FIELD OF THE INVENTION

The present invention relates to milk powder.

In particular, the present invention is concerned with milk powder comprising a protein complex which contributes to the improvement of creaminess, mouthfeel and texture, in particular of products based on lower and no fat formulation. A process for preparing such milk powder and the products obtained from the milk powder are also part of the present invention.

BACKGROUND OF THE INVENTION

Powder milk or dried milk is a manufactured dairy product made by evaporating milk to dryness. It involves the gentle removal of water at the lowest possible cost under stringent hygiene conditions while retaining all the desirable natural properties of the milk, such as colour, flavour, solubility and nutritional value. Whole (full) milk contains, typically, about 87% water and skim milk contains about 91 % water. During milk powder manufacture, the water is removed by boiling the milk under reduced pressure at low temperature, a process known as evaporation. The resulting concentrated milk is then sprayed in a fine mist into hot air to remove further moisture and to obtain a powder. Alternatively, removal of the water can be achieved by freeze drying or roller drying of the concentrated milk.

Powdered milk can be made by spray drying non-fat (skimmed milk), whole milk or buttermilk. Pasteurized milk is first concentrated in an evaporator to approximatively 50% milk solids. The resulting concentrated milk is then sprayed into a heated chamber where the water almost instantly evaporates, leaving fine particles of powdered milk.

EP 1 127494 relates to a process for the preparation of fat-containing milk powder.

EP 0333288 relates to spray dried milk powder product and processes for its preparation. It was found that a spray dried whole-milk powder with a coarser fat dispersion can be prepared by causing the spraying to be effected in such conditions that a considerable portion of the fat in the concentrated milk product to be dried is in the solid state.

Spray-draying of a milk composition is also described in, for instance, US 5,350,590.

Alternatively, the powder milk can be dried on roller dryer. Roller drying is a well-known technology and is described for example in "Food Processing Technology: Principles and practice" from P.J. Fellow, 3 ^rd edition (2009), Woodhead Publishing Limited, Part III.A, pages 512-516. Milk is applied as a thin film to the surface of heated drum or drums, and the dried milk solids are then scraped off and the product can be milled to a finished flake or powder form. The powder milk dried on drum (or roller) tends to have a typical cooked and caramel flavours due to the Maillard reaction induced by the heating on the hot roller. Roller-drying of milk is also described in the chapter "Dairy Protein Powders" by P. Schuck, in "Advances in Dairy Ingredients" edited by G.W. Smithers and M.A. Augustin, 1 ^st edition (2013), John Wiley & Sons, Inc. and the Institute of Food Technologists, Chapter 1 , pages 3-29. Issues with roller- drying milk include severe heat damage and protein denaturation, low evaporative capacity, low flexibility to control powder properties.

The technique of roller drying is for example disclosed in US 1 954 602 and US 5 672 373. One disadvantage of this drying method is that the obtained milk powder is not wholly soluble in water.

US 1 574 233 and US 2 1818 003 disclose pre-treatment of the milk before concentration and drying with alkali to reduce the calcium content of the milk, thereby improving the dissolution of milk powder in water. Mouthfeel and creaminess as well as lower or reduced fat are key drivers of consumer liking for dairy based products such as coffee mixes or coffee enhancers as well as high number of other products. Today, there is a challenge to increase or retain mouthfeel and creaminess of milk powders when fat is reduced or removed. Addition of thickeners (hydrocolloids, starches, etc.) has shown no big success due to the unexpected texture change and flavour loss, increased length of ingredient list and also increased formulation cost.

It is known since 1980's that a slight pH adjustment of native fresh milk prior to heat treatment results in a change of aggregation behaviour between casein micelles and whey proteins. However, the pH range that was explored in milk never went lower than 6.3 [F. Guyomarc'h.2006. Formation of heat-induced protein aggregates in milk as a mean to recover the whey protein fraction in cheese manufacture, and potential heat-treating milk at alkaline pH values in order to keep its rennet coagulation properties. A review. Lait, 86, 1 -20].

