Patent Publication Number: US-7582743-B2

Title: Texturizing lactic bacteria

Description:
A subject of the present invention is strains of lactic bacteria comprising at least one sequence selected from the group constituted by the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8 as well as a process for constructing these strains. Finally, the invention relates to food products comprising and/or produced with said strains. 
     The food industry uses numerous bacteria, in the form in particular of ferments, in particular lactic bacteria, in order to improve the taste and the texture of foods but also in order to extend the shelf life of these foods. In the case of the dairy industry, lactic bacteria are used intensively in order to bring about the acidification of milk (by fermentation) but also in order to texturize the product into which they are incorporated. 
     Among the lactic bacteria used in the food industry, there can be mentioned the genera  Streptococcus, Lactococcus, Lactobacillus, Leuconostoc, Pediococcus  and  Bifidobacterium.    
     The lactic bacteria of the species  Streptococcus thermophilus  are used extensively alone or in combination with other bacteria for the production of food products, in particular fermented products. They are used in particular in the formulation of the ferments used for the production of fermented milks, for example yogurts. Certain of them play a dominant role in the development of the texture of the fermented product. This characteristic is closely linked to the production of polysaccharides. Among the strains of  Streptococcus thermophilus  it is possible to distinguish texturizing and non-texturizing strains. 
     By texturizing strain of  Streptococcus thermophilus  is meant a strain which generates fermented milks having, under the conditions described as an example, a viscosity greater than approximately 35 Pa·s, a thixotropic area of less than approximately 2000 Pa/s and a yield point of less than approximately 14 Pa. A strain of  Streptococcus thermophilus  can be defined as strongly texturizing in that it generates fermented milks having, under the conditions described as an example, a viscosity greater than approximately 50 Pa·s, a thixotropic area of less than approximately 1000 Pa/s and a yield point of less than approximately 10 Pa. 
     In order to meet the requirements of the industry, it has become necessary to propose novel texturizing strains of lactic bacteria, in particular of  Streptococcus thermophilus.    
     Thus the problem that the invention proposes to resolve is to provide a strain of lactic bacterium having good properties for texturizing food products. 
     For this purpose the invention proposes a strain of lactic bacterium which comprises at least one sequence selected from the group constituted by the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8. 
     The invention also proposes a novel strain of  Streptococcus thermophilus  deposited on 26th Feb. 2003 at the Collection Nationale de Cultures de Microorganismes. located at Institut Pastuer, 25 rue du Docteur Roux, F-75724 Paris, France Cedex 15, which is an International Depository Authority, with the accession No. I-2980, under the provisions of the Budapest Treaty; all restrictions upon public access to the deposit will be irrevocably removed upon the grant of a patent on this application; and the deposit will be replaced if viable samples can not be dispensed by the depository. 
     A subject of the invention is also the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8, as well as a nucleic acid comprising at least one of these nucleotide sequences. 
     Another subject of the invention is also the plasmids, cloning and/or expression vectors comprising at least one of the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8, as well as a nucleic acid comprising at least one of these nucleotide sequences. 
     The invention also extends to host bacteria transformed by the plasmids or the vectors described above. 
     The invention also relates to the process for constructing the strains described above characterized in that these strains are obtained by transformation using a plasmid or vector comprising at least one of the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8, or with a vector comprising a nucleic acid comprising at least one of these nucleotide sequences. 
     The invention also proposes bacterial compositions comprising at least one strain described above or comprising at least one strain obtained according to the process of the invention. 
     Finally the invention relates to a food or pharmaceutical composition comprising at least one strain according to the invention or at least one strain obtained according to the process of the invention or the bacterial composition according to the invention. 
