A process for preparing milk concentrates by adding a fraction of the fat phase to the milk liquid within one or more effects of an evaporator, rather than to the milk liquid prior to the evaporation step, is described in EP-A-624317. This process uses a liquid container downstream of the evaporator for accommodating fluctuations in the composition of the mixture and for adding further components. Such a downstream container requires low temperatures for minimising microbial growth and increases the risk of microbial contamination. It is therefore either uneconomical from an energy point of view or of insufficient microbial safety, or both. When a greater proportion of fat has to be added, this may cause clogging and fouling problems in the subsequent stages of the evaporator. Furthermore, a complete mixing of the fat fraction and the aqueous phase with optimum particle size distribution is not always possible.

A process has been found which allows the preparation of a food product comprising an aqueous phase and a fat phase, having the following advantages: -the fat phase can be added in such a manner that a well homogenised food product having desired particle size distribution is obtained; -a fat phase containing sensitive components, such as long-chain poly-unsaturated fatty acid derivatives, can be added with minimised degradation of these sensitive components; -the process does not require storage of the emulsion before final drying, which storage usually requires a tank capacity of 20 to 70 m3; this results in energy savings and in optimum microbial safety; -the food product is treated in such a manner that deterioration of heat-sensitive components in the food product, such as whey proteins, poly-unsaturated fatty acids and fat soluble components, is minimised.

Thus, the present invention provides a process for the preparation of a food product as defined in the appending claims.

The process of the invention comprises the addition of a fat phase to an aqueous phase and dehydrating the aqueous phase, as such and/or as part of an emulsion, by means of a series of evaporator effects. The fat phase is added in a line connecting two consecutive evaporator effects, or in a line issuing from the last evaporator effect and the mixture is homogenised immediately downstream of the point of addition by means of a homogeniser or other high-shear device. Preferably, a pump is located immediately before the point of fat addition, in the line conducting the aqueous phase. This mode of fat addition allows the process to be operated in a truly continuous manner. It also obviates the need for a liquid container downstream of the evaporator system to allow for final homogenation and tuning of the product composition; the homogenation and tuning are already achieved in the in-line homogeniser used according to the invention.

The fat phase to be added may be the entire fat phase of the final food product or a major part (at least 35%, preferably at least 50% by weight) of the fat phase comprising sensitive fatty components such as long-chain poly-unsaturated fatty acids (fish oil and the like). Most preferably, essentially the entire fat phase is added in-line, for example after UHT treatment of the aqueous phase. The addition of the fat phase between two evaporator effects or after the evaporator effects rather than before or within one of the effects themselves was found to result in an optimum balance between fat quality (a heat-sensitive fat requiring exposure to heat being minimised), a total microbial safety, a homogeneous distribution of the fat phase in the aqueous phase and a saving in energy consumption required for complete homogenation. The process avoids creaming-up (e. g. after coalescence) of the fat phase after its addition to the aqueous phase, and thus further increases product homogeneity. Preferably no storage container is present before the spray-drying step and after the evaporator, other than an optional flow buffering unit. Such a unit is not used for adding or mixing components as is the case with prior art containers, but rather serves to accommodate minor capacity changes or other fluctuations. The average residence time in such a buffering unit (including the connecting lines) is less than 50 minutes, preferably less than 20 minutes, more preferably less than 10 minutes; for a large-scale installation these preferences correspond to a tank volume of less than about 2000 1 and 1000 1, respectively.

The treatment according to the invention results in an emulsion with sufficiently small fat particles. This avoids clogging of process lines and devices and contributes to a high degree of homogeneity of the product. Preferably the particle size distribution of the fat phase in the aqueous phase has a D (4,3) of less then 0.8 um and more than 0.3, um; most preferably, the D (4,3) is below 0.6, ut. Preferably less than 2%, especially less than 1%, of the fat particles will have a particle size of more than 3 Fm. The product obtained according to the invention is further characterised by a low oxidation state of the fat phase, in particular by a peroxide value of less than 1 meq, especially less than 0.8 meq per kg fat.

The fat phase is preferably added to the aqueous phase when the latter has a water content of between 48 and 92 % by weight, more preferably between 55 and 90% and especially between 60 and 85 % by weight. If the evaporator system comprises more than two effects, the fat may be added between the first and the second evaporator effect or between two later evaporator effects or even after the last evaporator effect.

