Chemical Fingerprint Analysis of Zea mays L. (Corn Silk) Flavonoids in Commercial Extracts using HPTLC

The styles and stigmas of Zea mays L. (Family, Gramineae), commonly known as corn silk, have been traditionally used as a diuretic and are reportedly used in treating urinary problems such as nephritis, urethritis, lithiasis and prostatis in Traditional Chinese Medicine and also in South American countries such as Costa Rica, Mexico, Guatemala, and Trinidad [1]. Several unique flavonoids have been identified in corn silk that could be used for identity markers. A simple, precise and rapid high-performance thin layer chromatography (HPTLC) method was developed for the qualitative analysis of these four flavonoids [Rhamnosyl isoorientin (1), Maysin (2), Apimaysin (3), and De-Rhamnosyl-Maysin (4)] in corn silk. Compounds were separated on silica gel ⁶⁰F₂₅₄ eluted with ETOAC: Formic acid: Acetic acid: H₂O (10:1.1:1.1:2.5v/v/v/v) with detection at 366nm wavelength after spraying with 1% methanolic diphenylboric acid -β-ethylamino ester reagent. Evaluation of the HPTLC plates was done by using the CAMAG DigiStore2 digital system with winCATS software. The samples were identified by matching the colors and R _f values of the bands with those of the standard compounds. Figure 1 reveals the presence of these compounds in an authenticated corn silk reference sample. Figure 2 demonstrates the application of this method for identification of various commercial samples. In Figure 2, Track-1 shows the presence of all four flavonoids in standard reference material. Tracks 2–3 and 5–7 are commercial samples that did not appear to contain the flavonoid marker compounds. Exposure to temperatures higher than 100°C destroy these flavonoids, which may explain they are not detected in commercial samples processed at high temperatures such as spray drying or steam treatment. This analytical method provides a good separation of four corn silk flavonoids and is useful for quality control of commercial samples.

Fig.1: Track-1 & 7: Authenticated corn silk; Track-2: Rhamnosyl isoorientin; Track-3: Maysin; Track-4: Std Mix-4; Track-5: Apimaysin; Track-6: De-Rhamnosyl- Maysin.

Fig.2: Track- 1: Authenticated corn silk; Track 2–3, 5–7: Commercial extracts; Track-4: Std Mix-4 [Rhamnosyl isoorientin (1), Maysin (2), Apimaysin (3), and De-Rhamnosyl-Maysin (4)].

Acknowledgements: This research is supported in part by Global Science, Product Safety and Compliance, Herbalife International of America, Torrance, CA 90502, USA, and the United States Department of Agriculture, Agricultural Research Service, Specific Cooperative Agreement No. 58–6408–2-0009 and the authors would like to thank Annette Ford for the extraction of plant samples and Dr. Maurice Snook USDA/ARS for providing standard compounds.

References: [1] Caceres A, et al. J Ethnopharmacol, (1987) 19: 233–245.