Starter cultures are used in freeze-dried or frozen form for preservation, flavour development, colour formation and colour stabilization in meat products with a longer production period (especially raw sausages and some raw cured products). The bacterial strains in question must be capable of autolysis and thus of releasing enzymes for flavour formation under the given conditions. However, this must not occur too rapidly because otherwise, depending on the strain, this results in insufficient lactic acid formation.
Current starter cultures consist mainly of lactic acid bacteria (lactobacilli, pediococci) and micrococcaceae (cocuria, staphylococcae suitable for food). The purpose of lactic acid bacteria is firstly to form lactic acid and to achieve the pH-reduction connected with it, which is important for preservation, colour stabilization, sliceability and drying (lower water-binding capacity) they also contribute to flavour formation (—> proteolysis). Secondly, individual lactic acid bacteria are able to produce bacteriocins (see below). In the case of micrococcaceae, the formation of enzymes for flavour formation and for reduction of nitrate to nitrite (cf. curing) is of primary importance. In the literature, reference is made to the use of streptomycetes for flavour formation (—> proteolysis, lipolysis). Yeasts are also fairly widely circulated (candida, debaryomyces); their purpose is flavour formation, stabilization of curing and better adhesion of surface moulds.
Staphylococcus carnosum — a frequent example of micrococcaceae in meat starter cultures
Unlike starter cultures which are introduced into the product, the effect of surface cultures is concentrated on the product surface. The following effects are important: better flavour (smell, taste), greater protection against drying out, prevention of light oxidation, greater competition to unfavourable microorganisms, more uniform appearance, easier peeling of the skin. Mould of the penicillum genus (main example: P. nalgiovense, P. chrysogenum) is primarily used in surface cultures. Aspergilla are hardly ever added because of their potential to form mycotoxins. On the other hand, interest in the use of yeasts in surface cultures seems to be on the increase.
Apart from the classical use of starter cultures, other areas of application such as e.g. protective cultures (cf. bacteriocins, below), probiotic cultures with positive microorganisms or cultures for product identification are now being discussed.
Bacteriocins are substances which are formed by bacteria and have an antimicrobial effect particularly against gram-positive bacteria (e.g. bacilli, clostridia). They are mainly produced by lactic acid bacteria (e.g. Lactobacillus curvatus, Lactobacillus sakei, Leuconostoc mesenteroides), where the optimum is a temperature of 25°C and a pH of 5.5.
Lactobacillus sakei — a potential bacteriocin former
In practice, bacteriocin-forming microorganisms are being specifically used in the first commercial protective cultures. However, their effects can be limited in meat by the fact that bacteriocins contain protein and are therefore sensitive to proteolytic processes (cf. meat's own protein-degrading enzymes in meat aging).