Potential of High Pressure Homogenization for the production of yeast autolysates for winemaking

Yeast derivatives (YDs – e.g. inactive dry yeasts and yeast autolysates) are extensively used in winemaking for a wide series of applications: fermentation enhancers, flavor and aroma modulators, scavengers against undesired compounds and antioxidant preparations. Their ability in releasing soluble compounds and macromolecules suggests their potential application to simulate the traditional practice of ageing on the lees. Nevertheless, one of the problems connected with the use of such additives during wine ageing is that they may be responsible of the release off-odors into the wine. These compounds are mostly originated from the development of Maillard reaction or lipid oxidation, during the thermal treatments applied for YDs manufacturing. Thus, the development of non-thermal alternative processes for the obtainment of such products may open new opportunities for the production of commercial preparations, specifically tailored for winemaking use. High pressure homogenization (HPH) is a mechanical processing method, used since 1970s to promote the extraction of intracellular components from microorganisms, including Saccharomyces spp. The ability of HPH to induce cell breakdown is connected with different phenomena (i.e. turbulence, cavitation and shear), occurring when a yeast suspension is forced through the homogenization valve. In the present study, HPH was tested in different conditions (pressure, number of passes) and temperature regimes (controlled vs. uncontrolled), concerning its potential application for the production of yeast autolysates. The performances of this technology were assessed on a commercial strain of Saccharomyces bayanus for winemaking. The autolysates obtained were characterized for their ability to release soluble molecules (e.g. proteins and free amino acids) and glucidic colloids (e.g. glycoproteins) in wine-like medium, for the number of viable cells after the treatment, as well as for their composition regarding volatile compounds, in comparison with both thermolysis and a commercially available YD preparation. HPH demonstrated its capacity in promoting yeast autolysis in a short time and without intensive heating. The release of glucidic colloids increased by increasing the pressure applied and the number of passes and was comparable, or slightly higher, respect to the amounts detected in both thermolysates and the commercial YD preparation. HPH processing variables affected the volatile composition of the final products and their content in amino acids and colloids: in particular, the choice to control or not the processing temperature may allow to obtain autolysates with different characteristics, and suitable for different winemaking applications (i.e. fermentation enhancers or ageing supplements). Compared to thermal treatment, HPH was less effective in promoting Saccharomyces bayanus inactivation. The autolysates produced by HPH showed a more interesting volatile composition, with respect to those obtained by thermolysis, because of the higher content of ethyl esters.