Effect of sonication on retention of anthocyanins in blackberry juice

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 similar to 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. (C) 2009 Elsevier Ltd. All rights reserved.