Filamentous moulds and yeasts are t

Filamentous moulds and yeasts are the main spoilage organisms of various products such as fermented dairy foods (cheese, yogurt), bread, stored crops and feed hay and silage [1] and [2]. Moreover, the food/feed contamination with various types of toxigenic moulds is a serious problem nowadays [3]. The moulds' growth causes alterations in the texture and harms the external aspect of the products [2] and [4] which leads to significant economic losses. Five to ten percent of the world's food production is lost due to fungal contamination [5] and [6], 27% of the foods produced in U.S. are annually destroyed by fungi [7]. In addition, the toxigenic and spoilage fungi are responsible for numerous diseases and health risks [8], due to the potential production of mycotoxins or allergenic conidia, spores and mycelia [2].

The society wants to reduce the chemical additives in products and at the same time, there is a requirement of high quality, preservative-free safety food, with an extended shelf life [9]. Likewise, the problem of increasing antibiotic resistance is worsens and also there are new legislations which has restricted the use of some currently accepted preservatives in different food products [9]. All these important issues raise the need to seek alternative methods of foods/feeds producing and preserving of the human food chain. There is a centuries-old tradition of using lactic acid bacteria (LAB) in food processing. LAB represents the microbial group, which is the most commonly used as protective cultures [10]. Recently, several reports on LAB with antifungal activities and their possible applications as biopreservatives have been published [4], [8], [11], [12], [13], [14], [15], [16] and [17]. The LAB belonging to the species Lactobacillus rhamnosus and Lactobacillus fermentum [18], Lactobacillus acidophilus, Lactobacillus plantarum strain VTT E78076, L. rhamnosus, Lactobacillus coryniformis subsp. coryniformis, Lactobacillus sanfrancisensis strain CB1, Lactobacillus casei, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus lactis subsp. cremoris [19], possess a strain-specific spectrum and mechanism of inhibitory activity against the different moulds and yeasts respectively. In vitro assays showed the presence of a broad antifungal strain-specific spectrum of activity of lactobacilli, based on acids, hydrogen peroxides, diacetyl and/or proteinaceous active compounds [18], [19] and [20]. Therefore, a large screening with different test-cultures is initially needed in order to find active LAB. Moreover, some habitats are not well-studied in this aspect and they are a promising source of active bio-protective LAB strains. In Bulgaria, a very limited data exists on antifungal activity of lactic acid microbiota of traditional fermented products [21] and [22]. Our recent in vitro studies have showed the ability of lactobacilli from traditional Bulgarian dairy products to inhibit the growth of different pathogens, food-born and spoilage microorganisms [23] and a rich laboratory collection of 219 newly isolated LAB have been created [24]. Concerning the species occurrence, L. plantarum and L. delbrueckii were more frequently isolated species from artisanal samples of Bulgarian white cheese and yogurt, respectively [23] and [24], while in “katak” a variety in LAB microbiota was detected, but the species identification was not completed yet. The artisanal samples of cheeses, yogurts and “katak” have been proved as a promising source for isolation of new Lactobacillus strains with antibacterial [23], [24] and [25] and antifungal activity [26]. “Katak” (or krutmatch, kutmatch) is a fermented curd/yogurt-like product with a specific salted milk-acid taste. The recipe is inherited from the proto-Bulgarians. Nowadays, the long-lasting “katak” is made in some rural regions from leavened ewe's milk. There is no valuable information on its starter/non-starter microbiota.

In the present study 4 active strains, isolated from traditional product “katak” were pre-selected for further characterization. The aim was to identify them and to characterize their antifungal properties. The taxonomic characterization and identification of the isolates was an important part of our work, due to the lack of data on the molecular identification of the microbiota of this traditional and still insufficiently studied milk product. We examined in vitro their ability to inhibit the mould's growth, including different deteriorative food moulds and toxin-producing aspergilli.