Comparative mono- and co-culture fermentation of Parijoto (Medinilla speciosa Blume) juice: strain-specific metabolomic signatures and functional profiles of an underutilized Indonesian fruit

Abstract

Parijoto (Medinilla speciosa) is an underutilized Indonesian fruit rich in bioactive compounds, yet its poor sensory attributes limit its commercial application. Lactic acid bacteria fermentation offers a route for valorization, but the impact of strain selection on its functional properties is unknown. This study aimed to characterize how different fermentation strategies—using Lactiplantibacillus plantarum (E1), Lactobacillus acidophilus (E2), or their co-culture (E3)—modulate the phytochemical profile of Parijoto juice. Comprehensive physicochemical, phytochemical, and in vitro bioactivity analyses were integrated with untargeted metabolomics. Fermentation outcomes were highly strain specific. While E2 showed the strongest acidification, the co-culture (E3) uniquely enhanced ascorbic acid content in the juice and achieved the highest total phenolic content and ABTS radical scavenging activity in the extract; E1, in contrast, excelled in ferric reducing power. Metabolomics revealed that this superior ABTS radical scavenging activity was strongly associated with the exclusive accumulation of gallic acid in E3. Fermentation with E1 dramatically increased α-amylase inhibition by 81 % compared to the unfermented control, identifying it as a promising candidate for further investigation rather than a proven antidiabetic agent. Antibacterial activity was also strain-dependent, with E2 showing the strongest inhibition of Serratia marcescens (90.8 %). Correlation analysis revealed a perfect positive association between ferric reducing power and α-amylase inhibition (ρ = 1.00), generating the testable hypothesis of a mechanistic link. By demonstrating that strain selection is associated with distinct metabolomic and functional profiles, this work provides a hypothesis-generating foundation for the targeted development of fermented functional beverages from underutilized fruits.