Serum protein concentrate production process

Abstract

The invention relates to a process for the production of serum protein concentrates in which at least one of the steps for reducing microorganisms involves UV-C irradiation treatment, thereby increasing the content of the heat-sensitive biologically active component and improving the sustainability of the process for the production of serum protein concentrates.

Description

[0001] PROCESS FOR THE PRODUCTION OF SERUM PROTEIN CONCENTRATE

[0002] The present invention relates to a process for the production of serum protein concentrate.

[0003] The best nutrition supplied to an infant is generally considered to be its own mother's milk; i.e. human milk. However, situations may arise wherein the infant cannot be fed human milk. In such cases, bovine milk-based formula milk is generally used to nourish the infant. These formulas contain a mixture of casein and whey proteins to provide an amino acid profile as close as possible to that of human milk.

[0004] Unfortunately, the protein compositions of human milk and bovine milk differ substantially, both quantitatively and qualitatively. A prominent difference is the lower total protein content of human milk: the total protein content (i.e. the total nitrogen content multiplied by 6.25) of human milk is generally around 11 g / L; that of bovine milk around 33-35 g / L.

[0005] Human milk and bovine milk further differ in the type of proteins they contain.

[0006] The total nitrogen containing components in milk can be divided into true protein and non-protein nitrogen (NPN), with caseins and serum proteins (also called whey proteins) as the main classes of proteins. Caseins are the proteins that precipitate at pH 4.6, whereas whey proteins remain soluble at this pH. In human milk, the ratio of whey protein to casein varies from about 90:10 in the first days after birth to about 60:40 in mature human milk, whereas the whey protein to casein ratio is around 20:80 in bovine milk.

[0007] Also the composition of the casein and whey protein fractions differ between human and bovine milk. The most abundant whey proteins in human milk are a-lactalbumin, lactoferrin and immunoglobulins, whereas the whey protein fraction of bovine milk comprises approximately ~50% p-lactoglobulin and ~15% a-lactalbumin. The most abundant casein in human milk is beta-casein, whereas bovine milk comprises about 50% alpha-casein and about 35% beta-casein. Another important difference is the relatively high content of essential amino acids in human milk. These amino acids cannot be synthesized in the human body and need to be introduced into the human body via food.

[0008] Formula milk, including infant formulae and follow-up formulae, is able to supply the complete nutritional requirements of infants in the first months of their life up to the introduction of appropriate complementary feeding. Legal requirements exist which regulate the required ingredients in such formula milks. One of the these requirements being the minimum content of the essential amino acids and several conditionally essential amino acids as aligned with the composition of human milk. See for instance the CODEX Alimentarus or Ell Commission Directive 2016 / 127 / EC dated September 25, 2015.

[0009] In order to ensure the minimum amounts of these (conditionally) essential amino acids, the protein content of conventional dairy-based formula milk is significantly higher than that of human milk.

[0010] For instance, conventional protein sources in formula milk are combinations of a milk powder or milk concentrate and demineralized whey protein concentrate; generally a demineralized cheese whey concentrate. The whey protein concentrate is added to bring the whey:casein ratio closer to that of human milk.

[0011] In order to ensure the required content of essential amino acids, the total protein content of infant formulas is generally in the range 1 .8-3.0 g / 100 kcal. The high end of this range has the drawback that - as shown by several studies - it causes a rapid weight gain during the first year of life, which may affect body composition later in life. As a result, a lot of research is ongoing towards infant formulas with lower total protein content, without compromising on essential amino acid content.

[0012] Examples of ways in which this problem can be solved include the addition of free amino acids, the use of caseinoglycomacropeptide (CMP)-depleted whey, the addition of protein hydrolysates, and / or the use of a-lactalbumin enriched whey.

[0013] CMP is a cleavage product of K-casein, which is formed during cheese production under the influence of the enzyme chymosin. High levels of CMP negatively affect the amino acid pattern of formula milk, especially the amount of essential amino acids. Furthermore, CMP is rich in threonine and its oligopeptide form allows quick absorption of threonine by the body, which may lead to overdosing causing hyperthreoninemia in prematures.