     The present invention has numerous advantages in terms of texturizing the media into which it is incorporated. In particular, it makes it possible to obtain gels from, for example, fermented milks, which are thick, sticky, coating, stringy and resistant to stirring and which are not granular. 
     Other advantages and characteristics of the invention will become clearly apparent on reading the following description and non-limitative examples given purely by way of illustration. 
     The invention firstly relates to a strain of lactic bacterium which comprises at least one sequence selected from the group constituted by the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8. 
     The lactic bacteria are Gram-positive procaryotes which belong to the taxonomic group of the Firmicutes. They are heterotropic and chemo-organotropic; generally anaerobic or aerotolerant, their metabolism can be homo- or hetero-fermentary: the lactic bacteria essentially produce lactic acid by fermentation of a glucidic substrate. Devoid of catalase, the lactic bacteria constitute a heterogeneous group of bacteria in the form of cocci for the genera  Aerococcus, Enterococcus, Lactococcus, Leuconostoc, Oenococcus, Pediococcus, Streptococcus, Tetragenococcus, Vagococcus  and  Weissella , or in the form of rods for the genera  Lactobacillus  and  Carnobacterium . The name lactic bacterium is often extended to other related bacteria, such as  Bifidobacterium.    
     Among the strains of lactic bacteria which are suitable for the present invention there can be mentioned the genera  Streptococcus, Lactococcus, Lactobacillus, Leuconostoc, Pediococcus  and  Bifidobacterium.    
     The preferred strain of lactic bacterium according to the invention is  Streptococcus thermophilus.    
       Streptococcus thermophilus  is a species naturally present in milk and widely used in the food, and in particular dairy, industry because it makes it possible to acidify and texturize the milk. It is a homofermentary thermophilic bacterium. 
     The invention then relates to the strain of  Streptococcus thermophilus  deposited on 26th Feb. 2003 at the Collection Nationale de Cultures de Microorganismes under number 1-2980. 
     A subject of the invention is also the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8. 
     The nucleotide sequences SEQ ID No. 2 to SEQ ID No. 8 form part of an operon of approximately 14,350 base pairs involved in the synthesis of polysaccharides (PS). This operon is included in the sequence SEQ ID No. 1. This means that according to the invention the sequences SEQ ID No. 2 to SEQ ID No. 8 are included in the sequence SEQ ID No. 1. 
     The structure of the operon according to the invention has been determined (see  FIG. 1 ). Between the genes deoD (upstream of the operon PS) and orfl4.9 (downstream), 17 ORFs (open reading frames) called eps93A, eps13B, eps13C, eps13D, eps13E, eps13F, eps13G, eps13H, eps13I, eps13J, eps13K, eps13L, eps13M, epsl3N, epsf30, epsl3P and IS1193 have been identified. The first 16 ORFs situated on the “sense” strand potentially code for polypeptides involved in the production of the exocellular or capsular polysaccharides; the 17th ORF situated on the “antisense” strand potentially codes for a functional transposase belonging to the family IS1193 (insertion sequence). 
     It is possible to name each ORF and to position it. The name of each ORF is given below, then secondly the putative function of the derived protein, and finally, thirdly, the position of the region comprising this ORF (in relation to the sequence SEQ ID No. 1 as indicated in the sequence listing):
         eps13A: Transcription regulator (342 . . . 1802)   eps13B: Polymerization (chain length regulation) and/or export of the polysaccharides (1803 . . . 2534)   eps13C: Polymerization (chain length regulation) and/or export of the polysaccharides (2543 . . . 3235)   eps13D: Polymerization (chain length regulation) and/or export of the polysaccharides (3245 . . . 3985)   eps13E: Undecaprenyl-phosphate glycosyltransferase (4042 . . . 5409)   eps13F: Undecaprenyl-phosphate glycosyltransferase (5611 . . . 6195)   eps13G: Undecaprenyl-phosphate glycosyltransferase (6251 . . . 6634)   eps13H: Beta-1,4-galactosyltransferase (6643 . . . 7092)   eps131: Beta-1,4-galactosyltransferase (7092 . . . 7607)   eps13J: Rhamnosyltransferase (7597 . . . 8493)   eps13K: Glycosyltransferase (8763 9797)   eps13L: Repetitive unit polymerase (9827 . . . 10969)   epsl3M: Repetitive unit polymerase (10984 . . . 11793)   eps13N: Glycosyltransferase (11844 . . . 12578)   eps130: Glycosyltransferase (12633 . . . 13016)   eps13P: Transmembrane transporter (13049 . . . 14482)   IS1193: Transposase (complement (14614.15870)).       

