It is interesting to consider that the industrial starters for the majority of cheeses are based on a single mesophilic species, namely Lactococcus lactis. Strains of this species are employed for the manufacture of various cheese types and, although they exhibit different characteristics, they have several biochemical attributes in common (11,12). The most important properties are their ability to produce acid in milk and to form flavor components.
For the manufacture of Gouda cheese, the undefined mixed-strain starters are composed of acid-forming lactococci, Lactococcus lactis subsp. lactis and L. lactis subsp. cremo-ris, possibly in combination with the citrate-utilizing strains L. lactis subsp. lactis biovar diacetylactis, and Leuconostoc spp. (Fig. 1). These starters are thus composed of complex mixtures of strains, forming a bacterial population that is equipped with the properties suitable for the production of the desired cheese. Because their composition would change depending on the conditions of cultivation (13), their subculturing is minimized and the cultures are preserved by freezing or lyophilization.
Also, the manufacture of Cheddar cheese and several other cheese types is entirely dependent on the fermentative activity of lactococci, sometimes in the form of defined-strain starters, consisting of L. lactis subsp. lactis varieties in case of Cheddar cheese, but frequently still in the form of undefined mixed-strain starters.
Mesophilic lactococci are generally considered to be associated with the milk environment (14) but they can also be isolated from other sources (15). Lactococci isolated from artisanal manufacture of fermented dairy products without the application of industrially prepared starter cultures and from nondairy environments are generally referred to as
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