EFFECT OF FREEZE-DRYING PROCESS ON VIABILITY OF PURE AND MIXED CULTURES OF O. oeni AND WINE YEASTS

ALE, C. E.; PASTERIS, S.E.; OTERO, M.C.; MORATA, V

Simposio; IV SIMPOSIO INTERNACIONAL DE BACTERIAS LÁCTICAS (SIBAL) ALIMENTOS, SALUD Y APLICACIONES.; 2013

Alcoholic and malolactic fermentations during winemaking confer quality and stability of wines. When a starter culture exhibits an appropriate fermentative potential, their conservation would ensures reproducibility of the final product in winemaking. Although lyophilization is a common process used to preserve microorganisms, low cost lyoprotectants must be added to the microbial cell suspensions to guarantee both, a higher viable cell recovery and a diminution in the production costs. Thus, in the present work Saccharomyces cerevisiae mc2, Kloeckera apiculata mF and Oenococcus oeni X2L (potentially starter strains) were selected to evaluate their viability after freeze-drying in different lyoprotectants. The strains were grown in pure and mixed cultures in Natural Grape Juice medium added with Tween 80 (NGJ-T, pH 5.5) at 28°C. After 24 h, cells were collected and resuspended in 300 µL of the following solutions: glucose, fructose, saccharose, maltose, trehalose, sodium glutamate, yeast extract, natural grape juice (NGJ). Water was used as control. Fractions of these cultures were freeze-drying and cell viability (UFC/mL) of each strain was determined by using ANOVA and Tukey?s test for comparisons. A survival factor (SF) was defined for this study which decreased when cell viability diminished. Overall, an interaction strain-lyoprotectants was observed. O. oeni X2L was the most resistant strain to the freeze-drying process, then K. apiculata mF and S. cerevisiae mc2. When evaluating the interaction strain-lioprotectants, sodium glutamate exerted the highest protective effect. S. cerevisiae mc2 showed higher viability when co-cultured with K. apiculata mF or O. oeni X2L-K. apiculata mF (media SF= 0.51 and 0.54, respectively). Also, only in mixed cultures, S. cerevisiae showed interaction with lioprotectants, sodium glutamate, glucose and maltose being the best protective agents. K. apiculata showed strain-lioprotectant interaction in both, pure and mixed culture. All the sugars were excellent protective agents of pure cultures, with the exception of maltose. When the apiculate strain was co-cultured with the others microorganisms, fructose was the best lyoprotectant (media SF =0.72). With respect to the lactic acid bacteria strain, it showed the highest viability values when pure cultures where freeze-dried in NGJ, while trehalose, saccharose and glutamate were the best lyoprotectants when O. oeni X2L was co-cultured with both yeast strains. Taking into account the lioprotectants availability, the production costs and the quality of the wine, we propose to inoculate the fresh must with S. cerevisiae + K. apiculata lyophilized in 10% fructose (~1.16x1015 and 7.4x1014 UFC/g, respectively) and O. oeni X2L lyophilized in 17% NGJ (3.94 x1013 UFC/g).