In more recent work, as described in US 2009/0041920, milk protein concentrate is prepared by insolubilisation of milk proteins. Insolubilisation is achieved by aggregation of the whey protein and/or caseil, by adjusting the milk protein concentrate to a pH of from 4.1 to 5.4, or from 4.3 to 5.3, preferably the isoelectric point of the milk protein concentrate. Thereafter, the pH-adjusted milk concentrate may be heat-treated and homogenised. This process result in a cream cheese product.

AU 2014274496 relates to a ready-to-drink (RTD) product made with controlled pH and heat- treatment, comprising partially denatured protein system which contribute to improvement of texture and sensory attributes of such RTD products. SUMMARY OF THE INVENTION

The inventors have surprisingly found that by milk acidification in the area of pH 5.7-6.3 in combination with controlled heat treatment (temperature, pressure and hold time), the whey proteins form complexes with the casein micelles which results in increased colloidal particle size, water binding and overall viscosity. The problem also addressed by the present invention is therefore to maintain the structure and function during the drying step of the milk composition. It was observed that current high pressure spray drying conditions for standard milk powder manufacture resulted in high shear effect that destroyed the controlled aggregation of proteins and thus the functionality during spray drying conditions. It was also observed that during drying on rollers, the casein was affected by the high temperature with potential impact on the controlled aggregation of proteins.

Thus it is an object of the present invention to improve mouthfeel and/or texture and/or thickness and/or creaminess of the milk powder, particularly with lower fat or no fat. It is also an object of the present invention to keep mouthfeel and/or texture and/or thickness and/or creaminess of the milk powder constant while reducing fat content. Furthermore, it is also an object of the present invention to keep mouthfeel and/or texture and/or thickness and/or creaminess of the milk powder while keeping the production process simple and cost effective, meaning avoiding to have a pre-treatment step of the milk before drying.

The present invention relates to a milk powder obtained by a process wherein controlled protein aggregation is performed during a drying step of a milk composition and wherein the milk powder upon reconstitution in an aqueous medium comprises casein-whey proteins/fat aggregates having a mean diameter value Dv50 of at least 1 μηη as measured by laser diffraction. One aspect of the present invention relates to a reconstituted roller dried powder milk at a minimum of 10 wt% total solids exhibits a shear viscosity of at least 6 mPa.s measured at shear rate of 10 sec ^"1 , a shear viscosity of at least 5 mPa.s measured at a shear rate of 100 sec ^"1 and a viscosity ratio between these two conditions of at least 1.2 as determined on flow curves obtained with a rheometer at 20°C

Another aspect of the present invention relates to a process for preparing a milk powder according to any of the preceding claims comprising the steps of:

a) Providing a milk composition comprising milk at TS of at least 15 wt% at a temperature below 15°C;

b) Adjusting pH between 5.7 and 6.4;

c) Drying the milk composition of step b) on a roller dryer for a residence time of between 1 and 30 seconds; and

d) Milling to obtain a milk powder.

BRIEF DESCRIPTION OF THE FIGURES

The present invention is further described hereinafter with reference to some of its embodiments shown in the accompanying drawings in which:

Figure 1 shows the measure of viscosity of reconstituted milk powders (Sample 1 and Sample 2) according to the present invention.

Figure 2 shows the measure of viscosity of reconstituted milk powders (Sample 1 and Sample 2) according to the present invention compared to reference milk powder (Ref 2). DETAILED DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

The expression "aggregates having a mean diameter value Dv50" refers to protein network comprising casein micelles and whey proteins either present in aggregates. At pH below 6.5 the whey proteins show a strong tendency to form covalent aggregates with the casein micelles. Alternatively, the protein aggregate may be in contact with fat droplets.

The term "aggregates" refers to the structure formed by the aggregation of the whey proteins with casein micelles and fat droplets where fat is present. By the term "aggregation" it is meant that the proteins and the fat droplets (where fat is present) are in contact and form together a 3D network. In case where fat is removed, the term aggregation refers to the 3D network formed by the casein micelles and the whey proteins. The expression "casein-whey proteins/fat aggregates" refers to structure formed by the aggregation of the whey proteins and the casein micelles with/without fat droplets.

