Effect of ultrasound on microbiological load and antioxidant properties of blackberry juice

Abstract

The objective of this study was to evaluate the effect of ultrasound (60 and 80% amplitude, 15 and 25 min) of blackberry juice on physicochemical (pH and total soluble solids), microbiological analysis (total plate count and Enterobacteria), and in vitro intestinal bioaccessibility of polyphenols and antioxidant activity (ABTS, DPPH). Ultrasound treatment caused a decrease of microbial count of blackberry juice and remained its physicochemical properties without change. The blackberry juice had a high antioxidant activity, however, after of the in vitro digestion process only 28% of total polyphenols were considered as intestinally bioaccessible, with the contribution of 30 to 60% of antioxidant activity in the bioaccesible fraction. The treatment at 80% amplitude for 15 min was the better treatment due it had an increase of bioaccessibility of polyphenols and antioxidant activity measured by ABTS. Our results showed that ultrasound treatment can preserve the blackberry juice without impairing to its antioxidant characteristics. Practical applications Blackberries are mostly consumed fresh but are also commercialized as individually quick frozen packs, bulk, frozen, seedless or seeded puree, freeze-dried, juice, or concentrate. During fruit juices processing, thermal treatment and other conditions such as oxidation, light exposure, sugar addition, changes in pH, and temperature readily reduce the content of antioxidant compounds and its nutritional properties. Ultrasound is a non-thermal processing technology with potential to replace the traditional thermal pasteurization, achieve microbial safety in fruit juices and remained its antioxidant properties of the blackberry juice.