Substitution of synthetic nutrients for the lactic acid fermentation
2007
Venus, J.
Microbial lactic acid production is carried out in technical bioreactors by using a suitable strain of lactic acid bacteria. These bacteria convert easily monosaccharids like glucose or fructose into cell mass and lactic acid. This microbial synthesis is a multistep reaction, the partial reactions of which are catalyzed by enzymes. In this process, the cells grow and multiply forming biomass. Energy necessary for growth and maintenance is obtained by producing lactic acid. Lactic acid formation and cell growth are closely coupled in lactic acid fermentation. The microorganisms have a need for a carbon source, a source of nitrogen and nutrients, and a phosphorus source. The latter is available when inorganic phosphate salts are added to the medium. The demand for nitrogen can't be covered by inorganic salts only. Lactic acid bacteria need also a series of nitrogen-containing nutrients (amino acids, peptides etc.) for growth and therefore, the medium have to be supplied by complex protein hydrolysates (yeast extract, peptone etc.). The protein extracts mentioned are very expensive and their substitution by low-priced nutrient extracts is necessary when a large-scale production is planned. In this research, the objective was to test the suitability of grains and green masses for use as raw materials in lactic acid fermentation. According to the intention to substitute expensive nutrient supplements by cheaper materials from renewable resources there were tested green material from lucerne and lupine for the cultivation of lactic acid bacteria. For the lactic acid fermentation with suspended cells in a stirred bioreactor it was necessary to prepare a liquid with a certain content of nitrogen and raw protein respectively. For that purpose fresh green material was pressed to separate the juice and the cake.
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