WO1994026124A1

WO1994026124A1 - Unripened soft cheese containing flavouring bacteria

Info

Publication number: WO1994026124A1
Application number: PCT/FR1994/000547
Authority: WO
Inventors: Clair-Yves Boquien; Naïma BASSIT; Daniel Picque; Georges Corrieu
Original assignee: Institut National De La Recherche Agronomique
Priority date: 1993-05-10
Filing date: 1994-05-09
Publication date: 1994-11-24
Also published as: FR2705015A1; FR2705015B1; AU6724994A

Abstract

Method of production of unripened soft cheese type products, in which the starting milk is treated using rennin and an inoculum bacteria comprising only the acidifying lactic bacteria, which results in the formation of curd. The curd is subjected in a manner known per se to heating, then undergoes centrifugation or filtration to form treated curd. A flavouring base prepared separately by treating a first dairy substance with flavour-producing bacteria is then added to the treated curd to product the desired soft cheese.

Description

Fresh cheese containing aromatic bacteria

The invention belongs to the field of food products and more particularly relates to products of the fresh cheese type as well as their process for obtaining.

Within the meaning of the present description, the expression "fresh cheeses" encompasses many types of cheese known under various names according to regions or countries. The expression "fresh cheeses" is used in France. In Anglo-Saxon countries, it is called "quarg", "cottage-cheese". In Germany, the name "quark" is used more. Cheeses of this type are still known in the Scandinavian countries under the name "viili". There are also similar products in Greece or in the Balkans, these products being _{, in} particular related to drained yoghurts. The present invention covers all these types of products. As a relevant bibliographic reference concerning fresh cheeses and their production, we can cite the work of PERNODET G. "Le fromage", pages 219-248, (1984) ECK (Ed.) LAVOISIER Paris. An illustrative diagram of a process of the prior art for the manufacture of such fresh cheeses is shown in Figure 1. In general, we start with skimmed milk which is first subjected to a heat pasteurization treatment. To the pasteurized skim milk are added, on the one hand, rennet, for example at a rate of about 0.1% by weight and, on the other hand, a complex bacterial inoculum, in particular at a rate of 2% expressed in volume. A mixed culture of acidifying bacteria and aromatic bacteria, such as Lactococcus lactis subsp., Is used for this purpose. lactis and Lactococcus lactis subsp. cremoris for the former, and Lactococcus lactis subsp. lactis biovar diacetylactis and Leuconostoc spp for the seconds. For simplification, the expressions L-lactis, L-cremoris and L-diacetylactis will be used in the following description. The fermentation, which is performed between 22 and 25 ^° C. provides a curd which is itself subjected to heat treatment heating to about 60 ^° C, so as to improve the texture and the recovery of soluble proteins. Then, the whey or whey is separated by centrifugation or by filtration and a product which can be used as fresh cheese is recovered. When starting with skim milk, this product is free of fat, so it may be wise to adjust its fat content at the end of the process. The various products of the fresh cheese type are distinguished in particular from each other by their respective moisture and fat content: in France, we can then speak of "petit suisse" or "fromage blanc" and in the other countries mentioned above. above, for example, it may be a question of quark, quarg or drained yogurt. For good storage, the product is cooled, for example at 4 ^° C, stored and packaged for commercialization.

The above data are known to those skilled in the art and have been simply recalled to illustrate the technical field to which the present invention belongs. Although a large tonnage of products is produced by such a process, it has a number of drawbacks. First of all, the mixture of acidifying and aromatic bacteria making up the inoculum must be carefully chosen, using a combination of various strains for this purpose. Being since these bacteria are used at the same time, their culture conditions are not optimal. Indeed, the fermentation must be carried out at a relatively low temperature (22-25 ^° C) to provide a suitable production diacetyl principal agent responsible for the aroma. This results in fairly long fermentation times, which reach 15 to 18 hours in industrial practice. Also, the known process, by its very nature, leads to weakly flavored products, containing for example 2 ppm of diacetyl, since the fermentation conditions do not allow validly to increase the content of aromatic compounds in the final product. . In fact, the industrial culture conditions are chosen to ensure both rapid acidification and satisfactory aroma production. For temperature, these are antithetical conditions, since acidification is faster at high temperature, while aroma production is better at low temperature. The productivity of such a process cannot therefore be high. It can also be noted that the known method only allows a limited number of products to be obtained, which differ only in their moisture content, which can vary for example between 80 and 87% by weight, and in fat, this which can be found in a range of 0 to 60% by weight (fat / dry).

