Synergistic impact of multi-frequency ultrasound on sea buckthorn juice fermentation: A holistic study on bioactive compounds, micromorphology, sensory quality, and computational evidence

This study investigates the combined effect of multi-frequency ultrasound-assisted fermentation on enhancing the functional and nutritional quality of sea buckthorn (Hippophae rhamnoides L.) juice. A defined tri-strain lactic acid bacteria (LAB) consortium; Lactiplantibacillus plantarum, Lacticaseibacillus paracasei, and Lactobacillus helveticus was employed to evaluate its impact on phytochemical enrichment, antioxidant potential, and sensory characteristics. The integrated bioprocess resulted in a substantial increase in total phenolic content (23.8-fold) and total flavonoid content (1.18-fold) compared to the unfermented control. Antioxidant activity showed significant enhancement with DPPH radical scavenging increasing from 88.63 % to 122.73 % and FRAP rising from 100.91 to 566.58 µmol/L. HPLC analysis revealed notable increases in quinic acid (1.29-fold), gallic acid (3.20-fold), and citric acid (7.34-fold), while FTIR, SEM, and XRD analyses confirmed microstructural alterations and improved bioactive accessibility. Sensory evaluation indicated elevated fruity and floral aroma intensities, with scores rising from 2.5 to 4.5. These findings demonstrate that multi-frequency ultrasound coupled with LAB fermentation is an effective, non-thermal approach for enhancing the bioactive, structural, and organoleptic attributes of sea buckthorn juice, supporting its potential as a next-generation functional beverage with broad nutraceutical applications.