Freeze-Drying of Wine Yeasts and Oenococcus oeni and Selection of the Inoculation Conditions after Storage

Abstract

Modern winemaking industry has new challenges focused on the application of preserved starter’s microbial cultures for the optimization of the fermentation process that ensuring flavor characteristics and the reproducibility of the final products obtained. Thus, the aim of the present work was to select the inoculation conditions for preselected Saccharomyces cerevisiae mc2 (SC), Kloeckera apiculata mF (KA) and Oenococcus oeni X2L (OO) after freeze-drying and storage in both pure and mixed cultures. The strains were grown in 17% Natural Grape Juice (NGJ) and then lyophilized in 10% individual sugars (glucose, fructose, sucrose, maltose and trehalose), 2.4% sodium glutamate, 4% yeast extract and NGJ by using different culture combinations: 1)- pure cultures (KA1, SC1, OO1), 2)- mixed yeast cultures (KA2, SC2), 3)- mixed microbial cultures (KA3, SC3, OO3). After lyophilization, the strains were stored for 12 months at 4 and 25°C. Viability post-lyophilization was culture/lyoprotectant-dependent while survival to storage depended on time and temperature being O. oeni the more resistant strain to the all process, then K. apiculata and S. cerevisiae, respectively. Freeze-drying of mixed KA-SC in 10% fructose and OO in 17% NGJ up to 6 months of storage at 4°C were the best conditions for the maintenance of the fermentative properties of the strains and for glycerol production. The inoculation of grape musts with KA-SC and OO lyophilized individually with low-cost lyoprotectants would ensure the proper development of the fermentation processes and glycerol synthesis, thus increasing the organoleptic characteristics of wines by a non-Saccharomyces strain. Therefore, the starter culture should include K. apiculata, S. cerevisiae and O. oeni strains.