Enhancing safety and bioactivity of blueberry-watermelon smoothies through combined ultrasound and lactic acid fermentation with potential probiotics

Abstract

This study evaluated the impact of combining ultrasound technology and lactic acid fermentation with potential probiotics Lactiplantibacillus plantarum strains LpAv and 73a on blueberry-watermelon smoothies (BWS), focusing on microbial spoilage inhibition, lactic acid bacteria (LAB) viability, physicochemical, and bioactive properties. It also analyzed the influence of ultrasonication order relative to fermentation on LAB survival after in vitro digestion, bioaccessibility of phenolic compounds, and cellular anti-inflammatory and antioxidant properties. Combining fermentation and ultrasonication synergistically inhibited spoilage microbial growth, regardless of the order of ultrasonication. However, ultrasonication after fermentation decreased LAB viability from 9 to 7 log colony forming units (CFU)/mL. LpAv and 73a strains showed strong survival through digestion, maintaining levels above 6 log CFU/mL during the intestinal phase. Fermentation and ultrasonication of BWS reduced antioxidant activity and phenolic content but enhanced post-digestion recovery, with the bioaccessibility of certain phenolics, like (+)-catechin, significantly improved by ultrasonication (40–65 %) compared to non-ultrasonicated BWS (15–25 %). Digested BWS exhibited significant anti-inflammatory effects, reducing nitric oxide and pro-inflammatory cytokines such as IL-1β and TNF-α, with elevated levels of the anti-inflammatory cytokine IL-10 in BWS fermented with the LpAv strain and ultrasonicated after fermentation. A preliminary sensory evaluation indicated that this formulation also achieved good consumer acceptability, particularly in texture and overall liking. The combined effects of lactic acid fermentation and ultrasonication on BWS highlight their promising applications for improving microbial safety and health benefits in functional fruit smoothies.