Yeast cells are important host systems for the industrial production of bioproducts, like proteins, enzymes, and nanoplexes. These products are, in many cases, accumulated in the intracellular space. Product release is usually performed by mechanical cell-disruption methods, which are lacking specificity. Thus, a range of impurities and proteases are liberated with the sought material. This situation negatively affects the purification operations downstream and compromise product integrity. Attempts have been made to implement non-mechanical, selective methods for cell permeabilization and product release. Among them, the application of an electric field - under optimized conditions - can be proposed as a gentle "electroextraction" of intracellular products. Extraction by electrical fields can be performed either in batch or in continuous mode, adding flexibility to the technique. In this article, we describe the concepts behind this novel method in the frame provided by standard biomass-disruption operations.

Introduction
In the current century, the biopharmaceutical industry is one of the fastest growing sectors in the global economy [1]. With the completion of the primary DNA mapping of the human genome and the advances made in high-throughput technology for drug discovery, a notable growth in the development of therapeutic products was observed, with more than 500 products in active clinical trials [2]. Proteins constitute an important class of biopharmaceutical products, but they are also important in the food and the green chemical industries. Advances in the recombinant DNA and cell culture technology have permitted the large scale production of virtually any protein by fermentation routines at increased titers [2], thereby shifting the bottleneck in biopharmaceutical process development to the production of such bioproducts [3]. Downstream processing is often the most challenging and expensive phase in producing a substance of biological origin. The efficiency of the primary recovery unit operations can influence the overall production cost and they have a direct impact on the success of high-resolution purification operation, which follow. Yeast cells are industrially favored for the manufacture of many proteins, enzymes, and nanoplexes because they can handle posttranslational modifications and high production levels.

In many cases those products are biosynthesized by yeasts under appropriate environmental conditions but remain accumulated in the biomass as intracellular products [4]. Cell disruption is then required in order to render a soluble product fraction.

Technical Challenge
Improving any unit operations during downstreaming could slash down the production costs, increase final product
quality, and accelerate time to market. As said, cell disruption is a critical unit operation; identification and selection of a
suitable cell disruption method is extremely important since the nature of the disruption operation directly affects process efficiency, quality, and yield of the product involved [5]. Yeast cells could be difficult to disrupt due to the existence of cell walls, which makes up to 15-30 % of the dry cell weight. The walls are mainly composed of (outer) O- and N- glycosylated mannoprotein and fibrous (inner) β1,3 glucan, the latter forming complexes with chitin. The β1,3 glucan-chitin complex is the major constituent of the inner wall and forms the fibrous scaffold of the wall. There is also branched β1,6 glucan that links the various components of the cell wall. Overall, the cell wall is made up of 40 % of mannoprotein, 50 % of β1-3 glucan, 8 % of β1-6 glucan and 2 % of chitin (fig. 1). The above components make intact cell walls to be densely packed and thus, limit the diffusion of soluble species. In order to liberate the intracellular material it is usually necessary to establish a gentle disruption method to maximize product recovery. On the other hand, once the cells are disrupted, it is essential to protect the (labile) product from proteolysis or other chemical events e.g., oxidation.

Classical Methods
A few unit operations are available in industry in order to accommodate for effective bioproduct release. However, these methods usually produce a complete destruction of the cell envelop and the release of the entire intracellular content, including contaminants and proteases. Common techniques for cell disruption are based on mechanical effects (high-pressure homogenization, bead milling), addition of chemicals (organic solvents, enzymes, detergents), physical action (production of cavity shocks, freezing and thawing, application of an electrical field), and synergetic combinations of the above-mentioned methods.