TECHNICAL FIELD

The invention relates to a milk processing plant for the processing of milk and the preparation of proteinaceous fractions. In particular, the invention relates to a configuration of membranes for use in a milk processing plant for the processing of milk and the preparation of proteinaceous fractions.

BACKGROUND Bovine milk consists of 85 to 88% water and 12 to 15% "solids". The solids fraction of milk comprises fat, minerals, lactose (milk sugar) and protein. The proteins of bovine milk may be separated into two classes based on their physicochemical properties.

Casein proteins are relatively insoluble and exist in milk as a dispersion of casein micelles. Acidification of the milk results in the casein proteins being precipitated. Casein (paracasein) is the predominant phosphoprotein found in cheese. Casein proteins are relatively heat stable.

Whey proteins are a collection of globular proteins isolated from whey, a byproduct of cheese manufacture. Whey proteins have high biological activity, but are relatively heat labile. Denaturing whey protein triggers hydrophobic interactions leading to aggregation with other milk proteins.

The bulk processing of bovine milk for human consumption typically includes a pasteurization step. Pasteurization typically uses temperatures below boiling since at temperatures above the boiling point for milk the milk proteins will irreversibly aggregate or "curdle".

Pasteurization results in the microbial load of the milk being reduced by devitalization of the contaminating microorganisms. Pasteurization also results in the denaturation of at least a portion of the milk proteins, especially the whey proteins.

Where the processing of the milk is solely for the purpose of supplying milk and milk fractions for human consumption as a food, the loss of biological activity of the milk is not a significant concern. However, the inclusion of pasteurisation or other heat treatments as a processing step is incompatible if the objective is to retain the biological activity of the milk proteins.

Methods of processing milk using microfiltration to reduce the bacterial load of the source milk are known. Lindquist (1997) describes a method of producing aseptic consumer milk with a certain fat content by microfiltration. In this method, denaturation of the whey proteins is avoided by separation of the fat and the major fraction of the casein from the whey protein prior to heat treatment of the former.

A continuous flow of milk with a certain fat content passes through a microfilter with a membrane having a pore size of 0.05 to 0.2 μm. In the microfilter, the milk is divided up into two part flows; a permeate flow and a retentate flow. The retentate flow, which contains fat and the major fraction of the casein, then undergoes a high temperature treatment (HTT) before being remixed with the permeate flow which contains the major fraction of the whey proteins.

Methods of processing milk that exclude pasteurization and other heat treatments such as HHT are known. Bounous et al (1994) describes a process for producing an undenatured whey protein concentrate involving microfiltration of skim raw milk to provide bacterial reduction followed by microfiltration to separate the casein and ultrafiltration to give a whey protein concentrate having a serum albumin content of about 10% or more.

Bhaskar et al (1996) describes the use of microfiltration (MF) and ultrafiltration (UF) to separate casein and whey proteins from a skim milk starting material. The MF permeate and retentate and the UF permeate and retentate may be separately processed and recombined in part or in total. This enables the predetermination of the composition and functional properties of the resulting dairy products.

Although the purified components of milk may be of high value it is economically advantageous if the combination of concentration and fractionation steps also permits the production of milk products suitable for human consumption as food or drink.

It is an object of the invention to provide a configuration of membrane assemblies for use in a milk processing plant that processes milk suitable for human consumption without the requirement for heat treatment.

It is an object of the invention to provide a configuration of membrane assemblies for use in a milk processing plant that allows for the production of proteinaceous milk fractions including an improved proportion of native protein.

DISCLOSURE OF INVENTION

It is an object of the invention to provide a configuration of membrane assemblies for use in a milk processing plant that processes milk suitable for human consumption without the requirement for heat treatment.

It is a further object of the invention to provide a configuration of membrane assemblies for use in a milk processing plant that allows for the production of proteinaceous milk fractions including an improved proportion of native protein.

In a first aspect, a milk processing plant is provided that includes:

• a microfiltration membrane assembly having a retentate side and a permeate side;

• a first ultrafiltration membrane assembly having a retentate side and a permeate side; and

• a second ultrafiltration membrane assembly having a retentate side and a permeate side; wherein the membrane assemblies are configured so that the retentate side of the microfiltration membrane assembly is in fluid communication with the retentate side of the first ultrafiltration membrane assembly, and the permeate side of the microfiltration membrane assembly and the permeate side of the first ultrafiltration membrane assembly are both in fluid communication with the retentate side of the second ultrafiltration membrane assembly.