[0014] A suitable source of CMP-depleted whey is ideal whey. Ideal whey is obtained by separating milk in a casein-rich and a serum-rich fraction using microfiltration. The serum-rich fraction is called ideal whey. Not only is ideal whey free of CMP, its protein composition and, thus, the (essential) amino acid composition, can be steered towards high alpha-lactalbumin and beta-casein contents thereby better aligning its overall protein and amino acid composition with that of human breastmilk.

[0015] Ideal whey is preferably added to infant formulae in the form of a powdered concentrate. In the present specification, an ideal whey concentrate is referred to as serum protein concentrate (SPC). The preparation of SPC involves microfiltration of skimmed milk, resulting in a concentrated (micellar) casein retentate and a serum fraction containing most of the whey proteins as the permeate (ideal whey), said permeate fraction being then concentrated by ultrafiltration in order to remove lactose, ash, and water. An SPC powder can then be obtained by spray-drying the concentrate.

[0016] The use of SPC allows for the preparation of a formula milk with a low protein content and a relatively high essential amino acid content. Furthermore, its preparation only has a small number of processing steps that can denature bioactive ingredients such as heat-sensitive vitamins and proteins. Examples of the latter are lactoferrin and immunoglobulins.

[0017] Nevertheless, conventional SPC production still contains heat treatment steps that may cause denaturation of bioactive ingredients. These process steps are microbial reduction steps, conducted in order to guarantee microbiological quality. An example of such a germicidal heat treatment step is thermal pasteurization (at least 72°C for at least 15 seconds). Denaturation of most bioactive proteins starts above 65°C, meaning that the nutritional value of the SPC will be negatively affected by such heat treatment. In addition, such heat treatment requires a significant amount of energy.

[0018] Thermal pasteurization is generally conducted to the skimmed raw milk; before the microfiltration step. Removal of micro-organisms at this early stage is important in order to prevent an increase in the bacterial load during processing and to prevent microorganisms from clogging the microfiltration membrane.

[0019] Another such heat-treatment is conventionally applied just before spray-drying, when the SPC is heated in a pasteurizer under thermal pasteurization conditions, transported via a tower feeding line to the top of the spray-drying tower, and atomized in the spray-dryer. During transport to the top of the spray-drier, the product is not actively cooled and thus stays around 72°C, as cooling would negatively impact the capacity and energy input of the spray-drying process and would negatively affect the size of the spray-dried particles. In practice, this means that the SPC is at a temperature of at least 72°C for a period several minutes.

[0020] Another microbial reduction step often applied to milk, also in the production of SPC, is ceramic microfiltration (CMF). This ceramic microfiltration step involves the use of a microfiltration membrane with a pore size in the range 0.1 -10 pm and is therefore capable of removing bacteria and spores, but not able to separate casein and whey proteins. In contrast to pasteurization, CMF avoids high temperature (>65°C) treatment and thus does not affect heat-sensitive components such as proteins, flavour and viscosity. In addition, CMF is able to remove heat resistant microorganisms that are more resistant to conventional thermal pasteurization conditions.

[0021] However, ceramic microfiltration requires a significant amount of water and energy. Removal of this step, without negatively affecting microbiological quality and nativity of heat-sensitive components, would therefore significantly improve the sustainability of the SPC production process.

[0022] The object of the present invention is the provision of a more sustainable and energy efficient process for producing microbiologically safe SPC. A further object is the provision of a process that minimizes denaturation of heat-sensitive bioactive ingredients in said concentrate.

[0023] It has now been found that these objects can be achieved by applying a treatment with UV-C radiation during at least one of the microbial reduction steps in the production of serum protein concentrates. In a preferred embodiment, at least one thermal pasteurization and / or a CMF step is replaced with a UV-C treatment, thereby increasing the content of heat-sensitive bioactive ingredients and / or improving the sustainability of the SPC production process.

[0024] In addition, it has been found that IIV-C is able to destroy thermoresistant bacteria, such as Streptococcus thermophilus and Microbacterium spp., that are resistant to thermal pasteurization conditions.

[0025] Ultraviolet (UV) irradiation is subdivided by wavelength into UV-A (320-400 nm), UV- B (280-320 nm), UV-C (200-280 nm), and Vacuum-UV (100-200 nm). UV-C has the highest germicidal effect, specifically between 250 and 270 nm, and is capable of destroying bacteria, viruses, protozoa, yeasts, molds and algae. The penetration depth of UV-C depends on the absorbance and scattering of UV light by a liquid.

