Influence of freezing temperatures prior to freeze‐drying on viability of yeasts and lactic acid bacteria isolated from wine

Aims: To determine the effect of three different freezing temperatures on post-freeze-drying survival rates of wine yeasts and lactic acid bacteria (LAB). To know if a similar freeze-drying protocol can be used for both micro- organisms. Methods and Results: Cells from liquid culture media were recovered and concentrated in appropriate lyoprotectants. Aliquots of each strain were frozen at 20, 80 and 196°C before vacuum drying. Viable cell counts were done before freezing and after freeze-drying. Survival rates were calculated. Freezing temperatures differently affected yeast and bacteria survival. The highest survival rates were obtained at 20 and 80°C for yeasts, but at 196° C for LAB. Major differences in survival rates were recorded among freeze-dried yeasts, but were less drastic for LAB. Yeasts Pichia membranifaciens, Starmerella bacillaris and Metschnikowia pulcherrima, and LAB Lactobacillus paracasei, Pediococcus parvulus and Lactobacillus mali, were the most tolerant species to freeze-drying, regardless of freezing temperature. Conclusions: Yeast and LAB survival rates differed for each tested freezing temperature. For yeasts, 20°C ensured the highest post-freeze-drying viability and 196°C for LAB. Significance and Impact of the Study: Freezing temperature to freeze-dry cells is a crucial factor for ensuring good wine yeast and LAB survival. These results are important for appropriately preserving micro-organisms and for improving starter production processes

Selection criteria and tools for malolactic starters development: an update

The use of malolactic starter cultures to improve the fermentation process and enhance wine quality and safety is becoming a common winemaking practice, increasingly preferred to spontaneous fermentation. Given its great oenological properties, Oenococcus oeni is the species most present in commercial brands of wine lactic acid bacteria (LAB) starters. Stress resistance, technological performances and safety are the key selection criteria to take into account when designing effective malolactic starters. Nowadays, new LAB strains are selected by exploiting advanced technological applications rather than the traditional screening methods based on a trial and error approach. In particular, the progress made in the fields of genetics and molecular biology, as well as in the whole genome sequencing projects, offers new tools to better characterize candidate starter strains. This review aims at providing an updated picture of the technological approaches that should be used to select LAB strains suitable for winemaking. In the near future, the full integration of phenotypic and genetic data will make it possible to rationally develop malolactic cultures that are specific for different types of wine