Methods in which the aromatic bacteria are added to the curd already formed are described in US Patents 4,191,782 and US 4,318,928.

US Patent 4,191,782 relates to a process for the production of "cottage cheese" specifically, comprising the addition of Streptococcus diacetylactis (former name of L. diacetylactis) in the form of a organic concentrate which was previously frozen and stored in the cold, then was thawed at the time of addition to the curd. The results mentioned in Table II of this patent indicate that no odor of diacetyl is observed after one week. The presence of diacetyl is not demonstrated until two weeks after addition of the bacteria.

It should also be noted that no indication is given as to the concentrations of diacetyl produced. The presence of this molecule has only been evaluated by taste tests.

US Patent 4,318,928 relates to a comparable process in which the Streptococcus diacetylactis bacteria are isolated by centrifugation of the cultures which eliminates the diacetyl possibly present in the supernatant. They are then frozen at -50 ^° C before being added to the curd. Diacetyl production is observed only from 20 days after the addition of the bacteria. These two patents describe processes in which: diacetyl is produced within a significant time after addition of the bacterial concentrate, - the quantities produced are small. In addition, they are only used on a very specific type of cheese: cottage cheese.

Finally, it is only during storage of the cottage cheese that diacetyl is produced, without there being any possibility of controlling it. The present invention relates to new products of the fresh cheese type which are distinguished by many advantageous aspects from similar products known from the prior art. They can have a higher content of aromatic compounds, which makes it possible to diversify more widely. costs to adapt their production to the needs and habits of consumers.

A subject of the invention is also products of the fresh cheese type containing bacteria which are still alive, thus conferring on such products a probiotic quality, whereas in known analogous products, the final cheese contains only bacteria which are totally inactivated, due even the production process, which involves a heating step after the formation of the curd. This step destroys almost all of the acidifying lactic acid bacteria and aromatic bacteria that had been used during fermentation.

The subject of the invention is also a method for obtaining products of the fresh cheese type, making it possible to greatly improve the productivity and the flexibility of manufacture, by optimizing the conditions under which the various kinds of bacteria are used. . In a first aspect, the invention relates to products of the fresh cheese type containing before storage on the one hand aromatic bacteria, living, capable of producing aromatic compounds having a bacterial population greater than 10 ⁶ cfu / ml and on the other hand at least one aromatic compound with a sufficient content to give the product an aroma, said aromatic compound being derived from said bacteria.

The abbreviation cfu is a classic abbreviation in microbiology, from the English "colony forming unit".

Thus, according to a defining characteristic of the products of the invention, these contain living bacteria, known to provide aromatic compounds useful in fresh cheeses. In all first, preference is given to bacteria capable of producing diacetyl. These include: L. diacetylactis. Leuconostoc spp., Lactobacillus spp. as well as other strains which can be used for this purpose, such as Lactobacillus casei subsp. casei described in patent EP-0.430.406 (ATCC 334, ATCC 11007, ATCC 19.254). The strains of bacteria must be chosen from among those which produce diacetyl, while achieving as low a bioconversion as acetoin, which constitutes a non-aromatic by-product.

The invention is not limited to the use of diacetyl producing bacteria, but it also covers bacteria capable of producing other aromatic compounds; such bacteria can be chosen from the genera Lactobacillus and Pediococcus, for example P. Pentosaceus. Thanks to the aromas thus developed, fresh cheeses can be given various tastes or sensations for consumption, for example:

- a creamy taste, particularly desirable for products with a low fat content,

- a more pronounced cheese taste, - a fruity taste, which can make it possible to eliminate the synthetic aromas currently added in certain products,

- and all kinds of tastes corresponding to the needs and habits of consumers in certain countries.

According to an advantageous characteristic of the invention, the aromas of products of the fresh cheese type are provided by living bacterial cultures and are therefore to be considered as natural, according to the regulations currently accepted. The new products of the invention have contents of aromatic compounds at least equal and which can be much higher than those encountered in similar known products. As mentioned above, fresh cheeses, the main flavor of which is diacetyl, contains for example around 2 ppm of this aromatic compound. The products of the invention can have a much higher diacetyl content. Indeed, thanks to the manufacturing process, which will be described below, there is practically no limit to the content of aromatic compounds other than that desired for the needs of consumption. This represents an important additional advantage of the present invention. According to another characteristic of the invention, products of the fresh cheese type may contain, in addition to the aromatic bacteria, concentrated bacterial cultures having a different or additional function from that of the aromatic bacteria. It can be, for example, cultures of Bifidobacterium, Lactobacillus acidophilus or Lactobacillus casei, whose role is beneficial for human consumption due to their activity in the intestine. Such products are called probiotics and / or "fresh".

