Comparative assessment of food-grade osmolytes for enhancing yeast fermentation performance under salt stress

High salt concentrations impose severe osmotic and oxidative stress on Saccharomyces cerevisiae, limiting growth and fermentation efficiency in food industrial processes. Osmolytes, small compatible solutes such as sugars, polyols, and amino acids, can protect cells by stabilizing proteins, preserving water balance, and maintaining cellular integrity. While individual osmolytes have been studied, no systematic assessment across diverse commercial classes under uniform stress conditions has been reported. Here, we evaluated 12 commercially relevant osmolytes representing sugars (trehalose, sucrose, and lactose), sugar alcohols and polyols (sorbitol, mannitol, xylitol, myo-inositol, and glycerol), amino acids (proline, glycine, and β-alanine), and urea for their ability to mitigate 6% sodium chloride (NaCl) stress in yeast. Growth performance was quantified using optical density, viability, budding efficiency, cell morphology, biomass productivity, and multivariate analysis. Osmolyte supplementation strongly modulated yeast stress responses. Myo-inositol, sucrose, and lactose emerged as the most effective treatments, restoring growth up to ~85% of unstressed controls and increasing viability by >70% compared to salt-stressed cells. These osmolytes enhanced antioxidant capacity (up to +47%) and restored budding frequency and cell shrinkage, indicating partial recovery of normal morphogenesis. Principal component analysis and heatmap clustering distinguished osmolyte classes, with sucrose, lactose, and myo-inositol clustering with unstressed controls, underscoring their superior osmoprotective potential. This study provides the first direct comparative ranking of commercial osmolytes, identifying myo-inositol, sucrose, and lactose as the superior osmoprotectants for mitigating salt-induced stress in S. cerevisiae. These osmolytes enhance growth, redox balance, and morphogenesis, providing a quantitative framework for selecting osmoprotectants to improve productivity in high-osmolarity industrial fermentations or high-gravity fermentation.

Saccharomyces cerevisiae plays a vital role in brewing, baking, alternative protein production, and food biotechnology, but its performance often declines under high salt conditions typical of industrial fermentations. Salt stress causes water loss, cell shrinkage, and oxidative damage, resulting in impaired metabolism and reduced productivity. This limitation is increasingly significant as sustainable bioprocessing utilizes saline byproducts such as soybean meal extracts, fish sauce residue, whey permeate, and molasses. Enhancing yeast salt tolerance is therefore critical for reliable and scalable biomanufacturing. Osmolytes are small molecules that stabilize proteins, maintain turgor, and protect cellular integrity, yet their comparative effectiveness in improving Saccharomyces cerevisiae performance under food-relevant and industrial stress conditions remains unclear. Here, we present a systematic evaluation of major commercial osmolyte classes under salt stress. Myo-inositol, sucrose, and lactose significantly improved yeast growth, viability, and oxidative stress tolerance, supporting more robust and efficient bioprocessing using circular bioresources.