Optimisation of ultrasonic-assisted extraction of natural dyes from pomegranate rind using response surface methodology and its characterisation

This paper reports the optimal ultrasonic-assisted extraction (UAE) conditions for the maximum recovery of natural dyes from pomegranate rind using response surface methodology. The optimum UAE conditions were found to be an extraction time of 60 minutes, an extraction temperature of 65 degrees C, a water to material ratio of 19 mL/g and an ultrasonic power of 132 W. The yield of the extracted pomegranate rind dyes (PRD) under optimum conditions was 17.1% +/- 0.1%, which closely agrees with the predicted value of 17.2%. Fourier Transform-infrared and ultraviolet-visible absorption spectroscopy indicated that there were no significant structural changes in the PRD under optimal UAE conditions. The PRD particle size was clearly reduced, and the distribution was more uniform under the action of the ultrasonic waves. The total anti-oxidant activity of the PRD was analysed using DPPH center dot assay, and the results indicated that a proper and reasonable ultrasonic-assisted treatment can enhance the anti-oxidant capacity of the pomegranate rind natural dyes. Furthermore, in comparison with Staphylococcus aureus using the Agar plate method, the anti-bacterial activity indicated that the fabrics dyed with PRD under UAE conditions displayed outstanding anti-bacterial activity.

Automated summary

This study identified the optimal ultrasonic-assisted extraction conditions for natural dyes from pomegranate rind using response surface methodology. The extracted pomegranate rind dyes (PRD) under the optimum conditions had a yield of 17.1% +/- 0.1%, consistent with the predicted value of 17.2%. Additionally, the structure of PRD did not undergo significant changes, and the particle size was reduced with a more uniform distribution under ultrasonic waves. Also, the anti-oxidant capacity and anti-bacterial activity of PRD were enhanced under appropriate ultrasonic-assisted treatment.