Differential antibacterial efficacy and probiotic biocompatibility of Starmerella bombicola-derived sophorolipids: evaluation in a model food system.

Abstract

Sophorolipids, a class of glycolipid biosurfactants produced by Starmerella bombicola, represent high-value green alternatives to petroleum-derived surfactants. In this study, biosynthesized sophorolipids from S. bombicola MTCC 1910 were systematically evaluated for their structural architecture and multi-target biological activities. Submerged fermentation of Starmerella bombicola MTCC 1910 yielded 18.21 ± 2.22 g L- 1 of sophorolipids. Reference surface-active standards were previously catalogued to establish strain performance; the present investigation resolves the high-resolution structural architecture and multi-target biological efficacy of the purified congener isolate. Cell-free antioxidant profiling revealed modest baseline radical-scavenging capacities ([Formula: see text] of [Formula: see text] for DPPH and [Formula: see text] for ABTS, alongside a ferric-reducing power of [Formula: see text]). High-resolution mass spectrometry (HR-ESI-TOF-MS) and [Formula: see text] NMR spectroscopy elucidated a heterogeneous congener mixture dominated by diacetylated lactonic and open-chain acidic forms harbouring di-unsaturated ([Formula: see text]) and mono-unsaturated ([Formula: see text]) acyl backbones. In vitro antibacterial screening against eight pathogenic bacteria established bactericidal activity, with Minimum Inhibitory Concentrations (MIC) spanning [Formula: see text] and Minimum Bactericidal Concentrations (MBC) spanning [Formula: see text] ([Formula: see text]). Direct evaluation of membrane integrity in representative Gram-negative (E. coli) and Gram-positive (S. aureus) models confirmed bactericidal action accompanied by cell membrane permeabilization (AO/EtBr dual staining), intracellular cytoplasmic leakage, and severe cell envelope disintegration (SEM). Sophorolipids also disrupted adherent biofilm biomass ([Formula: see text] for S. aureus; [Formula: see text] for Gram-negative pathogens) while preformed biofilm biomass reduction ([Formula: see text]) ranged from [Formula: see text], accompanied by substantial reductions in sessile cell viability and metabolic activity. In a targeted in situ pathogen challenge model using Silver pomfret (Pampus argenteus) fillets stored at 10 °C, sophorolipids demonstrated dose-dependent suppression of inoculated S. aureus over 72 h, restricting populations to 5.08 [Formula: see text] at 1500 µg compared to 6.42 [Formula: see text] in untreated control, while outperforming a traditional 10% (w/v) NaCl hypertonic salting benchmark. Furthermore, sophorolipids exhibited broad physiological compatibility with five intestinal Lactobacillus strains, demonstrating no antimicrobial suppression up to [Formula: see text], showing differential susceptibility between foodborne pathogens and probiotic lactobacilli alongside low in vitro cytotoxicity in primary human Peripheral Blood Mononuclear Cells (PBMCs; [Formula: see text] mortality at [Formula: see text] over 48 h). Cytosolic lactate dehydrogenase (LDH) release, and minimal erythrocyte haemolysis ([Formula: see text]) also demonstrate preliminary in vitro cytocompatibility in human primary blood cells, while providing proof-of-concept efficacy of localized pathogen containment within a perishable food matrix.

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