Pulsed Electric Field Technology for the Extraction of Glutathione from Saccharomyces cerevisiae.

Glutathione is a potent antioxidant that has shown promise in enhancing the processing of various foods and drinks such as bread and wine. Saccharomyces cerevisiae stands as a primary microorganism for glutathione production. This study sought to assess the potential of pulsed electric fields (PEFs) in extracting glutathione from S. cerevisiae cells. Yeast cells were subjected to PEF treatment (12 kV/cm, 150 µs) followed by incubation at varying pH values (4.0, 6.0, and 8.0) and temperatures (4 °C and 25 °C). Glutathione and protein extraction were assessed at different incubation times. Within one hour of incubation, PEF-treated yeast cells released over 60% of their total glutathione content, irrespective of pH and temperature. Notably, the antioxidant activity of the resulting extract surpassed that obtained through complete mechanical cell destruction and hot water, which form the conventional industrial extraction method in the glutathione industry. These results suggest that PEF could offer a rapid and more selective procedure, improving the extraction of this bioactive compound.

Sequential extraction of compounds of interest from yeast biomass assisted by pulsed electric fields.

One strategy to reduce cost and improve feasibility of waste-yeast biomass valorization is to obtain a spectrum of marketable products rather than just a single one. This study explores the potential of Pulsed Electric Fields (PEF) for the development of a cascade process designed to obtain several valuable products from Saccharomyces cerevisiae yeast biomass. Yeast biomass was treated by PEF, which affected the viability of 50%, 90%, and over 99% of S. cerevisiae cells, depending on treatment intensity. Electroporation caused by PEF allowed access to the cytoplasm of the yeast cell without causing total breakdown of the cell structure. This outcome was an essential prerequisite to be able to perform a sequential extraction of several value-added biomolecules from yeast cells located in the cytosol and in the cell wall. After incubating yeast biomass previously subjected to a PEF treatment that affected the viability of 90% of cells for 24 h, an extract with 114.91 ± 2.86, 7.08 ± 0.64, and 187.82 ± 3.75 mg/g dry weight of amino acids, glutathione, and protein, respectively, was obtained. In a second step, the extract rich in cytosol components was removed after 24 h of incubation and the remaining cell biomass was re-suspended with the aim of inducing cell wall autolysis processes triggered by the PEF treatment. After 11 days of incubation, a soluble extract containing mannoproteins and pellets rich in ß-glucans were obtained. In conclusion, this study proved that electroporation triggered by PEF permitted the development of a cascade procedure designed to obtain a spectrum of valuable biomolecules from S. cerevisiae yeast biomass while reducing the generation of waste.

Assessing the efficacy of PEF treatments for improving polyphenol extraction during red wine vinifications.

The influence of the electric field intensity and pulse width on the improvement of total polyphenol index (TPI) and colour intensity (CI) during extraction in an ethanolic solution (30%) and during fermentation-maceration has been investigated in different grape varieties: Grenache from two harvesting times, Syrah and Tempranillo. The aim of this study was to develop a procedure to establish the PEF treatment conditions that cause enough permeabilization in the skin cells of different grape varieties to obtain a significant improvement in the vinification process in terms of increment on the polyphenol content or reduction of maceration time. Results obtained in this investigation indicate that extraction of polyphenols in a solution of ethanol (30%) for 2 h could be a suitable procedure to know if the PEF technology is effective for improving extraction of polyphenols from the grapes during vinification and to determine the most suitable PEF treatment conditions to obtain this objective. Improvement in the extraction during vinification only was observed with those grapes and under treatment conditions in which the improvement of the polyphenol extraction was higher than 40%. Other interesting observation from this research is the highest efficacy of PEF when treatments of the same duration are applied using longer pulses. Therefore, in a continuous process, where the flow processed is determined by the frequency applied by the PEF generator, it is possible to increase the processing capacity of the PEF installation. INDUSTRIAL RELEVANCE: Benefits from PEF treatment of the grapes before the maceration step in the vinification process have been demonstrated. Nevertheless, the characteristics of the grapes may change in different vintages and grape varieties. Therefore, it is of high importance to be able to determine the optimum PEF conditions in order to obtain the desired benefit during the vinification. The rapid method developed permits to determine PEF process parameters before the application of the PEF treatment with the objective of facilitating the phenolic extraction and therefore, reducing the maceration time. In these cases, it would be possible to remove the skins from the rest of the wine earlier, and therefore, increase the processing capacity of the winery.