Patent Description:
Fermented dairy products are recognized by consumers as healthy food having nutritional benefits. Among these fermented dairy products, strained fermented dairy products present the interest to contain higher levels of proteins than in conventional fermented dairy products, which represent an additional nutritional benefit.

Such strained fermented dairy products are generally prepared by the same method as for conventional fermented dairy products, with an additional step consisting in the separation of a liquid phase also called whey (containing generally water, lactose, minerals, etc.) from the conventional fermented dairy products. The remaining solid phase constitutes the desired strained fermented dairy products having an increased protein content. Such processes are disclosed notably in <CIT>, <CIT> or <CIT>.

The separation step can be performed notably by centrifugation. However, due to the formation of a thicker dairy product (solid phase) during this step, clogging issues of the separating device can occur after only few hours of operation of the production line and can impair the capacity of production.

In view of the large consumers enthusiasm for this type of product, there is also an important expectation to have a good product with a good texture, a good taste, a good stability in the time (for example a weak post-acidification) and/or a sugar reduction.

There is thus a need for improved methods for manufacturing strained fermented dairy products.

The present invention relates thus to a method for manufacturing a strained fermented dairy product comprising the following successive steps:.

In the context of the present invention, "dairy product" designates more particularly a dairy product ready for human consumption made from milk of animal or vegetal origin.

The dairy product based on milk of animal origin can be made from milk and milk components having a cow, goat, sheep, buffalo, donkey or camel origin, preferably a cow origin.

The dairy product based on milk of vegetal origin can be made from grain milk such as barley milk, oat milk, rice milk or spelt milk; legumes-based milk such as lupin milk, pea milk, peanut milk or soy milk; nut milk such as almond milk, cashew milk, hazelnut milk or walnut milk; or seed milk such as hemps milk, quinoa milk, sesame seed milk, sunflower seed milk or coconut milk. It contains thus vegetal proteins. Preferably, the dairy product based on milk of vegetal origin will be made from soy milk, oat milk, rice milk or almond milk.

According to a preferred embodiment, the dairy product is made from milk and milk components of animal origin, and in particular of cow origin.

Food additives can also be present in the dairy product, notably chosen among:.

If need be, the skilled person will be able to choose appropriate food additives among all the well-known food additives available on the market. These food additives can be added at different stages of the method of manufacturing of the strained fermented dairy product.

The dairy product produced by the method according to the present invention is a strained fermented dairy product.

In the context of the present invention, "strained fermented dairy product" designates more particularly a strained fermented dairy product ready for human consumption, such as a strained fermented milk such as, skyr, greek or a strained yoghurt "also called concentrated yoghurt, Greek-style yoghurt or labneh.

The terms "fermented milk" and "yoghurt" are given their usual meanings in the field of the dairy industry, that is, products intended for human consumption and originating from acidifying lactic fermentation of a milk substrate, having an animal or vegetal origin, preferably an animal origin.

The expression "fermented milk" is thus reserved in the present application for a dairy product prepared with a milk substrate which has undergone treatment at least equivalent to pasteurisation, seeded with microorganisms belonging to the characteristic species or species of each product.

The term "yoghurt" is reserved for fermented milk obtained, according to local and constant usage, by the development of specific thermophilic lactic bacteria known as Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus, which must be in the living state in the finished product, at a minimum rate. In certain countries, regulations require the addition of other lactic acid bacteria to the production of yoghurt, and especially the additional use of strains of Bifidobacterium and/or Lactobacillus acidophilus and/or Lactobacillus casei. These additional lactic acid bacteria strains are intended to impart various properties to the finished product, such as that of favouring equilibrium of intestinal flora or modulating the immune system.

In practice, the expression "fermented milk" is therefore generally used to designate fermented milks other than yoghurts.

The term "strained" dairy product refers to a dairy product obtained by a separation step in which a liquid whey is separated from a solid phase (the strained dairy product), such as in step (c) of the method according to the invention.

The strained fermented dairy product obtained by the method according to the invention can have a total protein content comprised between <NUM> and <NUM>%, notably between <NUM> and <NUM>%, such as between <NUM> and <NUM>%.

The "total protein content" of a dairy product corresponds to the weight of the proteins present in the dairy product relatively to the total weight of the dairy product. The total protein content is expressed as a weight percentage.

The total protein content can be measured by Kjeldahl analysis (NF EN ISO <NUM>-<NUM>) as the reference method for the determination of the total protein content of dairy products based on measurement of total nitrogen content. The method is described in both AOAC Method <NUM> (<NUM>) and international Dairy Federation Standard (IDF) 20B:<NUM>.

