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R Grappin

Publications and source records attributed to R Grappin.

12 recordsLinked to original sources
PubMed2003

Genotypic and phenotypic characterization of the dynamics of the lactic acid bacterial population of adjunct-containing Cheddar cheese manufactured from raw and microfiltered pasteurised milk.

AIMS: This study investigates the dynamics of the microflora, particularly the lactobacilli, in Cheddar cheese manufactured from raw and microfiltered milk containing different adjunct cultures. METHODS AND RESULTS: Sixteen cheeses - raw milk, adjunct and control cheeses - were manufactured in four trials. Lactobacilli were identified by PCR methods in one trial, and by phenotypic typing for all trials. Numbers of lactobacilli were significantly different at day 1 and 3 months in the control and adjunct-containing cheeses. In the raw milk cheeses, Lactobacillus paracasei was detected throughout ripening, Lact. curvatus at the end, and Lact. plantarum at day 1 only. Lactobacillus strain diversity decreased from raw, control to adjunct cheeses. Enteroccoci and coliform numbers further differentiated raw cheeses from the others. Lactococcal starter numbers also differed in the three cheese types and differences were observed within adjunct cheeses. Although adjunct lactobacilli dominated in the cheese to which they were added, strains with similar phenotypic profiles were also detected on occasions in some of the control cheeses. CONCLUSIONS: The addition of adjunct lactobacilli modified the growth kinetics of both adventitious lactobacilli and starter lactococci during ripening. Appropriate strain tracking is necessary to monitor changes in the population profiles of control and experimental cheeses in trials utilizing adjunct cultures. SIGNIFICANCE AND IMPACT OF THE STUDY: Investigations of the role of adjunct strain(s) in cheeses may be complicated by the interactions between the adjunct and the other cheese strains, and effective strain monitoring by genotypic or phenotypic methods is essential if valid comparisons are to be made.

Animals↗
PubMed2001

Diversity of Geotrichum candidum strains isolated from traditional cheesemaking fabrications in France.

The diversity of French fungus-ripened cheeses is due partly to the succession of fungi that colonize the cheese during ripening. Geotrichum candidum appears in the early stages of ripening on soft cheeses such as Camembert and semihard cheeses such as St. Nectaire and Reblochon. Its lipases and proteases promote flavor development, and its aminopeptidases reduce bitterness imparted by low-molecular-weight peptides in cheese. We assessed the genetic diversity of G. candidum strains by using random amplification of polymorphic DNA (RAPD)-PCR correlated with phenotypic tests for carbon assimilation and salt tolerance. Strains were isolated from milk, curd, and cheese collected in seven major cheesemaking regions of France. Sixty-four isolates were characterized. We found high genetic diversity of G. candidum even within the same cheesemaking regions. Strains did not group according to region. All of the strains from the Haute-Savoie were able to assimilate lactate as the sole source of carbon, while lactate assimilation varied among strains from the Auvergne. Strains varied in D-mannitol assimilation, and none used citrate as the sole source of carbon. Yeast-like colony morphology predominated in Reblochon, while all of the strains isolated from St. Nectaire were filamentous. The RAPD-PCR technique readily differentiated Geotrichum fragrans isolated from milk and curd in a St. Nectaire cheesemaking facility. This study reveals an enormous diversity of G. candidum that has been empirically selected through the centuries by the cheesemakers of France.

Animals↗
PubMed1998

Preliminary characterization of microflora of Comté cheese.

The evolution of the microflora of three Comté cheeses made in duplicate with raw milk from three different sources was followed during ripening. The same starter was used with each type of milk. The comparison of the cheeses did not reveal any significant difference in the development of the microflora. Starter lactic acid bacteria (Streptococcus thermophilus and Lactobacillus helveticus), which are added at the beginning of manufacture, decreased quickly in the first stages of ripening supporting the hypothesis of cell autolysis. Other microorganisms, i.e. homofermentative and heterofermentative lactobacilli (Lact. delbrueckii ssp. lactis, Lact. paracasei ssp. paracasei, Lact. rhamnosus and Lact. fermentum), pediococci, enterococci and propionibacteria grew in cheese from small numbers in fresh curd. The characterization of Strep. thermophilus by pulsed-field gel electrophoresis showed that wild strains were also able to grow in the curd. The values for the genome size of 11 Strep. thermophilus strains determined in this investigation were in the range of 1.8-2.3 Mbp. The potential role of starter and raw milk microflora in cheese flavour development was considered.

