Humans have long used different micro-organisms to season and conserve foods. The Sumerians, for example, used yeast fungus to make beer 4,000 years ago. Other micro-organisms that humans have utilized for a long time are lactic acid bacteria and propionic acid bacteria. Lactic acid bacteria have been used to make cultured milk, cheese, yoghurt, and fermented sausage, and they are also put to work in silaging. Propionic acid bacteria have primarily been exploited in the production of certain large-hole cheeses, such as Swedish Grevé and Emmental.
Jörgen Sjögren has studied the fungus-inhibiting function of a number of strains of lactic acid bacteria and propionic acid bacteria in order to find strains that can be used to inhibit the growth of mold in silage, for instance. It has long been known that lactic acid bacteria and propionic acid bacteria produce the organic acids lactic acid, acetic acid, and propionic acid. All of these acids can inhibit mold fungi, but Jörgen Sögren and his associates have also seen that certain lactic acid bacteria and propionic acid bacteria moreover produce other substances (metabolites) with fungus-inhibiting properties. Twelve such substances are reported in the dissertation.
One lactic acid bacterium (Lactobacillus plantarum MiLAB 393) has been patented, and the rights have been sold to Medipharm AB, which this year is launching a biological conservation agent for silage in Europe.
An important element of the dissertation work involved finding an efficient method of isolating the fungus-inhibiting substances of bacteria, a method that is based on growing cultures in a water-based substrate, followed by centrifuging, filtering, stepwise fractionating, and finally determining the structure with the aid of nuclear magnetic resonance (NMR) and mass spectrometry (MS).
The findings are presented in a doctoral dissertation that will be publicly defended on April 15.