The strained fermented dairy product obtained by the method according to the invention can have a fat content comprised between <NUM> and <NUM>%, notably between <NUM> and <NUM>%, such as between <NUM> and <NUM>%.

The "fat content" of the dairy product corresponds to the weight of the fat components present in the dairy product relatively to the total weight of the dairy product. The fat content is expressed as a weight percentage.

The fat content can be measured by the Weibull-Berntrop gravimetric method described in the standard NF ISO <NUM>-<NUM>.

The strained fermented dairy product used in the method according to the present invention is a high textured dairy product, i.e. a thick dairy product having a viscosity comprised between <NUM> and <NUM> mPa. s, notably between <NUM> and <NUM> mPa. s, advantageously between <NUM> and <NUM> mPa.

The viscosity is measured at <NUM> (i. e <NUM> after the production of the product) by a viscometer, more particularly of Rheomat type, equipped with a measuring bob / measuring tube system of type <NUM> / <NUM> with a shear rate of <NUM>-<NUM> during <NUM> at <NUM>. The viscometer can be for example a Rheomat RM200. The measuring bob / measuring tube system of <NUM>-<NUM> type is a system in which the measuring bob is of type <NUM> and has a diameter of <NUM> and the measuring tube is of type <NUM> and has a diameter of <NUM>.

The viscosity of the dairy product is the viscosity as measured after <NUM> cold storage at <NUM> to <NUM> after the end of step (c). Indeed, this viscosity can change during the shelf life of the product. In particular, the viscosity of a fermented dairy product increases during its shelf life.

The dairy product used as a starting material to prepare the strained fermented dairy product according to the invention is a non-fermented dairy product, also called dairy mix or dairy starting material, containing milk and milk components of animal or vegetal origin, and optionally other food additives such as those indicated previously. The dairy product is thus obtained by the mixing of its various ingredients.

The milk and milk components of animal original can be whole milk and/or wholly or partly skimmed milk, which can be used in a powder, concentrated or retentate form which can be reconstituted by addition of water. Other milk components can be added such as cream, casein, caseinate (for ex. calcium or sodium caseinate), whey proteins notably in the form of a concentrate (WPC), milk proteins notably in the form of a concentrate (MPC), milk protein hydrolysates and mixtures thereof.

The milk and milk components of animal origin can have a cow, goat, sheep, buffalo, donkey or camel origin, preferably a cow origin.

The milk and milk components of vegetal origin can be obtained from grain milk such as barley milk, oat milk, rice milk or spelt milk; legumes-based milk such as lupin milk, pea milk, peanut milk or soy milk; nut milk such as almond milk, cashew milk, hazelnut milk or walnut milk; or seed milk such as hemps milk, quinoa milk, sesame seed milk, sunflower seed milk or coconut milk. It contains thus vegetal proteins. Preferably, the dairy product based on milk of vegetal origin will be made from soy milk, oat milk, rice milk or almond milk.

The dairy product provided in step(a) can have a total protein content comprised between <NUM> and <NUM>%, notably between <NUM> and <NUM>%, such as between <NUM> and <NUM>%.

The dairy product provided in step(a) can have a fat content between <NUM> and <NUM>%, preferably between <NUM> and <NUM>%, notably between <NUM> and <NUM>%, such as between <NUM> and <NUM>%.

According to an embodiment, the dairy product provided in step a) is a heat-treated dairy product.

The heat-treatment of the dairy product is also called pasteurisation. It aims to kill microorganisms, including pathogenic microorganisms, in the dairy product in order to preserve the quality and the organoleptic properties of the final product and to prevent the consumer to be infected by pathogenic microorganisms present in the dairy product and develop diseases.

The heat-treatment is commonly performed at a temperature (heat-treatment temperature) comprised between <NUM> and <NUM>, preferably during <NUM> seconds to <NUM> minutes.

The heat-treatment can also be performed in several steps, notably two steps, where the dairy product is heated at distinct temperatures in each step. For example, the heat-treatment can be performed according to the two following successive steps:.

Advantageously, a homogenisation step is performed between the <NUM> heating steps, notably at a pressure comprised between <NUM> and <NUM> bars (<NUM>-<NUM><NUM> Pa), notably between <NUM> and <NUM> bars (<NUM>-<NUM><NUM> Pa).