Advantageously, the aromatic compound contained in said cheese product is diacetyl, advantageously at a minimum concentration of 0.010 mM. According to yet another characteristic of

In the invention, bacteria of different species can be combined in order to limit the concentrations of certain metabolites.

Thus, L. diacetylactis produces diacetyl but it also produces acetaldehyde. This aromatic compound gives a smell of "freshness" to fresh cheese, provided that its concentration is not too high (less than 20 pp). Beyond that, it gives an unpleasant odor ("green"). Leuconostoc spp. has an alcohol dehydrogenase capable of degrading acetaldehyde to ethanol. It is therefore possible to add a strain of Leuconostoc to a pure culture of L. diacetylatis in order to reduce the acetaldehyde content. In another aspect, the invention also relates to a process for obtaining products of the fresh cheese type, characterized in that the starting milk is treated with rennet and a bacterial inoculum comprising only acidifying lactic acid bacteria , which leads to a curd, it is subjected, in a manner known per se, to heating and then to centrifugation or filtration, thereby obtaining a treated curd, an aromatic base is prepared separately by treating a raw material dairy by bacteria producing aroma and said aromatic base is introduced into said treated curd, which provides the desired fresh cheese.

According to an essential characteristic of the process of the invention, the production of the curd, on the one hand, and the preparation of an aromatic base, on the other hand, is carried out separately.

Alternatively, it is also possible to separately prepare a bacterial culture, producing or not producing aromas, which is introduced into the treated curd. If necessary, this culture can be concentrated, before addition to the curd, by centrifugation or ultrafiltration, so as to obtain high populations of live bacteria in the product.

The curd is produced by treating the starting milk, generally after, heating or pasteurization, with rennet and with a bacterial inoculum containing, according to the particularity of the invention, only acidifying lactic acid bacteria. Rennet is used in amounts similar to those of the conventional process, namely between 0.005% v / v and 0.1% v / v, for example 0.02% by volume per volume relative to milk. It is the same for the bacterial inoculum which can be used at a rate of 0.1% v / v to 5% v / v, for example at 2% by volume per volume relative to milk. The bacteria inoculated at this stage of the process only belong to the category of lactic acidifying bacteria. In practice, mixtures of acidifying strains, such as L. lactis or L. cremoris, are used. Other analogous strains can be used, which are chosen because of their specific properties, for example for their yield or for their influence on the quality of the finished products, in particular the texture of fresh cheeses. These choices are within the reach of those skilled in the art and need not be described further.

According to an advantageous characteristic of the process of the invention, the culture of lactic acidifying bacteria in milk can be carried out at higher temperatures than those traditionally used for such fermentation. A range of suitable temperature is 25 to 32 "C, for example in the range of 30 ^° C. Because of the nature of the stem, it is also not necessary to control the gas from the fermenter atmosphere. This is particularly advantageous in industrial practice.

Also, the duration of the culture is reduced compared to the traditional process. With the process of the invention, durations of 5 to 14 hours are in generally sufficient to obtain a good quality curd. The curd is then subjected, in a known manner, to a heating minutes at a temperature of 45 "C to 75" C, eg 60 ^° C, after which removes the whey or whey by centrifugation or filtration.

It is at this stage of the process that the separate addition of an aromatic base, containing living flavoring bacteria, takes place, which constitutes an essential characteristic of the invention. According to the latter, in effect, a concentrated aromatic base is produced separately by treating a dairy raw material with aroma-producing bacteria. As dairy raw material, milk, for example skimmed milk, or a medium based on whey, or any other material in which aromas useful for fresh cheeses can develop, under the action of bacteria known as flavoring. Before being subjected to fermentation, the dairy raw material generally undergoes a heat treatment of pasteurization or sterilization.

The flavor producing bacteria which may be used are those which have already been indicated above. It is possible to use a single flavoring strain, which may have advantages, or a mixture of such strains. According to an advantageous characteristic of the process of the invention, the culture is carried out under the optimal conditions for the production of aromatic substances in particular at an optimal temperature, for example a temperature below approximately 22 "C, in particular from 15 to 22 ° C for an aromatic base rich in diacetyl. The process of the invention therefore makes it possible to optimize the production of aromatic compounds intended for fresh cheeses, whereas in the traditional process, the culture conditions of the bacterial inoculum, which comprises both acidifying lactic acid bacteria and flavor producing bacteria, required a compromise temperature for the fermentation of two very different types of bacteria.

