Synergistic effect of low-intensity ultrasound and co-culture lactic acid bacteria fermentation on the antioxidant properties of Echium amoenum

This study investigates the dynamic physicochemical and microbiological changes during low-intensity ultrasound-assisted co-culture lactic acid bacteria (LAB) fermentation (Lactobacillus acidophilus, Lactiplantibacillus plantarum, and Limosilactobacillus reuteri) of Echium amoenum over 24 h. The pH decreased from an initial 6.5 to 3.9 after fermentation, coinciding with a peak bacterial biomass of 6.8 CFU/mL, demonstrating robust microbial activity and growth. In the unfermented sample, the maximum phenolics (147.23 ± 0.17 mg of gallic acid equivalents (GAE)/g of dry weight (DW)) and flavonoids (53.11 ± 0.41 mg of quercetin (QE)/g DW) amounts, along with antioxidant activity measured by means of 2,2-diphenyl-1-picrylhydrazyl (DPPH, 35.08 ± 1.56 mg GAE/g DW), and ferric reducing antioxidant power (FRAP, 1.02 ± 0.05 mmol FeSO4 equivalents/g DW) were reached at 24 h. In contrast, the ultrasound-assisted co-culture LAB fermentation using L. acidophilus and L. plantarum exhibited the highest phenolic (299.42 ± 0.89 mg GAE/g DW) and flavonoid (88.39 ± 1.53 mg QE/g DW) values, as well as the highest antioxidant activity (DPPH 64.02 ± 1.67 mg GAE/g DW and FRAP 1.96 ± 0.01 mmol FeSO4 equivalents/g DW), after 12 h of fermentation, indicating enhanced extraction efficiency, metabolite biosynthesis, and reduced processing time. Furthermore, FTIR analysis confirmed structural alterations in polyphenolic functional groups. Low-intensity ultrasound and co-cultured LAB fermentation synergistically accelerated microbial growth, bioactive compound release, and antioxidant capacity in E. amoenum, highlighting the efficiency of bioprocessing for functional foods and nutraceuticals