Effect of microwaves and ultrasound on bioactive compounds and microbiological quality of blackberry juice

Blackberry mash added with citric acid (0-500 mg/kg) was treated with microwaves (0-60 s), and the resulting juice was evaluated to determine the effects on bioactive compounds and antioxidant activity using surface response methodology. This methodology allowed the selection of the parameters for the microwave treatment and concentrations of citric acid that yielded the highest content of total poly phenols, monomeric anthocyanins and antioxidant activity of the juice. Mash samples were sonicated (40% amplitude, 20 KHz, 10 min) and stored at 5 degrees C + 1 degrees C for a month. Then the contents of total polyphenols and monomeric anthocyanins, as well as microbiological quality were analyzed. Analysis of polyphenols was carried out by UPLC-DAD in the raw juice and the sample selected by surface response methodology and treated with ultrasound. The highest levels of polyphenols and monomeric anthocyanins in juice were obtained at a time of 60 s of microwave processing and a concentration of 500 mg/kg citric acid in the blackberry mash. Phenolic acids, flavonols and cyanidin were detected in both samples. During storage, juice processed with ultrasound retained more than 90% of monomeric anthocyanins and showed a significant microbial load reduction, agreeing with the quality parameters established by the Mexican standards. This study highlights the potential application of microwaves and ultrasound to increase the functional value of blackberry juice. (C) 2017 Elsevier Ltd. All rights reserved.