Lactase and a culture of bacteria are added to the dairy product, in particular to a dairy product which has been heat-treated. The dairy product is fermented at a temperature (fermentation temperature) between <NUM> and <NUM>, notably between <NUM> and <NUM>, in particular for <NUM> to <NUM> hours, preferably for <NUM> to <NUM> hours.

The lactase and the culture of bacteria cannot be added to the dairy product at a too high temperature and are generally added at the fermentation temperature. Consequently, when the dairy product has been heat-treated, it is necessary to cool the heat-treated dairy product obtained at the end of the heat-treatment step to the fermentation temperature before inoculating the lactase and the culture of bacteria and performing the fermentation step.

The fermentation step is commonly a lactic fermentation which involves techniques well-known to the skilled person.

When reference is made to a "lactic fermentation", this means an acidifying lactic fermentation which results in milk coagulation and acidification following the production of lactic acid which may be accompanied by the production of other acids, carbon dioxide and various substances such as exopolysaccharides (EPS) or aromatic substances, for example diacetyl and acetaldehyde.

Various bacteria can be used for performing the fermentation of the dairy product and in particular lactic acid bacteria such as:.

Preferred lactic acid bacteria to be used in the present invention are selected from Lactobacillus bulgaricus, Streptococcus thermophilus, and combinations thereof.

More preferred lactic acid bacteria to be used in the present invention are selected from:.

In the framework of the present invention, the culture of bacteria comprises:.

By "thermophilic lactic acid bacteria" is meant, in the present invention, lactic acid bacteria that grow best at a temperature above <NUM>, notably between <NUM> and <NUM>. The thermophilic lactic acid bacteria is selected in the group consisting of Streptococcus sp. , Lactobacillus sp. , Bifidobacterium sp. and combinations thereof, such as defined previously, and notably Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Bifidobacterium animalis subsp. lactis, or a combination thereof.

By "mesophilic lactic acid bacteria" is meant, in the present invention, lactic acid bacteria that grow best at a temperature between <NUM> and <NUM>. The mesophilic lactic acid bacteria can be in particular Lactococcus sp. such as defined previously, and even more particularly Lactococcus lactis subsp.

According to a preferred embodiment, the culture of bacteria used in the present invention comprises: at least one strain of thermophilic lactic acid bacteria selected from Streptococcus thermophilus, Streptococcus lactis, Streptococcus raffinolactis, Streptococcus cremoris, Lactobacillus bulgaricus, and especially Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus acidophilus, Lactobacillus paracasei, Lactobacillus casei, Lactobacillus pentosus, Lactobacillus helveticus, Lactobacillus reuteri, Lactobacillus plantarum, Lactobacillus bifidus, Bifidobacterium bifidum, Bifidobacterium infantis, Bifidobacterium animalis and especially Bifidobacterium animalis subsp. lactis, Bifidobacterium breve, Bifidobacterium longum and a mixture thereof,.

According to a particular embodiment, the culture of bacteria used in the present invention comprises at least one strain of thermophilic lactic acid bacteria strain selected from Streptococcus sp. , Lactobacillus sp. , and a mixture thereof. Such cultures are available on the market. Examples include culture YoMix® <NUM> marketed by Dupont.

According to another embodiment, the culture of bacteria comprises at least one strain of Bifidobacterium sp. The Bifidobacterium sp. can be Bifidobacterium bifidum, Bifidobacterium infantis, Bifidobacterium animalis and especially Bifidobacterium animalis subsp. lactis, Bifidobacterium breve, Bifidobacterium longum or a combination thereof.

The fermentation step will be stopped, notably by cooling, advantageously when the breaking pH is reached, i.e. a pH comprised between <NUM> and <NUM>, notably between <NUM> and <NUM>.

The lactase used in the present invention can be any kind of lactase such as Maxilact® marketed by DSM, in particular Maxilact® Lgi <NUM> or Ha-lactase™ <NUM> commercialized by CHR Hansen. Lactase or beta-galactosidase (E. <NUM>) is an enzyme, which catalyzes the hydrolysis of lactose (a disaccharide) into its component monosaccharides glucose and galactose. Lactases have been isolated from a large variety of micro-organisms. The lactase may be an intracellular or an extracellular produced lactase.

In the framework of the present invention, the lactase is advantageously added in an amount of <NUM> wt% to <NUM> wt%, in particular <NUM> wt% to <NUM> wt%, preferably <NUM> wt% to <NUM> wt%, based on the total weight of the dairy product.