The above indications concerning the temperature preferably apply in the case of the production of an aromatic base rich in diacetyl. If it is an aromatic base rich in flavor compounds other than diacetyl, the optimal conditions will depend on the strain cultivated. A person skilled in the art is able to choose the temperature according to the nature of the strain.

It is the same for the variant of the process of the invention according to which a culture concentrated in bacteria other than aromatic bacteria is added to the curd. According to the inventive concept exposed in the present description, such a culture is carried out independently, which makes it possible to optimally adjust the culture conditions, in particular the temperature, to the nature of the strain (or mixture of strains) cultivated. . Thus the temperature can be adjusted to a temperature close to the optimal temperature for growth of the bacteria or bacteria considered, which can be very different from that of traditional acidifying lactic acid bacteria. The invention therefore makes it possible to adjust the culture conditions to the properties that are desired in the final product.

According to the invention, it has also been found that, in particular in the case where the aromatic compound is diacetyl, the production is clearly improved when the oxygen concentration is increased in the fermentation medium. It has been found that the best results are obtained when the initial oxygen content is equal to 100% of the saturation of the medium with oxygen. In accordance with the invention, it has indeed been found that the production of diacetyl is improved when the culture of the aromatic bacteria is carried out under pure oxygen. In the state of knowledge of the Applicant, all similar cultures have hitherto been carried out by providing air and / or by stirring the culture medium. It has now been observed that lactic acid bacteria can grow under pure oxygen, whereas they are facultative anaerobic bacteria. This somewhat unexpected phenomenon will be illustrated below. It has also been found, according to the invention, that optimal culture conditions could imply a combined temperature / oxygen effect. To ensure optimal production of aromatic bases rich in diacetyl, a hermetic bioreactor is used, in which the oxygen content can be continuously monitored. To this end, the bioreactor comprises means for supplying oxygen as well as means for measuring the partial pressure of oxygen in the culture medium, with regulation to enable the desired oxygen content to be reached. Furthermore, as is usual in this type of device, the bioreactor also includes means for measuring the pH, the temperature and the redox potential. The first allow to follow the evolution of the culture and the second ensure, by regulation (thermostat), the maintenance of the optimal fermentation temperature. It is also useful, in particular in the case where the dairy raw material is milk, that the culture medium is agitated, so as to avoid the formation of a curd in the reactor. Other additional means can be fitted to the bioreactor, for example means for permanently measuring the pressure (pressure gauge) and means making it possible to evacuate the gases.

Whatever the culture medium and the dairy material used, food additives can be added in order to further improve the production of aromatic bases. It is known, for example, that the bacteria L. diacetylactis use citrate to produce flavor compounds such as acetic acid, acetoin and diacetyl, the latter being the most sought after flavor compound in fresh cheeses. It may thus be advantageous for the fermentation medium to be enriched with citrate.

Other food additives, authorized by regulation, can also be added to the medium, for example hemin or amino acids, such as leucine and valine, the concentration of which in the final fresh cheese must be less than 9 g respectively. and 6 g / kg. Additives providing metal ions, such as Cu ⁺⁺ and Fe can also be introduced. These examples of additives are in no way limiting, since the process of the invention makes it possible to act independently of the acidifying fermentation to produce an aromatic base in an optimal manner. This fermentation step by flavor-producing bacteria can be carried out batchwise, in a bioreactor operating in successive batches, or continuously, in which case a bioreactor comprising free or immobilized bacteria is used, as is known to the man of job .

When the culture is sufficiently advanced, which can be determined by measuring the pH, the fermentation medium constitutes the aromatic base which, according to the invention, can be directly used in cheese-making to be introduced into the curd prepared separately as well as 'it was stated above. The quantity of aromatic base to be introduced depends on its richness and on the desired final product. Rates as high as 20% aromatic base volume relative to curd volume are quite possible, but in general, to obtain fresh cheese that conforms to consumer taste, aromatic base rates from 0.2 to 10 % v / v, in particular about 0.5 to 5% v / v and even better between 0.5 and 2% v / v have been found to be suitable.

These figures are only illustrative.

The process of the invention in fact makes it possible to vary the content of aromatic compounds, in particular diacetyl, in the final product at will. It is thus possible to obtain an organoleptic optimum and the contents of aromatic compounds can be very high. The content of aromatic compounds, in particular diacetyl, in the aromatic base before addition to the curd can be chosen to a value as high as desired, which is generally at least five times greater than in a fresh cheese obtained from traditional way. To adjust the content of aromatic compounds in the final product of the fresh cheese type, it suffices to vary the proportions of aromatic base added to the curd.

