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Huc D.,IRSTEA | Huc D.,European University of Brittany | Huc D.,Agro ParisTech | Huc D.,French National Institute for Agricultural Research | And 11 more authors.
International Dairy Journal | Year: 2014

Eye growth in semi-hard cheeses was previously found to be subject to a strong spatial-dependency between the periphery and the core zone, and salt appeared to be a key factor to be studied to better understand the phenomenon of eye growth. An experiment was therefore designed to study salted and unsalted cheeses, by combining magnetic resonance imaging and a method for determining CO2 production based on gas pressure measurements. Chemical and rheological tests were also performed to make sure that only the salt content was modified between the two types of cheeses. It appeared that the presence of salt induced a delay in both bacterial development and CO2 production. The eyes in salted cheeses were found to be six times smaller, and their growth kinetics were slower. The combination of these two techniques thus made it possible to decorrelate factors and to quantify the influence of salt on eye development. © 2013 Elsevier Ltd.

Yee A.L.,French National Institute for Agricultural Research | Yee A.L.,Agrocampus Ouest | Maillard M.-B.,French National Institute for Agricultural Research | Maillard M.-B.,Agrocampus Ouest | And 11 more authors.
International Journal of Food Microbiology | Year: 2014

Flavor is an important sensory property of fermented food products, including cheese, and largely results from the production of aroma compounds by microorganisms. Propionibacterium freudenreichii is the most widely used species of dairy propionibacteria; it has been implicated in the production of a wide variety of aroma compounds through multiple metabolic pathways and is associated with the flavor of Swiss cheese. However, the ability of other dairy propionibacteria to produce aroma compounds has not been characterized. This study sought to elucidate the effect of interspecies and intraspecies diversity of dairy propionibacteria on the production of aroma compounds in a cheese context. A total of 76 strains of Propionibacterium freudenreichii, Propionibacterium jensenii, Propionibacterium thoenii, and Propionibacterium acidipropionici were grown for 15. days in pure culture in a rich medium derived from cheese curd. In addition, one strain each of two phylogenetically related non-dairy propionibacteria, Propionibacterium cyclohexanicum and Propionibacterium microaerophilum were included. Aroma compounds were analyzed using headspace trap-gas chromatography-mass spectrometry (GC-MS). An analysis of variance performed on GC-MS data showed that the abundance of 36 out of the 45 aroma compounds detected showed significant differences between the cultures. A principal component analysis (PCA) was performed for these 36 compounds. The first two axes of the PCA, accounting for 60% of the variability between cultures, separated P. freudenreichii strains from P. acidipropionici strains and also differentiated P. freudenreichii strains from each other. P. freudenreichii strains were associated with greater concentrations of a variety of compounds, including free fatty acids from lipolysis, ethyl esters derived from these acids, and branched-chain acids and alcohols from amino acid catabolism. P. acidipropionici strains produced less of these compounds but more sulfur-containing compounds from methionine catabolism. Meanwhile, branched-chain aldehydes and benzaldehyde were positively associated with certain strains of P. jensenii and P. thoenii. Moreover, the production of compounds with a common origin was correlated. Compound abundance varied significantly by strain, with fold changes between strains of the same species as high as in the order of 500 for a single compound. This suggests that the diversity of dairy propionibacteria can be exploited to modulate the flavor of mild cheeses. © 2014 Elsevier B.V.

Deutsch S.-M.,French National Institute for Agricultural Research | Deutsch S.-M.,Agrocampus Ouest | Le Bivic P.,French National Institute for Agricultural Research | Le Bivic P.,Agrocampus Ouest | And 10 more authors.
Applied and Environmental Microbiology | Year: 2010

