Studies on obtaining active dry wine yeast using different nitrogen sources

Most of research on wine microbiology has concentrated on Saccharomyces yeasts for development of starter cultures, especially on Sacch. cerevisiae. As the importance of the role of S. cerevisiae in winemaking has been established, the number of wine yeast strains available in the world market for use as winemaking starters grew in the last years. The upstream process of producing Sacch. cerevisiae biomass on a culture medium based on sugar was performed by testing different sources of inorganic and organic nitrogen (yeast extract and monoammonium phosphate) in submerged fermentations using a Biostat B plus bioreactor (4L working volume). The upstream parameters have been monitored on-line (oxygen flow; pH around 4.35; temperature 300C; stirring rate 250 rpm) and off-line (total soluble dry matter; pH). The biomass obtained after the downstream process has been dried through freeze-drying. Through the combination of two carbon sources as yeast extract (0.7%) and monoammonium phosphate 10.71 g/L dry cell weight (DCW) has been obtained, compared with 9.6 g/L DCW in the case of the fermentation without monoammonium phosphate. From the economic reasons, the monoammonium phosphate as an inorganic nitrogen form has been excluded from the experiments. Finally, the higher content of dry yeast biomass (14.43 g/L DCW) was obtained when 11% yeast extract as the only nitrogen source has been added at the fermentation media

Optimization of the Fermentation Conditions for Brewing Yeast Biomass Production Using the Response Surface Methodology and Taguchi Technique

Yeast (including brewing yeast) and yeast-based preparations derived from bioprocesses or agroindustrial byproducts represent valuable feed additives and ingredients for ruminants. The optimization of brewing yeast biotechnological processing through fermentation mediated by the brewing yeast strain Saccharomyces pastorianus ssp. carlsbergensis W34/70 was investigated. The cultivation conditions (temperature, pH, carbon source, and nitrogen source) were selected and designed according to a Taguchi fractional experimental plan, with four factors on three levels, and their influence on the evolution of the bioprocess of obtaining the brewing yeast biomass was evaluated. The dependent variables were the yeast biomass amount in wet form, yeast biomass amount in dried form after lyophilization, dried yeast biomass wettability assayed through the contact angle (CA), protein content (PC), and dry matter content (DS). The effects that the experimental conditions had on the system responses were visualized in tridimensional space using the response surface methodology, and the combination of biotechnological parameters that ensured process quality and robustness was then determined using the Taguchi technique through its performance indicator, i.e., the signal-to-noise ratio. By optimizing the biotechnological parameters, this study provides a valuable contribution in the area of brewing yeast biomass processing, with the aim of producing probiotic yeast for ruminant nutrition