The product resulting from the mixture of the curd and the aromatic base constitutes the desired fresh cheese. As is known, its fat concentration can still be adjusted. Thus, an addition of fat may be provided before or after the introduction of the aromatic base into the curd, in particular if one has started with skimmed milk.

As will be understood by a person skilled in the art, the process of the invention makes it possible to obtain products of the fresh cheese type, the content of aromatic compounds depending on the rate at which the aromatic base has been added to the curd. It is thus possible to create new products, more or less rich in aromatic compounds, in particular in diacetyl.

The bacterial population present in fresh cheese corresponds to that of the aromatic base. As mentioned above, it is at a high level, greater than 10 ⁶ cfu / ml, in particular 10 7 cfu / ml and often 5.107 cfu / ml.

Also, as indicated above, it is possible to enrich the curds with other aromatic bases in order to develop new aromas in fresh cheeses. These aromas are for example of fruity, cheese, creamy and other types. It then suffices to use in the stage of manufacturing the aromatic base the strains responsible for the formation of the desired aromas. The process of the invention makes it possible to control and optimize the production of such flavors, given that this is carried out independently of the actual production of the curd. The curd with the aromatic base already constitutes a "fresh" product, because it is suitable for a living population of aromatic bacteria.

It should also be noted that the curds can still be enriched with a culture of bacteria which do not produce aromas. The final product can be thus qualified as fresh and / or probiotic, depending on the strain cultivated.

The process of the invention therefore offers advantages in terms of productivity gain, due to the optimal use of bacteria and also increased flexibility compared to the traditional process for making fresh cheeses.

The invention will be further illustrated without being in any way limited by the description and the examples which follow, with reference to the appended drawings in which:

Figure 1 is a block diagram showing a process for manufacturing fresh cheeses according to the prior art. Figure 2 is a similar block diagram illustrating the process of the invention.

Figure 3 is a diagram of a bioreactor usable in the process of the invention.

Figure 4 is a diagram illustrating the production of diacetyl by L. diacetylactis at 30 "C, the quantity of diacetyl in mM being plotted on the ordinate, for different initial oxygen concentrations as a function of the time (hours) plotted on the abscissa. Figure 5 is a graph illustrating the evolution of the D / A ratio of the maximum concentrations of diacetyl (D) and acetoin (A) produced by L. diacetylactis at 30 ° C., the D / A ratio being plotted on the ordinate, for different initial concentrations in oxygen (abscissa).

Figures 6 and 7 illustrate the evolution of the production of diacetyl (in mM, on the ordinate) as a function of time (on the abscissa) respectively with regulation of the concentration of dissolved oxygen at 85% of the saturation of the medium with oxygen and under oxygen pressure (2 bar absolute or 1 bar above atmospheric pressure).

The block diagrams of Figures 1 and 2 have been put, for convenience, in the form of drawings, but it will be emphasized that they form an integral part of the present description. They indeed illustrate without ambiguity the respective stages of a method according to the prior art (Figure 1) and of the method according to the invention (Figure 2). As regards more particularly the process of the invention, all the indications concerning the stages of the process have already been provided in the description above and therefore do not have to be repeated now.

However, it will be noted with reference to FIG. 2 that the addition of acidifying lactic acid bacteria, provided for the formation of the curd, can also be accompanied by the addition of texturing bacteria, as is known to those skilled in the art.

Also, there is shown in dotted lines at the bottom right of Figure 2 the variant of the invention according to which a bacterial culture or a non-aromatic bacterial concentrate can be introduced into the curd after centrifugation thereof. Such an additive can be prepared separately, in advance or during the actual production of fresh cheese, under conditions similar to those of the aromatic base, but of course adapted to the bacteria to be cultivated.

