Selection of Autochthonous Saccharomyces Yeasts from Queretaro Vineyards Based on Safety and Enological Qualities

Introduction: The main concern about safety on wine production lays on chemical hazards such as sulfites and mycotoxins produced by microorganisms, issues widely handled by strains selection. Queretaro State in Mexico, recently holds an emerging wine industry with little information about the autochthonous microorganisms involved (among these: yeasts) and their effect in quality, tipicity and safety of the products. Thus arises the necessity to study the local yeasts' characteristics, regarding safety (sulfite production) and local needs like high sugar/ethanol yield.

Purpose: To study and select autochthonous Saccharomyces yeasts from Queretaro vineyards, based on their enological and safety qualities.

Methods: Saccharomyces strains were isolated from local grapes submitted to spontaneous fermentation and differentiated from non-Saccharomyces by culture in a selective media (Lysine). Afterwards they were selected based on their resistance to ethanol (12 %), sulphitation (200 ppm) and killer effect, performed on a turbidimetric analyzer (Bioscreen). Also fermentative and enological performances (including sulfites production) were evaluated in microvinification assays within two grape varieties. Strains selected were identified by the amplification and sequence of D1/D2 domain.

Results: From 198 isolated yeasts, 52 belonged to Saccharomyces spp., 8 were selected based on the resistance tests and identified by sequencing as belonging to S. cerevisiae and S. paradoxus. In the microvinification assays, strains produced dry wines with pH, volatile and titratable acidity ranging within the typical values for red wines. Moreover with statistical significance (Tukey P ≤ 0.05), the lower values regarding SO₂ production were obtained by the strains SR19 and SR26 (below 38 mg/l), N5 (autochthonous) and K1 (control) obtained the highest sugar/ethanol yields (≈16.5g glucose/°ethanol), alcoholic degrees (≈15 %), and fermentative efficiency (≈0.91). 

Significance: This study revealed the existence of autochthonous yeasts from Queretaro suitable for selection as starter cultures to improve the safety, quality and tipicity of the wines produced.