CA2856249A1 - A milk treatment process - Google Patents

Description

Onai Research Pty. Ltd.
CANADA
Patent Act (R.S.C., 1985, c. P-4) PATENT SPECIFICATION
for the invention entitled:
"A Milk Treatment Process"
The invention is described in the following statement:

A MILK TREATMENT PROCESS
The present invention relates generally to a process for the treatment of milk. In particular, the invention relates to a process for the production of milk with an extended shelf life, and to milk obtained thereby and milk products made from said treated milk.
Milk obtained from cows, sheep goats and other animals has played an important role in the diet of humans since the beginning of recorded history. It serves as a convenient source of proteins, carbohydrates, vitamins and minerals essential for human growth, development and functioning.
The presence of bacteria, moulds and yeasts in milk result in its rapid deterioration, and after removal from the cow by mechanical milking, the milk, usually at 34 C, has to be cooled as rapidly as possible to about 4.4 C or below to maintain quality. At this low temperature, enzyme activity and growth of microorganisms are minimized such that the milk can be transported to the site of further processing without spoilage.
The advent of pasteurization methods has lead to an increase in the keeping qualities of milk. Pasteurization is the process of heating milk to kill the yeasts, moulds and bacteria and to inactivate certain enzymes without substantially altering the flavour of the milk. A number of different heat treatment methods are used to treat the milk so that it is still in an acceptable state for consumption by the time it eventually reaches the consumer.
High temperature-short time (HTST) pasteurization is a process whereby the milk is heated at temperatures of about 62-63 C or 71-74 C for about at least 30-40 seconds or at least 10-15 seconds respectively. The milk is then shock cooled. Milk treated by this process generally has a consumable life of about 10-13 days when refrigerated at about 4 C.
Ultra high temperature (or ultra-heat treatment) (UHT) pasteurization uses higher temperatures to heat the milk for a shorter period, eg about 1-2 seconds. The milk is then packaged and sterilized in sealed packages. UHT pasteurization does generally afford milk with greater keeping qualities (up to 6 months in its unopened sealed packaging), however, once the original packaging is opened, the life of the milk is much the same as that of HTST pasteurized milk. Furthermore, many consumers find that the taste of UHT
pasteurised milk is affected by the UHT treatment.
Other forms of milk which have an extended shelf life include dry (powdered) milk evaporated and condensed milk. Dry milk can be produced by a drum or spray drying method, and evaporated and condensed milk are produced by removing water under vacuum followed by packaging and sterilization in cans. However, when reconstituted, a difference in the flavour of the milk can be detected and these forms are not generally favoured for drinking milk but are used as the milk source in food preparation and manufacture. Thus for many consumers, fresh milk (which as used herein includes pasteurized milk treated by HTST and UHT methods as well as milk obtained directly from the animal) remains the milk form of preference, with, powdered and canned milk often only used by consumers for cooling and when fresh milk is unavailable.
Therefore, there exists a continued need for processes for treating milk in order to extend its shelf life, whether it is to be consumed as "fresh milk" or to be eventually processed into other milk products.
Accordingly, the present invention provides a method for treating milk comprising the steps of:
(a) subjecting the milk to a pasteurization treatment; and (b) passing the milk through a magnetic field for a time and under conditions sufficient to increase the consumable life of the milk when compared to milk that has been subjected only to step (a).
In general, milk as referred to herein refers to milk is obtained from the cow, however, the invention is also applicable to milk obtained from other animals which provide milk for human consumption, eg goats, sheep, and buffalo.

The term "consumable life" is intended to refer to the time for which the milk is in a form fit for human consumption when stored at a specified temperature. Preferably the milk is stored at a temperature of about 4 C, or less.
Generally, the consumable life of the milk can be detected by the consumer by simple tests such as smell, taste, appearance and dispersibilty in hot liquids.
Alternatively, the milk can be tested using methods of microbiological analysis as known in the art.
Extending the consumable life of pasteurised milk is a highly desirable goal in the dairy industry. The relatively short consumable life of HTST pasteurized milk means that the milk must be transported to its final destination within a few days of pasteurization. This can also significantly affect production costs since the use of more cost effective, but slower, transport means is precluded.
By subjecting pasteurised milk, preferably HTST pasteurised milk, to a magnetic field treatment, the consumable life of the milk may be extended to at least 30 days from pasteurisation (compared to 10 to 13 days). More preferably, the consumable life may be extended to at least 32 days, even more preferably, to 34 or 35 days.
Extending the consumable life of the milk may therefore allow for transport of the milk over long distances using cheaper forms of transport. In addition, by treatment of the milk in accordance with the invention it may also be possible to further reduce transport costs by reducing cooling costs.
Pasteurisation methods are known in the art and are described in references such as Encyclopedia of Chemical Technology, Volume 15, 3rd Edition, (1984), John Wiley &
Sons, Inc ; and Diciionary al Dairy Technology (1974), Compiled by the International Dairy Federation. Pasteurization methods may be carried out in a batch process or a continuous flow process (whereby the milk passes in a continuous flow through heating and cooling equipment). In an example of the batch process the milk is heated to at least 62-3 C and held continuously at or above this temperature for at least 30 minutes In an example of the continuous process the milk is heated to at least 72 C for at least 15 seconds.
This is known as HTST pasteurisation.