Figure 3 schematically shows a bioreactor used in the process of the invention for the production of the aromatic base rich in diacetyl. In the example illustrated, it is a bioreactor operating batchwise, that is to say in batches. It includes an airtight tank 1 into which a load 2 has been introduced beforehand culture medium (milk or whey-based medium). The reactor includes stirring means 4 driven by a motor 3. A pipe 5 is provided for a sequential supply of oxygen into the reactor 1. The partial oxygen pressure is measured by means 6, 7, acting on a regulation 8 which controls a valve 9 mounted on the pipe 5. There is shown diagrammatically means 10 for measuring the pH and means 11 for measuring the temperature, these being connected to a thermostat (not shown). The bioreactor 1 also includes a pressure gauge 12 and a line 14, controlled by a valve 13, for the outlet of the gases at the top of the reactor. It is thus possible to pressurize the bioreactor 1, which is hermetic, and to permanently control the regularity of the internal pressure by means of the pressure gauge 12. It is also possible to measure the redox potential using the redox probe (15). In the case of milk, agitation 4 avoids the formation of a curd, but the bacterial growth and the production of lactic acid cause a modification of the structure of the micelles. All the useful indications concerning the fermentation medium and any additives have already been given;

The following examples illustrate the process of the invention for the production of fresh cheeses. EXAMPLE 1 1.1 - Production of a curd

Three Erlen-Meyers containing 40 ml each of reconstituted milk at 10%, renneted at 0.1% (calf rennet at 520 mg / 1 of active chymosin) and sterilized at 110 "C for 10 minutes, are prepared. is made with: 0.6 ml of a culture on milk of L. lactis

(strain # 1),

0.6 ml of a culture on milk of L. cremoris

(strain # 2) The inoculum therefore only consists of acidifying strains.

Upon inoculation, the pH of the culture is 6.44. The bacterial populations, counted on M16 medium (Thomas T.D., N.Z.J. Dairy Sci. Tech., 1973, 8:70 - 71), are:

- 5.10 'cfu / ml for strain no.1,

- 9.10 ⁶ cfu / ml for strain no. 2.

Culturing is carried out at 30 ^° C with an uncontrolled gas atmosphere. After 13 h of culture, the pH is 4.40. The populations are:

- 1.6.10 ⁹ cfu / ml for the strain n '1 o.

- 3.5.10 ° cfu / ml for strain no 2.

No trace of acetoin and diacetyl is detected.

The culture is heated at 60 ^° C for 3 minutes and centrifuged at 1000g for 10 minutes. The serum (approximately 20 ml / Erlen-Meyer) is removed and the curd recovered. In the curd, the bacterial concentration of the strains is zero.

1.2 - Production of an aromatic base rich in diacetyl

40 ml of reconstituted milk at 10% and sterilized at 110 ° C for 10 minutes are prepared. The seeding is carried out with 1.2 ml of a culture on milk of L. diacetylactis (strain No. 3).

The inoculum therefore consists only of a flavoring strain. At the inoculation, the population, bacterial. counted on the middle of Kempler and Me Kay (Appl

E Ennvviirroonn Microbiol, 1980, 39: 926 - 927) is 1.0.10 ⁸ cfu / ml.

Culturing is carried out at 18 ^° C and with stirring. The initial oxygen content is equal to 100% of the saturation of the medium with oxygen.

After 14 h of culture, the pH reaches 6.13. The population is 1.5.10 ⁹ cfu / ml.

The concentrations of acetoin and diacetyl are 3.3 mM and 0.32 mM respectively.

1.3 - Addition of the aromatic base to the curd

The aromatic base is added to the curd at three different rates: 4%, 10% and 20% (added volume / curd volume). The mixture is then cooled to + 4 ° C.

The only bacterial population present is that of L. diacetylactis (strain No. 3). The results are collated in Table 1.

Except for the D / A ratio (around 10.6%), the results differ depending on the rate at which the aromatic base rich in diacetyl is added:

- the concentration of strain n ^* 3 in the final product varies between 5.10 ⁷ and 2.5.10 ⁸ cfu / ml;

- the acetoin concentration varies between 0 and 0.51 mM (44.4 ppm);

- the diacetyl concentration varies between 0.016 mM (1.4 ppm) and 0.052 mM (4.5 ppm). EXAMPLE 2

Influence of initial oxygen concentration and temperature on the production of diacetyl and acetoin by L. diacetylactis.

The reaction conditions are similar to those reported in Example 1.2 above except with regard to the temperature, which was chosen equal to 30 ^° C. In addition, we used the bioreactor of Figure 3 to measure the oxygen concentration and temperature.

The results obtained are illustrated in Figures 4 and 5 and in Table 2 below. It is clear that diacetyl production is improved, temperature 30 ^° C, when the initial oxygen concentration increases. The same is true of the D / A ratio representing the ratio of the maximum quantities of diacetyl and acetoin produced.

