Development of green solubilizer based on acidic sophorolipid

Solubilization of oil-soluble substances in aqueous solution is essential in daily chemistry. Commonly used synthetic solubilizers are environmentally harmful and have limited applications. In this study, sophorolipid, a biosurfactant, was purified through an efficient, simple, and solubilization-compatible method, yielding an aqueous acidic sophorolipid (acid-SL) with high purity of 96 wt%. The bola structure of acid-SL conferred reversible pH-responsive micelle behavior and therefore a distinctive solubilization effect on polar small molecules under neutral pH environment. Based on this, the synergistic solubilization effect of acid-SL in combination with rhamnolipid (RL) was confirmed, with the optimal compound ratio being acid-SL/RL = 0.95:0.05. The compound system significantly improved the solubilization ability under acidic conditions and had superior solubilization capacity for oil-soluble substances such as essential oils, fragrances, and preservatives compared to commonly used solubilizers like Polysorbate 20 and Polyoxyethylene 40.