Field of The Invention

The invention relates to an improved method for concentrating fresh milk products and aseptically packaging the concentrates. The improved packaged products are free of stabilizers and keep at grocery shelf temperatures for several months without age gelation. The concentrates can be reconstituted with water to make fresh-tasting milk that has the mouth-feel of fresh milk and is consumer-acceptable as "fresh milk". Specifically, the method comprises concentrating fresh milk by reverse osmosis, sterilizing under UHT conditions, homogenizing and aseptically packaging.

BACKGROUND OF THE INVENTION

Milk products such as whole milk, low fat milk and skim milk are generally preferred by the consumer in their fresh form. However, fresh milk products have drawbacks because the fresh products do not keep for more than a few days and must be kept under virtually constant refrigeration during those few days.

In order to reduce shipping costs, reduce storage costs and to achieve longer storage time, it has been known to concentrate milk by evaporation and to aseptically package the concentrate so that it can be kept fit for human consumption for longer periods of time.

The Ranjith patent, USP 4,921,717 relates to concentrating milk by evaporation and subsequently packaging the concentrate aseptically.

Although it has been known in the art to concentrate milk products using reverse osmosis, the prior art has not dealt with a process comprising UHT processing, aseptic packaging, and long term storage, wherein the packaged product does not require the addition of stabilizer.

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SUMMARY OF THE INVENTION

The present invention relates to a packaged concentrated sterile milk product and to a new process for production of packaged concentrated sterile milk products.

Concentrated sterile milk of the invention is a dairy product which will have a worldwide market. It has proved particularly valued for its long keeping properties without refrigeration and the fact that it will retain its fresh qualities for these long periods. This is especially important in many countries without their own dairy industries, where the product of the invention will be diluted for use in place of fresh milk, or used as is for coffee cream.

The production process for manufacturing and packaging the inventive concentrated sterile milk involves the separation of water from the milk supply by pumping the milk supply stream through reverse osmosis (RO) filters until the solids content is as desired; passing the milk concentrate through a UHT (Ultra High Temperature) sterilization process, and aseptically packaging the concentrated sterile milk into containers sized to fit the market segment as needed. Packaging may be in packages as small as 1 ounce to 1 gallon for home or other use, or in up to 300 gallon bulk packages for export or interplant shipment.

The superior color and flavor of the concentrated sterile milk product of the invention has now been recognized. The product also has the advantage of not using stabilizers or other additives to prevent gelation during long term storage.

There are an increasing number of countries which insist that milk and milk products should be free from stabilizers and there is a general trend towards the avoidance of such materials wherever possible.

This invention provides a process which removes only water from the milk and therefore leaves the balance of all other elements as in the original milk. It is believed that this balance is responsible for natural prevention of gelation during storage.

It has been found that the disadvantages of prior processes can be avoided by the use of the inventive process in which milk is R.O. concentrated.

Accordingly, the present invention provides a process for producing a concentrated sterile milk product comprising the following steps of

(a) concentrating milk or milk product,

(b) sterilizing the concentrate in an appropriate manner, and

(c) aseptically packaging under the sterile conditions.

After opening the aseptic package, water may be added to reconstitute the product, returning it to a normal solids content for use as fresh milk.

PETAI EP PESCRIPTIPl*

The process of the present invention is a process for making aseptically packaged concentrated milk from fresh milk feedstock comprising (a) concentrating the fresh milk feedstock by reverse osmosis; (b) sterilizing the concentrate, and (c) aseptically packaging the concentrate wherein only water is removed from the feedstock, and wherein spontaneous formation of a gel in said concentrate during unrefrigerated storage is avoided without the use of stabilizers or other additives to prevent age gelation.

The process of the present invention may be used for concentrating, sterilizing, and packaging any milk or fluid milk product, hereinafter referred to as "feedstock". The feedstock of the invention may be raw or pasteurized. The feedstock can be other milk

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products such as cream and buttermilk. Whole milk is generally a milk with a milk fat content of at least 3.0%. Skim milk is defined in most states as having a maximum milk fat content of 0.1-0.5%. Low fat milk has a fat content falling between the fat content of whole milk and skim milk. Generally, low fat milk has a fat content in the 1% - 2% range.

In the example of the invention, the feedstock is cow's milk although it is contemplated that the milk of any mammal might be used, for instance goat's milk.