In certain embodiments, the milk processing plant provides the separation of a casein protein fraction and a whey protein fraction of a flow of milk. In other embodiments, the milk processing plant provides the separation of a casein protein fraction and a whey protein fraction of the flow of milk without heat treatment of the flow of milk.

In a second aspect, a method of processing milk is provided that includes the steps of:

• delivering a flow of milk to the retentate side of a microfiltration membrane assembly to provide a retentate;

• delivering the retentate to the retentate side of a first ultrafiltration membrane assembly; and • delivering both the permeate of the microfiltration assembly and the permeate of the first ultrafiltration membrane assembly to the permeate side of a second ultrafiltration assembly.

In certain embodiments, the method provides the separation of a casein protein fraction and a whey protein fraction of the flow of milk. In other embodiments, the method provides the separation of a casein protein fraction and a whey protein fraction of the flow of milk without heat treatment of the flow of milk.

In the description and claims of the specification, the following terms and phrases have the meaning provided: "Diafiltration (DF)" means the process of diluting a concentrate and reapplying the diluted concentrate to a membrane.

"Flow of milk" means a flow of milk including a flow of skim milk.

"Fluid communication" means a fluid may pass from a side of a first membrane assembly to a side of a second membrane assembly without passing through a membrane.

"High temperature treatment (HTT)" means a process of applying a high temperature (130 to 150 ⁰ C) for a short period of time (2 to 6 seconds).

"Membrane" means a permeable (porous) filter used to separate the components of solutions and suspensions based at least partly on their molecular size.

"Membrane assembly" means a membrane, housing and associated means for delivery of fluid (e.g. pipework) to and from the retentate and permeate sides of the membrane.

"Microfiltration (MF)" means the process of delivering a liquid to a membrane with a pore size of 0.1 to 10 μm.

"Nanofiltration (NF)" means the process of delivering a liquid to membranes with a pore size of 10 to 100 A, including the use of membranes that are charged such as negatively charged membranes.

"Permeate" means the liquid that passes through a membrane (may also be referred to as the "filtrate").

"Retentate" means the liquid that does not pass through a membrane (may also be referred to as the "concentrate"). "Reverse osmosis (RO)" means the process of delivering a liquid to a membrane with a pore size of 1 to 10 A.

"Sealed" means fluid communication from the environment is prevented.

"Ultrafiltration (UF)" means the process of delivering a liquid to a membrane with a pore size of 30 to 1,000 A.

An exemplary embodiment of the invention will now be described in detail with reference to the Figures of the accompanying drawing pages.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a block diagram of a milk processing plant including a configuration of membrane assemblies according to the invention (broken line block). Figure 2 is a block diagram of a milk processing plant including a configuration of membrane assemblies according to the invention (broken line block) and excluding the use of a separator.

DETAILED DESCRIPTION

The mechanisms governing mass transport and therefore separation of the proteinaceous components of milk in different membrane processes vary as a function of the membrane type, process conditions and the configuration of the membrane assemblies (Rosenberg (1995)).

The four major membrane processes are referred to in the art as ultrafiltration (UF), reverse osmosis (RO), microfiltration (MF) and nanofiltration (NF), albeit with some inconsistency concerning the application of the terms microfiltration and ultrafiltration. Membrane processes have been employed in the dairy industry for many years. Membrane applications may involve a single pressure-driven membrane process. However, in more advanced approaches, two or more membrane processes are used in a given application.

Bounous (1994) provides a process for producing an undenatured whey protein concentrate employing a configuration of membranes where a first microfiltration, a second microfiltration, and a ultrafiltration are performed in series. The process to produce the whey protein concentrate is represented schematically in Figure 1 of the specification accompanying this application.

Bhaskar et al (1996) provides a number of schematics illustrating various configurations of membrane assemblies. For example, Figure 3 of Bhaskar et al. provides a schematic illustrating a configuration where the retentate and permeate from a first microfiltration membrane assembly are applied separately to a second microfiltration membrane assembly and an ultrafiltration membrane assembly, respectively.

