Effect of sonication on retention of anthocyanins in blackberry juice

Abstract

Blackberry juice samples were sonicated with processing variables of amplitude levels ranging from 40% to 100% at a constant frequency of 20 kHz and sonication times (0–10 min) and pulse durations of 5 s on and 5 s off. The effects of sonication on anthocyanins (Cy3Gl) and colour values ( L, a, and b) were determined. Response surface methodology (RSM) based on two factor five level central composite design was applied to determine the effect of amplitude level and sonication time. A second-order polynomial model fitted well to the experimental data ( R 2 > 0.89). Significant retention of anthocyanin content (>94%) was observed at the maximum treatment conditions of 100% amplitude level for 10 min, indicating stability of anthocyanin during sonication. Colour changes observed during sonication were subtle (TCD ∼ 5%). RSM was demonstrated to be an effective technique to investigate the influence of sonication on colour and anthocyanin retention. Sonication could be employed as a preservation technique for blackberry juice processing where anthocyanin retention is desired.