Ultrasound-assisted fermentation of buttermilk by Limosilactobacillus fermentum and Lacticaseibacillus rhamnosus: Effects on bacterial proliferation, antioxidant potential, and enzymatic inhibition

This study investigated the effect of ultrasound pretreatment (5–15 min, 37 kHz, 300 W) on the fermentation performance and functional properties of buttermilk inoculated with Limosilactobacillus fermentum and Lacticaseibacillus rhamnosus . Buttermilk was sonicated prior to 24 h fermentation to assess microbial proliferation, acidification kinetics, total phenolic content (TPC), antioxidant capacity, and inhibitory activities against α-amylase, α-glucosidase, and lipase. Ultrasonication significantly (P ≤ 0.05) enhanced bacterial growth, with the B+10 treatment achieving 9.3 log CFU/mL, the highest viable count among treatments. Sonicated samples exhibited accelerated acidification (pH 3.4 in B+15) and a marked increase in TPC (9.2 mg/mL in B+10). Antioxidant properties improved substantially, as reflected by a 78.9% increase in reducing power and 82.1% superoxide radical scavenging activity. Enzyme inhibitory activities were also enhanced, with α-glucosidase and lipase inhibition reaching 29.2% and 19.3%, respectively. Notably, L. rhamnosus -fermented samples consistently demonstrated superior phenolic release and bioactivity compared with L. fermentum. Overall, ultrasonic pre-treatment effectively enhanced fermentation performance and biofunctional attributes of buttermilk, highlighting its potential as an innovative approach for developing value-added functional dairy products. • Ultrasound-assisted fermentation boosted growth of L. fermentum and L. rhamnosus. • Sonication accelerated acidification and increased phenolic content in buttermilk. • Antioxidant capacity rose markedly under combined ultrasound and fermentation. • Enzyme inhibition (α-amylase, α-glucosidase, lipase) improved with sonication. • L. rhamnosus outperformed L. fermentum in all functional and bioactive traits.