The fat phase is added to the aqueous phase according to a predetermined ratio between fat phase and aqueous phase, allowing a perfectly matched fat addition which is adapted to possible fluctuations in the composition of the aqueous phase. This is achieved by in- line measurement of the composition of the aqueous phase and the composition of the fat phase, feeding the measured data to a data processor and controlling the fat addition on the basis of the output of the data processor, e. g. by means of a processor-controlled pump. The composition of either phase can be determined by measuring its (volume) flow or mass flow and its density and/or dry substance content. As the density of the fat phase will usually be constant, its measurement can be dispensed with. If necessary a temperature correction can be applied. It will be obvious to the skilled person that the flow, mass flow, density and dry substance content are measured by equipment that actually measures other physical parameters such as refractive index, changes in coriolis tube frequencies and electric field changes.

The matched fat addition by measuring the composition of the two phases and controlling the addition on the basis of these measurements constitutes a separate aspect of the invention.

A system of dosing accurate amounts of fat to an aqueous phase is shown in figure 2.

The aqueous phase can be the concentrated phase issuing from a first effect of an evaporator, which is conducted by means of pump 15. Before the aqueous phase is pumped to the static mixer 17, the flow or mass flow, density or dry solids content and, if necessary, the temperature are measured. The results are used for calculating the total solids flow of the aqueous phase (TSFa) in kg/h, using the formula (1): TSFa = mFlowa * TSa = Flowa * Da * TSa (1) in which TSa = the total solids content of the aqueous phase as can be measured or calculated from the density and the temperature, in wt. %, mFlowa = mass flow of aqueous phase in kg/h, Flowa = flow of aqueous phase in 1/h, Da = density of the aqueous phase in kg/1 The desired amount of fat is calculated from the total solids flow of the aqueous phase and the desired composition of the final product, using formula (2): FatR = [Tf/(Tf+Ta)] * 100 = [TSFf/(TSFf+TSFa)] * 100, or TSFf = TSFa * FatR/ (100-FatR) (2) and TSFf = Flowf * Df (3) in which FatR = desired fat content of the final product in wt. % Tf = total fat content per kg of the final product Ta = Total amount of water-soluble solids per kg of final product TSFa = total solids flow of the aqueous phase TSFf = total solids flow of the fat phase corrected for temperature Dft = density of the fat phase corrected for temperature Flowf = flow of liquid fat in 1/h.

Substituting (2) in (3) gives formula (4) and substituting (1) in (4) gives formula (5) Flowf = [TSFa FatR/ (100-FatR)]/Dft (4) Flowf = [Flowa * Da * TSa * FatR/ (100-FatR)]/Dft, or (5) Flowf = Flowa TSa FatR/ (100-FatR) * Da/Dft (5) This amount of fat Flowf is pumped by pump 16 to the static mixer 17. The amount of

fat actually pumped is checked by measurement of the flow and the temperature, and a programmable logic controller (PLC) will instruct the speed control Sc to adapt the speed of the pump 16, in order to maintain the flow as accurately as possible to the setting by applying methods (e. g. PI D regulation) known in the art.

In the process of the invention, the aqueous phase is prepared by using techniques that are known in the art. Milk, skimmed milk or solutions of caseinates, whey, demineral- ised whey, whey protein concentrates and/or other protein concentrates in water are used as basis for the aqueous phase. Appropriate amounts of water-soluble components such as lactose or other carbohydrates, minerals, trace elements, emulsifiers and/or some vitamins are dissolved in this liquid and homogeneously mixed in tank 1. Whole milk can be selected as a basis ingredient, if butter oil must be an important part of the fat composition in the final product.

A fat phase that is suitable for manufacturing according to the invention is prepared under conditions that prevent deterioration of the fat by using methods that are known in the art. The fat phase may comprise vegetable oils like soybean oil, rapeseed oil, palm kernel oil, coconut oil, sunflower oil, evening primrose oil, maize oil and/or fats from animal origin like butter oil or fish oil and/or structured fats and/or oils derived from microorganisms such as algae. The fat phase may also comprise emulsifiers like soy lecithin and/or fat soluble vitamins and/or antioxidants, added separately or as premix, or other compounds.

