Characterization of Bacterial Microbiota of P.D.O. Feta Cheese by 16S Metagenomic Analysis

Background: The identification of bacterial species in fermented PDO (protected designation of origin) cheese is important since they contribute significantly to the final organoleptic properties, the ripening process, the shelf life, the safety and the overall quality of cheese. Methods: Ten commercial PDO feta cheeses from two geographic regions of Greece, Epirus and Thessaly, were analyzed by 16S metagenomic analysis. Results: The biodiversity of all the tested feta cheese samples consisted of five phyla, 17 families, 38 genera and 59 bacterial species. The dominant phylum identified was Firmicutes (49% of the species), followed by Proteobacteria (39% of the species), Bacteroidetes (7% of the species), Actinobacteria (4% of the species) and Tenericutes (1% of the species). Streptococcaceae and Lactobacillaceae were the most abundant families, in which starter cultures of lactic acid bacteria (LAB) belonged, but also 21 nonstarter lactic acid bacteria (NSLAB) were identified. Both geographical areas showed a distinctive microbiota fingerprint, which was ultimately overlapped by the application of starter cultures. In the rare biosphere of the feta cheese, Zobellella taiwanensis and Vibrio diazotrophicus, two Gram-negative bacteria which were not previously reported in dairy samples, were identified. Conclusions: The application of high-throughput DNA sequencing may provide a detailed microbial profile of commercial feta cheese produced with pasteurized milk.

Potential of indigenous lactobacilli as starter culture in dairy products

Traditional production of fermented dairy products involves lactic acid bacteria that are normally present in the milk and production environment. These lactic acid bacteria represent the niche microbiota of the geographical area and they are responsible for local types of fermented products. In order to standardize indigenous products, the basic requirement is the application of the determined indigenous lactic acid bacteria as starter cultures affecting their specific characteristics by performing fermentation and influencing the ripening process. In the process of cheese fermentation usually participate bacteria of the genus Lactococcus and homofermentative lactobacilli. However, the process ripening is influenced mainly by the so-called nonstarter lactic acid bacteria - lactobacilli and secondary microflora. Lactobacilli during ripening of cheese continue to breakdown the rest of lactose, but they are primarily important in the process of protein breakdown. During metabolism of sugars and amino acids, lactobacilli produce aromatic compounds which have a positive effect on the flavor of the product. Some species of lactobacilli are available as probiotics. Some lactobacilli produce bacteriocins, which prevent the growth of pathogens, as well as many spoilage microorganisms. Indigenous lactobacilli have application especially in the production of typical local dairy products that are well accepted by the local population. Besides that, the use of indigenous lactic acid bacteria as starter cultures allows the production of cheese with designated geographical origin that could be placed on the international market. Consequently, indigenous lactic acid bacteria are a challenge for further research and possible their practical application in the dairy industry.