Scale-up to pilot plant dimensions of plasma processed water generation for fresh-cut lettuce treatment

The increasing demands of society for healthy nutrition in combination with continuously decreasing willingness to spend time for food preparation leads to a rising consumer demand for minimal processed ready-to-eat (RTE) products (convenient food). The USA is the leading nation in the consumption and therefore, the biggest market for these kinds of products. Thus, the U.S. Food and Drug Administration (FDA) has long term experience in the evaluation of consequences of the consumption of minimal processed RTE products. This authority publicized a list of the ten riskiest foods with leafy greens on the top. Sanitation steps based on plasma processes could be an promising addition to conventional cleaning procedures. Plasma, often introduced as forth state of matter, differs from the gaseous state of matter by a certain amount of free charge carriers caused by ionization processes of the gas atoms and molecules due to the supply of energy. The electrical conductivity allows supplying the energy needed to sustain this state electrically, giving access to a huge variety of plasma generation methods with excitation frequencies from DC to several GHz offering wide parameter ranges e.g. electron energies from 0.5 eV to 10 eV. The treatment of natural products with changing parameters like size, shape or water content is a challenging task for design and optimization of plasma processes. The lack of effectiveness of sanitation processes on the surfaces of food products is a general problem of all discussed methods. In order to overcome these problems a specific plasma process was established, based on a microwave plasma torch operated with compressed air delivering plasma processed air (PPA) as antimicrobial acting process gas. If PPA is brought into contact with water, plasma processed water (PPW) is generated which has antimicrobial properties. This PPW process was implemented into a pilot-plant scale salad-rinsing unit in order to demonstrate the scalability and applicability of this treatment procedure. During the trial 45 kg Endive (Cichorium endivia) and about 1.500 l of plasma generated disinfectant were consumed. Off the cuff, the process was competitive to industrial established chemical processes.