Effect of continuous ultra-sonication on microbial counts and physico-chemical properties of blueberry (Vaccinium corymbosum) juice

- Ultrasonication at sufficiently high intensity reduces microbial counts in blueberry juice.
- Ultrasonic processing preserves the anthocyanins and color of blueberry juice better than conventional thermal processing.
- Ultrasonication is an alternative pasteurization treatment to thermal processing.

Blueberries have received considerable attention due to their content of health promoting compounds such as polyphenols and anthocyanins. Thermal processing is known to cause degradation of anthocyanins and juice color. The objectives of this research were to study the effect of continuous ultrasonication processing on the microbiological, chemical and physical properties of blueberry juice (BJ). Unpasteurized BJ was pumped at 24 mL/min or 93.5 mL/min to the continuous flow cell of an ultrasonic processor, where it was sonicated at three treatment levels, 13.88 ± 2.45, 43.45 ± 4.12, and 73.60 ± 5.35 (J/mL) energy density. Sonicated and unsonicated juices were analyzed for coliforms, total aerobes, yeasts and molds. Total anthocyanin content, total phenol content, antioxidant activity, °Brix, titratable acidity, pH and color were also determined for both sonicated and unsonicated juices. Continuous flow sonication successfully reduced microbial counts. Sonication at higher intensities significantly (p < 0.05) reduced microbial counts. The highest log reduction in total aerobes (1.36 log cycles) was achieved at high flow rate (93.5 min/mL) with high intensity (100 amplitude) sonication condition compared to untreated and control juice samples. Continuous flow sonication processing preserved the anthocyanins and color of blueberry juice. This study demonstrated that ultrasonication can be an alternative pasteurization treatment to thermal processing.