Microencapsulation of <i>Lactobacillus plantarum</i> and <i>Bacillus subtilis</i> using baker's yeast cell wall: characterization and stability assessment under stress conditions.

Abstract

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 (<i>Saccharomyces cerevisiae</i>) cell wall as an encapsulant for improving the stability and gastrointestinal survivability of probiotics. Two probiotic strains with complementary functional traits were selected: <i>Lactobacillus plantarum</i> (a non-spore-forming lactic acid bacterium sensitive to gastric stress) and <i>Bacillus subtilis</i> (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 <i>Bacillus subtilis</i> and <i>Lactobacillus plantarum</i> 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 <i>B. subtilis</i> (D50 = 0.89 μm; span = 0.79) and a moderately polydisperse profile for <i>L. plantarum</i> (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 (<i>B. subtilis</i>) and -30.36 ± 0.42 mV (<i>L. plantarum</i>), indicating enhanced colloidal stability (<i>p</i> < 0.05). Encapsulation efficiencies were 89.6% ± 3.19% (<i>B. subtilis</i>) and 86.57% ± 1.50% (<i>L. plantarum</i>), significantly higher than their non-encapsulated counterparts (75.0% ± 2.26% and 40.6% ± 16.3%, respectively; <i>p</i> < 0.05). Encapsulated probiotics exhibited significantly improved survival in simulated gastric and intestinal fluids compared with free cells (<i>p</i> < 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.