Many food-grade bacteria produce exopolysaccharides (EPS) that affect the texture of fermented food products and that may be involved in probiotic properties. Propionibacterium freudenreichii is a Gram-positive food-grade bacterium with reported probiotic capabilities that is widely used as starter in Swiss-type cheese. In this study, 68 strains of P. freudenreichii were screened for the β-glucan capsular phenotype by immuno-agglutination with a specific antibody and for the presence of the gtf gene coding for polysaccharide synthase. All strains were positive for PCR amplification with gtf gene-specific primers, but the presence of β-glucan capsular EPS was detected for only 35% of the strains studied. Disruption of gtf in P. freudenreichii revealed that gtf is a unique gene involved in β-glucan capsular EPS production in P. freudenreichii. The gtf gene was transferred into and expressed in Lactococcus lactis, in which it conferred an agglutination-positive phenotype. Expression of the gtf gene was measured by performing quantitative reverse transcription-PCR assays with RNA from four capsular and three noncapsular strains. A positive correlation was found between the β-glucan capsular phenotype and gtf gene expression. Sequencing of the region upstream of the gtf open reading frame revealed the presence of an insertion element (IS element) in this upstream region in the four strains with the β-glucan capsular phenotype. The role of the IS element in the expression of neighboring genes and its impact on interstrain variability of the P. freudenreichii capsule phenotype remain to be elucidated. Copyright © 2010, American Society for Microbiology. All Rights Reserved.

Pogacic T.,French National Institute for Agricultural Research | Pogacic T.,Agrocampus Ouest | Maillard M.-B.,French National Institute for Agricultural Research | Maillard M.-B.,Agrocampus Ouest | And 8 more authors.
Applied Microbiology and Biotechnology | Year: 2016

New strains are desirable to diversify flavour of fermented dairy products. The objective of this study was to evaluate the potential of Leuconostoc spp. and Lactobacillus spp. in the production of aroma compounds by metabolic fingerprints of volatiles. Eighteen strains, including five Lactobacillus species (Lactobacillus fermentum, Lactobacillus helveticus, Lactobacillus paracasei, Lactobacillus rhamnosus, Lactobacillus sakei) and three Leuconostoc species (Leuconostoc citreum, Leuconostoc lactis, and Leuconostoc mesenteroides) were incubated for 5 weeks in a curd-based slurry medium under conditions mimicking cheese ripening. Populations were enumerated and volatile compounds were analysed by headspace trap gas chromatography–mass spectrometry (GC–MS). A metabolomics approach followed by multivariate statistical analysis was applied for data processing and analysis. In total, 12 alcohols, 10 aldehydes, 7 esters, 11 ketones, 5 acids and 2 sulphur compounds were identified. Very large differences in concentration of volatile compounds between the highest producing strains and the control medium were observed in particular for diacetyl, 2-butanol, ethyl acetate, 3-methylbutanol, 3-methylbutanoic acid and 2-methylbutanoic acid. Some of the characterized strains demonstrated an interesting aromatizing potential to be used as adjunct culture. © 2015, Springer-Verlag Berlin Heidelberg.

Pogacic T.,French National Institute for Agricultural Research | Pogacic T.,Agrocampus Ouest | Maillard M.-B.,French National Institute for Agricultural Research | Maillard M.-B.,Agrocampus Ouest | And 10 more authors.
Food Microbiology | Year: 2015

Microorganisms play an important role in the development of cheese flavor. The aim of this study was to develop an approach to facilitate screening of various cheese-related bacteria for their ability to produce aroma compounds. We combined i) curd-based slurry medium incubated under conditions mimicking cheese manufacturing and ripening, ii) powerful method of extraction of volatiles, headspace trap, coupled to gas chromatography-mass spectrometry (HS-trap-GC-MS), and iii) metabolomics-based method of data processing using the XCMS package of R software and multivariate analysis. This approach was applied to eleven species: five lactic acid bacteria (Leuconostoc lactis, Lactobacillus sakei, Lactobacillus paracasei, Lactobacillus fermentum, and Lactobacillus helveticus), four actinobacteria (Brachybacterium articum, Brachybacterium tyrofermentans, Brevibacterium aurantiacum, and Microbacterium gubbeenense). , Propionibacterium freudenreichii, and Hafnia alvei. All the strains grew, with maximal populations ranging from 7.4 to 9.2 log (CFU/mL). In total, 52 volatile aroma compounds were identified, of which 49 varied significantly in abundance between bacteria. Principal component analysis of volatile profiles differentiated species by their ability to produce ethyl esters (associated with Brachybacteria), sulfur compounds and branched-chain alcohols (H.alvei), branched-chain acids (H.alvei, P. freudenreichii and L.paracasei), diacetyl and related carbonyl compounds (M. gubbeenense and L.paracasei), among others. © 2014 Elsevier Ltd.

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