Determination of natural turmeric dyes using near-infrared spectroscopy

Turmeric extracted from natural plants serves as a commonly natural dye but currently faces quality challenges due to the absence of standardization. Rapid determination of natural turmeric dye contents before the dyeing process is paramount. In this study, to determine the content of total and separate curcuminoid compounds, 155 samples of turmeric dyes were analyzed using both high-performance liquid chromatography and near-infrared technology. The near-infrared spectra within the range of 8000-5000 cm(-1) were selected, and after method optimization, the spectral preprocessing method of Savitzky-Golay smoothing (SG) + standard normal variate transformation (SNV) / multiplicative scatter correction (MSC) + first derivative (1st-Der) were used to construct the partial least squares (PLS) quantitative prediction models. Method validation results showed that the optimized model revealed exceptional prediction accuracy. In general, the total curcuminoid compounds quantitative prediction model demonstrated higher accuracy than that of the separate compounds, with R-2 > 0.99 and RPD > 10. In contrast, the separate curcuminoid compounds quantitative prediction model has R-2 > 0.97 and RPD > 6. Both models are suitable for turmeric dyes, and as fast and flexible detection methods, they are suitable for industrial production.