[0026] The use of UV-C irradiation in microbial reduction or disinfection of transparent liquids is well known. Milk and dairy products, however, are not transparent. M.M. Delorme, Trends in Food Science 102 (2020) 146-154, reviewed the treatment of milk and dairy products with UV-C radiation. Advantages of UV-C treatment of dairy products are an effective deactivation of microorganisms with minimal loss in nutritional and sensory quality and the absence of toxic effects and waste generation. Compared to conventional heat pasteurization, UV-C treatment may require 1000 times less energy. A major disadvantage, however, relates to the fact that milk and dairy products are non-transparent and have a high absorption coefficient at UV-C wavelengths. In other words, the penetration power of the UV-C light is limited, which makes it difficult to ensure that all microorganisms are directly exposed to UV-C light.

[0027] In other words, the UV-C treatment of milk or whey - as disclosed in, e.g., WO 2017 / 027091 , WO 2019 / 057257, WO 2021 / 063462, WO 2019 / 076413, US 2022 / 0305155, C. Schubert et al., Int. Dairy J. 147 (2023) 105785, L. Christen et al., PLOS ONE (8) 2013 e68120, W. Zhang et al., LWT - Food Sci. Techn., 141 (2021 ) 110945, P. Padademas et al., Animals 11 (2021 ) 42, C. Michel et al., Int. Dairy J. 122 (2021 ) 105149, and J. A. Ansari et al., Innovative Food Science and Emerging Technologies 52 (2019) 387-393 - is already a challenge; the successful microbial reduction in more concentrated dairy streams such as whey protein concentrates, is considered to be an even bigger challenge. Despite these expected problems, the inventors have found that IIV-C treatment is able to reduce the bacterial load in more concentrated dairy streams to such an extent that it can replace at least one of the conventionally applied microbial reduction steps in the production of serum protein concentrate.

[0028] The present invention therefore relates to a process for producing a serum protein concentrate, said process comprising the steps of: a) de-creaming raw milk to provide skim milk, b) subjecting said skim milk to at least one microbial reduction step to provide a decontaminated skim milk, c) microfiltration of said decontaminated skim milk to obtain a casein-rich retentate and a serum-rich permeate, d) concentrating the serum-rich permeate by ultrafiltration to obtain a serum protein concentrate as the retentate, e) subjecting said serum protein concentrate to at least one microbial reduction step, and f) spray-drying the serum protein concentrate, wherein at least one of the microbial reduction steps comprises a treatment with UV- C radiation.

[0029] The process of the present invention is able to result in SPC with a plate count at least similar to that obtained with solely thermal pasteurization steps, while at the same time significantly reducing the denaturation of bioactive compounds. It additionally results in SPC from which thermo-resistant bacteria, such as Streptococcus thermophilus and Microbacterium spp., are inactivated; bacteria that cannot be inactivated with thermal pasteurization treatments.

[0030] In one embodiment, IIV-C radiation is used in step e). The advantage of performing IIV-C treatment just before spray-drying is that is allows to ensure the microbial quality of the final product.

[0031] In another embodiment, a treatment with IIV-C radiation is performed in step b), optionally in combination with either a CMF or a thermal pasteurization step. The advantage of performing IIV-C at this early stage of the process is that it ensures a clean process. Step b) may involve a treatment with IIV-C radiation, followed by thermal pasteurization, or vice versa.

[0032] Alternatively, step b) may involve ceramic microfiltration followed by a treatment with IIV-C radiation, or vice versa. The advantage of performing IIV-C treatment after ceramic microfiltration is that the microbial reduction achieved by ceramic microfiltration improves the effectiveness of the IIV-C treatment. The advantage of performing IIV-C treatment before ceramic microfiltration is that the liquid prior to ceramic microfiltration might have a lower dry matter content and thus lower absorbance and scattering and deeper penetration of IIV-C radiation.

[0033] In a preferred embodiment, neither a CMF nor thermal pasteurization treatment is conducted prior to microfiltration step c) and treatment with IIV-C radiation is the sole microbial reduction step before microfiltration step c).

[0034] In a further embodiment, no thermal pasteurization is applied during the entire process. Even more preferred is a process in which the only microbial reduction steps are UV- C treatments, without any thermal pasteurization or CMF steps. This allows the highest retainment of bioactive compounds in the most sustainable way.