As used herein, a microfiltration membrane is defined as having a pore size of 0.05 to 0.5 μm, more typically 0.07 to 0.2 μm, and an ultrafiltration membrane is defined as having a molecular weight cutoff of less than 100 kDa, more typically less than 3O kDa.

Advantages accrue from the concentration and fractionation of proteinaceous fractions of milk where a microfiltration membrane assembly and a first ultrafiltration membrane assembly (as defined herein) are in a configuration that permits the combined permeates to be delivered to a second ultrafiltration assembly.

This configuration of microfiltration membrane assembly, first ultrafiltration membrane assembly, and second ultrafiltration membrane assembly is most advantageously adopted in a plant for the processing of a flow of milk where the objective is to prepare proteinaceous fractions that are susceptible to denaturation by heat treatment.

The configuration allows for the reduction of the microbial load and fractionation of the source milk whilst avoiding significant denaturation. Reduction in the microbial load is achieved by separation of the microbial contaminants.

Referring to Figure 1, whole milk is delivered from a source (1) to a separator (2). The whole milk is separated by the separator (2) into a fat fraction delivered to a receiver (3) and a skim milk fraction delivered by a pump (4) as a flow (A) to a microfiltration assembly (5).

The microfiltration assembly (5) comprises ceramic membranes of either 0.1 or 0.2 μm porosity. In a process for the preparation of micellar casein the first microfiltration assembly (5) provides a volume concentration factor of at least 3.0. Diafiltration of the retentate and delivery (A') to the retentate side of the first ultrafiltration assembly (6) reduces the lactose content to produce a retentate (A") of about 18% solids with approximately 20% of the original skim milk feed volume added as water in diafiltration. The retentate may then be evaporated and spray dried by known processes (7, 8, 9 and 10) to provide a powder anticipated to be 3.5% water, 1.9% fat, 86.0% protein, 2.1% lactose and 6.5% minerals.

In a process for the production of whey protein concentrate, the permeates of the microfiltration assembly (5) and first ultrafiltration assembly (6) are combined to produce a composite whey permeate (C) with a predicted composition of 94 % water, 0 % fat, 0.86 % protein, 4.3 % lactose and 0.5 % minerals. The protein content is expected to be 0.015 % casein protein, 0.472 % whey protein and 0.373 % NPN.

The composite whey permeate (C) is applied to the second ultrafiltration assembly (11) with diafiltration to produce a retentate (C). Water is added at approximately 50% of the permeate flow (C). When dried by known processes (12, 13, 14, 15) the retentate (C) is anticipated to be 4 % water, 0.4 % fat, 2.5 % casein protein, 82.6 % whey protein, 5.2 % NPN, 4.4 % lactose and 0.9 % ash.

Referring to Figure 2, a configuration for a milk processing plant that excludes the separator (2) and associated receiver (3) is presented. The configuration of the micro-filtration assembly (5), first ultrafiltration assembly (6) and the second ultrafiltration assembly (11) permits the preparation of proteinaceous fractions from whole milk without the requirement for the preliminary step of preparing skim milk.

In both the configurations of the milk processing plants presented schematically in Figures 1 and 2 the fluid communication is sealed to prevent contamination of the flow of fluid. The fluid communication between the micro-filtration assembly (5), first ultrafiltration assembly (6) and the second ultrafiltration assembly (11) excludes intermediate ballast tanks, pumps, clarifiers and A-tanks thereby reducing the capital costs of establishing the milk processing plants. Although the invention has been described by way of exemplary embodiments it should be appreciated that variations and modifications may be made with out departing from the scope of the invention. Furthermore, where known equivalents exist to specific features, such equivalents are incorporated as if specifically referred to in this specification.

REFERENCES

Bhaskar et al (1996) Physical Separation of Casein and Whey Proteins, International Patent Application no. PCT/NZ95/00086 (Publication no. WO 96/08155)

Bounous et al (1994) Process for Producing an Undenatured Whey Protein Concentrate, International Patent Application no. PCT/CA93/00518 (Publication no. WO 94/13148)

Lindquist (1997) A Method of Producing Aseptic Consumer Milk, International Application no. PCT/SE97/01141 (Publication no. WO 97/49295)

Rosenberg (1995) Current and Future Applications for Membrane Processes in the Dairy Industry, Trends in Food Science, 6, 12-19.