Animals↗
PubMed1983

[Attempts at preventing experimental Staphylococcus aureus mastitis by immunization and intramammary insertion of a polyethylene device (Stérilait)].

The susceptibility of lactating cows to experimental challenge with two strains of Staphylococcus aureus was investigated 30 days after calving. These cows were previously immunized during the dry-period and udder quarters were fitted at drying-off with a polyethylene intramammary device (IMD). Incidence of infection recorded in device-fitted quarters and control quarters was not significantly different. There was no difference between IMD-fitted and control quarters in milk yield, contents in butterfat and protein. Lactose mean concentration was significantly decreased in milk collected from quarters fitted with polyethylene loop (P less than 0.05). The somatic cell counts in milk from quarters depended on: a) fraction collected, b) time of sampling, c) presence of intramammary loop, d) result of experimental challenge. Milk somatic-cell counts determined at mid-lactation for fractions collected before udder stimulation and total milk in IMD fitted quarters were greater than for control quarters (P less than 0.05). In general, these differences were greater in quarters which were experimentally infected than uninfected quarters. The count in total milk collected at mid-lactation for uninfected device-fitted quarters averaged 720 000 cells/ml.

Animals↗
PubMedDate not supplied

Determination of nitrogen content in milk by the Kjeldahl method using copper sulfate: interlaboratory study.

Copper sulfate was substituted for mercury as the catalyst in the International Dairy Federation (IDF) Standard 20A:1986 method for the determination of nitrogen content in milk. The substitution was supported by results obtained in an interlaboratory study by 24 laboratories in 12 countries. Each laboratory analyzed 12 test samples of milk as blind duplicates in a double split level design with high, medium, and low nitrogen concentrations. The method protocol requires the concurrent analyses of an ammonium salt solution and a tryptophan solution as internal quality control standards with a minimum nitrogen recovery between 99 and 100% for the former and at least 98% for the latter. The repeatability and reproducibility relative standard deviations are 0.5 and 1%, respectively, for the range 0.35-0.70 g N/100 g. The performance of the laboratories that did not meet the required quality control specifications was clearly poorer than that of those that did meet the specifications.

Animals↗
PubMedDate not supplied

View of the International Dairy Federation on interlaboratory analytical studies.

The International Dairy Federation develops and studies methods for the analysis of milk and milk products. A first draft of an IDF protocol for conducting interlaboratory studies is presented. Major features of the protocol are type and number of participating laboratories; nature, duplication, and number of sample materials; final design (numbers of samples and laboratories); statistical analysis of the data; report of the final results.

Dairy Products↗
PubMedDate not supplied

Determination of fat, protein, and lactose in raw milk by Fourier transform infrared spectroscopy and by analysis with a conventional filter-based milk analyzer.

The accuracy of fat, crude protein (CP), true protein (TP), and lactose determinations of raw milk by Fourier transform infrared (FTIR) spectroscopy and by analysis with a conventional filter-based milk analyzer was assessed in 6 trials performed over a 10-month period. At each trial, 30 bulk milk samples collected from 15 European countries and 11 reconstituted milks made from raw milk components were analyzed. When calibrations were performed with reconstituted milks at each trial, accuracy standard deviations for fat, CP, TP, and lactose were, respectively, 0.050, 0.048, 0.035, and 0.076 g/100 g for the filter instrument and 0.047, 0.046, 0.042, and 0.065 g/100 g for the FTIR instrument. When a single calibration was made instead of calibrations at each trial, accuracy standard deviations increased for the filter instrument to 0.130, 0.119, 0.121, and 0.083 for fat, CP, TP, and lactose, respectively, and for the FTIR instrument to 0.082, 0.053, 0.044, and 0.084 g/100 g. Because the FTIR instrument provides more spectral information related to milk composition than does the filter instrument, single-calibration FTIR analysis of milk samples collected in different seasons is more accurate. Using reconstituted milks, prepared such that there is no correlation between fat, CP, and lactose, provides a more robust calibration than using genuine bulk milk, especially when milks with unusual composition are analyzed.

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