[0035] The germicidal properties of UV radiation are mainly due to inactivation of bacteria and viruses through DNA mutations induced through absorption of UV light by DNA molecules at very specific germicidal wavelengths, which are normally between 253.

[0036] 7 nm and 254.1 nm.

[0037] The main commercial UV sources that emit sufficient energy in the germicidal wavelength range are mercury and deuterium lamps. The radiation of mercury lamps is more intense, while deuterium lamps have a broader emission spectrum.

[0038] For non-transparent liquids, UV-treatment requires sufficient turbulence.

[0039] Turbulence can be expressed with the Reynolds number (Re) and is influenced by the diameter of the tube through which the liquid is transported, the flow through the tube, and the viscosity of the liquid. Said viscosity, in turn, depends on the nature of the liquid, its dry matter content, and its temperature.

[0040] The UV-C treatments in the process of the present invention are preferably conducted on liquid streams with a Reynolds number (Re) of at least 700, preferably at least 1 ,000, more preferably at least 1 ,500, even more preferably at least 2,300, more preferably at least 3,000, even more preferably at least 4,000, more preferably at least 6,000, and most preferably at least 10,000.

[0041] In order to prevent protein denaturation, the IIV-C treatment is preferably performed at a temperature below 70°C, more preferably below 60°C.

[0042] On the other hand, in order to lower the viscosity, it is desired to conduct said IIV-C treatment at temperatures above the standard treatment temperature of dairy streams (5°C). Therefore, the IIV-C treatment is preferably performed at a temperature in the range 10-70°C, more preferably 10-60°C, even more preferably 20-60°C, most preferably 30-60°C.

[0043] Oxidation of any compounds can be minimized by using extra light filters to narrow the bandwidth of the light spectrum (as disclosed in WO 2021 / 063462), or by degassing the feed stream before the IIV-C treatment in order to remove oxygen / air.

[0044] In this specification, the term "milk" refers to milk obtained from cattle (e.g. cows, buffalos, sheep, goats, horses, and camels), but also to human milk. The preferred milk for use in the process of the present invention is bovine milk.

[0045] Milk can be de-creamed / skimmed via conventional techniques, such as centrifugal cream separation, resulting in cream and skim milk.

[0046] According to the process of the invention, skim milk is subjected to a microbial reduction step to provide a decontaminated skim milk. Skim milk is considered to have been decontaminated if the total plate count has been reduced to a lower value. Total plate count can be determined by ISO 4833-1 :2013, part 1 (pour plate). The total plate count is preferably reduced to less than 1000 CFU / ml, more preferably less than 100 CFU / ml, and most preferably less than 10 CFU / ml.

[0047] The microbial reduction may involve either thermal pasteurization, preferably combined with a preceding ceramic microfiltration (CMF) step, or a treatment with UV- C radiation, optionally combined with either thermal pasteurization or CMF.

[0048] For thermal pasteurization, various suitable time and temperature combinations can be used. Examples of suitable combinations are: 72-75°C for 15-20 seconds, 63-65°C for 30-40 minutes, and 80-85°C for 1 -5 seconds. Legal pasteurization requires a composition to be held at >72°C for at least 15 seconds for every part of the product, or equivalent as defined in the Pasteurized Milk Ordinance of the FDA.

[0049] Ceramic microfiltration (CMF) is a well-known technique for the removal particles, such as bacteria and spores. Membranes with a pore size the range 0.1-10 pm, preferably 0.5-2 pm, even more preferably 0.5-1 .8 pm, and most preferably around 0.7-1.5 pm, are preferably used. A skim milk with low bacterial content is achieved in the CMF permeate. CMF can be performed at a temperature in the range 45-60°C or 5-20°C. Lower temperatures are preferred from microbiological perspective; higher temperature processing, on the other hand, results in more efficient separation and allows the use of a smaller membrane surface. The temperature is preferably in the range 40-60°C, more preferably 45-55°C.

[0050] UV-C treatment can replace the CMF and / or the thermal pasteurization. The advantage of applying UV-C treatment at this stage of the process is that the absorbance and scattering in milk is rather limited compared to that in the more concentrated streams further down the process, thereby improving the UV-C effectiveness.

