## 1 Introduction  
Milk in general, goat milk included, has been considered a complete food which can be also indicated as a functional food [1, 2]. Functional food means a food having functional (naturally occurring, biologically active) components, which confer health benefits far more than ordinary nutrition. The health benefits of goat milk make it a remedy for some disease conditions. It is milk with a low allergenicity and high digestibility, which makesit a popular dairy product also for immune-compromised individuals [1]. The current trend of naturally driven foods with digestibility and therapeutic benefits resulted in an increased demand for goat milk and products made from it [3]. Besides many beneficial components such as proteins, lipids, fats, vitamins, and minerals [1], raw goat milk also contains beneficial bacteria from the phylum Firmicutes [4]. Regarding, e.g., proteins, the study revealed new insights into whey proteomics at various stages of lactation with an abundance of 238 proteins [5]. The developmental changes of casein micellar structure of goat milk were also analyzed formerly. Fifteen proteins were identified during the whole lactation cycle [5]. An advantage of goat milk is also that it provides a smooth texture to milk products, due to its small-sized fat globules in comparison to other kinds of milk. It has a relatively lower amount of \(\alpha\)s1-casein, which results in a softer gel structure with higher water-holding capacity and lower viscosity which is a desirable attribute in many fermented milk products [1]. Lactic acid genera commonly detected in raw goat milk include _Lactococcus_, _Lactobacillus_, _Lactiplantibacillus_, _Pediococcus_, _Limosilactobacillus_, _Leuconstoc_, and _Lacticaseibacillus_ but also those novel genera mostly detected from raw cow milk such as _Schleiferilactobacillus_, _Holzapfelia_, _Amylolactobacillus_, _Ligilactobacillus_, _Agrilactobacillus_, etc. [6]. However, the most frequently isolated bacteria from goat milk using the standard microbiological technique represent _Lactococci_[7; 8; 9]. They are one of the most important lactic acid bacteria (LAB) used in the dairy industry [8; 9], especially the species strains _Lactococcus lactis_. This Gram-positive bacterial species belongs to the phylum Firmicutes, the class Bacilli, the order _Lactobacillus_, the family _Streptococcus_ and, finally, to the genus _Lactococcus_[7; 8; 9]. The species _Lactococcus lactis_ does not produce spores and is non-motile. It has generally recognized as having safe status (GRAS) [9]. The species _L. lactis_ is one of the best characterized bacteria regarding genetics, metabolism and biodiversity [10]. In milk, it uses enzymes to produce energy molecules (ATP) from lactose. The byproduct of ATP energy production is lactic acid, which curdles milk, and curd is formed, which has been used for cheese production [11]. Moreover, certain strains of the species _L. lactis_ can produce a multitude of different antagonistic compounds, including bacteriocins [7; 12]. Bacteriocins are substances of proteinaceous character with antimicrobial effect [12]. Those substances produced by _Lactococci_ are mostly small, thermo-stable proteins; they are most frequently recognized as inhibiting the growth of closely related bacteria, but also Gram-negative species strains [12; 13]. Recently, bacteriocins have been assigned to the group of postbiotics which are defined as preparations of inanimate microbiota and/or their components, conferring a health benefit to the host [7; 13]. _Lactococci_, with postbiotic activity from raw goat milk, were also reported in our previous study, informing the fortification of yogurts by them, to use as functional food [7]. The strains were shown to be stable in yogurts and their concentrated postbiotic substances inhibited the growth of _Enterococci_ and _Staphylococci_ by up to 97.8%. The strain MK1/3 has been also isolated from raw goat milk. Firstly, it has been found with bacteriocin-like activity testing by the Skalka method [14].