Mesophilic lactic acid bacteria constitute the main flora of Feta cheese (21,22). Their number significantly increases during the first 15-day period in the warm room (at about 16°C) and remains high throughout the ripening time (about 8 log cfu/mL). This explains the high proteolytic activity observed at the beginning of the ripening period.
Research has showed that nonstarter lactic acid bacteria (NSLAB) constitute a large part of this flora; they originate from milk (indigenous milk flora) and the environment of the cheese plant (21). Most species of NSLAB isolated from Feta are lactobacilli. They have an important role in the ripening process and contribute to the development of the characteristic flavor of the product due to the environment of this type of cheese, which favors their development and activity (21). Lactobacillus plantarum is the dominant species, representing about 50% of the isolates. Many different strains of this microorganism, isolated from Feta cheese, have been characterized as to their enzyme and plasmid profiles, acidifying and proteolytic abilities, and other characteristics; a marked genotypic variability is observed but phenotypic differences are small (23). NSLAB are also the dominant group of bacteria in the brine; Lactobacillus paracasei subsp. paracasei and Lactobacillus plantarum are the principal species identified (24).
Pediococci and enterococci are also present, but in lower numbers (21). However, investigations showed that some strains of Enterococcus durans (21) or E.faecium (25) could improve the sensory properties of Feta cheese if used as adjunct cultures in combination with mesophilic starters (e.g., Lactococcus lactis subsp. lactis, Lactobacillus casei, Leuco-nostoc mesenteroides subsp. cremoris). Micrococci are also found, mainly as part of the surface flora: staphylococci (not S. aureus), micrococci and coryneforms are the main species (N. Tzanetakis, personal communication, 1995).
Salt-resistant yeasts grow at high numbers (6-8 log cfu/mL) on the surface of Feta during dry salting but their number decreases with ripening time (26). Among the species that have been isolated, Saccharomyces cerevisiae was predominant (47.9% of the isolates) followed by Debaryomyces hansenii and Pichia farinosa (30.9% and 11.2%, respectively). Although they seem to be of minor significance for the ripening process (25,27), they do exhibit some aminopeptidase and esterase activity (26).
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