Biosurfactants such as sophorolipids are natural and eco-friendly surfactants that are used in cosmetics and health care products. In addition to surfactant properties, sophorolipids also possess antimicrobial and skin healing properties. In the present work, castor oil (10%) was used as a non-conventional carbon source in combination with glucose (10%) or with glycerol (15%) for fermentative production of novel sophorolipids by using Starmerella bombicola (ATCC 22214). The yields of sophorolipids are 6.1 g/L on castor oil with glucose as a carbon source and 2.7 g/L on castor oil with glycerol as a carbon source analyzed by anthrone method and HPLC. The structures of sophorolipids synthesized on castor oil were elucidated by liquid chromatography–mass spectrometry and 1H NMR of the purified compounds. The results indicated the incorporation of ricinoleic acid into sophorolipids without omega-1 oxygenation step that is required for incorporation of oleic acid into sophorolipids. It resulted in the production of novel sophorolipids that can find various applications as cosmetic ingredients and antimicrobial agents.
Practical applications: Castor oil, widely produced in India, contains palmitic acid (1–2%), strearic acid (1–2%), oleic acid (6–8%), linoleic acid (0.5–1%), and mainly ricinoleic acid (80–90%). The presence of hydroxyl fatty acid as ricinoleic acid makes castor oil different from other vegetable oils. Therefore, castor oil is being used as a valuable raw material in various chemicals industries. The present work proved that castor oil can be used as a new substrate for the production of sophorolipids with a novel structure having hydroxyl group on the moiety. The end product can be used for enhancement of surfactant properties in combination with a chemically synthesized surfactant.