Multi-frequency sono-fermentation with mono and co-cultures of LAB synergistically enhance mulberry juice: Evidence from metabolic, micromorphological, sensorial, and computational approaches

The effect of multi-frequency ultrasound-assisted (20/28/40 KHz) lactic acid bacteria (LAB- Lacticaseibacillus casei, Lactiplantibacillus plantarum, Lacticaseibacillus paracasei, Lactobacillus acidophilus, and Lactobacillus helveticus) fermentation (mono and co-cultures) on the metabolic, structural, micromorphological, and sensorial properties of mulberry juice were evaluated. Results indicated that multi-frequency ultrasound-assisted fermentation significantly modified the microstructure of mulberry juice powder, resulting in more porous and rougher surfaces with irregular indentations. Total phenolic content in the best-performing sample (S10) increased to 365.36 mg GAE/mL, while total flavonoid content rose to 139.20 mg RE/mL (p < 0.05). Antioxidant activity, as measured by DPPH and FRAP assays, also showed considerable improvement, with DPPH scavenging activity increasing to 87.45 % and FRAP-value to 3.27 mM TE/mL (p < 0.05). Additionally, HPLC-UV analysis revealed that the amendment in the concentrations of cyanidin-3-rutinoside (47.47 mg/L) and peonidin-3-O-glucoside (66.86 mg/L) in the S2-based sample. E-nose analysis demonstrated intense flavor profiles in fermented samples, particularly in sample S15. Sensory evaluation also highlighted that the fruity and floral aromas in co-culture fermented samples were enhanced, notably in S10, S7, and S14. Thus, combining multifrequency ultrasonication and fermentation significantly enhances the antioxidants capacity, flavor profile, micro-morphology, and overall quality of mulberry juice.