[0051] The separation of milk into a casein-rich retentate and a whey protein-rich permeate (step c) can be performed in conventional ways, well-known to the person skilled in the art. For instance, the skim milk, optionally diluted with water in a volume ratio water / milk of 0.5-1.5, can be subjected to crossflow filtration using a microfiltration membrane at a temperature in the range of either 10-20°C or 50-55°C. The temperature is preferably in the range 10-20°C, more preferably 10-15°C. This low temperature enables beta-casein transmission through the membrane.

[0052] All conventional types of microfiltration membranes - spiral wound, ceramic, hollow fibre, etc. - can be used. The membrane can be constructed from various polymer types - such as polysulfone (PS), (modified) polyethersulfone (PES), polyvinylidene difluoride (PVDF), polyacrylonitrile (PAN), cellulose acetate (CA), and polypropylene (PP) - and several ceramic materials - such as aluminum oxide, zinc oxide, and titanium oxide.

[0053] The molecular weight cut-off (MWCO) and pore size of the membrane is preferably in the range 50-1000 kDa and / or 0.01 -1 .0 micrometer, more preferably in the range 100- 800 and / or 0.02-0.5 micrometer, most preferably in the range 100-500 kDa and / or 0.05-0.2 micrometer.

[0054] The microfiltration is preferably operated with a trans-membrane pressure of 0.1-5 bar, more preferably 0.2-3 bar, most preferably 0.2-1 bar.

[0055] The microfiltration may be implemented as a single pass filtration or by using a series of membranes arranged in series. Preferably, the microfiltration is arranged as crossflow filtration.

[0056] The feed flow rate is preferably in the range 15 to 20 m3 / hr.

[0057] The flux over the membranes, i.e. the ratio between product flow and membrane surface, is preferably relatively low, more preferably in the range 2-30, preferably 2-10 l / m2 / hr. This allows only the smallest casein molecules to pass the membrane, thereby obtaining a high whey protein-to-casein ratio.

[0058] The microfiltration is preferably combined with diafiltration, more preferably with a ratio between diafiltration flow and membrane surface in the range 2-30, preferably 2-10 l / m2 / hr.

[0059] The cross flow over the membranes is preferably in the range of 50-300 m3 / hr.

[0060] The serum-rich permeate resulting from the microfiltration step - i.e. the microfiltration permeate - is concentrated with ultrafiltration (UF), optionally preceded by a reverse osmosis step in order to increase the dry matter content. Ultrafiltration results in removal of water, lactose and minerals. The resulting UF retentate is a serum protein concentrate (SPC).

[0061] Ultrafiltration is preferably performed using 1-20 kDa membrane; preferably a 5-10 kDa membrane.

[0062] The ultrafiltration temperature is preferably in the range 10-20°C, preferably 10-15°C, most preferably 10-12°C.

[0063] All conventional types of ultrafiltration membranes - spiral wound, ceramic, hollow fibre, etc. - can be used. The membrane can be constructed from various polymer types - such as polysulfone (PS), (modified) polyethersulfone (PES), polyvinylidene difluoride (PVDF), polyacrylonitrile (PAN), cellulose acetate (CA), and polypropylene (PP) - and several ceramic materials - such as aluminum oxide, zinc oxide, and titanium oxide. Preferred ultrafiltration membranes are spiral-wound membranes. Even more preferred are hydrophilic polyethersulfone (PES) membranes. The trans membrane pressure during ultrafiltration is preferably in the range 0-6.0 bar, more preferably 3.5-5.0 bar, and most preferably 3.5-4.0 bar.

[0064] The ultrafiltration is preferably combined with diafiltration.

[0065] If so desired, the SPC may be further concentrated, demineralized and / or dried, for instance by nanofiltration, ion-exchange, electrodialysis, reverse osmosis, desalination, and / or evaporation.

[0066] According to the process of the invention, the SPC is subjected to a microbial reduction step prior to the subsequent spray-drying step. This step may either involve thermal pasteurization or treatment with IIV-C radiation.

[0067] In order to achieve the required turbulence for the IIV-C treatment, the SPC may have to be diluted with water in order to reduce its dry matter content. The extent of this dilution will depend on, e.g., the viscosity of the SPC at the applied temperature, the tube diameter through which the SPC flows during the IIV-C treatment, and the flow rate through the tube. An appropriate dry matter content is generally in the range 5-15 wt%, preferably 6-12 wt%.