In other tests, the temperature was also varied between 18 and 30 "C. It was found that this could optimize the production of diacetyl, which, in all cases, is highest when chosen concomitantly an initial oxygen concentration equal to 100% and a temperature of 18 ^'C. EXAMPLE 3: Culture of L.diacetylactis CNRZ 483 in 7-liter fermenter with control of the concentration of dissolved oxygen at 85% saturation of the medium with 1 'oxygen.

The culture medium comprises clarified sweet whey (40 g / 1), peptone (5 g / 1), yeast extract (3 g / 1) and citrate (2 g / 1). The temperature is regulated at 30 ^° C. The agitation is 400 rpm.

The bacterial population, counted on M17 (Terzaghi and Sandine, 1975, Appl. Microbiol, 29; 807-813) is 1.7 10 ⁹ cfu / ml and the pH of 5.13 after 4 hours of culture. The concentration of diacetyl then reaches 0.30 mM (FIG. 6), that of acetoin 3.2 mM. The ratio of the concentrations of diacetyl and acetoin (D / A) is therefore 9.4%. EXAMPLE 4:

Culture of L. diacetylactis CNRZ 483 as a fermenter

7 liters under oxygen pressure.

After saturation of the medium with oxygen and inoculation, the fermenter is put under oxygen pressure. The pressure is 1 bar above atmospheric pressure. It is maintained at this value throughout the culture. The culture medium is the same as that used in Example 3.

The bacterial population is 8 10 ⁸ cfu / ml and the pH of 5.62 after 6 hours of culture. The concentration of diacetyl then reaches 0.60 mM (FIG. 7), that of acetoin 2.4 mM. The D / A ratio is therefore 25%. EXAMPLE 5:

Culture of Lactobacillus casei subsp. rhamnosus CNRZ 212.

Culturing is carried out in conical flasks at 37 ^° C without stirring. The culture medium is the same as that used in Example 3. The initial oxygen content is equal to 100% of the saturation of the medium with oxygen. There is no regulation of the dissolved oxygen concentration. After 8 hours of culture, the pH reaches 4.7. The diacetyl and acetoin concentrations are 0.50 mM and 1.30 mM, respectively. The D / A ratio is therefore 38%.

TABLE 1

Addition at different rates of an aromatic base rich in diacetyl in a curd

Bacterial Concentration Rate Related Content

% alien * of L. diacety¬ diacetyl acetoin D / A (%) *** v / v lactis (cfu / ml) M ppm mM ppm

4 5.10 ⁷ 0.016 1.0 ** 0 10 1.10 ⁸ 0.032 2.8 0.29 25.2 11 20 2.5.10 ⁸ 0.052 4.5 0.51 44.4 10.2

* The concentrations of acidifying strains are zero.

** Content below the detection threshold of the method used (HPLC)

*** Diacetyl / acetoin concentration ratio in%

TABLE 2

Maximum amounts of diacetyl (C _diac ) and acetoin (C _acto ) produced by L_. diacetylactis at different initial concentrations of oxygen and at 30 ^° C

% of oxygen ^c diac ("" - ^C acto ("" M) D / A (%) *

100 0.180 ± 0.014 5.20 + 0.07 3.40 ± 0.20

50 0.063 ± 0.011 4.63 + 0.38 1.40 + 0.19

21 0.021 ± 0.002 3.30 ± 0.42 0.64 ± 0.01

0 0.009 ± 0.002 2.46 ± 0.23 0.36 + 0.05

* D / A represents C _diac / C _acto

Claims

1. Products of the fresh cheese type containing before storage on the one hand living aromatic bacteria capable of producing aromatic compounds, having a bacterial population greater than 10 ° cfu / ml and other by at least one aromatic compound with a sufficient content to impart a flavor to the product, said aromatic etan compound derived from said bacteria.

2. Products according to claim 1, characterized e that the aromatic compounds include diacetyl.

3. Products according to one of claims 1 or 2 characterized in that the aromatic bacteria are L. diacetylactis, Leuconostoc spp, Lactobacillus spp. as well as other diacetyl producing strains.

4. Products according to claim 1, characterized e that they contain bacteria, for example of the genus Lactobacillus and Pediococcus, capable of giving them a creamy taste, a pronounced cheese taste or a fruity taste, or any other desired taste.

5. Products according to any one of claims to 4, characterized in that their content of aromatic compound, in particular diacetyl, is at least equal to that of traditional fresh cheeses and can be significantly higher than the latter.

6. Products according to one of claims 1 to 5 characterized in that said aromatic compound is diacetyl and in that it is present at a minimum concentration of 0.010 mM.