The expression "milk concentrate" refers to milk concentrated above total natural solids. For example commercial full fat milk has around 12.5 wt% total solids, this milk is typically concentration up to 50 wt% total solids by evaporation. The milk may be full-fat milk, skimmed milk or semi-skimmed milk.

The expression "reconstituted milk powder" is synonymous to the expression "milk powder upon reconstitution in an aqueous medium".

All percentages are by weight unless otherwise stated. The expression "weight %" and "wt%" are synonymous. They refer to quantities expressed in percent on a dry weight basis. In addition, in the context of the invention, the terms "comprising" or "comprises" do not exclude other possible elements. In some particular embodiments, the terms "comprising" or "comprises" also encompass the expression "consisting of", "consists of", consisting essentially of, "consists essentially of". It is noted that the various aspects, features, examples and embodiments described in the present invention may be compatible and/or combined together.

The present invention relates to a powder milk obtained by a process wherein controlled protein aggregation is performed during a drying step of said milk powder and wherein the milk powder upon reconstitution in an aqueous medium comprises casein-whey proteins/fat aggregates having a mean diameter value Dv50 of at least 1 μηη as measured by laser diffraction.

The controlled aggregation between whey proteins and casein micelles will happen at an acidic pH and when the milk composition is heated under specific conditions (time and temperature). Therefore, in one embodiment of the present invention, the controlled aggregation can be initiated before the drying step by adjusting the pH of the milk composition and heating under certain conditions (time and temperature) and will be achieved during the drying step.

In another embodiment, the controlled aggregation can happen entirely during the drying step.

Creaminess and texture of reconstituted milk powder is directly impacted by the aggregation of the casein-whey proteins and fat droplets. Indeed, the inventor have observed that the structure formed by the protein complex (i.e. whey and casein micelles) and the fat droplets might have a direct influence on the texture and the creaminess of the dried milk powder once reconstituted in an aqueous medium. Interestingly, the aggregation between casein micelles and whey proteins is also taking place when fat is removed. Therefore, as previously mentioned, it is an advantage of the present invention to maintain the structure formed by the protein complex and the fat droplets during the drying step when using whole milk or semi- skimmed milk for example. In particular, the solution of the present invention even more advantageous when fat is reduced or removed, for example in case where skimmed milk is used.

The advantage of the present invention is that the aggregation of the whey proteins with the casein micelles and the fat droplets is achieved during the drying step therefore resulting in a milk powder upon reconstitution in an aqueous medium comprising casein-whey proteins/fat aggregates having a mean diameter value of at least 1 μηι. In one embodiment of the present invention the mean diameter value Dv50 is at least 1 μηι. In some specific embodiments, the mean diameter value Dv50 may be at least 2 μηι, or at least 3 μηι, or at least 4 μηι, or at least 5μηι, or at least 6μηι, or at least 7 μηι, or at least 8 μηι, or at least 9 μηι or at least 10μηι. The texture and therefore the mouthfeel of the reconstituted milk powder of the present invention is impacted by the particle size. Therefore, having the mean diameter value Dv50 of at least 1 μηι allows ensuring the improved texture and mouthfeel.

In some embodiments the mean diameter value Dv50 of the present invention may range from 1 μηι to 500 μηι, such as from 1 μηι to 400 μηι, or from 1 μηι to 300 μηι, or from 1 μηι to 200 μηι, or from 1 μηι to 150 μηι or from 1 μηι to 100 μηι. In some other embodiments, the mean diameter value Dv50 may range from 5 μηι to 500 μηι, such as from 5 μηι to 400 μηι, or from 5 μηι to 300 μηι, or from 5 μηι to 200 μηι, or from 5μηι to 150 μηι or from 5μηι to 100 μηι. In some particular embodiments, the mean diameter value Dv50 may range from 10 to 500 μηι, such as from 10μηι to 400 μηι, or from 10 to 300 μηι, or from 10 μηι to 200 μηι, or from 10 μηι to 150 μηι or from 10μηι to 100 μηι.

