Isolation, Technological Characterization and Safety Assessment of Potential Adjunct Cultures of Lactic Acid Bacteria

Abstract

Adjunct cultures are non-starter microorganisms contributing to the development of favorable flavor and texture during cheese ripening. The present study was designed to isolate and characterize potential adjunct cultures of lactic acid bacteria (LAB) from pickled Domiatti cheese and Ras cheese. Fifty-four cheese samples including 33 and 21 samples of pickled Domiatti cheese and Ras cheese, respectively were randomly collected from Mansoura city and villages in its vicinity and assessed for their flavor by panelists. Given the association of the adjunct cultures with typical flavor in cheese, cheese samples with good or acceptable flavor were further analyzed as a potential source of adjunct LAB cultures. A total of 162 suspected LAB isolates could be recovered from theses samples, of which 37 and 4 isolates were confirmed to belong to the Enterococcus and Lactobacillus genera, respectively. Further biochemical identification to the species level showed that the Enterococcus isolates involved Ent. faecalis (2 isolates), Ent. faecium (7 isolates), Ent. gallinarum (2 isolates), Ent. durans (1 isolate), Ent. mundtii (2 isolates), Ent. casseiliflavus (2 isolates), Ent. pseudoaavium (12 isolates), and Enterococcus spp. (9 isolates). Whereas, Lactobacillus isolates could be identified as Lb. plantarum (1 isolate) and Lactobacillus spp. (3 isolates). Enterococcus and Lactobacillus isolates were examined for technological properties including acidity development, proteolytic activity, and lipolytic activity. They showed phenotypic diversity in those technological characteristics. Isolates were also assessed for safety-associated traits including antibiotic resistance, biogenic amine production, and hemolytic activity. Enterococcus isolates showed resistance to several antibiotics and were able to produce the biogenic amines histamine and tyramine. Hemolytic activity could be also detected in thoseisolates. Lactobacillus cultures showed resistance to only 2 out of 9 antibiotics and were unable to produce histamine or tyramine. They did not also show hemolytic activity. This study presents a collection of Enterococcus and Lactobacillus isolates to be assessed for use as adjunct cultures based on their technological and safety-related traits.