Saturated fatty acid-mediated non-covalent modification of inactivated yeast cells for enhanced interfacial behavior and Pickering emulsion stability.

Inactivated yeast cells (YC) possess postbiotic functionality and are considered ideal stabilizers for developing green and healthy Pickering emulsions. However, their inherent hydrophilicity limits interfacial adsorption efficiency. To overcome this, saturated fatty acids (SFAs) with different carbon chain lengths-lauric acid (LA, C12), myristic acid (MA, C14), palmitic acid (PA, C16), and stearic acid (SA, C18)-were used to non-covalently modify YC at various mass ratios. All YC-SFAs composite particles maintained a size of 4.7-4.8 μm and a Zeta potential between -27.00 and - 31.00 mV. Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) confirmed successful loading of fatty acids onto YC via hydrogen bonding and hydrophobic interactions. At a 100:1 ratio, MA-, PA-, and SA-modified particles reduced interfacial tension from 13.35 to 14.28 mN/m to 4.17-4.37 mN/m, significantly lower than LA (6.56 mN/m). Among these, MA (C14)-modified particles exhibited the highest diffusion and rearrangement rates, with a Turbiscan stability index below 2.0 and coalescence index below 20% after 28 days, indicating superior interfacial adsorption and emulsion stability. Confocal laser scanning microscopy (CLSM) and rheological analysis demonstrated that appropriate fatty acid modification enabled tight particle adsorption at the oil-water interface, forming a dense viscoelastic film. Excessive modification (100:10) led to particle aggregation and weakened interfacial structure. Overall, MA with a 14‑carbon chain at a low modification ratio most effectively enhanced YC interfacial activity, while shorter (LA) or longer (PA, SA) chains were less effective due to weak anchoring or excessive hydrophobicity-induced aggregation. This study reveals the synergistic regulatory mechanism of fatty acid carbon chain length and modification ratio on YC interfacial behavior and emulsion stability, providing a theoretical basis for designing yeast-based postbiotic Pickering emulsion stabilizers.