Effect of co-inoculation of Saccharomyces and non- Saccharomyces yeasts and nutrients addition during malolactic fermentation on apple cider composition

Apple cider production is a complex fermentation process that involves the conversion of apple juice into cider through the actions of yeast and malolactic bacteria. This study aimed to investigate the effects of the co-inoculation of Saccharomyces and non- Saccharomyces yeasts, as well as nutrient supplementation in the presence of malolactic bacteria Oenoccocus oeni on the composition of apple cider. The amino acid profile of the samples was not significantly influenced by the addition of lactic bacteria or nutrients in cider processing. The highest ester content was recorded in the single yeast strain fermented ciders (55.32%–88.13%). This increase was visible also for the malolactic ciders, independent from nutrient supplementation. Co-inoculated Saccharomyces and Torulaspora delbrueckii ciders showed increased higher alcohols contents, both after the alcoholic (42.66%–53.51%) and malolactic fermentations (42.81%–65.94%). Following the hydroxycynnamic acids class (141.47–327.44 mg/L), flavonoids (114.81–253.44 mg/L) were the second most abundant class of phenolic compounds in ciders, which generally registered a considerable increase following malolactic fermentation. The sour/acidic taste was the most prevalent sensory attribute of the cider. Lower values were recorded for sweet, bitter, and astringent. The strongest apple aroma was perceived in the co-inoculated Saccharomyces and T. delbrueckii yeast strains. The co-fermentation of Saccharomyces and Torulaspora delbrueckii yeasts led to increased levels of desirable aroma compounds, contributing to a more complex and appealing sensory profile, while the nutrient supplementation provided an improved malolactic fermentation efficiency and overall cider quality.