Microbial inactivation and physicochemical properties of ultrasound processed pomegranate juice

The effects of ultrasound treatment at various amplitudes (50, 75, and 100%) and times (0, 6, 12, 18, 24, and 30 min) on Escherichia coli ATCC 25922 (a surrogate for E. coli O157:H7) and Saccharomyces cerevisiae ATCC 2366 levels and physicochemical characteristics (monomeric anthocyanins, color values, total phenolics, pH, and soluble solids) were determined in pomegranate juice. More than a 5-log inactivation of E. coli ATCC 25922 and a 1.36-log inactivation of S. cerevisiae ATCC 2366 were achieved after 30 min of ultrasound treatment at 100% amplitude. The log-linear and Weibull models were successfully used to estimate the microbial inactivation as a function of ultrasound treatment time (R(2) > 0.97). No significant changes were observed in total phenolics, pH, and soluble solids of the treated juice (P > 0.05). The ultrasound treatment for up to 30 min resulted in more than 92 and 89% anthocyanin retention at 75 and 100% amplitude, respectively. The redness (a*) of the juice did not change significantly after the ultrasound treatment at amplitudes of 75 and 100% for up to 24 and 12 min, respectively. No significant changes in L* and b* values were observed after ultrasound treatment at all amplitudes and after up to 30 min of treatment for 50 and 75% amplitudes. Small differences in juice color were noted based on total color difference scores.