The lactase enzyme is introduced in the dairy material such that at least <NUM>%, preferably at least <NUM>%, preferably <NUM>% of lactose of the dairy material is degraded to glucose and galactose, preferably at pH above <NUM> preferably at a fermentation temperature.

The lactase and the culture of bacteria are added to the dairy product simultaneously or separately. Advantageously, the lactase is added before or along with the culture of bacteria. Preferably, the lactase is added to the dairy product before the culture of bacteria, notably <NUM> to <NUM> before the culture of bacteria, in particular <NUM> to <NUM> before the culture of bacteria.

Indeed, it has been surprisingly demonstrated that the addition of lactase to the dairy product slightly before the culture of bacteria allows further improving the separation step.

It was also been believed that the addition of lactase to the strained dairy product allows improving the control of the texture and/or the appareance and/or the taste of the product and/or the stability, for example with the reduction of post-acidification in the strained fermented dairy product and/or allows an improved sugar reduction in the strained fermented dairy product and/or enriched liquid whey composition, that can be further valorized.

According to a preferred embodiment, no other enzyme will be added in this step (b) or another step of the method according to the invention. In particular, no chymosin (present in rennet) will be added in this step (b) or another step of the method according to the invention.

After fermentation, the fermented dairy product is subjected to a separating step in order to form a strained fermented dairy product having a higher total protein amount than the one of the starting fermented dairy product.

In this step, a liquid phase (the whey) containing mainly water, lactose and minerals is separated from the fermented dairy product so that the strained fermented dairy product remains.

This step is performed by centrifugation with a centrifugal separator having disks.

This step is advantageously performed at a temperature (separation temperature) comprised between <NUM> and <NUM>, notably between <NUM> and <NUM>. Consequently, it could be necessary to heat or cool (notably heat) the fermented dairy product obtained at the end of the fermentation step (b) to the separation temperature before performing the separation step (c).

Advantageously, most of the proteins contained in the fermented dairy product remains in the final strained fermented dairy product. The protein recovery rate (PRR) is thus advantageously above <NUM> wt%, preferably above <NUM> wt%.

By "protein recovery rate" is meant, in the present invention, the percent ratio between the total protein content (in wt) in the fermented dairy product and the total protein content (in wt) in the strained fermented dairy product (i.e. the ratio of the total protein content (in wt) in the dairy product before and after the separation step (c)). The strained fermented dairy product obtained at the end of this step will have thus advantageously a total protein content comprised between <NUM> and <NUM>%, notably between <NUM> and <NUM>%, such as between <NUM> and <NUM>%. Indeed, the aim of the separation step (c) is to obtain a target total protein content.

In the absence of lactase, a clogging of the separating device might be observed after only few hours of operation of the production line requiring to stop the production line and to clean the separating device.

Actually, the clogging issue referred here is not related to standard nozzles clogging, commonly observed in standard centrifugal separation processes, when small particles collapses one or two nozzles and the outlet flow rates of the device are affected as immediate consequences.

The clogging phenomenon described here can be observed between the separation disks of the centrifugal device (see <FIG>) and also all along the rising channels of the device. An accumulation of proteins present at a very high concentration (around <NUM>% protein analysed) seems to be the most probable source of encountered problem. Therefore, the impact on flow rates modifications observed when a standard nozzles clogging occurs are not observed in this type of clogging. In this case main impacts that can be observed are:.

It can be hypothesized that a small part of proteins not solubilized could "initiate" the clogging by sticking onto the walls of the separating device due to a specific biofilm produced by the specificity of the bacteria strains used in the fermentation step. Then, the more the process is going ahead, the more the proteins accumulate on the disks.

When a clogging issue occurs, the total protein content in the liquid phase or whey increases, whereas the total protein content in the strained fermented dairy product decreases. In addition to the clogging issue, it is then difficult or impossible to reach the target total protein content in the final strained fermented dairy product, no matter the inlet flow applied.

Without wishing to be bound by any theory, the inventors are of the opinion that this disks clogging issue could be due to the production of exopolysaccharides (EPS) by the bacteria which could lead to the obtaining of a gel structure having a lower permeability, an increased water binding, and the formation of a biofilm which can stick to the inner walls of the separating device. It is believed that the lactase addition, at the time of the fermentation step, allows overcoming this clogging issue probably by modifying the metabolism of the bacteria used for the fermentation step impacting then the EPS production (notably in amount and/or in nature).

A smoothing step (e) can also be performed after the separation step (c).

This smoothing step can be carried out by means of a rotor stator mixer such as defined in <CIT>.