     The invention also relates to a nucleic acid comprising at least one sequence selected from the group constituted by the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8. By nucleic acid comprising at least one of the sequences listed above is meant, within the meaning of the invention, nucleic acids which comprise at least one ORF the translation product of which has a significant sequence similarity (percentage of identical residues greater than or equal to 80%, after alignment of the sequences for a maximum correspondence between the positions of the residues) with at least one of the polypeptide sequences derived from the ORFs identified in the sequences SEQ ID No. 1 to SEQ ID No. 8. 
     The nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8 can be inserted into a vector by genetic engineering, in particular by recombinant DNA techniques which are widely known to a person skilled in the art. 
     The invention also relates to a cloning and/or expression vector comprising at least one sequence selected from the group constituted by the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8 or a nucleic acid as defined above. 
     The preferred vector according to the invention is a plasmid. It can be a replicative or integrative plasmid. 
     Starting with these vectors and/or plasmids it is possible to transform a bacterium in order to include these vectors and/or plasmids in it. This transformation can be carried out by the technique of electroporation or by conjugation, in a standard manner for a person skilled in the art. 
     The invention also relates to host bacteria transformed by a plasmid or a vector as defined above. 
     Preferably, the bacteria transformed are lactic bacteria. In particular, they are lactic bacteria which can be chosen from the genera  Streptococcus, Lactococcus, Lactobacillus, Leuconostoc, Pediococcus  and  Bifidobacterium.    
     The preferred strain of lactic bacterium according to the invention is  Streptococcus thermophilus.    
     The invention also relates to a process for constructing a strain or transformed host bacterium according to the invention characterized in that they are obtained by transformation using a vector comprising at least one sequence selected from the group constituted by the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8, or with a nucleic acid comprising at least one sequence selected from the group constituted by the nucleotide sequences SEQ ID No. 1, SEQ ID No. 2, SEQ ID No. 3, SEQ ID No. 4, SEQ ID No. 5, SEQ ID No. 6, SEQ ID No. 7, SEQ ID No. 8. 
     According to the process of the invention, the preferred vector is a plasmid. 
     Advantageously according to the process of the invention the transformation is followed by an insertion into the genome of the strain or of the host bacterium transformed by at least one recombination event. 
     The invention also relates to a bacterial composition comprising at least one strain according to the invention or comprising at least one strain obtained according to the process of the invention or comprising at least one bacterium transformed according to the invention 
     By bacterial composition is meant a mixture of different strains, in particular a ferment, or a leaven. 
     The mixtures of preferred strains according to the invention are mixtures of  Streptococcus thermophilus  with other  Streptococcus thermophilus , or mixtures of  Streptococcus thermophilus  with  Lactobacillus delbrueckii  subsp.  bulgaricus , or mixtures of  Streptococcus thermophilus  with other Lactobacillus and/or with  Bifidobacterium , or mixtures of  Streptococcus thermophilus  with  Lactococcus , or mixtures of  Streptococcus thermophilus  with other strains of lactic bacteria and/or yeasts. 
     The invention also relates to the use of a strain according to the invention or of a strain obtained according to the process of the invention or of the bacterial composition according to the invention in order to produce a food product or food ingredient. 
     As preferred food product or food ingredient according to the invention there can be mentioned a dairy product, a meat product, a cereal product, a drink, a foam or a powder. 
     The invention also relates to a food or pharmaceutical composition comprising at least one strain according to the invention or at least one strain obtained according to the process of the invention or the bacterial composition according to the invention. 
     A subject of the invention is also a dairy product comprising at least one strain according to the invention or at least one strain obtained according to the process of the invention or the bacterial composition according to the invention. 
     In the case of the production of a dairy product, the latter is carried out in a manner usual in this field, and in particular by fermentation of a dairy product by incorporation of a strain according to the invention. 
     As dairy product according to the invention, there can be mentioned a fermented milk, a yogurt, a matured cream, a cheese, a fromage frais, a milk beverage, a dairy product retentate, a process cheese, a cream dessert, a cottage cheese or infant milk. 
     Preferably the dairy product according to the invention comprises milk of animal and/or plant origin. 
     As milk of animal origin there can be mentioned cow&#39;s, ewe&#39;s, goat&#39;s or buffalo&#39;s milk. 
    
