Preparation of lutein through biotransformation in a microemulsion medium

Abstract To address the issues of low purity, poor stability and environmental pollution associated with traditional organic solvent extraction methods for lutein production, and to meet the requirements for food-grade lutein in industrial applications, this study developed a microemulsion system using n-propyl acetate as the oil phase, Tween 80 as the surfactant and ethanol as the co-surfactant. A microemulsion with 60% water content was successfully formulated as the reaction medium. Lipase was introduced to catalyse the hydrolysis of lutein esters, followed by optimization of key reaction parameters and evaluation of the stability of the resulting free lutein. The results demonstrated that under optimized conditions, the conversion rate of lutein ester reached 72.53 ± 2.80%, representing a 153.87% improvement compared with the 28.57 ± 1.81% conversion achieved when using an acetonitrile–aqueous solution as the enzymatic reaction medium. Furthermore, the lutein microemulsion exhibited superior storage and thermal stability relative to lutein in ethanol solution. Notably, all components of the microemulsion system are approved food additives, making the system suitable for use in food manufacturing. This work provides a solid scientific foundation and a feasible technical pathway for the production of food-grade lutein. With further research, this approach has the potential to become an efficient and environmentally sustainable method for the extraction of water-insoluble pigments.