In another embodiment, the milk powder of the present invention upon reconstitution in an aqueous medium at a minimum of 10 wt% total solids exhibits a shear viscosity of at least 6 mPa.s measured at shear rate of 10 sec ^"1 , a shear viscosity of at least 5 mPa.s measured at a shear rate of 100 sec ^"1 and a viscosity ratio between these two conditions of at least 1 .2 as determined on flow curves obtained with a rheometer at 20°C.

The compositions processed outside the conditions of the invention were not able to fulfil these 3 criteria simultaneously, indicating that the structure formed by the protein aggregates had a direct influence on the flow behaviour of the system, and possibly on its textural properties.

In a particular embodiment, the powder milk of the present invention the drying step is done by roller drying.

In one embodiment, the milk powder according to the present invention comprises semi- skimmed milk, skimmed milk and/or whole milk powder.

The present invention relates also to a process for preparing a milk powder according to any of the preceding claims comprising the steps of:

a) Providing a milk composition comprising milk at TS of at least 15 wt% at a temperature below 15°C;

b) Adjusting pH between 5.7 and 6.4;

c) Drying the milk composition of step b) on a roller dryer for a residence time of between 1 and 30 seconds; and

d) Milling to obtain a milk powder.

The inventors have surprisingly found that texture and mouthfeel of reconstituted milk powder obtained by the claimed process is enhanced as result of optimized process of preparation including controlled use of heat and acidic conditions.

In one particular embodiment, the milk composition provided in step a) of the process of the present invention comprises milk at TS of at least 15 wt%, or at least 17.5 wt%, or at least 20 wt%, or at least 22.5 wt% or at least 25 wt%. In another embodiment, the milk composition provided in step a) comprises milk at TS between 15 wt% and 35 wt%, or at TS between 15 wt% and 30 wt% or at TS at between 15 wt% and 25 wt%.

In one embodiment, the temperature of the milk composition provided in step a) is below 15°C, preferably below 12.5°C, more preferably below 12°C. In another embodiment, the milk composition provided in step a) has a temperature of 15°C, preferably a temperature of 12.5°C, most preferably a temperature of 10°C. In another embodiment the temperature of the milk composition is between 10 °C and 15°C, preferably between 10°C and 12.5°C.

The acidic pH is thought to favor the aggregation of casein-whey proteins. These protein aggregates form a network that is suspected of binding water and entrapping fat globules (in case of presence of fat) and increase mix viscosity to create a uniquely smooth, creamy texture that mimics the sensory experience (mouthfeel and creaminess) of full fat products and even on products where fat was reduced or removed. The pH of the milk composition of step a) is then adjusted between 5.7 and 6.4. In one embodiment of the present invention, the pH is adjusted between 5.8 and 6.4, or between 5.9 and 6.4, or between 6.0 and 6.4, or between 6.1 and 6.4. In yet another embodiment, the pH may be adjusted at 6.4, or at 6.3, or at 6.2 or at 6.1 , or at 6.0, or at 5.9 or at 5.8.

The pH can be adjusted with acidic solution, with a preference for acidic solution which do not impact the taste of the powder milk or do not introduce undesired off-taste. For example, the pH can be adjusted using acetic acid solution.

The residence time of the milk film on the roller during the drying step can be adapted according to different interrelated parameters, such as the TS of the milk composition before drying, the targeted final water content of the milk powder and the size or type of roller used. For example, for a given TS and a given diameter of the roller, the residence time can be increased but the temperature used for drying has to be decreased in order to avoid burning of the product.

In one embodiment of the present invention, the milk composition of step b) is dried on a roller dryer for a residence time of between 1 and 30 seconds, or for a residence time between 1 and 25 seconds, or for a residence time between 1 and 20 seconds, or for a residence time between 1 and 15 seconds, or for a residence time between 1 and 10 seconds, or for a residence time between 1 and 5 seconds or for a residence time between 1 and 3 seconds. In yet another embodiment, the milk composition of step b) is dried on a roller dryer for a residence time between 2 and 10 seconds, or for a residence time between 2 and 5 seconds, or for a residence time between 2 and 3 seconds. In a particular embodiment, the milk composition of step b) is dried on a roller dryer for a residence time of 2.3 seconds.

