(563g) Mechanical Steam Treatment of Plant Material

Since approx. 15 years it is known by the research work of the Lemgo University of Applied Sciences that bacterial cells can be separated efficiently from plant surfaces by flash evaporation. A short steam treatment is followed by an extremely fast evacuation which results in an intensive evaporation that reduces the cell count of microbes.

First investigations were undertaken in a special lab-scale VSV-apparatus (Vacuum-Steam-Vacuum) with a treatment chamber of 0.7 L. The plant material as a fixed bed and the model systems (inoculated wooden lamellae or small glas plates) were treated with saturated steam. Even heat resistant bacterial spores are reduced up to 4 decades in only 10 s steam treatment of approx. 120 °C /1/. The formation of a thin layer onto the surfaces of the model material is important to reduce the bonding forces between the cells and the surface. The obtained type of kinetic is unusual and can be divided in two steps: a first phase with a steep linear spores reduction; with an activation energy E_A of about 10 kJ/mol and a second step with a flatter linear diminution with an E_A of ca. 200 kJ/mol (typical for heat-influenced inactivation). The 2^nd step is not necessary for an industrial application, resulting in a short batch time of an industrial process. There must be a minimum temperature of the saturated steam depending on the specific bonding force in the range of 110 to 125 °C /2/.

A lot of research was done in the last years to decontaminate dry plant materials (spices, herbs and drugs) which confirms the mild process parameters giving a good quality concerning active substance concentration. Additional experiences are existing of an industrial scale decontamination with a solid mixer as treatment chamber.

In this contribution a summary of the research work of this â??Mechanical Steam Decontaminationâ? is given.

/1/ Müller U, Wilhelm P.: Lebensmitteltechnik 2002; 9: 58-59

/2/ Lilie M, Dissertation, University of Bielefeld/D. 2009