The concentrate may be sterilized by any sterilization method as long as the balance of all elements of a feedstock except water is not adversely disturbed. Preferably the concentrate is sterilized by a UHT continuous flow process wherein the product is passed over one or more heat exchangers or is sterilized by a steam heated process. Heating rates and holding times may be selected as convenient for the equipment in use.

The process can be built to operate as a continuous flow of the feedstock through the process or a batch process with the feedstock being held for a period between steps of the process. In one embodiment, the process may be interrupted after step (a) and the concentrate can be transported to a different site before being subjected to steps (b) and (c) . In this case, it may be convenient to conduct step (a) at the farm or at a processing plant, with steps (b) and (c) being performed at a distance away. The product may then be transported and/or stored for a period of time before being reconstituted for use as fresh milk. Alternately, the concentrate of step (a) can be mixed with similarly processed concentrate.

Preferably the process is conducted in a continuous manner in which case step (a) suitably involves a reduction in volume to half or less than half the volume

of the original feedstock. Most preferably, step (a) involves concentrating feedstock to one third of its original volume, with a solids content of approximately 34% for a whole milk feedstock and 24% for a skim milk feedstock.

The process of the invention offers several advantages including improved energy efficiency in the concentration/sterilization plant as well as in the transportation of the products. In addition, the need for refrigerated storage in stores and at home is eliminated.

In one embodiment of the invention, it is contemplated that flavoring or other suitable additives that enhance taste or mouth feel might be added to the concentrate before it is aseptically packaged. One particularly popular flavor that might be added is chocolate flavor.

The concentrate may be packaged in large containers. It is contemplated that containers with a capacity of up to 300 gallons would be suitable for use in the wholesale market. In a further embodiment, the large packages of concentrate for the wholesale market might be aseptically repackaged into smaller sized containers for the retail market.

The process of the invention is new and surprisingly useful because it has been discovered that the aseptically packaged concentrate of the invention does not spontaneously form a gel at normal storage temperatures for periods of 6 months or more. Normal storage temperatures can be defined as temperatures as low as refrigerator temperatures up to about 80*F. It has been determined that higher storage temperature are permissible. If the storage temperature is no higher than about 75"F, the packaged product will not gel spontaneously and will retain its flavor for at least one year.

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The equipment that was used to sterilize the concentrate included means for homogenizing the milk and therefore the milk was homogenized. However, homogenization can be an optional step. It is contemplated that in an alternate embodiment the feedstock could be homogenized before it is concentrated.

EXPERIMENTAL WORK LEADING TO THE INVENTION As a first step in the research that led to the invention, a non-cellulosic R.O. membrane, identified as Type ZF 99, was obtained from the Damrow Company of Fond du Lac, Wisconsin. The memDrane was maαe DV Patterson Candy International, Ltd.

In the example reported below, 100 gallons of fresh milk was R.O. processed using this membrane. The milk was heated to about 130'F (54*C) before being R.O. processed. However, it is not necessary to heat the milk before it is concentrated. Heating the milk allowed the process to be carried out a little faster.

After the milk was concentrated, it was sterilized under UHT conditions, homogenized and aseptically packaged in four-ounce clear plastic sterile containers. The containers were cylindrical and rigid.

When 100 ml of milk was added to the container, the container was filled up to a level of 10 cm. In order to test the keeping qualities of the stabilizer-free concentrate as compared with concentrate containing stabilizer, four sets of packaged milk were prepared. One (1) ml of an additive was combined with the 100 ml of milk in each package before the package was capped. A first set of packages (set 1) illustrate the invention. The additive of set 1 was one (1) ml of sterile pure water. The packages in the other three sets each contained one (1) ml of a salt solution (a

stabilizer) . In set 2, set 3 and set 4, the salt solutions used were: one (1) ml 10% sodium citrate; one (1) ml 10% disodiu phosphate; and one (1) ml 10% sodium hexametaphosphate respectively. The samples were stored at room temperature (75 ^β F + 5 ^β F) .

Periodically, samples were observed in their undisturbed state and the observations were recorded. Periodically, three samples from each set were warmed in an incubator (30*.5'C ± 0.5*C), opened and an amount of the enzyme rennet was added to each sample. The samples were then allowed to incubate for at least 30 minutes before the samples were observed and were pH tested. The enzyme used was New Zealand rennet with an activity 185RU/ml. Each of the three samples was treated with 0.93, 1.85, and 3.70 RU/ml of sample respectively. As it turned out, the results observed and the pH values were about the same regardless of which of the three concentrations of enzyme was added to the sample.