In one embodiment of the present invention, the milk powder is obtained by milling the dry film. In a particular embodiment, the dry film is mechanically broken and then sieved onto a 2 mm sieve. In one particular embodiment, the process for preparing the milk powder according to the present invention comprises the steps of:

a) Providing a milk composition comprising milk at TS between 15 wt% and 35 wt% at a temperature between 10 °C and 15°C;

b) Adjusting the pH between 6.0 and 6.3;

c) Drying the milk composition of step b) on a roller dryer for a residence time of between 2 and 10 seconds; and

d) Milling to obtain a milk powder. In yet another particular embodiment, the process for preparing the milk powder of the present invention comprises the steps of:

a) Providing a milk composition comprising milk at TS of at least 15 wt% at a temperature between 10 °C and 15°C;

b) Adjusting the pH between 5.7 and 6.4 ;

c) Drying the milk composition of step b) on a roller dryer for a residence time between 2 and 2.5 seconds; and

d) Milling to obtain a milk powder.

In one embodiment of the present invention, the process for preparing the milk powder comprises in-between steps b) and c) the step of heat treating the milk composition of step a) at temperatures between 80 C° and 150°C for 3 to 300 seconds.

This heating step is performed on the milk composition with a pH that has been adjusted in step a) and allows initiation of the casein-whey proteins/fat aggregation. Thereafter, the milk composition is applied as thin film on the roller dryer where the aggregation can continue. As the residence time on the roller drier is limited, as for example too long residence time would result in burning the milk film or too short residence time would not allow to have a satisfactory drying of the milk composition, adding this intermediate heating step has the advantage to promote further the aggregation of casein-whey proteins/fat and therefore to improve the texture and the mouthfeel of the reconstituted milk powder.

In another embodiment, the milk composition of step a) is heat treated at temperatures between 90°C and 150°C, or between 95° C and 150°C. In another embodiment, the milk composition of step a) is heat treated at temperatures between 80°C and 120°C, or between 80°C and 100°C, or between 80°C and 95°C. In a particular embodiment, the milk composition of step a) is heat treated at temperature of 85°C, or of 90°C, or of 95° or of 100°C. In one embodiment of the present invention, the milk composition of step a) is heat treated for 10 to 300 seconds, or for 50 to 300seconds, or for 100 to 300 seconds, or for 200 to 300 seconds. In yet another embodiment of the present invention, the milk composition of step a) is heat treated at temperatures between 85°C and 100°C for 200 seconds to 300 seconds. In a particular embodiment, the milk composition of step a) is heat treated at temperature of 95°C for 300 seconds. In another embodiment of the present invention, the milk composition of step a) which has been heat treated to initiate the aggregation by heating at temperatures between 80 °C and 150°C for 3 to 300 seconds can be further heat treated at UHT conditions before being applied on the roller for drying. In one embodiment of the present invention, the milk powder is used to produce dairy beverages, ready-to-drink beverages, infant formula, growing-up milk, coffee mixes, creamers, cocoa-malt beverages or confectionery products.

The invention will be now described in further details in the following non-limiting examples.

Example 1 Preparation of the samples

The milk compositions used to obtain the milk powders of the present invention were prepared as followed.

Skimmed milk (MSK) samples were prepared by reconstituting low heat skimmed milk powder at a TS of 25 wt% in water at a temperature of 25°C and stirred over-night at 4°C.

Full fat milk or whole milk (FF) were prepared by mixing anhydrous milk fat heated at a temperature of 40°C for a few hours with skimmed milk powder. The mixture was homogenised using pre-hear Utrathurax and then submitted to high pressure homogenisation at 200/50 bars, at a temperature of -55°C.

Reference 1 sample is MSK powder reconstituted as described above (no drying on the roller dryer). Reference 2 sample is MKS powder reconstituted as described above and dried on a roller dryer for a residence time of 2.3 seconds. Sample 1 was produced by reconstituting low heat skimmed milk powder at a TS of 25 wt% and adjusting the pH to 6.1 using 10 wt% acetic acid. The composition was thereafter heat treated at 84°C for 60 seconds (pasteurization). The milk composition was then diluted with water up to a TS of 15.13 wt% and then dried on a roller drier for a residence time of 2.3 seconds and milled through a sieve of 2mm.