7. Products according to any one of claims to 6, characterized in that they contain concentrated bacterial cultures having a different or additional function from that of aromatic bacteria, in particular from cultures of Bifidobacterium, Lactobacillus acidophilus o of Lactobacillus casei.

8. Process for obtaining typ products fresh cheeses, according to any one of claims 1 7, characterized in that the starting milk is treated with rennet and a bacterial inoculum comprising only acidifying lactic acid bacteria, which leads to a curd and is subjected to this curd , in a manner known per se, by heating and then by centrifugation or filtration, thereby obtaining a treated curd, an aromatic stocking is prepared separately by treating a dairy raw material with aroma-producing bacteria and said stocking is introduced aromatic in said treated curd, which provides a fresh cheese type product, which contains living aromatic bacteria and aromatic compounds in quantities corresponding to the desired organoleptic properties.

9. Method according to claim 8, characterized in that the curd is produced by treating the starting milk, generally after pasteurization, with rennet and with a bacterial inoculum containing only lactic acidifying and texturing bacteria, rennet rennet used in amounts of 0.005% to 0.1% by volume / volum compared to the starting milk and the etan bacterial inoculum used at a rate of 0.1% to 5% by volume / volume by ratio with milk.

10. Method according to one of claims 8 or 9, characterized in that the culture of lactic acidifying bacteria in milk is carried out at a temperature between 25 and 32 ^* C, in particular of the order of 30 ^" C.

11. Method according to any one of claims to 10, characterized in that the duration of the culture of acidifying lactic acid bacteria in milk is between 5 and 14 hours.

12. Method according to any one of claims to 11, characterized in that, for the separate preparation of an aromatic base, a dairy raw material, such as milk, in particular skim milk, is treated with flavor-producing bacteria. , or a medium based on whey o any other material in which aromas useful for fresh cheeses can develop.

13. The method of claim 12, characterized in that one uses a single flavoring strain or a mixture of such strains, the culture temperature being alor adapted to the strain - or mixture - used.

14. The method of claim 13, characterized in that one uses a flavoring strain and a strain of Leuconostoc sp. capable of degrading the acetaldehyde possibly produced by the flavoring strain, into ethanol.

15. Method according to one of claims 12 to 14, characterized in that, for the production of a low aromatic rich in diacetyl, the culture is carried out at a temperature below about 22'C, in particular from 15 to 22 ^* vs.

16. Method according to claim 15, characterized in that the aromatic culture is carried out in the presence of oxygen, in particular by choosing an initial oxygen content equal to 100% of the saturation of the medium with oxygen, ie controlling dissolved oxygen either by growing under pressure oxygen.

17. Method according to one of claims 15 or 16 characterized in that a continuous or discontinuous hermetic bioreactor is used, comprising means (5, 9) for supplying oxygen, means (6, 7, 8) for measuring the partial pressure of oxygen in the culture medium (2), with regulation to allow the desired oxygen content to be reached, as well as other ancillary means, such as means (10) for measuring the pH and means (11) for measuring the temperature, stirring means (3, 4) as well as means (12) for measuring the pressure means (13, 14) for evacuating the gases, and means (15) to measure the redox potential.

18. Method according to any one of claims 15 to 17, characterized in that the fermentation medium is enriched in citrate, in particular in the case where the material first dairy is milk.

19. Method according to any one of claims 15 to 18, characterized in that the fermentation medium is enriched with various food additives, for example hemin or amino acids, such as leucine and valine whose concentration in the final fresh cheese must be less than 9 g / kg and 6 g / kg respectively, as well as additives providing metal ions, such as Cu ++ and Fe ++

20. Method according to any one of claims to 19, characterized in that the aromatic base is introduced separately into the curd at concentrations suitable for the desired organoleptic properties in the final product, in particular up to 20% by volume of aromatic base by compared to the volume of the curd, more particularly between 0.2 and 10 v / v, advantageously between 0.5 and 5% v / v and even better between 0.5 and 2% v / v.

21. Method according to any one of claims to 20, characterized in that, when starting from skimmed milk, o adjusts the fat concentration of the fresh cheese e adding fat before or after introduction of the aromatic base in the curd.

22. Method according to any one of claims to 21, characterized in that a culture concentrated in bacteria other than aromatic bacteria is added to the curd, said culture being carried out separately, in advance or at the time of manufacture of the product. fresh cheese type.

23. aromatic base used in the process according to any one of claims 9 to 21, said base before addition to the curd, having a content of aromatic compound, in particular diacetyl, at least five times greater than in cheese traditional fresh.