Stability of high cell density brewery fermentations during serial repitching

Green Process: Improved Semi-Continuous Fermentation of Pichia pastoris Based on the Principle of Vitality Cell Separation

The large-scale fermentation of Pichia pastoris for recombinant protein production would be time consuming and produce a large amount of waste yeast. Here we introduce a novel semi-continuous fermentation process for P. pastoris GS115 that can separate vitality cells from broth and recycle the cells to produce high-secretory recombinant pectate lyase. It is based on differences in cell sedimentation coefficients with the formation of salt bridges between metal ions and various cell states. Compared to batch-fed cultivation and general semi-continuous culture, the novel process has significant advantages, such as consuming fewer resources, taking less time, and producing less waste yeast. Sedimentation with the addition of Fe3+ metal ions consumed 14.8 ± 0.0% glycerol, 97.8 ± 1.3% methanol, 55.0 ± 0.9 inorganic salts, 81.5 ± 0.0% time cost, and 77.0 ± 0.1% waste yeast versus batch-fed cultivation to produce an equal amount of protein; in addition, the cost of solid-liquid separation was lower for cells in the collected fermentation broth. The process is economically and environmentally efficient for producing recombinant proteins.

Modeling the inactivation of Lactobacillus brevis DSM 6235 and retaining the viability of brewing pitching yeast submitted to acid and chlorine washing

This study aimed to model the inactivation of Lactobacillus brevis DSM 6235 while retaining the viability of yeasts during washing brewer's yeast with phosphoric acid and chlorine dioxide. The independent variables in the acid washing were pH (1-3) and temperature (1-9 °C), whereas in the washing with chlorine dioxide, concentration (10-90 mg/L) and temperature (5-25 °C) were assessed. The predictive models obtained for the four response variables γ_LA, γ_Cl (decimal reduction of L. brevis DSM 6235), V_f/V0_LA, and V_f/V0_Cl (brewer's yeast viability ratio) were found to have R² > 0.80 and values of F_calc > F_reference. Then, the models were considered predictive and statistically significant (p < 0.10). Our results indicated that phosphoric acid and chlorine dioxide washing resulted in up to 7 and 6.4 (log CFU/mL) decimal reductions of L. brevis DSM 6235, respectively. On the other hand, the viability of the brewer's yeast ranged from 22.3 to 99.4%. L. brevis DSM 6235 inactivation was significantly influenced by parameters pH(Q) and T°C(Q) when phosphoric acid was applied, and by parameters mg/L(L), mg/L(Q), T°C(Q), and mg/L × T°C when ClO₂ was applied. The validation of the models resulted in bias (γ_LA, 0.93/V_f/V_0LA, 0.99 - γ_Cl, 1.0/V_f/V_0Cl, 0.99) and accuracy values (γ_LA, 1.12/Vf/V_0LA, 1.01 - γ_Cl, 1.08/V_f/V_0Cl, 1.03). The results of this study indicate that it might be possible to decontaminate brewer's yeast through acid and chlorine dioxide washing while keeping its viability. This procedure will result in the reduction of costs and the lower generation of brewer's waste.

Analysis of aging in lager brewing yeast during serial repitching

Serial repitching of brewing yeast inoculates is an important economic factor in the brewing industry, as their propagation is time and resource intensive. Here, we investigated whether replicative aging and/or the population distribution status changed during serial repitching in three different breweries with the same brewing yeast strain but different abiotic backgrounds and repitching regimes with varying numbers of reuses. Next to bud scar numbers the DNA content of the Saccharomyces pastorianus HEBRU cells was analyzed. Gene expression patterns were investigated using low-density microarrays with genes for aging, stress, storage compound metabolism and cell cycle. Two breweries showed a stable rejuvenation rate during serial repitching. In a third brewery the fraction of virgin cells varied, which could be explained with differing wort aeration rates. Furthermore, the number of bud scars per cell and cell size correlated in all 3 breweries throughout all runs. Transcriptome analyses revealed that from the 6th run on, mainly for the cells positive gene expression could be seen, for example up-regulation of trehalose and glycogen metabolism genes. Additionally, the cells' settling in the cone was dependent on cell size, with the lowest and the uppermost cone layers showing the highest amount of dead cells. In general, cells do not progressively age during extended serial repitching.

The microbiology of malting and brewing

Brewing beer involves microbial activity at every stage, from raw material production and malting to stability in the package. Most of these activities are desirable, as beer is the result of a traditional food fermentation, but others represent threats to the quality of the final product and must be controlled actively through careful management, the daily task of maltsters and brewers globally. This review collates current knowledge relevant to the biology of brewing yeast, fermentation management, and the microbial ecology of beer and brewing.