A comprehensive study on fermentation and aroma contributions of Torulaspora delbrueckii in diverse wine varieties: Insights from pure and co-fermentation studies.

As a well-commercialized and utilized non-Saccharomyces yeast, Torulaspora delbruineckii is gaining increasing relevance in the winemaking industry. However, its ability to produce distinctive aromas in wine has been inconsistently reported in the literature. This study aimed to evaluate the fermentation performance and aroma properties of T. delbrueckii isolates through pure and co-fermentation with Saccharomyces cerevisiae across eight different wine varieties: Merlot, Zidaifu, Petit Verdot, Marselan, Italian Riesling, Sauvignon Blanc, Ugni Blanc, and Petit Manseng. A comprehensive analysis using HS-SPME-GC-MS, OPLS-DA, and Spearman's correlation analysis was conducted. Key findings include: (1) The strain T. delbrueckii R12 exhibited higher extracellular enzyme activity compared to S. cerevisiae CECA and demonstrated superior sugar tolerance compared to six other native T. delbrueckii strains. (2) T. delbrueckii R12 exhibited strong fermentative capability, completing fermentation in 23 days across the eight wines, producing lower levels of acetic acid (0 ∼ 0.8 g/L reduction) and ethanol (0.1 ∼ 4.0 % v/v reduction), and higher levels of glycerol (0.1 ∼ 0.9 g/L increase) in the majority of wines. (3) Co-fermentation with T. delbrueckii and S. cerevisiae altered glycosidase activity, enhancing the varietal aroma intensity and complexity of the eight wines by releasing C compounds, terpenes and esters, and reducing higher alcohols and fatty acids. (4) The aroma contribution of T. delbrueckii R12 was variety-dependent, with isobutyl alcohol, isopentyl alcohol, 1-pentanol, and 1-propanol prevalent in red wines, and (Z)-2-hexen-1-ol more associated with white wines. Additionally, T. delbrueckii R12 consistently enhanced aromas in all eight experimental wines by increasing levels of 1-hexanol, farnesyl alcohol, linalool, citronellol, ethyl acetate, isobutyric acid and decanoic acid, while decreasing 1-pentanol, octanoic acid, isoamyl acetate, and ethyl laurate. Seven of the increased compounds were identified as signature aromas of T. delbrueckii R12, potentially contributing grass, floral, muscat, rose, fruit, caramel and buttery notes to the wines. This study confirms the significant role of T. delbrueckii in winemaking and wine aroma, resolving previous discrepancies in the literature. It provides new knowledge for innovating and diversifying wine production across various grape varieties.