[0068] Furthermore, the temperature of the whey protein phospholipid concentrate during the IIV-C treatment is preferably in the range 10-70°C, preferably 10-60°C, more preferably 20-60°C, most preferably 30-60°C

[0069] Prior to or after such IIV-C treatment, the serum protein concentrate may be preheated to a temperature in the range 40-65°C, preferably 50-65°C, most preferably 55-65°C, which is below the denaturation temperature of most (health promoting) bioactive molecules. Pre-heating should not result in temperatures exceeding 65°C. This pre-heating serves to lower the electric energy input during the subsequent spraydrying step and thus to make the process more energy-efficient. This pre-heating can be performed batch-wise or continuously in any suitable equipment. Batch-wise preheating can be performed in a vessel; continuous pre-heating can be performed using a heat exchanger (e.g a plate heat exchanger). The pre-heating is preferably performed continuously.

[0070] After reaching the desired pre-heating temperature, the pre-heated liquid composition is transported to the top of a spray-drying tower. There is no need for holding the composition at the desired temperature for a certain time period before conducting said transport. Therefore, the entire process can be performed in a continuous manner. If not pre-heated, the serum protein concentrate is preferably held in step e) below 20°C, more preferably below 15°C, and most preferably below 10°C until reaching the top of the spay-drying tower.

[0071] The resulting SPC is spray-dried. Spray-drying is preferably performed using hot air with a temperature in the range 140-300°C, preferably 150-260°C, and most preferably 170-210°C.

[0072] Any type of spray-dryer can be used, such as Single Stage, 2-Stage, Multi Stage and Filtermat® type spray dryers.

[0073] The SPC prepared according to the process of the present invention can be used to prepare formula milk by combining the SPC with at least a lipid source, a carbohydrate source, vitamins, and minerals.

[0074] The lipid source may be any lipid or fat suitable for use in formula milk. Preferred fat sources include milk fat, safflower oil, egg yolk lipid, canola oil, olive oil, coconut oil, palm kernel oil, soybean oil, fish oil, palm oleic, high oleic sunflower oil and high oleic safflower oil, and microbial fermentation oil containing long-chain, polyunsaturated fatty acids. In one embodiment, anhydrous milk fat is used. The lipid source may also be in the form of fractions derived from these oils such as palm olein, medium chain triglycerides, and esters of fatty acids such as arachidonic acid, linoleic acid, palmitic acid, stearic acid, docosahexaeonic acid, linolenic acid, oleic acid, lauric acid, capric acid, caprylic acid, caproic acid, and the like. It may also be added small amounts of oils containing high quantities of preformed arachidonic acid and docosahexaenoic acid such as fish oils or microbial oils. The fat source preferably has a ratio of n-6 to n-3 fatty acids of about 5:1 to about 15:1 ; for example about 8:1 to about 10:1. In a specific aspect, the infant formula comprises an oil mix comprising palmitic acid esterified to triacylglycerols, for example wherein the palmitic acid esterified in the sn- 2 position of triacylglycerol is in the amount of from 20% to 60% by weight of total palmitic acid and palmitic acid esterified in the sn-1 / sn-3 position of triacylglycerol is in the amount of from 40% to 80% by weight of total palmitic acid.

[0075] Examples of vitamins and minerals that are preferably present in formula milk are vitamin A, vitamin B1 , vitamin B2, vitamin B6, vitamin B12, vitamin E, vitamin K, vitamin C, vitamin D, folic acid, inositol, niacin, biotin, pantothenic acid, choline, calcium, phosphorous, iodine, iron, magnesium, copper, zinc, manganese, chloride, potassium, sodium, selenium, chromium, molybdenum, taurine, and L-carnitine. Minerals are usually added in salt form.

[0076] Examples of carbohydrates that are preferably present in formula milk are lactose, non-digestible oligosaccharides such as galacto-oligosaccharides (GOS), fructooligosaccharides (FOS), inulin, xylo-oligosaccharides, and human milk oligosaccharides (HMOs). Suitable HMOs include 2’-FL, 3-FL, 3’-GL, 3’-SL, 6’-SL, LNT, LNnT, and combinations thereof. HMO’s are commercially available or can be isolated from milk in particular from human breast milk.

