Comparative study of sonochemical and conventional methods for extracting natural red dye from Delonix regia petals: Food applications and stability evaluation

Abstract This study investigates the extraction of natural red dye from the petals of Delonix regia flowers, comparing sonochemical and conventional methods to optimize dye yield, characterize its chemical properties, and assess its potential in food applications. Three extraction techniques, i.e., magnetic stirring (500 rpm at 50°C for 60 min), probe sonication (20 kHz, 650 W for 30 min), and ultrasonic water bath (40 kHz, 500 W at 80°C for 60 min) were evaluated under fixed operational parameters. The ultrasonic water bath method at 80°C for 45 min, using water as the solvent, yielded the maximum dye concentration and high color intensity, with UV-visible spectrophotometry revealing prominent absorbance peaks at 480 nm and 530 nm, indicative of the red dye’s color profile. FTIR analysis confirmed the presence of functional groups, including hydroxyl, aromatic, aldehydic, and polyphenol compounds. It revealed the formation of polymerised anthocyanins that exhibited pH-dependent structural variations across a range of pH values (3–10). The red dye extract, rich in flavonoids (78.23 ± 5.67 µg GAE/mg) and total phenolic compounds (69.19 ± 1.02 µg QE/mg), demonstrated significant antioxidant properties, surpassing the synthetic antioxidant Butylated hydroxyanisole (BHA) at 250 µg/ml in DPPH radical scavenging activity. Incorporating the extracted dye into a jelly candy formulation highlighted its functional potential, with the most intense coloration observed at pH 3. This study not only establishes the ultrasonic water bath-assisted extraction method as the most efficient and eco-friendly approach for obtaining natural red dye but also emphasizes the dye’s promising applications as a natural food colorant with antioxidant benefits, offering a sustainable alternative to synthetic dyes.