    
     
       As milk of plant origin there can be mentioned any fermentable substance of plant origin which can be used according to the invention in particular originating from soya seed, rice or malt. 
         FIG. 1  represents the genetic structure of the PS operon of the strain according to the invention compared with the PS operon of other already known strains of  Streptococcus thermophilus.    
         FIG. 2  represents the factorial design 1-2 of the principal component analysis (PCA) obtained from the sensory data on fermented milks obtained with the different strains of the study. 
         FIG. 3  represents the means of the scores obtained on the descriptors of TEXTURE ON SPOON for each of the strains of the study. Interpretation of the results of the Newman-Keuls test: the difference between the strains connected by the same letter is not significant. 
         FIG. 4  represents the means of the scores obtained on the descriptors of TEXTURE IN MOUTH for each of the strains of the study. Interpretation of the results of the Newman-Keuls test: the difference between the strains connected by the same letter is not significant. 
     
    
    
     Concrete but non-limitative examples of the invention will now be described. 
     EXAMPLES 
     1/Sequencing of the PS Operon of  Streptococcus thermophilus  CNCM I-2980 
     The DNA fragment carrying the PS operon of the  Streptococcus thermophilus  strain CNCM I-2980 was obtained by PCR (polymerase chain reaction) amplification from the genomic DNA extracted from said strain. The amplification was carried out with the Mastercycler thermocycler (Eppendorf) using LA-Taq DNA polymerase (BioWhittaker/Cambrex) and the following primers: 5′-GGGTGMCGTATCTCAGTMTGGGGACTGG-3′ and 5′-CCTGAGTTATGCGACGATTACTTGGCTG-3′. The experimental conditions of this amplification are the following: 14 cycles alternating denaturation at 98° C. for 30 seconds and hybridization-extension at 68° C. for 15 minutes, then 16 cycles alternating denaturation at 98° C. for 30 seconds and hybridization-extension at 68° C. for 15 minutes with an increment of 15 seconds per cycle, then 1 additional extension cycle at 72° C. for 10 minutes. The PCR product was sequenced according to a fragment cloning approach. 
     2/ Molecular Characterization of the Strain According to the Invention Compared with Already Known Strains of  Streptococcus thermophilus    
     
         
         
           
             Sequence of the PS Operon 
           
         
       
    
     The sequence of the PS operon of the strain  Streptococcus thermophilus  CNCM I-2980 was obtained from a DNA fragment of approximately 17,100 base pairs synthesized by PCR in the presence of a purified genomic DNA template of the strain and using two specific primers of preserved genes (deoD coding for a purine-nucleotide phosphorylase, and orf14.9 of unknown function) generally framing the PS operon in the  Streptococcus thermophilus  described in the literature. The sequence comprised between the genes deoD and orf14.9, corresponding to the sequence SEQ ID No. 1, is given with the sequence listing.
         Genetic Organization of the PS Operon       

       FIG. 1  shows diagrammatically the genetic structure of the PS operon of the strain CNCM I-2980 established by analysis of its nucleotide sequence, as well as the structure of the PS operon of 7 other strains of  Streptococcus thermophilus . For the different structures, identified by the name of the strain and by the GENBANK accession number (in parenthesis), the arrows represent the position, size and orientation of the genes from the initiation codon to the stop codon. The significance of the colours and/or units inside the arrows is given by the legend to  FIG. 1 .
         Comparison with the Literature       
     The structural analysis of the PS operon of the strain CNCM I-2980 shows that it has an overall organization similar to that of the PS operons already known (see  FIG. 1 ); a first ORF potentially involved in the regulation of the transcription of the PS operon, followed by 3 ORFs probably involved in the regulation of the polymerization of the repetitive units of the PS and/or their export, followed by 11 ORFs coding for glycosyltransferases and a polymerase ensuring the assembly of the repetitive unit, themselves followed by 1 ORF potentially involved in the transport of the repetitive units through the plasmid membrane. 
     The genetic environment of the PS operon of the strain CNCM I-2980 is also similar to that of other known PS operons: upstream the ORF deoD coding for a purine-nucleotide phosphorylase, and downstream in the opposite direction the ORFs IS1193 and orf14.9 respectively coding for a transposase (belonging to the family of the IS1193 insertion sequences, mobile genetic elements) and a protein of unknown function. 
     However, a sequence comparison carried out between the proteins potentially coded by the ORFs of the operon of the strain CNCM I-2980 and those available in the public databases (GENBANK) show that the genetic content of the PS operon of the strain CNCM I-2980 is novel in its distal part.
         The proximal part of the PS operon of  Streptococcus thermophilus , and more generally of the streptococci known at present, comprises 4 ORFs called epsA (or cpsA, or capA, or wzg), epsB (or cpsB, or capB, or wzh), epsC (or cpsC, or cpaC, or wzd) and epsD (or cpsD, or capD, or wze) the derived polypeptide products of which, for each of the 4 ORFs, have significant sequence similarities between strains. At this level, the polypeptide products derived from the ORFs eps13A, eps13B, eps13C and eps13D of the PS operon of the strain CNCM I-2980 are not distinguished from those derived from the other PS operons (percentage of identical amino acids greater than or equal to 94%).   Immediately following the ORF epsD, ORF epsE (or cpsE, or capE, or wchA) is present in the majority of the known PS operons in  Streptococcus thermophilus . In this case also, the sequence similarities are significant between homologous polypeptide products originating from the different known sequences; the translation product of the ORF eps13E of the strain CNCM I-2980 is strongly similar to its homologues originating from other strains.   The organization of the following 4 ORFs (eps13F, eps13G, eps13H and eps13I), of the PS operon of the strain CNCM I-2980, although already described, is less frequent among the different known structures of PS operons of  Streptococcus thermophilus . This organization is found, sometimes incompletely, in the strains IP6757 (GENBANK accession number AJ289861), “type VII” (GENBANK accession number AF454498) and “type III” (GENBANK accession number AY057915).   In the distal part of the operon, the 7 ORFs eps13J, eps13K, eps13L, eps13M, eps13N, eps13O and eps13P are novel and specific to the PS operon of the strain CNCM I-2980. Although slight, their sequence similarity at protein level, or in certain cases the existence of specific protein units, makes it possible to assign a putative function to the products of these ORFs: potential glycosyltransferase or polymerase activity for the product of the ORFs eps13J to eps13O, transmembrane transport activity of the PS for the product of the ORF epsl3P.
 
