Quantification of Purple Corn (Zea mays L.) Anthocyanins Using Spectrophotometric and HPLC Approaches: Method Comparison and Correlation

Abstract

Purple corncob is a rich source of anthocyanins with great potential as food colorant. Accurate quantification of anthocyanin content in cereals such as purple corn is critical to evaluate their nutritional value and facilitate their application in foods. Our objective was to determine the advantages and disadvantages of four common spectrophotometric and chromatographic methods to quantify cereal anthocyanins. Anthocyanins from 14 purple corncob samples were extracted, identified by high-performance liquid chromatography (HPLC)-PDA-MS, and quantified different methods commonly cited in the literature or used by analytical laboratories: total anthocyanins, pH differential, and HPLC methods with intact or acid hydrolyzed pigments. Polymeric color was also determined as it affects color quality. Among the four methods, the total anthocyanin method produced the highest value, followed by the pH differential method and HPLC with intact pigments, which produced very similar results, while the HPLC with hydrolyzed pigments produced the lowest values. The quantitative differences among the four methods are likely due to the differences in their specificity. Despite the differences in quantitative results, three of the methods, pH differential and both HPLC methods, showed good linear correlation (R 2 ≥ 0.98). In addition, the effect of wavelength selection and the criteria for HPLC integration were also evaluated. In summary, anthocyanin quantification results were dependent on the method chosen to quantify the pigments in the material. So, reporting methodology is critical and recommended when interpreting the anthocyanin quantification results for better inter-literature comparison.