Lactococcus lactis strains from raw ewe's milk samples from the PDO Ossau-Iraty cheese area: levels, genotypic and technological diversity
Résumé
The aims of this work were to assess the levels of Lactococcus lactis (L. lactis) in ewe's milk produced in three Ossau-Iraty cheese sub-areas and to investigate the genotypic and technological diversity of isolated wild strains of L. lactis in order to assess their suitability for use as components of starter formulations. Thirty-two milk samples from 32 farms were collected. Strains of L. lactis were identified and quantified using a combination of species and subspecies-specific polymerase chain reaction (PCR) and PCR amplification of repetitive bacterial DNA elements (Rep-PCR). The genotypic and technological diversity of the indigenous strains was compared to that of 12 commercial strains. L. lactis was detected in milk samples from only 20 farms. The levels detected were below 4 log(10) cfu.mL(-1) in 75% of the milks. L. lactis subsp. lactis dominated in 66% of the samples. Forty-three genotypic profiles of wild L. lactis strains were detected and showed greater diversity than those of the commercial strains. Milks containing L. lactis contained one to four distinct strains. With the exception of two strains, each strain was found in milk from only one farm. The Prt(+) strains were the most acidifying. Sensitivity to phages collected from wheys differed widely between the commercial (60%) and indigenous strains (5%). Wild strains of L. lactis displayed a wide genotypic and technological diversity. Genotypic diversity seemed to be linked to the farm of origin. This study addresses questions regarding the environmental factors which influence such natural diversity. A deeper knowledge of the strain-dependent technological properties would be useful in selecting strains for use in starter blends.
Origine : Accord explicite pour ce dépôt
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