3/ Comparative Rheology Test of the Strain  Streptococcus thermophilus  CNCM I-2980
       

     The  Streptococcus thermophilus  strains used, CNCM I-2423, CNCM I-2429, CNCM I-2432, CNCM I-2978 and CNCM I-2979 are strains from the Rhodia Food collection. They are for the most part used for the industrial production of fermented milks or yogurts and are recognized for their texturizing properties. They are representative of the strains described in the literature. They are studied hereafter in comparison with the strain CNCM I-2980 and considered as representative of the texturizing strains currently used in the agri-food industry. 
     The  Streptococcus thermophilus  strains RD736 and RD676 are Rhodia Food industrial strains with a reputation for their low texturizing ability. The polysaccharides which they could produce and their PS operon are not known. They are studied hereafter in comparison with the strain CNCM I-2980 and considered as representative of the non-texturizing strains. 
     The fermented milk used is obtained by supplementing 100 ml of UHT skimmed milk (Le Petit Vendeen®) with 3% (weight/volume) of skimmed milk powder. The sterility of the solution is obtained by a pasteurization at 90° C. for 10 minutes, the temperature is measured in the core of the milk. The fermentation support thus obtained is inoculated with the strain to be tested at a rate of 10E+6 cfu/ml (colony forming unit/ml) then incubated at 43° C. (in a water bath) until a pH of 4.6 is obtained. The monitoring of the pH is continuously recorded. Fermented milks thus obtained are placed in a ventilated oven at 6° C., until analyzed. 
     Two types of rheological measurements are carried out: viscosity and flow. The viscosity measurements are carried out at 8° C. on fermented milks, after storage for 1, 7, 14 and 28 days at 6° C. The apparatus used is an RVF-type Brookfield® viscometer (Brookfield Engineering Laboratories, Inc.) mounted on a Helipath stand (Brookfield Engineering Laboratories, Inc.) The viscometer is equipped with a type C needle and the oscillation speed applied to the needle is 10 rpm. The flow measurements are carried out at 8° C. on fermented milks, after storage for 14 days at 6° C. and which have been previously stirred. The apparatus used is an AR1000-N rheometer (TA Instruments) equipped with co-axial cylinders (Radius 1=15 mm, Radius 2=13.83 mm, Height=32 mm, Air gap=2 mm). For the ascending segment, the stress applied in a continuous sweep varies from 0 to 60 Pa for a duration of 1 minute according to a linear mode. For the descending segment, the stress applied in a continuous sweep varies from 60 to 0 Pa for a duration of 1 minute according to a linear mode. The values taken into account are the thixotropic area and the yield point; the latter is calculated according to the Casson model. 
     The viscosity of the fermented milk obtained with the strain  Streptococcus thermophilus  CNCM I-2980 was measured after storage for 1, 7, 14 and 28 days at 6° C. (Table 1). The viscosity value measured after storage for one day is 53.3 Pa-s. This value varies little over time showing the stability of the fermented milk obtained with the  Streptococcus thermophilus  strain CNCM I-2980. Comparatively (Table 1), the viscosities measured for fermented milks produced with the strains RD736 and RD676, reputed to have a weak texturizing ability, are comprised between 26 and 30 Pa-s. The other strains tested produce fermented milks having lower viscosities than that obtained with the strain CNCM I-2980. It is possible to distinguish one group of strains generating viscosities of the order of 40 Pa·s (CNCM I-2979, CNCM 1-2423 and CNCM I-2432) and a second, to which CNCM I-2980 belongs, generating viscosities of the order of 50 Pa·s. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Viscosity and pH of the fermented milks obtained with the different 
               
               
                 strains tested, after different storage periods at 6° C. 
               