In an ultra high temperature (UHT) process the milk is heated to temperatures of 87-102 C and held at the temperature for 1 -2 seconds. Preferably the pasteurisation treatment is an HTST
treatment although a UHT pasteurisation treatment is also considered to be within the scope of the methods of the invention.
Preferably the milk is pasteurised in accordance with the Canadian Food and Drugs Act as amended from time to time , by:
(a) (i) heating to a temperature of not less than 72 C and retaining it at such a temperature for not less than 15 seconds and immediately shock cooling the milk to a temperature below 4.5 C; or (ii) heating the milk and immediately shock cooling, using any other time and temperature combination of equal or greater lethal effect on the bacteria, moulds and yeasts present: or (b) ultra-heat treatment by subjecting the product to a temperature of not less than 132 C for not less than 1 second.
It will, of course, be recognised that pasteurisation can be carried out in accordance with the appropriate food standards of the relevant authorities in other jurisdictions such as the Grade A Pasleurized Milk Ordinance, United States Department of Health, Education and Welfare, Public Health Service Publication No 299, 1965.
The strength of the magnetic field and the duration of exposure of the milk to the magnetic field can be varied to achieve the desired effect. The milk can be treated in a batch wise or continuous flow process and thus field strength and exposure time will depend upon the volume or flow rate of milk to be treated. Preferably, the milk is passed through the magnetic field in a continuous flow process, by passing the milk through a conduit such as tubing, which is situated in a magnetic field either at ninety degrees or parallel to the flow of the milk.
An electromagnet provides a constant and static magnetic field which can be varied (by varying the current) to accommodate the flow of the milk.
A magnetic plate or bar rod formation incorporating one or more magnetic plates or bar rods located parallel with the milk flow provides a static magnetic field which can be varied (by varying number and length of plates or rods and magnetic strength) in a tube of sufficient dimension to maintain the required processing flow rate. (See Fig 1 pp 10) A magnetic plate or bar rod formation of one or more magnetic plates or bar rods in a grid or grate formation ninety degrees to the milk flow provides a static magnetic field which can be varied (by varying number of magnetic plates, rods and magnetic strength) in a tube or structure of sufficient dimension to maintain the required processing rate Disc, plate or rod magnets can be located on the external surface of a tube to produce a magnetic field within the tube in which the milk passes through. (See Fig 2 pp10) The skilled person will be able to readily determine suitable conditions by routine trial and experimentation. For example, a field strength of about 2000 Gauss may be used when milk is passed through a 5 cm length conduit at a flow rate of about 20m1/second. When the conduit is lengthened to 10 cm and the flow rate is maintained at 20m1/seconds, the field strength can be adjusted to 1000 Gauss.
Alternatively, an increase in flow rate to 40m1/sec through a conduit of 5 cm in length can be compensated for by increasing the field strength to about 4000 Gauss. Other variations in field strength, flow rate and conduit length can be determined. Generally the quantitative effect of the magnetic field is the sum of the time of the milk in the field x the strength of the field, eg a

2 second exposure to a 1000 Gauss Field has generally the same effect as a 10 second exposure to a 200 Gauss Field.
The milk treated by the process of the invention may optionally be subjected to a further homogenisation treatment. Homogenization is the process by which a mixture of components is treated mechanically to give a uniform product that does not separate. In milk, the fat globules are broken up into small particles that form a more stable emulsion in the milk. Generally they are about 1-15 im in diameter and are reduced to about 1-2 [tm by the homogenization process. Milk is homogenized by forcing the liquid at a high pressure through small openings, and the resulting product preferably has an index of homogenization not exceeding 10Ø Methods of homogenization are known to the person skilled in the art.
Preferably, the homogenization treatment step is carried out before the milk is passed through the magnetic field of step (b), ie before, during or after the pasteurization step.
The milk obtained by the method of the invention may be used to prepare other manufactured milk products including cream (non-homogenized milk) evaporated and condensed milk, sweetened condensed milk, powdered milk, (frozen) yoghurt, ice cream and other frozen desserts, flavoured milk (eg chocolate, strawberry, banana and coffee), skim milk, reduced fat milk, nutrient fortified milk, and various types of cheeses which can be made from pasteurized milk.
Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise" and variations such as "comprises" and "comprising" will be understood to imply the inclusion of a stated integer or step or group of integers but not the exclusion of any other integer or step or group of integers.
The invention will now be described with reference to the following examples which are included for the purpose of illustrating certain embodiments of the invention but are not to be construed as limiting the generality hereinbefore described.
EXAMPLES
Example Apparatus:
2 x 45 mm circular magnets producing a field of approximately 1500 Gauss at a separation of approximately 7 mm.
40 cm length of 10 mm tubing with funnel.
300m1 Plastic sample bottles with lids The tubing, funnel and sample bottles were boiled in water for 3-4 minutes to minimize contamination. The magnets were mounted on the tubing to a gap of 7 mm in a N-S
configuration (magnets attracting each other) and disposed at right angles to the tubing or flow conduit. (See Fig 2 and Fig 3 pp10) Commercially available (pasteurized and homogenised) milk was purchased with a "Use By"
date 10 days from the date of purchase.
The following treatments were applied:
(i) Milk was poured through the magnetized conduit into 15 x 300 ml sample bottles which were immediately sealed, (ii) Treatment (i) was repeated 3 times before bottling the milk in 20 x 300 ml sample bottles, ie triple exposure to the magnetic field.
As a control, 6 x 300 ml bottles were filled and sealed using the above method with the magnets removed.
The milk was then stored in the refrigerator 4 C. Periodic samples were taken and tested for smell, appearance, taste and dispersion (as mixed with hot coffee). The results are tabulated in Tablel.
Day Control Treatment (i) Treatment (ii) 12 Failed smell and dispersion tests. Taste test avoided.
14 Coagulation Passed all tests Passed all tests Slight odor, but passed all Passed all tests other tests 35 Samples had deteriorated Slight odor but all other smell, appearance and tests passed dispersion tests failed (taste test avoided) 37 Failed all tests Failed all tests Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the spirit and scope. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more of said steps or features.