Making Milk Concentrate Raw milk with a fat content of 3.37%, a total solids content of 12.45%, and a pH of 6.50 was heated to about 13OT and concentrated by reverse osmosis with a non-cellulosic membrane (Type ZF99) obtained from Paterson Candy International Limited, having an operative area of 18.85 sq. ft., using an initial permeate rate of 1100 ml per min at a pressure of 500 psi. The milk was concentrated to total solids content of 25.0%.

Sterilizing and Homogenizing Concentrate

Under UHT Conditions

Concentrate was preheated to 177'F (80.5*C) ; UHT processed at 284*F (120*C) for about 4 seconds and homogenized at a temperature of about 135-136*F (57'C -

58*C) using pressures of 2000 psi (first stage) and 500

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psi (second stage) . Sterilization and homogenization was done using an Alfa Laval Sterilab System.

Aseptic Packaging of Samples Concentrate was packaged at about 126*F (52*C) manually in sterile plastic containers using an aseptic laminar flow hood. The heated milk was added to the 100 ml mark on each of the plastic containers.

In addition to the milk, one (1) al water was added to each package illustrating the invention, Set 1. Similarly one (1) ml of a solution of each of: 10% sodium citrate 10% disodium phosphate; and 10% sodium hexameta-phosphate was added to each package of set 2, set 3 and set 4. Samples of concentrate were observed at room temperature without disturbing the closed container. The results of these observations are set forth in Table 1. Some samples of concentrate were enzyme treated, incubated for at least 30 minutes and then observed and tested. The results are set forth in Table 2.

OBSERVATIONS RELATED TO STABILITY OF UNDISTURBED ROOM TEMPERATURE PACKAGED WHOLE MILK CONCENTRATE OVER TIME

Set 1 - No Stabilizer Added

Storage Time In Weeks Observations

12 no observable change 15 slight cream ring and no sediment 18 no change, a small 1mm layer of white on bottom cream ring, about 3mm sediment on bottom

24 about 2mm sediment on bottom 27 about 2mm sediment on bottom 33 2mm sediment on bottom 39 2mm sediment on bottom 46 4mm sediment on bottom

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Set 2 - Sodium Citrate Added Storage Time in ee s Pbgeryatigng

15 slight cream ring, no sediment

18 one am layers of white on bottom

21 cream ring, 3mm layer of sediment

24 do

27 do

33 do

39 do

46 3mm layer of sediment; signs of gelation on edge of container

Set 3 - Disodium Phosphate Added

Storage Tig?

In WeeftS Observations

15 slight cream ring, no sediment

18 visible separation into layers and 4mm sediment 21 gelled clear whey/liquid, some separation of particles

24 do

27 curd seems a lot softer. Not as much separation between the whey and curd as before.

33 gelled curd and whey seem like they are coming together again

39 gelled curd and whey seem to be softening

46 gelled.

Set 4 - Sodium hexameta phosphate added

Note: The presence of a cream ring or sediment in the concentrate did not have a permanent effect on the concentrate. If a sample only showed signs of a cream ring and/or sediment, it was possible to shake the concentrate in order to eliminate the cream ring and/or sediment. After shaking, the concentrate returned to a stable system.

Set 3 - Disodium phosphate added

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Note: The presence of a cream ring or sediment in the concentrate did not have a permanent effect on the concentrate. If a sample only showed signs of a cream ring and/or sediment, it was possible to shake the concentrate in order to eliminate the cream ring and/or sediment. After shaking, the concentrate returned to a stable system.

Cgnglυsigns Tg Be Drawn rrgg

Data in Tables 1 and 2

The data shows that the aseptically packaged stabilizer-free concentrate of the invention can be kept at usual room storage temperatures (not under refrigeration) for aore than 6 months without showing any signs of age gelation.

When a stabilizer is added to the concentrate, and the stabilizer is sodium citrate or disodium phosphate, the stabilizer does not prevent age gelation and in fact appears to cause age gelation. Age gelation is evident in the concentrate as early as the 2l£i week of storage.

When the stabilizer is sodium hexametaphosphate, the stabilizer does not appear to have any effect one way or the other on age gelation.

The data indicates that the stabilizer-free milk concentrate of the invention will keep on the grocer's shelf or under like conditions for aore than 6 months without showing age gelation. The concentrate of the invention has a stability which makes it possible to make a reconstituted milk product rom the concentrated that is equivalent to fresh milk in gel stability.