Sample 2 was produced by reconstituting low heat skimmed milk powder at a TS of 25 wt%. The pH was adjusted to 6.1 with 10 wt% acetic acid and the milk composition was heated at 95°C for 300 seconds. Thereafter, the composition was diluted with water up to a TS of 21 .7 wt% and then dried on a roller dryerfor a residence time of 2.3 seconds and then milled through a sieve of 2mm.

Example 2 Measure of Particle Size Distribution The milk powders of the present invention were compared and were characterized by laser diffraction in order to determine particle size distribution (PSD).

Results are shown in Table 1 below wherein the PSD measured by laser diffraction represents a mean value Dv50 (μηι). The size particles, expressed in micrometres (μηι) at 50% of the cumulative distribution was measured using Malvern Mastersizer 2000™ (laser diffraction unit). Ultra-pure and gas free water was prepared using Honeywell™ water pressure reducer (maximum deionized water pressure: 1 bar) and ERMA water degasser (to reduce the dissolved air in the deionized water). Powdered samples were reconstituted before measurement. Distilled water was poured into a beaker and heated up at 42°C-44°C with water bath. A volume of 150 ml. of distilled water at 42°C-44°C was measured and transferred into a glass beaker using a volumetric cylinder. An amount of 22.5 g milk powder is added to the 150 mL distilled water at 42°C and mixed with a spoon for 30 seconds.

Dispersion of the reconstituted milk powder sample was achieved in distilled or deionized water and measurement of the PSD by laser diffraction.

Measurement settings used are a refractive index of 1 .46 for fat droplets and 1 .33 for water at absorption of 0.01. All samples were measured at an obscuration rate of 2.0-2.5%.

The measurement results are calculated in the Malvern software based on the Mie theory. Table 1 Dv50 values

It can be seen from the mean values Dv50 in the Table 1 that the milk powder of the present invention maintains the structure formed by the protein complex and the fat droplets during the drying step when using skimmed milk (sample 1 ). Initiating the aggregation process before the drying step is even allowing to increase the particle size (sample 2). Therefore, despite the low fat content of the milk powder according to the present invention, the inventors have observed a positive impact on the texture and therefore an improvement of the mouthfeel. Example 3 Measure of viscosity

A controlled-stress rheometer (MCR 500 or 501 Anton Paar Physica, Germany) was used to obtain shear viscosity values of fluid samples. Experiments were performed with concentric cylinders (Couette - Cylinder/Cup) geometry having a rough surface (Type CC27S, gap: 1 .14mm) to ensure the absence of wall slip.

Powdered samples were reconstituted before measurement. Distilled water was poured into a beaker and heated up at 40°C with water bath. A volume of 150 mL of distilled water at 40°C was measured and transferred into a glass beaker using a volumetric cylinder. An amount of 10 g milk powder is added to the 90 mL distilled water at 40°C. The mixture was kept under magnetic stirring for 2 hours at 40°C. Samples are then stored at room temperature. As soon as sample temperature reaches 25°C, samples were put into the cylinder cup. The Peltier element (Cell type TEZ-150P, Anton Paar) was set at the measurement temperature (25°C). The measurement was started when the sample reached 25°C. A step of pre-shear (see Table 2) was performed prior to each viscosity characterization. The rheological methods and conditions used to measure the viscosity are described in Table 2. Table 2 Rheological methods and conditions used

The results of the measure of viscosity are shown in Figures 1 and 2. It can be seen from the Figure 1 that the Sample 1 (i.e. where the agglomeration is performed on the roller during the drying step) has a higher viscosity than the Sample 2 (i.e. when the agglomeration is initiated before the drying step). On the other hand, the viscosity of the Reference 2 is similar to the viscosity of the Sample 2.

Although the viscosity does not correlate with the PSD, tasting of the different samples (Sample 1 , Sample 2 and Reference 2) resulted in a markedly improved mouthfeel for the Sample 1 as compared to Sample 2, and both Sample 1 and Sample 2 had superior mouthfeel than the Reference 2.