            
           
           
               
               
            
               
                   
                 Viscosity in Pa-s/pH 
               
            
           
           
               
               
               
               
               
            
               
                   
                 Storage 
                 Storage 
                 Storage 
                 Storage 
               
               
                 Strains 
                 1 day 
                 7 days 
                 14 days 
                 28 days 
               
               
                   
               
               
                 CNCM I-2980 
                 53.3/4.50 
                 53.0/4.44 
                 53.0/4.42 
                 53.5/4.40 
               
               
                 CNCM I-2429 
                 51.2/4.55 
                 51.9/4.45 
                 51.0/4.44 
                 51.2/4.44 
               
               
                 CNCM I-2978 
                 50.4/4.56 
                 51.8/4.52 
                 49.6/4.49 
                 51.0/4.45 
               
               
                 CNCM I-2432 
                 42.4/4.60 
                 42.2/4.56 
                 43.0/4.55 
                 43.0/4.45 
               
               
                 CNCM I-2423 
                 42.0/4.60 
                 41.9/4.40 
                 42.0/4.37 
                 43.0/4.30 
               
               
                 CNCM I-2979 
                 37.8/4.54 
                 40.7/4.45 
                 42.2/4.42 
                 42.2/4.33 
               
               
                 RD676 
                 29.6/4.60 
                 30.0/4.57 
                 30.0/4.57 
                 30.0/4.52 
               
               
                 RD736 
                 26.0/4.45 
                 26.0/4.34 
                 28.0/4.34 
                 27.0/4.26 
               
               
                   
               
            
           
         
       
     
     The flow measurements made it possible to define two significant rheological descriptors (yield point and thixotropic area) for the rheological description of the fermented milks (Table 2). For the fermented milk obtained with the strain CNCM I-2980, the mean values are 5.89 Pa and 488 Pa/s for, respectively, the yield point and the thixotropic area. These values are significantly different from those obtained for the fermented milks obtained with the strains reputed to be non-texturizing (RD676 and RD736). For example for the fermented milk obtained with the strain RD676, these mean values are respectively 17.01 Pa and 17083 Pa/s. In the case of the strains reputed to be texturizing, the yield point and thixotropic area values are much closer to those obtained with the strain CNCM I-2980, but significantly greater however, showing a greater texturizing ability than the strain CNCM I-2980. 
                     TABLE 2                  Yield point and thixotropic area values (mean of 3 repetitions) of       fermented milks obtained with the different strains tested after storage       for 14 days at 6° C. measured using the AR1000-N device                                 Strains   Yield point (Pa)   Thixotropic area (Pa/s)                                             CNCM I-2980   5.89   488           CNCM I-2429   13.32   1215 (2 values)           CNCM I-2978   10.51   728           CNCM I-2432   12.27   1245           CNCM I-2423   8.86   1344           CNCM I-2979   13.56   1786           RD676   17.01   17083           RD736   15.91   33100                        
4/ Sensory Characterization of the Strain  Streptococcus thermophilus  CNCM I-2980, Comparison with the Reference Strains
 
     Fermented milks were evaluated by sensory analysis after storage for 14 days at 6° C. The quantitative descriptive analysis of the fermented milks, maintained at an optimum tasting temperature of 12° C., was carried out by a jury of 9 experts on a non-structured linear scale of 0 to 6 points. This sensory profile analysis was duplicated at an interval of a few days. The judges, selected and trained beforehand, carried out their evaluation on 4 descriptors of texture on a spoon: brittle, resistance to stirring, stringy, granulosity, and on 4 descriptors of texture in the mouth: melting, sticky, thickness, coating. The sensory differences were evaluated by an analysis of variance (called ANOVA) with two factors, a fixed model, followed by a Newman-Keuls mean comparison test with an alpha threshold of 5% on each of the descriptors. A Principal Component Analysis (PCA) with the sensory descriptors as variables and the strains individually was implemented in order to visualize the space produced. An Ascending Hierarchical Classification (AHC) made it possible to isolate the groups of strains on the PCA. The software used for these statistical analyses are Fizz® (Biosystèmes), Statgraphics® and Uniwin plus®. 
     The fermented milk data obtained with the  Streptococcus thermophilus  strain CNCM I-2980 were compared with those of fermented milks obtained with the other reference strains. The mean values obtained with the different strains for the texture descriptors adopted are indicated in Table 3 and the significant differences emerging from the ANOVA and mean comparison test are listed in Table 4 and  FIGS. 3 and 4 . 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Mean of the marks allocated by the sensory analysis jury 
               
               
                 for fermented milks obtained with the different strains 
               
               
                 of the study on the texture descriptors. 
               
