Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE OF THE INVENTION
PROCESS FOR MAKING A LACTOSE-FREE MILK AND MILK SO PROCESSED
FIELD OF THE INVENTION
This invention relates to a process for reducing or substantially
eliminating lactose from milk. This invention further relates to a lactose-
free milk which has preserved organoleptic properties. This invention also
relates to a partially or totally defatted and lactose-free milk which has
preserved organoleptic properties.
BACKGROUND OF THE INVENTION
It is well known that some individuals are intolerant to lactose.
Further, it may be desirable at certain times for individuals to avoid
ingesting milk having a normal lactose content (about 4.6 - 4.9 % w/v),
particularly when the gastro-intestinal epithelium is momentarily
compromised in its capacity to convert lactose to the monosaccharides
glucose and galactose. Such situations occur, for example, when an
individual is afflicted with diarrhea, gastroenteritis or a gastro-intestinal
disorder caused by the administration of antibiotics. When the affected
individual is a nursing infant, it may be necessary to substitute the
mother's milk with a lactose-free milk. A soy based milk, which does not
naturally comprise lactose, is an acceptable alternative under
circumstances where lactose intolerance occurs or where lactose is to be
avoided for a given period of time. However, many individuals reduce or
eliminate milk consumption because they dislike the taste of soy-based
milk.
Different approaches exist to modify the composition of milk.
Enzymatic processes used to eliminate lactose from milk are well known
in the art. They usually comprise the step of adding lactase to milk for a
time sufficient to convert lactose into monosaccharides. The major
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problem occurring with this type of process is that the production of
monosaccharides increases the taste of the milk to an unacceptably sweet
level.
US Patent No. 4,957,752 describes a process for making an
ultrafiltrated milk which is used in the production of kefir. A partial
delactosylation is achieved which reduces the ratio of lactose to protein
from about 1.5:1 to about 1:1 (measured as percentages on a dry weight
basis). This reference does not identify any undesirable modifications of
the organoleptic properties of milk so delactosylated and further treated
with a lactase, and consequently does not provide solutions for solving the
problem arising from the action of lactase.
US Patent publication No. 4,956,186 describes a process for
making yogurt. This process also comprises the steps of ultrafiltering milk
and hydrolysing lactose with a lactase. Apparently the sweet taste of the
resulting milk was not a concern in this reference, because a sugar
substitute was added to the yogurt.
There is therefore a need for an improved process for preparing
lactose-free milk. In particular, there is a need for a process resulting in
lactose-free milk whose organoleptic properties are not negatively
affected.
SUMMARY OF THE INVENTION
The present invention provides a solution to the drawbacks or
inconveniences of existing processes and milk products.
It is a first object of the invention to provide a process by which
lactose is reduced or substantially eliminated from milk without negatively
affecting the taste of the milk.
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More particularly, a process is defined for producing a milk product
which is substantially lactose-free from an original milk having original
lactose and protein contents, which process comprises the steps of:
- reducing the lactose content of said original milk to a content which
represents a ratio of percentages lactose to protein of about 1:1 on
a dry weight basis, so as to obtain a milk having a residual lactose
content; and
- treating the milk having said residual lactose content with a lactase
enzyme until conversion of lactose into galactose and glucose is
substantially complete;
whereby a lactose-free milk is obtained without any substantial increase
of the sweet taste thereof consequent to the conversion into galactose and
glucose.
In a specific embodiment, the milk having a residual lactose content
has about 3% lactose on a dry weight basis, and is obtained by membrane
technology. Specifically, ultrafiltration and diafiltration were used.
In a more specific embodiment, the milk is standardized to achieve
a fatty matter content of about 0 to about 3.25% on a dry weight basis.
In the first most specific embodiment, the fatty matter content is
standardized to about 3.25%.
In the second most specific embodiment, the fatty matter content
is standardized to about 0%. The above process leads to a fat-free and
lactose-free product. In the latter case, the organoleptic properties of the
skimmed milk so treated are improved by increasing the milk protein over
the natural protein content of milk, preferably up to about 3.8-4.0% or
greater on a dry weight basis.
