Start cultures
Lactic acid bacteria have been used as start cultures in food making for a very long time. Yoghurt, cheese, cured sausages and sourdough bread are examples of products in which lactic acid bacteria are added as a start culture to ensure the quality of the finished product. The ability to produce acid is one of the most important properties of the start culture. Producing acid helps primarily by inhibiting the growth of undesirable micro-organisms, but it also gives products the desired consistency and taste. Some lactic acid bacteria are very suitable for use in start cultures, others are not. Systematic research is going on into understanding how the lactic acid bacteria control their production of lactic acid and other compounds. This knowledge can then be used to optimise the bacteria, or the conditions around them, when they are used in start cultures.
Probiotic effect
So-called functional food, such as dairy products or juice containing probiotic bacteria with documented health benefits, is being found on the market in increasing quantities. Many lactic acid bacteria have probiotic properties, which gives them a potential for beneficial health effects. Lactic acid bacteria are sorted according to a number of criteria which must be present in order for a bacterium to be called probiotic. Nofima Mat is carrying out research into potentially probiotic lactic acid bacteria with the intention of laying down basic principles for why one bacterium can have a probiotic effect and not another. This will be important for documentation and product development in this area.
Inhibit other bacteria
Lactic acid bacteria also have the ability to inhibit the growth of other and dangerous bacteria in products. The acid produced by the lactic acid bacteria makes the environment around a product so acidic that other bacteria cannot grow. Other compounds produced by these bacteria can also have an inhibiting effect. For example, some lactic acid bacteria produce small antimicrobial peptides (so-called bacteriocins). The ability to inhibit undesirable micro-organisms can be used to make food safer. The term protective cultures is used in this context. Some lactic acid bacteria can grow on many types of food without affecting taste, smell, structure or colour to any noticeable extent. This is important when the bacteria are used as a protective culture, because the taste properties of the product are not changed.
Studies in the human intestine
Our large intestine may be compared to a reactor in which many types of bacteria convert the components of food. Nofima Mat has a laboratory containing a so-called artificial intestine. The artificial intestine attempts to resemble this reactor. This laboratory gives researchers the possibility of investigating what happens to components in food in the human intestine in a model system. Here it is also possible to study lactic acid bacteria in a complex system that resembles an intestine. However an artificial intestine like this lacks the human cells and what happens between human cells and micro-organisms. To study this we must work with other model systems, such as cell lines. Some lactic acid bacteria appear to be well able to fasten themselves to intestinal cells. They are also able to give different immunological responses and to stimulate cells in the intestine to increase the production of proteins which act as a kind of glue between the cells of the intestinal wall and function as a barrier against the intrusion of harmful bacteria.
Bacterial strain collection
Nofima Mat has quite a large collection of strains of lactic acid bacteria. For many of them profiles of the DNA have been made with the aid of various methods, to provide a kind of "fingerprint". The profiles are compared and an attempt made to link them to various properties that are relevant for food production.
