Phenolic–Bioactivity Connectivity Networks Reveal How Lactic Fermentation Restructures Function in Murta Berry Juice

Lactic fermentation modulates polyphenol composition in plant matrices, yet how compositional shifts translate into functional outcomes across extractable (EP) and hydrolyzable (HP) fractions remains unclear. Here, we apply a phenolic–bioactivity connectivity framework to fermented murta (Ugni molinae Turcz) juice, integrating compositional profiling with three functional axes: antimicrobial activity (against Escherichia coli, Salmonella enterica, and Staphylococcus aureus), inhibition of carbohydrate-hydrolyzing enzymes (α-amylase, α-glucosidase) and DPP-IV, and modulation of oxidative stress in Caco-2 cells. Murta juice was fermented with Lactobacillus acidophilus, Lactiplantibacillus plantarum, and a 1:1 coculture under two optimized strategies (GDF and SAW). Principal component analysis separated fermented from unfermented samples (89.7% variance explained) and identified coculture fermentation (MIX-GDF) as the most compositionally distinct treatment. EP fractions drove antimicrobial and α-glucosidase inhibition, whereas HP fractions contributed preferentially to DPP-IV inhibition and intracellular reactive oxygen species (ROS). A bipartite correlation network revealed a dual-functional architecture: specific flavonoid–bioactivity associations governed enzyme inhibition, while diffuse collective interactions shaped antimicrobial responses. These results demonstrate that fermentation-induced phenolic remodeling yields structured, functional outcomes, providing a rational basis for designing fermentation strategies targeting specific bioactivity profiles.