectites proved to be capable of retaining red cabbage ACy, there by introducing a novel avenue for potential applications of regional materials with potential implications for health-related uses.