            
           
           
               
               
               
            
               
                   
                 Descriptors on spoon 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance 
                   
                 Descriptors in mouth 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Strains 
                 Brittle 
                 to stirring 
                 Granular 
                 Stringy 
                 Melting 
                 Sticky 
                 Thick 
                 Coating 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 CNCM I-2980 
                 0.89 
                 4.97 
                 0.04 
                 5.09 
                 1.32 
                 4.27 
                 5.06 
                 4.41 
               
               
                 CNCM I-2429 
                 4.12 
                 3.49 
                 1.53 
                 1.24 
                 3.36 
                 1.46 
                 3.54 
                 2.94 
               
               
                 CNCM I-2978 
                 3.39 
                 4.35 
                 0.42 
                 2.83 
                 2.96 
                 1.97 
                 3.86 
                 3.41 
               
               
                 CNCM I-2432 
                 3.28 
                 3.14 
                 1.60 
                 1.32 
                 3.11 
                 1.43 
                 3.01 
                 2.91 
               
               
                 CNCM I-2423 
                 1.64 
                 4.02 
                 0.16 
                 3.44 
                 2.25 
                 2.48 
                 3.61 
                 3.30 
               
               
                 CNCM-I 2979 
                 3.98 
                 2.79 
                 2.36 
                 0.74 
                 3.71 
                 0.72 
                 2.39 
                 2.22 
               
               
                 RD676 
                 4.98 
                 1.46 
                 5.14 
                 0.17 
                 4.98 
                 0.04 
                 0.91 
                 1.03 
               
               
                 RD736 
                 4.35 
                 1.45 
                 3.43 
                 0.04 
                 5.18 
                 0.31 
                 0.77 
                 0.67 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Mean comparison on each of the descriptors of texture on a 
               
               
                 spoon and texture in the mouth by the Newman-Keuls test at 5%. 
               
               
                 Interpretation of the results: the difference between the strains 
               
               
                 connected by the same letter is not significant. 
               
            
           
           
               
               
               
            
               
                   
                 Descriptors on spoon 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Resistance 
                   
                 Descriptors in mouth 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Strains 
                 Brittle 
                 to stirring 
                 Granular 
                 Stringy 
                 Melting 
                 Sticky 
                 Thick 
                 Coating 
               
               
                   
               
               
                 CNCM I-2980 
                 E 
                 A 
                 E 
                 A 
                 D 
                 A 
                 A 
                 A 
               
               
                 CNCM I-2429 
                 B 
                 C 
                 D 
                 D 
                 B 
                 C 
                 B 
                 BC 
               
               
                 CNCM I-2978 
                 C 
                 B 
                 E 
                 C 
                 B 
                 BC 
                 B 
                 B 
               
               
                 CNCM I-2432 
                 C 
                 CD 
                 D 
                 D 
                 B 
                 C 
                 C 
                 BC 
               
               
                 CNCM I-2423 
                 D 
                 B 
                 E 
                 B 
                 C 
                 B 
                 B 
                 B 
               
               
                 CNCM I-2979 
                 B 
                 D 
                 C 
                 E 
                 B 
                 D 
                 D 
                 C 
               
               
                 RD676 
                 A 
                 E 
                 A 
                 F 
                 A 
                 D 
                 E 
                 D 
               
               
                 RD736 
                 B 
                 E 
                 B 
                 F 
                 A 
                 D 
                 E 
                 D 
               
               
                   
               
            
           
         
       
     
