Optimization of the pitaya (Stenocereus spp.) betalain extraction process using Response Surface Methodology: Evaluation of their stability versus beetroot (Beta vulgaris)

A study was conducted to optimize the extraction of betalains from pitaya (Stenocereus spp.) and evaluate their stability compared to those from beetroot (Beta vulgaris). Optimal extraction conditions for betalains from pitaya were determined: pH 6, a solvent ratio of 30% ethanol, and a solvent ratio of 1 g/9.5 ml. These conditions yielded estimated concentrations of 76.44 and 54.01 mg/kg, as well as experimental concentrations of 76.45 mg/kg of BX and 52.64 mg/kg of BC in fresh fruit. pH analysis revealed that the hue stability range in aqueous media for pitaya was 3 to 9, maintaining an orange hue, while for beetroot, it was 2 to 8, maintaining a bright pink hue. Therefore, the degradation of BX and BC from both botanical sources was observed at pHs lower and higher than those mentioned above. A higher degradation rate was associated with ethanolic solutions. Thermal stability analysis showed that, at 40 °C, the hue of pitaya betalains remained unchanged. At 50 °C and 60 °C, a hue change from orange to yellow-orange was observed, with the greatest hue loss at 60 °C after 2.5 hours. Meanwhile, beetroot betalains showed hue changes at 60 °C after 1.5 hours, turning brown. Furthermore, the activation energy of pitaya and beetroot BCs was higher than that of BX, indicating that BC degradation reactions are more sensitive to temperature. These results highlight the importance of expanding our knowledge of pigments derived from diverse plant sources for their optimal utilization in industrial applications.