Microencapsulation of Lactobacillus plantarum and Bacillus subtilis using baker’s yeast cell wall: characterization and stability assessment under stress conditions

Yeast cell wall components, being natural, biodegradable, and generally recognized as safe, offer a promising alternative to synthetic encapsulants for probiotic delivery. This study aimed to evaluate baker's yeast (Saccharomyces cerevisiae) cell wall as an encapsulant for improving the stability and gastrointestinal survivability of probiotics. Two probiotic strains with complementary functional traits were selected: Lactobacillus plantarum (a non-spore-forming lactic acid bacterium sensitive to gastric stress) and Bacillus subtilis (a spore-forming, robust probiotic widely used in feed and pharmaceutical applications). Probiotic cells (≈10⁸-10⁹ colony forming unit mL^-1) were encapsulated within hollow yeast cell wall particles obtained via sequential acid-alkali treatment. Encapsulation efficiency, particle size, surface charge, structural integrity, and probiotic survival under simulated gastrointestinal conditions were evaluated. Scanning electron microscopy revealed a porous, honeycomb-like yeast cell wall structure (3-6 μm) facilitating probiotic encapsulation. FTIR analysis confirmed the successful encapsulation of Bacillus subtilis and Lactobacillus plantarum within the yeast cell wall matrix. Spectral changes indicated that encapsulation was driven primarily by non-covalent interactions, dominated by hydrogen bonding between yeast β-glucan hydroxyl groups and probiotic surface biomolecules. Dynamic light scattering showed a narrow and uniform size distribution of unloaded yeast cell wall (D50 = 0.63 μm; span = 0.42), while microencapsulation increased particle size, yielding a relatively uniform distributions for B. subtilis (D50 = 0.89 μm; span = 0.79) and a moderately polydisperse profile for L. plantarum (D50 = 1.67 μm, span = 1.28). Zeta potential values shifted from -16.4 ± 0.53 mV (unloaded yeast cell wall) to -32.73 ± 1.39 mV (B. subtilis) and -30.36 ± 0.42 mV (L. plantarum), indicating enhanced colloidal stability (p < 0.05). Encapsulation efficiencies were 89.6% ± 3.19% (B. subtilis) and 86.57% ± 1.50% (L. plantarum), significantly higher than their non-encapsulated counterparts (75.0% ± 2.26% and 40.6% ± 16.3%, respectively; p < 0.05). Encapsulated probiotics exhibited significantly improved survival in simulated gastric and intestinal fluids compared with free cells (p < 0.05). Baker's yeast cell wall-based encapsulation significantly enhances probiotic stability, colloidal behavior, and gastrointestinal tolerance through strain-specific physicochemical interactions. This approach offers a safe and effective delivery platform for functional feed and pharmaceutical applications.