[0077] If necessary, the nutritional composition may contain emulsifiers and stabilisers such as soy lecithin, citric acid esters of mono- and di-glycerides, and the like. It may also contain other substances which may have a beneficial effect such as lactoferrin, nucleotides, nucleosides, probiotics, and the like.

[0078] Suitable probiotics include Lactobacteria, Bifidobacterium lactis such as Bifidobacterium lactis Bb12, Streptococcus thermophilus, Lactobacillus johnsonii La1, Bifidobacterium longum BL999, Lactobacillus rhamnosus LPR, L rhamnosus GG, Lactobacillus reuteri, Lactobacillus salivarius. Such prebiotics are commercially available.

[0079] Formula milk is usually prepared for bottle-feeding or cup-feeding from powder (mixed with water) or liquid (with or without additional water).

[0080] Formula milk is generally available as a spray-dried powder. Spray-drying involves an additional heating step. In order to preserve as much of the native proteins as possible, it is desired to keep the heating conditions during spray-drying as mild as possible.

[0081] In order to reduce the number of processing steps that may denature any proteins, it is preferred to either dry blend the SPC with the other ingredients of the formula milk or mix liquid SPC with other liquid ingredients.

[0082] The formula milk according to the invention can be in the form of a dry, semi-dry or liquid composition. For example, it can be a powdered composition that is suitable for making a liquid composition after reconstitution with an aqueous solution, preferably with water. In another embodiment, it is a liquid composition, for instance a ready-to-consume drinkable or spoonable composition.

[0083] EXAMPLES

[0084] Comparative Example 1

[0085] A serum protein concentrate was prepared by subjecting legally pasteurized skim milk to microfiltration. The microfiltration permeate was subsequently subjected to ultrafiltration. The ultrafiltration retentate - i.e. the serum protein concentrate (SPC) - had a dry matter content of 26 wt% and a protein content of 60 wt% based on dry matter.

[0086] This SPC was subsequently pasteurized at different temperatures, ranging from 68°C to 76°C, using a continuous flow micro pasteurizer equipped with tubular heat exchangers and holders in order to mimic industrial pasteurization. The holding time in all experiments was 180 seconds, thereby representing an industrial 18 seconds pasteurization followed by 162 seconds of transport to a spray-drying tower.

[0087] Total plate count, also known as aerobic mesophilic count, was determined according to ISO 4833-1 :2013. 1 ml of product was poured in plate count milk agar and plates were incubated for 72 hours aerobically at 30°C. Plates were subsequently counted and the number of colony forming units (CFU) per ml of product was reported for a dilution where the number of observed colonies on the plate was between 10 and 300. For the low thermoresistant plate count, the sample was treated at 63.5°C for 30 minutes prior to plating. This method is equivalent to NEN 6807.

[0088] For the high thermoresistant plate count, the sample was treated at 80°C for 5 minutes prior to plating.

[0089] The total plate count in all experiments remained at the initial low level of 800 cfu / ml. The microbiology in the resulting SPC was therefore independent of the pasteurization temperature and consisted of high and low thermoresistant bacteria and spores.

[0090] As measure of the bioactivity of the proteins, the native IgG content was determined using the bovine IgG ELISA quantitation set as described by R.L. Valk-Weeber, T. Eshuis-de Ruiter, L. Dijkhuizen, and S.S. van Leeuwen, International Dairy Journal, Volume 110, November 2020, 104814.

[0091] The reduction in bioactive, i.e. native, IgG content was strongly temperature dependent and was reduced to 44% of its original value after pasteurization at 76°C. The native lactoferrin concentration was reduced to 10% of its original value.

[0092] The resulting SPC was spray-dried on a small scale pilot dryer.

[0093] Example 2

[0094] Comparative Example 1 was repeated, except that, instead of pasteurization, the SPC was submitted to IIV-C treatment using Lyras® pilot IIV-C equipment with a capacity of 100-800 L / h. In view of the high turbidity of the 26 wt% dry matter SPC suspension, the SPC was first diluted to a dry matter content of 9 wt%.

[0095] Cold (10°C) diluted SPC was pumped through spiral wound transparent tubes (7 mm diameter) with maximum possible flow (417 L / h) and a Reynolds number of 9270. This flow was limited by the pump capacity and the allowed pressure drop of the UV-C equipment.

