Innovative preservation of beetroot juice via nisin assisted thermo-sonication: Impact on antioxidants, physicochemical properties, enzymes, and microbial reduction

Abstract

Beetroot juice is rich in bioactive compounds with significant health benefits but is highly perishable due to enzymatic activity and microbial growth. This study evaluates the impact of nisin-assisted thermo-sonication on antioxidant activity, enzyme inactivation, and microbial reduction in beetroot juice. Beetroot juice was subjected to thermo-sonication at 45 °C, 50 °C, and 55 °C for 5, 10, and 15 min with nisin concentrations of 50, 100, and 200 ppm. The results showed that TPC increased from 22.25 to 67.12 mg GAE/100 mL, TFC from 5.06 to 9.21 mg QE/100 mL, and DPPH radical scavenging activity from 30.48 % to 57.45 %, with the highest values observed at 45 °C for 15 min with 200 ppm nisin. Additionally, this treatment effectively reduced PPO and POD enzyme activities to 33.33 % and 35.29 %, respectively, indicating a substantial decline in enzymatic browning and enhanced juice stability. The greatest microbial reduction was achieved at 55 °C for 15 min with 200 ppm nisin, yielding the lowest bacterial count of 3.58 log CFU/mL. These findings suggest that nisin-assisted thermo-sonication is a promising alternative to conventional preservation methods, effectively balancing microbial safety, antioxidant retention, and quality maintenance.