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Degree: Bachelor of Process Engineering
|Fig.1: REM picture of Lactobacillus sanfranciscensis|
In these days the requirements to basic food become more and more important and different processes to preserve them exist. One high efficient way of preserving liquids is thermal sterilising but the disadvantage of this method is the loss of temperature sensitive vitamins and flavouring agents. Another possibility is to apply high pressure in order to inactivate the microorganisms. The advantages of high pressure sterilisation are that quality of the sterilised liquids can be highly maintained. An important aspect is the efficiency of the process because in no energy is lost by heating up and cooling down the food. A big advantage of this process is the preservation of valuable molecules like vitamins or flavouring agents but also colour, taste and consistency. Contrary to thermal processes in which the molecules are chemically changed due to the high energy input.
|Fig.2: Growth of L.
in liquid MRS4 medium
At the institute for process technology and machinery (IPAT) of the university Erlangen-Nuremberg several experiments to conserve food have been done with a new method using dynamic high pressure. In order to examine the response of microorganisms to dynamic high pressure a selection of bacteria with different properties has been used. Up to now several experiments with Escherichia Coli and Saccharomyces cerevisiae have already been done. As a further spoiling organism a new bacterium, Lactobacillus sanfranciscensis, should be established. Lactobacillus sanfranciscensis belongs to the family of Lactobacteriaceae which grow under anaerobe conditions.
In this work the best predictable growth conditions of the aero tolerant Lactobacillus sanfranciscensis should be specified. Therefore the growth behaviour on MRS4 medium under diverse atmospheric conditions has been examined. Furthermore the growth kinetics of Lactobacillus sanfranciscensis have been determined and the batch curve recorded. The growth curve is important because the bacteria for the pressure experiments should stem from the stationary phase.
It could be shown that the bacteria grow under anaerobe and oxygen reduced atmosphere as well as under anaerobe conditions with no difference in their cell number. However, with regard to the pressure experiments it is advisable to use the anaerobe atmosphere. Otherwise it might be that the results cannot be clearly deduced to the influence of the pressure acting on the cell because the cells do not possess their optimum metabolism.
A maximum cell number of 108 in the stationary phase was obtained and the maximum growth rate µmax of 0.8 h-1 was calculated during their exponential growth phase. The resulting generation time was 80 min/cell. The stationary phase is reached after 35 hours and last for at least for further 35 hours.