A research team has developed a molecularly imprinted electrochemical sensor combined with a "conversion factor T" strategy to rapidly and selectively quantify the major lutein esters in marigold extracts. The sensor detects lutein dipalmitate as a representative marker, while predefined conversion factors enable the concentrations of three other major lutein esters to be calculated indirectly. By avoiding cumbersome saponification and reducing dependence on multiple expensive reference standards, the approach could support faster routine quality control of marigold extracts, dietary supplements, eye-care products, and other lutein-containing products.
Marigolds are the predominant commercial source of lutein, a carotenoid widely used in foods, beverages, animal feed, and dietary supplements. Lutein and related macular pigments can help protect the retina against oxidative damage and have been associated with a reduced risk of age-related macular degeneration. In marigold petals, however, lutein occurs mainly as esters formed with different fatty acids, creating a chemically complex mixture. Conventional analysis generally requires saponification to convert these esters into free lutein before measurement. This procedure requires heating, takes considerable time, and may degrade heat-sensitive carotenoids. Direct chromatographic quantification is also constrained by the limited availability and high cost of individual lutein ester standards. These limitations create a need for a rapid, selective, and comprehensive analytical method.
A study (DOI: 10.48130/els-0026-0010 ) published in Engineering in Life Sciences on 24 August 2026 by Axin Liang's team, Beijing Institute of Technology, reports a sensing-conversion platform that estimates four predominant lutein esters through the direct measurement of lutein dipalmitate.
The researchers first used high-performance liquid chromatography-mass spectrometry to characterize the lutein ester composition of marigold extracts. They identified four predominant compounds: lutein dimyristate, lutein myristate-palmitate, lutein dipalmitate, and lutein palmitate-stearate. Taking lutein dipalmitate as the reference marker, they calculated conversion factors from chromatographic peak areas and molecular masses. The resulting factors for lutein dimyristate, lutein myristate-palmitate, and lutein palmitate-stearate were 0.903, 0.964, and 1.035, respectively. Relative standard deviations were below 1% across different injection volumes, while tests involving different instruments, columns, temperatures, and flow rates generally produced values below 2%, demonstrating the robustness of the conversion approach. To measure the reference marker rapidly, the team synthesized a conductive Ni₃(HITP)₂ metal-organic framework and deposited it onto a screen-printed carbon electrode. A molecularly imprinted polymer film was then formed in the presence of lutein dipalmitate; after the template was removed, complementary recognition cavities remained available for selective rebinding. Structural and electrochemical analyses confirmed successful sensor fabrication, and the metal-organic framework increased the electrode's peak current approximately fourfold relative to the unmodified electrode. Under optimized conditions—12 electropolymerization cycles, a scan rate of 50 mV/s, four minutes of template removal, and 15 minutes of target rebinding—the sensor responded across a lutein dipalmitate concentration range of 0.01–100 μM and achieved a detection limit of 8.20 nM. It also showed substantially greater sensitivity toward lutein dipalmitate than toward lutein, α-tocopherol, glucose, or glutamic acid. When applied to marigold extract, the new method estimated lutein at 62.63 mg/g, compared with 71.73 mg/g using conventional saponification. For a commercial eye-care product, the corresponding results were 3.60 and 3.72 mg/g, indicating close agreement in a practical sample.
By linking selective electrochemical detection with stable conversion relationships, the study offers an efficient way to estimate several major lutein esters from a single target measurement. The platform simplifies sample preparation, shortens analysis, and lowers the need for multiple standards while retaining useful analytical accuracy. Although further validation is needed for samples with substantially different ester profiles or high levels of minor lutein esters, the method provides a promising foundation for rapid screening, industrial monitoring, and routine quality assessment of lutein-containing natural products.
