Viability of commercial wine yeasts during freezer storage in glycerol-based media

Glycerol-based medium (BM) with and without the addition of 1 g/L ascorbic acid (Asc) and/or 100 mg/L (+/-)-catechin (Cat) was tested for the storage of three commercial wine yeasts at -20 degrees C. The medium supplemented with Asc was also used to store 706 strains to verify the maintenance of the liquid state. A decline in survival throughout the storage period was observed. The media containing Asc maintained viability better than the other three. The BM caused a loss of viability of 7 orders for one strain and of 6 orders for the other two. All three strains exhibited a loss of viability of 4 orders when stored in BM+Asc. Two strains decreased viability by 5 orders while one strain by 4 orders, when stored in BM+Cat. Two strains decreased viability by 6 orders while one strain by 5 orders, when stored in BM+Asc+Cat. Regarding the physical state of the medium tested on 706 yeast strains, three cases were observed: completely liquid (56.5 %), liquid with only the upper part frozen (40.4 %) without involving the yeast biomass settled at the bottom, and completely frozen (3.12 %). It is practicable to prepare a BM that remains liquid at -20 degrees C enhancing yeast viability when Asc is added as cryoprotectant.