The process of the invention can be performed using an equipment as depicted in figure 1. In figure 1, vessel 1 is for storing and supplying the aqueous phase of the food product to be prepared, 2 is a pump for the aqueous phase, 3 is a heat exchanger, for example a steam infusion heater or steam injection heater for pasteurising or sterilising the aqueous phase, 11,21 and 31 are evaporator effects for stepwise dehydrating the aqueous phase, 12,22 and 32 are separators, 14 is a buffer tank, 19 is a homogeniser producing an emulsion which is fed to the next evaporator effect (21), 2 and 15 are pumps for the aqueous phase, 16 is a pump for supplying the fat phase of the food product, and 25 and 35 are pumps for the concentrated emulsion, with 35 pumping the concentrate to the spray-drier (not shown), optionally through a buffer tank and a preheater, but without a storage tank.

Example 1: Manufacturing process for infant formulae An infant formula is prepared from an aqueous phase and a fat phase. Table 1 lists the amounts of ingredients can be present in the aqueous phase of the infant formula.

Table 1: List of ingredients of aqueous phase Ingredient Amount in kg per 1000 1 skimmed milk protein 50-60 demineralised whey powder 50-60 lactose 100-130 calcium carbonate 2.0-4.3 calcium phosphate 0.2-3.5 calcium chloride 0.5-2.3 magnesium chloride 0.5-1.4 sodium chloride 0.2-1.0 other sodium salts 1.0-2.2 potassium hydroxide 0.1-1.3 other potassium salts 0.4-2.5 choline chloride 0.1-0.8 vitamin premixes 0.7-3.0 (B1, B2, B6, B12, folic acid, pantothenic acid, niacin, biotin, ascorbate, taurine) trace element premixes 0.1-0.6 (Fe, Cu, Zn, Mn, Mo, Se, Cr, I) The aqueous phase as produced in vessel 1 may be chilled for storage purposes or be used directly. It is heated in heat exchanger 3. The heating treatment that is applied must be sufficient to kill microorganisms that are present in the aqueous phase. Typical conditions are 70-150°C for 0.2 sec-15 min, preferably 100-140°C for 1 sec-5 min and most preferably 125-135°C for 2-30 seconds. Part of the water is subsequently evaporated from the aqueous phase in 11 until a dry solids content of 12-40% and more preferably 15-30% is obtained. The vapour separator 12 will separate the vapour (steam) from the product.

A fat phase that is suitable for manufacturing the infant formula is prepared under con- ditions that prevent deterioration of the fat by using methods that are known in the art.

Table 2 provides a list of fat ingredients for a typical infant formula. The fat phase can

be stored under appropriate conditions to prevent deterioration (such as creating a nitro- gen blanket above the fat) or be used directly. An appropriate amount of the fat phase is dosed to the aqueous phase that flows from the first evaporator effect 11 and the vapour separator 12, using the system as described above with reference to figure 2.

Step 12 is equipped with a buffer tank 14 in order to prevent homogeniser 19 from running dry.

Table 2: Fat composition of infant formula (fat blend) Ingredient Amount in kg per 1000 kg fat palm oil 200-400 rapeseed oil (low erucic acid) 180-350 sunflower oil (high oleic acid) 150-250 coconut oil 150-250 fish oil 1-50 butter oil 1-10 lecithins 1-100 vitamin premix 0.1-0.5 (vitamins D, E, K, A + stabilisers, e. g. ascorbyl palmitate) For manufacturing a typical infant formula, sufficient amount of aqueous phase and fat phase are mixed together to obtain a final fat content of 20-35 % (w/w, dry substance basis). Mixing occurs by pumping the mixture through a static mixer 17. After mixing the mixture is immediately homogenised by homogeniser or other high-shear device 19, using conditions that are known in the art: if a two-stage homogeniser is used, the temperature will normally be in the range of 50-70°C and the pressure will be 100-250 bar in the first stage and 15-40 bar in the second stage.

The emulsion is further concentrated in one or more evaporator effects (21 and/or 31) in order to obtain a solids content that is suitable for direct spray-drying; this emulsion can directly be pumped to the spray-drier. For some products an additional homo- genising step before the spray-drier may be advantageous. Various prior art spray- drying techniques can be applied.