Identification, typing, and functional characterization of Leuconostoc spp. strains from traditional, starter-free cheeses

Abstract

Selected Leuconostoc strains are required as aroma producers in dairy starters. In this work, 42 Leuconostoc isolates from different raw milk traditional cheeses made without the addition of commercial starters were identified by molecular methods. These isolates were assigned to the species Leuconostoc citreum (24), Leuconostoc mesenteroides (13), and Leuconostoc lactis (5). Typing the isolates by repetitive extragenic profiling (Rep-PCR) identified 22 strains, out of which 14 were selected for further characterization based on their behavior in milk. The biochemical, technological, and food safety variables recorded were examined to select appropriate candidates for use as adjunct cultures. In agreement with the wide genetic diversity recorded by Rep-PCR, wide phenotypic biodiversity was seen among the species and strains in terms of enzyme and carbohydrate fermentation profile, acidification rate, the production of volatile compounds in milk, and growth under different pH, salt, and temperature conditions. No production of biogenic amines was recorded even when suitable amino acid precursors were present in the growth medium. All 14 strains proved to be susceptible or intrinsically resistant to a set of 16 antibiotics except for one Leuc. citreum strain that showed an atypical resistance to ciprofloxacin. The remaining 13 strains could be confidently used as components of adjunct cultures in the dairy industry.