Analysis of the degradation of betanin obtained from beetroot using Fourier transform infrared spectroscopy

Betalains are vacuolar pigments present in tubers, flowers or fruits. Their use in the food industry is significant because they are considered bioactive completely safe to consume. However, betalains are susceptible to temperature which affects their stability. The most of the available methods that determine stability involve high costs, are destructive and generate waste. In this work was evaluated the thermal degradation of betalain at 75 °C for several intervals of time, by using different techniques. Colorimetry showed a change in the tone angle (h°) from 359.76° to 20.54° after the heat-treatment, suggesting thermal degradation by changing the color from violet to red–orange. High-pressure liquid chromatography, shows the decrease of the concentration of betanin in addition to the formation of neobetanin, the main degradation product in betalains. UV–visible spectrophotometry suggest also thermal degradation of betanin, by the decrease of the absorption at 538 nm caused by the heat treatment. Finally, Fourier transform infrared spectroscopy (FTIR) showed a decrease in the intensity of two absorption bands at 1243 and 879 cm⁻¹, corresponding to the C–O and C–C vibrations of the carboxylic acid respectively after heat treatment. These results suggest that the main route of degradation corresponds to decarboxylation. We propose the use of FTIR spectroscopy as a practical alternative for the analysis of the degradation of natural dyes during storage, making evident the possible use of this methodology for industrial applications.