Development and validation of a method based on liquid chromatography-mass spectrometry for comprehensive profiling of phenolic compounds in rice

The consumption of rice grains containing phytochemicals associated with antioxidant activity can potentially reduce the risk of chronic diseases. These phytochemicals, which include phenolic acids, anthoxanthins, and anthocyanins, are present in both free and bound forms in rice grains. However, there is limited documentation on the development of a method for determining the simultaneous amount of both free and bound phenolic compounds using sensitive analytical techniques. To address this gap, a study was conducted to develop and validate a liquid chromatography-mass spectrometric detection method for quantifying eighteen phenolic compounds in rice grains, both in free and bound forms. Paracetamol was used as the internal standard to minimize the effect of matrix interferences. The method was validated by measuring its working range, linearity, accuracy, precision, limits for detection and quantification, robustness, and expanded uncertainty. The method has a wide working range of 1.0 to 30.0 mg/kg for each phenolic compound and good linearity, with regression coefficients of calibration graphs greater than 0.999. Accuracy was determined using the recoveries after fortification at three concentration levels, which were in the range of 83.1 to 101.2%. Precision was expressed as a percentage of relative standard deviation (%RSD), which was below 7.62% for all determined phenolic compounds. The detection limits (LoD) and quantification limits (LoQ) ranged between 0.53 and 0.75 mg/kg and 0.54-0.77 mg/kg, respectively. The percentages of expanded uncertainties at the coverage factor of 2 (k = 2) were below 11.7%. The method was also evaluated for its robustness by obtaining recoveries at satisfactory levels for three different kinds of cereal; wheat, maize, and millet. The validated method is an accurate and reproducible approach for the simultaneous determination of phenolic compounds present at low levels in a complex matrix such as rice. The study also found that the phenolic profiles vary among rice genotypes, which can significantly impact human health by varying the nutraceutical properties of rice grains as health-promoting aspects.