Abstract
<title>Abstract</title> <p> Nutritional yeast spent powder (NYSP), a by-product of <italic>Saccharomyces cerevisiae</italic> processing, is rich in proteins, \(\:\beta\:\)-glucans, and mannoproteins, making it a promising clean-label stabilizer for food emulsions. This study evaluates NYSP as a stabilizer for oil-in-water emulsions and clarifies how pH controls interfacial and bulk stabilization. Emulsions (25% corn oil, 16.67% NYSP, and 58.33% water w/w) were prepared at pH 3.0, 5.7, 7.0, and 9.0. As pH increased, the zeta potential shifted from positive to negative values (\(\:+6.11\pm\:0.26\) to \(\:-26.23\pm\:0.53\text{\:mV}\)), while the particle size was reduced from \(\:881.80\pm\:31.03\) to \(\:343.73\pm\:23.27\text{\:nm}\). The surface tension peaked at pH 5.7 (\(\:{\gamma\:}_{\text{LV}}=38.43\text{\:mN/m}\)) and minimized at pH 9.0 (\(\:31.29\text{\:mN/m}\)). Bulk rheology shifted from shear-thinning behavior: \(\:K\) decreased from \(\:0.0541\) to \(\:0.0194\text{\:Pa}\cdot\:{\text{s}}^{}\), and \(\:{\eta\:}_{50}\) decreased from \(\:0.034\) to \(\:0.022\text{\:Pa}\cdot\:\text{s}\) (pH 3 to 9). Frequency sweeps revealed weak-gel behavior (\(\:G{\prime\:}{\prime\:}>G{\prime\:}\)) across all pH levels, alongside markedly reduced viscoelasticity at pH 9.0. Similarly, interfacial rheology indicated predominantly viscous interfaces (\(\:{G}_{i}{\prime\:}<{G}_{i}{\prime\:}{\prime\:}\)) under strongly acidic and alkaline conditions, whereas elastic interfacial behavior (\(\:{G}_{i}{\prime\:}>{G}_{i}{\prime\:}{\prime\:}\)) was observed at pH 5.7. Furthermore, maximum interface elasticity (lowest \(\:{\eta\:}_{i}^{*}\)) was achieved at pH 5.7. Long-term emulsion stability was maximal at acidic pH, where NYSP formed a weak, space-spanning gel network that increased bulk viscoelasticity and effectively suppressed coalescence, despite the higher interfacial tension. At pH 7.0–9.0, phase separation occurred due to diminished continuous-phase structuring, regardless of the higher surface charge. Overall, NYSP stands out as a promising, upcycled stabilizer that synergizes interfacial adsorption with continuous-phase structuring to yield pH-tunable (pH 3.0–6.0) emulsions. </p>