Dose-dependent structural remodeling and flavor evolution in a composite lactic acid bacteria-fermented whole-egg beverage: integrated physicochemical, structural and flavor analyses

Whole egg is a nutrient-dense matrix, yet its application in beverages is often constrained by poor colloidal stability and “eggy” off-flavor. This study elucidated dose-dependent effects of mixed lactic acid bacteria inoculation on the physicochemical properties, protein structural evolution, and flavor quality of a fermented whole-egg beverage (WEB). A 1:1 (V/V) mixture of L. delbrueckii subsp. bulgaricus and Streptococcus thermophilus (total viable count: (1.1 ± 0.1) × 10⁹ CFU/mL) was inoculated into pasteurized whole egg beverage matrix at 0%, 1%, 3%, 5% and 7% (V/V), corresponding to groups WE, FWE-1%, FWE-3%, FWE-5% and FWE-7%. Fermentation proceeded at 42 °C for 4 h, followed by 36 h ripening at 4 °C. All samples were characterized using dispersion metrics, spectroscopy, electrophoresis, in vitro digestion, gas chromatography-ion mobility spectrometry, electronic nose, electronic tongue, and sensory evaluation. Fermentation acidified WEB, to pH 4.15–4.36, decreased relative turbidity (normalized to the control), and improved dispersion uniformity (minimum polydispersity index was 0.305 at 7%). Soluble protein content increased to 10.24–12.27 mg/g (vs. 2.53 mg/g in the control), and antioxidant capacity was enhanced, with 1,1-diphenyl-2-picrylhydrazyl radical and 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) cation radical scavenging rates reaching 95.84% (FWE-5% group) and 82.14% (FWE-7% group), respectively. Second-derivative ultraviolet, intrinsic fluorescence, and Fourier transform infrared spectroscopy amide I redshift indicated protein conformational remodeling, supported by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showing progressive degradation of high-molecular-weight subunits. These changes improved nutritional functionality, with in vitro protein digestibility maximized at 3% inoculation. Flavor analyses revealed fermentation-driven reconfiguration of volatile and taste profiles, including aroma enrichment and reduced bitterness. Sensory results identified 3% inoculation as optimal, delivering the highest overall acceptability with balanced sourness and diminished eggy odor. This research provides a scientific basis for optimizing inoculation levels in fermented WEB and offers new perspectives for the development of functional egg-based fermented products.