Extraction of Lutein from Chrysanthemum by Menthol-based Deep Eutectic Solvents to Synthesize the Lutein-Menthol Cocrystal

To establish an eco-friendly and efficient method for extracting natural lutein while enhancing its stability, this study employed menthol-based deep eutectic solvents (DESs) for the extraction of lutein from chrysanthemum and the preparation of lutein-menthol cocrystals. The feasibility of this approach was evaluated through the analysis of the antioxidant activity of the extracted lutein solutions, as well as the stability and composition of the cocrystals. Firstly, the extraction efficiency of six DESs (menthol-acetic acid, menthol-propionic acid, menthol-octanoic acid, menthol-decanoic acid, menthol-hexanoic acid, and menthol-lactic acid) for lutein was compared, identifying the optimal eutectic solvent. Subsequently, single-factor investigations were conducted on ethanol content, solid-to-liquid ratio, extraction temperature, and extraction time, and the extraction process parameters were optimized by using the response surface method. At the same time, the antioxidant activity of the extracted lutein solution was evaluated, and the differences in light and heat stability between the lutein-piperonal complex and the commercially available lutein powder were investigated. The cocrystal was analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results indicated that menthol-acetic acid (DES-1) was the optimal eutectic solvent; the optimized extraction conditions were 47% (V/V) ethanol content, a material-to-liquid ratio of 1:45 (g/mL), and an extraction temperature of 69 ℃, under which the extraction yield of lutein can reached 644.11±1.99 μg/g. The lutein solution extracted and prepared with DES-1 exhibits scavenging rates of 77.52% and 84.58% for hydroxyl radicals and DPPH radicals, respectively, which were significantly higher than those achieved by traditional ethanol extraction methods (P<0.01). Under thermal conditions of 30 ℃ at 75% relative humidity and light conditions of 4500 Lux at 25 ℃, the lutein retention rates for the lutein-menthol cocrystal were 84.34% and 33.73%, both of which were significantly higher than those of commercially available lutein. The formed cocrystal structure could physically hinder oxygen penetration, while the hydroxyl groups at both ends of lutein can form strong hydrogen bonds with the hydroxyl groups of menthol, thereby significantly enhancing stability. Identification through LC-MS/MS revealed a total of 33 lutein-related components in the cocrystal, including lutein and lutein palmitate, with the highest content of free lutein reaching 107.93±11.36 μg/g. The lutein-menthol cocrystal prepared in this study significantly enhances the stability of lutein and may provide more possibilities for the practical development and utilization of lutein.