       FIGS. 3 and 4  show a histogram representation of the results obtained in Table 4. 
     For all the descriptors, the strains considered non-texturizing, RD676 and RD736, are significantly differentiated from the other strains. Among the texturizing strains, the strain CNCM I-2980 is clearly and significantly differentiated for all the descriptors, except for granulosity, where it cannot be differentiated from the strains CNCM I-2978 and CNCM I-2423. 
     The PCA makes it possible to position the strains as a function of their distance in relation to the sensory descriptors. 
     The design 1-2 of the PCA in  FIG. 2  represents 97.3% of the space produced. Component 1 contrasts two groups of sensory variables. The first group, constituted by the variables: resistance to stirring, thickness in the mouth, coating in the mouth, stringy on a spoon and sticky in the mouth, accounts for component 1 on the right. The second group, constituted by the variables: melting in the mouth, brittle on a spoon and granulosity on a spoon, accounts for component 1 on the left. The first group of variables is anti-correlated with the second group. These variables make it possible to analyze the positioning of the strains on this plan. Moreover, the AHC analysis makes it possible to classify the strains in different groups which are represented in the form of dotted circles on the factorial design 1-2. 
     The factorial design contrasts several groups of strains providing different texture properties. It emerges from these analyses that the strains RD736 and RD676 impart to the fermented milk a brittle and granular texture on a spoon and melting texture in the mouth. In the same manner, they do not produce a thick, sticky or coating texture in the mouth, neither resistant nor stringy on a spoon in comparison with the other groups of strains. They therefore produce a non-texturized fermented milk. By contrast, the strains CNCM I-2429, CNCM I-2432 and CNCM I-2979 produce averagely texturized fermented milks; the strains CNCM I-2423 and CNCM I-2978 produce texturized fermented milks, and the strain CNCM I-2980 produces a highly texturized fermented milk. This analysis shows that the strain CNCM I-2980 provides very particular texture characteristics in fermented milk compared with all of the reference strains. 
     5/ Comparative Test of Resistance of the  Streptococcus thermophilus  Strain CNCM I-2980 to Phages 
     The sensitivity of a strain to a bacteriophage is established by the lysis plaque method. 100 μl of a culture of the strain to be tested and 100 μl of an appropriate dilution of a serum containing the bacteriophage to be studied are used to seed 5 ml of a M17 glucose agar medium under superfusion (agar 0.6% weight/volume) supplemented at 10 mM with CaCl 2 . The whole is poured onto the surface of a solidified M17 glucose agar medium (agar 1.5% weight/volume) supplemented at 10 mM with CaCl 2 . After incubation at 42° C. for 16 hours, the sensitivity of the strain to the bacteriophage is evaluated by the presence of lysis plaques. The absence of a lysis plaque signifies the resistance of this strain to the bacteriophages tested. The sensitivity spectrum of a strain to bacteriophages (also called lysotype) is constituted by all of the sensitivities and resistances to the bacteriophages studied. 
     Table 5 below defines the bacteriophages used for this study and their strain of origin/propagation. These are strains and phages originating from the Rhodia Food collection. The bacteriophages were selected for their infectiousness vis-à-vis the reference texturizing strains. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Phages 
               
            
           
           
               
               
            
               
                 Name of the phage 
                 Strain of origin 
               
               
                   
               
               
                 2972 
                 CNCM I-2423 
               
               
                 4082 
                 RD729 
               
               
                 4074 
                 CNCM I-2429 
               
               
                 4154 
                 CNCM I-2429 
               
               
                 1272 
                 CNCM I-2978 
               
               
                 4128 
                 RD852 
               
               
                 1255 
                 CNCM I-2432 
               
               
                 1765 
                 RD728 
               
               
                 4121 
                 RD862 
               
               
                   
               
            
           
         
       
     
     In order to evaluate the industrial benefit of the strain CNCM I-2980 with respect to the problems associated with bacteriophages, the lysotype of the strain CNCM I-2980 was evaluated and compared with those of the reference texturizing strains. Table 6 shows the sensitivities of the strains to these different phages (lysotype) established by the lysis plaque method. It appears that the six strains of the study have different lysotypes. In particular, the strain CNCM I-2980 has a lysotype distinct from that of the other texturizing strains tested. In fact the strain CNCM I-2980 could not be infected by the phages tested. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Lysotype of the strains tested 
               
            
           
           
               
               
            
               
                   
                 Strains 
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 CNCM 
                 CNCM I- 
                 CNCM 
                 CNCM I- 
                 CNCM 
                 CNCM I- 
               
               
                 Phages 
                 I-2980 
                 2423 
                 I-2978 
                 2432 
                 I-2429 
                 2979 
               
               
                   
               
               
                 2972 
                 − 
                 + 
                 − 
                 − 
                 − 
                 − 
               
               
                 4082 
                 − 
                 + 
                 − 
                 − 
                 − 
                 − 
               
               
                 1272 
                 − 
                 − 
                 + 
                 − 
                 − 
                 − 
               
               
                 4128 
                 − 
                 − 
                 + 
                 − 
                 − 
                 − 
               
               
                 1255 
                 − 
                 − 
                 − 
                 + 
                 − 
                 − 
               
               
                 1765 
                 − 
                 − 
                 − 
                 + 
                 − 
                 − 
               
               
                 4074 
                 − 
                 − 
                 − 
                 − 
                 + 
                 − 
               
               
                 4154 
                 − 
                 − 
                 − 
                 − 
                 + 
                 − 
               
               
                 4121 
                 − 
                 − 
                 − 
                 − 
                 − 
                 + 
               
               
                   
               
               
                 +: sensitive to the phage tested; 
               
               
                 −: resistant to the phage tested