Yeast derivative products for precision enology: characterization and possible enological use

Products based on yeast derivatives (YDP) are widely used in winemaking thanks to the different functions they can perform. Specifically, YDPs can be used to ensure the smooth running of fermentation processes, to guarantee the protein and tartaric stability of wines, to implement the antioxidant capacity and to enrich the bouquet of wines. The International Organization of Vine and Wine has approved the use of different types of YDP, including: inactive yeasts, autolysates, extracts, peels and mannoproteins. They can be used at different moments of winemaking depending on the typology and, consequently, their oenological function. These products can represent an alternative to the use of chemicals, such as sulfur dioxide, and potentially limit the use of adjuvants or inorganic nutrient sources. In this study, several commercial YDPs (28) were characterized in terms of nitrogen, cysteine (Cys), and glutathione (GSH) contents, and antioxidant capacity. Preliminary tests were carried out to evaluate their effectiveness on tartaric and protein stability. Specifically, a Traminer wine and a Pinot Noir rosé wine were considered, they were used for the determination of tartaric and protein stability, respectively, monitored for up to 14 days of wine-YDP contact (40 g/hL). Furthermore, the impact of YDPs on color was also examined. The total nitrogen content was highly variable among the YDPs tested, even belonging to the same type, and between 2% and 12% (w/w). Considering the sum of the amino acid and ammoniacal forms of nitrogen, which constitute readily assimilable nitrogen (RAN), the average concentration detected is equal to 8.3 mg/g, with the exception of a yeast extract which was found to be the richest in RAN (21.7 mg/g). Therefore, their use can bring an increase in RAN of less than 10 mg/L (for an addition of YDP equal to 40 g/hL) which may not be sufficient to satisfy the nitrogen needs of the yeast during the fermentation process. However, the positive impact of YDPs on alcoholic fermentation may also be due to other compositional characteristics, such as the presence of vitamins and lipids. Cys and GSH were detected in concentrations lower than 10 mg/g in all YDPs suggesting the limited role of these sulfur compounds on antioxidant capacity. For some yeast extracts and inactive yeasts, an antioxidant capacity comparable to food-based phenolic extracts was observed, indicating their possible use in the conservation and aging phase to prolong the longevity of wines. As regards stabilization tests, preliminary results have shown that some mannoproteins are effective for tartaric stabilization already after 24 hours of contact. Protein stabilization was only partially achieved through the use of some inactive yeasts and mannoproteins; it cannot be ruled out that their use may limit the addition of bentonite. Significant variations in color were observed after 14 days in the presence of some autolysates and yeast hulls which led to an increase in coloring intensity with a perceptible color difference. Longer contact times are needed to evaluate color evolution in the wine-YDP system. The study highlights the compositional variability of YDPs and their use for stabilization. Further studies are necessary to clarify the role of YDPs on stabilization, considering the interactions with wine compounds, as well as a nutrient and antioxidant in order to better target their use for specific functions thus implementing precision oenology.