[0096] The SPC in the tubes was exposed to light using lamps placed at the outside of the spiral. Between the lamps and the tube, filters were placed in order to ensure a small wavelength peak around 254 nm, thereby minimizing chemical side reactions like oxidation reactions.

[0097] The UV-C power used - i.e. the percentage of the maximum power of the equipment - was 80%.

[0098] As a result of this UV-C treatment, the total plate count was reduced from 800 to 10 cfu / ml; and the thermoresistant microorganisms - that could not be inactivated by pasteurisation (LTR and HTR) - were reduced to 10 and 0 cfu / ml, respectively.

[0099] It was further observed that the native IgG and lactoferrin contents were not affected by UV-C treatment. They remained stable at 1 .54 wt% and 0.13 wt%, respectively. Example 3

[0100] Example 2 was repeated, except that the suspension was first diluted to a dry matter content of 12.5 wt% and heated to 30°C before being pumped through the spiral wound transparent tubes and exposed to IIV-C light. Total plate count, thermoresistant microorganism content and the extent of denaturation of the bioactive compounds was similar to that obtained in Example 2.

[0101] Example 4

[0102] Example 2 was repeated, except that the suspension was first diluted to a dry matter content of 14.7 wt% and heated to 52°C before being pumped through the spiral wound transparent tubes and exposed to IIV-C light.

[0103] Different flow rates, in the range 57-448 L / h, were used. With increasing flow rate, not only Reynolds numbers increase, but also residence time and, hence, IIV-C energy input. When correcting for the difference in energy input, it was observed that inactivation of microorganisms (total plate count), including thermoresistant microorganisms, significantly increased at Reynolds numbers of 1500 and above.

Claims

CLAIMS1 . Process for producing a serum protein concentrate, said process comprising the steps of: a) de-creaming raw milk to provide skim milk, b) subjecting said skim milk to at least one microbial reduction step to provide a decontaminated skim milk, c) microfiltration of said decontaminated skim milk to obtain a casein-rich retentate and a serum-rich permeate, d) concentrating the serum-rich permeate by ultrafiltration to obtain a serum protein concentrate as the retentate, e) subjecting said serum protein concentrate to at least one microbial reduction step, and f) spray-drying the serum protein concentrate, wherein at least one of the microbial reduction steps comprises a treatment with UV-C radiation.

2. Process according to claim 1 wherein said treatment with UV-C radiation is conducted on a liquid stream with a Reynolds number (Re) of at least 700, preferably at least 1 ,000, more preferably at least 1 ,500, even more preferably at least 2,300, more preferably at least 3,000, even more preferably at least 4,000, more preferably at least 6,000, and most preferably at least 10,000.

3. Process according to claim 1 or 2 wherein said treatment with UV-C radiation is performed at a temperature in the range 10-70°C, preferably 10-60°C, more preferably 20-60°C, most preferably 30-60°C.

4. Process according to any one of the preceding claims wherein step e) comprises a treatment with UV-C radiation.

5. Process according to claim 4 wherein the serum protein concentrate that is subjected to UV-C radiation has a dry matter content of in the range 5-15 wt%, preferably 6-12 wt%.

6. Process according to any one of claims 4-7 wherein the serum protein concentrate that is subjected to IIV-C radiation has a temperature in the range 10-70°C, preferably 10-60°C, more preferably 20-60°C, most preferably 30-60°C.

7. Process according to any one of claims 4-6 wherein step b) comprises a ceramic microfiltration and / or thermal pasteurization.

8. Process according to any one of claims 4-7 wherein step e) comprises a step of pre-heating the serum protein concentrate to a temperature up to 65°C, followed by IIV-C radiation treatment.

9. Process according to any of claim 4-8 wherein step e) comprises a IIV-C radiation treatment without heat treatment.

10. Process according to any one of claims 1-6 and 8-9 wherein step b) comprises a treatment with IIV-C radiation.11 . Process according to claim 10 wherein step b) comprises a treatment with IIV-C radiation, followed by thermal pasteurization.

12. Process according to claim 10 wherein step b) comprises ceramic microfiltration followed by a treatment with IIV-C radiation.

13. Process according to claim 10 wherein step b) comprises a treatment with IIV-C radiation as the sole microbial reduction step before microfiltration step c).