Evaluation of qPCR and plate counting for quantifying thermophilic starters in cheese.

The respective inputs of plate counting and qPCR for the quantification of starters in cheese were evaluated using hard-cooked cheeses made with various starter combinations. Five starter strains were quantified at their different growth phases, from 0.5 h to day 214 of manufacture: one strain of Streptococcus thermophilus (ST) and two strains each of Lactobacillus delbrueckii (LD) and Lactobacillus helveticus (LH).

Suitability of a new mixed-strain starter for manufacturing uncooked raw ewe's milk cheeses.

Most raw milk Ossau-Iraty cheeses are currently manufactured on-farm using the same commercial streptococcal-lactococcal starter (S1). One way to enhance the microbial diversity that gives raw milk its advantages for cheese-making is to formulate new starters combining diverse, characterized strains. A new starter (OI) combining 6 raw milk strains of lactococci, recently isolated and characterized, was tested in parallel with the current starter by making 12 Ossau-Iraty raw milk cheeses at 3 farmhouses under the conditions prevailing at each farm.

Traditional cheeses: rich and diverse microbiota with associated benefits.

The risks and benefits of traditional cheeses, mainly raw milk cheeses, are rarely set out objectively, whence the recurrent confused debate over their pros and cons. This review starts by emphasizing the particularities of the microbiota in traditional cheeses. It then describes the sensory, hygiene, and possible health benefits associated with traditional cheeses.

Quantitative PCR for the specific quantification of Lactococcus lactis and Lactobacillus paracasei and its interest for Lactococcus lactis in cheese samples.

The first objective of this work was to develop real-time quantitative PCR (qPCR) assays to quantify two species of mesophilic lactic acid bacteria technologically active in food fermentation, including cheese making: Lactococcus lactis and Lactobacillus paracasei. The second objective was to compare qPCR and plate counts of these two species in cheese samples. Newly designed primers efficiently amplified a region of the tuf gene from the target species.

Biodiversity and growth dynamics of lactic acid bacteria in artisanal PDO Ossau-Iraty cheeses made from raw ewe's milk with different starters.

The biodiversity and growth dynamics of Lactic Acid Bacteria (LAB) in farm-house Ossau-Iraty cheeses were investigated from vat milk to 180 days of ripening in six independent batches made from six raw ewe's milks using five typical cheese-making methods. Commercial starter S1 was used for three batches, starter S1 combined with S2 for one batch and no starter for two batches. Up to ten LAB species from five genera and up to two strains per species were identified per milk; up to eleven species from five genera and up to three strains per species were identified per cheese.

Multiple interactions between Streptococcus thermophilus, Lactobacillus helveticus and Lactobacillus delbrueckii strongly affect their growth kinetics during the making of hard cooked cheeses.

In hard cooked cheeses, any interactions between the thermophilic starters as they grow during the cheese-making are critical, since they modify bacterial growth kinetics and acidification kinetics, so affecting the ripening process and the final characteristics of the cheese. Twenty-four experimental hard cooked cheeses were made under controlled conditions, the milk being inoculated with various combinations of thermophilic strains of Streptococcus thermophilus, Lactobacillus helveticus and Lactobacillus delbrueckii. Over the first day of manufacturing we recorded a wide range of different growth kinetics for each starter species used, and a wide range of pH kinetics, depending on the starter combination.

Rapid identification of the three major species of dairy obligate heterofermenters Lactobacillus brevis, Lactobacillus fermentum and Lactobacillus parabuchneri by species-specific duplex PCR.

In this study, the biodiversity of 154 strains of lactic acid bacteria, including 112 dairy product isolates presumptively identified as obligately heterofermentative lactobacilli (OHL) by classical microbiological tests, as well as 23 OHL-type strains, was investigated by PCR-based methods and gene sequencing. Using these techniques, 51% of the cheese isolates were actually identified as OHL. The non-OHL isolates were identified to the Leuconostoc, Lactobacillus, Weisella, Pediococcus or Streptococcus genera.

Safety assessment of dairy microorganisms: bacterial taxonomy.

Safety assessment requires uniform and reproducible nomenclature schemes for all the micro-organisms deliberately added in fermented food products. The QPS approach described by EFSA is based on the identity of an isolate at the highest taxonomic unit that is appropriate for the purpose for which the evaluation is intended. This depends upon the body of knowledge available for the micro-organism to be assessed and upon the nature of the micro-organism being assessed.

Efficient transformation of Lactobacillus sake by electroporation.

A procedure to transform intact cells by electroporation was developed through a systematic examination of the effect of changes in various parameters on the transformation efficiency of strain 64F. The most critical factors were found to be the electrical parameters, the composition of washing and electroporation/storage solutions, and the presence of MgCI in the expression medium. Under optimal conditions transformation efficiencies up to 10 transformants (μg supercoiled DNA) were obtained.