This step can be carried out at a temperature (smoothing temperature) of between <NUM> and <NUM>.

Advantageously, the strained fermented dairy product is a refrigerated product, i.e. a product having a storage temperature of between <NUM> and <NUM>, notably between <NUM> and <NUM>.

The method according to the invention can thus comprise after step (c), and notably after step (d) when a smoothing step is performed, an additional step (e) of cooling the strained fermented dairy product to its storage temperature.

It could be envisaged to add to the strained fermented dairy product, after the separation step (c), and notably after step (d) when a smoothing step is performed, and notably after step (e) when a cooling step is performed, additional food additives, such as a cream material and/or a fruit preparation, if necessary.

The cream material can be cream or a mixture of cream and milk. It can have a fat content of from <NUM> to <NUM> wt%, in particular from <NUM> to <NUM> wt%.

The fruit preparation can be selected from fruits, fruit pieces, fruit puree, fruit compote, fruit sauce, fruit coulis, fruit jam, fruit jelly, fruit juice and mixtures thereof, optionally in a concentrated or dried form, optionally present in a matrix.

For example, the fruit(s) of the fruit-based preparation can be selected from strawberry, raspberry, blackberry, blueberry, cherry, apricot, peach, pear, apple, plum, pineapple, mango, banana, papaya, passion fruit, pomelo, orange, lemon, kiwi, coconut, vanilla and mixtures thereof.

The present invention relates also to the use of a lactase for preventing the clogging of the separating device used in the preparation of a strained fermented dairy product.

The strained fermented dairy product can be as defined previously. In particular, the strained fermented dairy product will have a total protein content comprised between <NUM> and <NUM>%, notably between <NUM> and <NUM>%, such as between <NUM> and <NUM>%. The strained fermented dairy product can be more particularly a refrigerated product, i.e. a product having a storage temperature of between <NUM> and <NUM>, notably between <NUM> and <NUM>.

This strained fermented dairy product is prepared from a fermented dairy product by a separation step, using a separating device. The separating device is advantageously a centrifugal separator. The separation step can be performed notably as defined above for step (c). The separation step can be followed by a cooling step of the strained fermented dairy product to its storage temperature.

The fermented dairy product used to prepare the strained fermented dairy product will have advantageously a total protein content comprised between <NUM>. 8and <NUM>%, notably between <NUM> and <NUM>%, such as between <NUM> and <NUM>%. The fermented dairy product can be prepared from a dairy product, notably as defined in step (a) above. The preparation of the fermented dairy product from the dairy product comprises at least a fermentation step using notably the culture of bacteria defined previously. This fermentation step is advantageously preceded by a heat-treatment step. The fermentation step and the heat-treatment step can be performed as defined previously (see steps (a) and (b)).

The lactase can be any kind of lactase such as:.

The lactase and the culture of bacteria can be added simultaneously or separately. Advantageously, the lactase is added before or along with the culture of bacteria. Preferably, the lactase is added before the culture of bacteria, notably <NUM> to <NUM> before the culture of bacteria, in particular <NUM> to <NUM> before the culture of bacteria.

Further details or advantages of the invention might appear in the following non-limitative examples.

A strained fermented dairy composition is prepared with the following dairy mix formulation:.

The dairy mix has a fat content of <NUM>% by weight and a protein content of about <NUM>% by weight.

A strained fermented dairy composition is prepared according to the following procedure:.

The strained fermented dairy composition has a protein content of <NUM>% and a fat content of <NUM>%.

Claim 1:
A method for manufacturing a strained fermented dairy product comprising the following successive steps:
(a) providing a dairy product,
(b) adding a lactase and a culture of bacteria comprising at least one strain of thermophilic lactic acid bacteria, with the provision that that it does not comprise any strain of mesophilic lactic acid bacteria, and fermenting the dairy product to obtain a fermented dairy product, and
(c) separating a liquid whey from the fermented dairy product by centrifugation with a centrifugal separator having disks to obtain a strained fermented dairy product,
wherein the lactase is introduced in the dairy product such that at least <NUM>% of lactose of the dairy product is degraded to glucose and galactose,
wherein the thermophilic lactic acid bacteria is growing best at a temperature above <NUM> and is selected in the group consisting of Streptococcus sp., Lactobacillus sp., Bifidobacterium sp. and combinations thereof,
wherein the mesophilic lactic acid bacteria is growing best at a temperature between <NUM> and <NUM> and is in particular Lactococcus sp..