Enhanced Analysis of Curcuminoids in Turmeric via Selective Homodecoupled 1D 1H NMR.

Abstract

Curcuminoids, including curcumin, demethoxycurcumin, and bisdemethoxycurcumin, are vital for quality control in food, nutraceuticals, and pharmaceuticals. Conventional 1D ¹H NMR can face challenges in spectral interpretation when dealing with overlapping signals and complex coupling patterns, especially in structurally similar compounds like curcuminoids. This study explores the use of selective homodecoupled 1D ¹H NMR spectroscopy as a complementary technique to enhance spectral resolution and facilitate peak assignment in curcuminoid analysis. By collapsing multiplet structures such as doublets observed in the 6.6- to 6.8-ppm region for vinylic protons into singlets, this method offers improved spectral clarity. Although absolute quantification still requires deconvolution, the approach aids in more straightforward relative integration and identification of components within curcuminoid mixtures from turmeric samples. The results demonstrate improved interpretability compared with conventional ¹H NMR under similar conditions. Comparative analysis with HPLC showed excellent agreement, with standard deviations under 2% for most samples. The selective homodecoupled 1D ¹H NMR method proved robust and reliable, offering an effective tool for profiling curcuminoids and potential application to other natural product mixtures.