How small lactic bacteria grow
Kaarel Adamberg, Young Researcher of the year of TUT, is dealing with the development of lactic bacteria for dairy industry.
Kaarel Adamberg is a versatile person, working on three posts. In TUT he is a senior researcher in the Institute of Chemistry of the Faculty of Science and in the Department of Food Processing in the Faculty of Chemical and Materials Technology, and is also working as a project manager in the Competence Center of Food and Fermentation Technologies (CCFFT). He is conducting research in lactic and other bacteria. „We try to understand bacteria, in order to use them in food production and also in chemical industry as cell plants,“ says Adamberg.
Lactic bacteria are used in the production of fermented milk and cream products, cheese and other products (such as acidified vegetables and sausages) as leaven. Recently there have been also attempts to use them in medicine industry, e.g. in the production of vaccines, but CCFFT is not dealing directly with this field.
While the bacteria Escherichia. coli, which is widely used in industrial production, is rather modest and grows on glucose, to which the components similar to fertilizer (ammonium, potassium and other salts) are added, the handling of lactic bacteria is much more difficult. Researchers must prepare themselves a mixture suitable for carrier medium, using 20 amino acids, several vitamins and other components, which must be weighed separately.
Bacteria are grown in a bioreactor. A human being can hardly perceive their size. The dimension of protozoa is about micrometer, which means that you could put thousand of them in a row on a single millimeter. If you eat one hundred grams of yoghurt, 1011 bacteria will enter your gastro-intestinal tract, Adamberg says.
Bacteria are pumped out from the bioreactor together with their caused products, which in this case is mainly lactic acid. In the reactor it is possible to measure temperature, oxygen content, acidity (pH) and other parameters affecting the process. These conditions should be optimised depending on the research task. Control is performed via computer, where also various diagrams can be monitored – e.g. decrease of the consumption of oxygen in time and inversely proportional increase of the production of lactic acid with small shift.
There are two reasons for research and development of lactic bacteria. On one hand, consumers want different products. Some like sour, some mild yoghurt. Different leavens (lactic bacteria) are needed for their production. On the other hand, dairy companies wish to optimise their production to maximum possible extent. „Unfortunately there are hundreds different species of lactic bacteria, with many different strains,“ Adamberg says. „For example, one strain may produce a specific flavour component, while another will sour milk more quickly.“ The most important parameter of lactic bacteria is the speed of souring and coagulation of milk under their influence.
Leaven industry would like to select the most suitable from these thousands of strains. Various equipment are used for this purpose, enabling to perform tens and hundreds of tests e.g. for analysing different milks or strains of lactic bacteria. In every test the characteristic parameters of cell growth are measured, such as production speed of acids with pH meter, emission of heat with micro-calorimeter or change of the number of cells with flow cytometer. Another area is analysis of aromatic compounds. „We are able to measure every molecule produced by bacteria during their life,“ says Adamberg. The main metabolic product of lactic bacteria is lactic acid, but they can also produce acetic acid, formic acid, ethanol and various aromatic compounds. „We want to know, why and under which conditions they are producing these compounds,“ explains Adamberg. The answer will enable to grow the biomass of bacteria in large industrial fermentors (10-100 thousand litres), to find the right growth conditions, pH, temperature and content of culture medium, in order to retain the qualities of bacteria also in dairy industry, where they are used for the production of dairy products.