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The milk protein content may be increased by concentrating the
original milk or by adding proteins to said original milk or to the milk
having
residual lactose content, or else to the milk treated with lactase. The
added proteins may be milk proteins or proteins from any exogenous
source.
The present invention further provides a process for producing milk
that is substantially lactose-free, which process comprises the steps of:
a) standardizing the fatty matter from an original milk so as to
obtain a milk having a fatty matter content of between 0 and
3.25% on a weight basis;
b) passing the reduced fat-milk of a) through a membrane system
so as to decrease the lactose content of said milk to
approximately 3% on a weight basis;
c) subjecting the milk resulting from b) to thermal treatment; and
d) submitting the milk resulting from c) to enzymatic hydrolysis.
The present invention further provides a process for producing milk
that is substantially lactose-free, which process comprises the steps of:
a) standardizing the fatty matter from an original milk so as to
obtain a milk having a fatty matter content of between 0 and
3.25% on a weight basis;
b) passing the reduced-fat milk of a) through a membrane system
so as to decrease the lactose content of said milk to
approximately 3% on a weight basis;
c) submitting the milk resulting from b) to enzymatic hydrolysis;
and
d) subjecting the milk resulting from c) to thermal treatment.
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The present invention further provides milk products produced by
the above processes.
The present invention further provides milk comprising about 0%
lactose and about 3% monosaccharides on a weight basis.
The present invention further provides dairy products derived from
the milks obtained in accordance with the present invention.
DESCRIPTION OF FIGURE 1
Figure 1 outlines the steps of a process according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE
INVENTION
The invention will be now be described by referring to the preferred
embodiments and Figure 1.
The process begins with a cow milk, the lactose content of which is
to be reduced from an original average value of 4.6 - 4.9% to a value
below the detection level thereof, as verified by enzymatic assays (i.e.,
below about 0.2%). This is considered to be a substantially complete
removal of lactose.
MATERIALS AND METHODS
The protein content (N x 6.38) and the total fat matter content were
determined in duplicate using the standard method of Kjeldahl and
Mojonnier, respectively.
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The lactose content was measured by a technique well known in
the art, such as Boehringer & Mannheim Enzymatic Method.
Total coliforms were quantified by the "most probable number"
technique, which consists of counting bacteria following growth for 48
hours at 37 C on Brilliant Green Medium.
To evaluate the number of total aerobic bacteria, incubation was
performed for 48 hours at 32 C on "plate count agar" medium.
These two methods for measuring bacterial contents are approved
by the International Federation and the American Public Health
Association.
Non-processed milk usually has the following average composition:
Lactose 4.6 - 4.9 %
Fatty Matter 3.6 - 3.8%
Proteins 3.1 - 3.3%
pH 6.6. - 6.9%
and the total aerobic microbial flora should be less than about 100,000
cfu, for example, in order to comply with governmental regulatory
standards.
EXAMPLE 1
Process for making a lactose-free milk
The steps of the process of this invention will now be described
with reference to Figure 1.
The first step is a partial or total removal of fatty matter, or
standardization, of the milk contents. Levels of fatty matter usually vary
from 0 to 3.25% on a dry weight basis.
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The second step of the present process is usually a thermal
treatment. The goal of this step is two-fold: (1) to destroy pathogenic
agents in the milk; and (2) to increase the permeation speed during the
following ultrafiltration step, thereby reducing the clogging rate of the
filtering walls.
Thermal treatment is not essential to the present invention if one or
both of the above goals are not sought. In the present case, standardized
milk having 3.25% fatty matter was heated at 72.8 C for a period of 16
seconds. The pressure used for the heat treatment may vary upon the
nature of the equipment and the method itself. Here, the equipment used
was a Tetra PakTM system and the parameters for heat treatment were
chosen in accordance with the manufacturer's recommendations.
The heat-treated milk was allowed to cool down to the temperature
used during the ultrafiltration step. Many other temperature and time
schedules may be used in replacement of the one mentioned above, as
may be appreciated by a person skilled in the art.
The third step is an ultrafiltration/diafiltration step. The filtration
temperature is stabilized. The filtration temperature affects the permeation
speed. An increase of 1 C has the effect of increasing the permeation
speed by about 2.5%. The filtration temperature should never exceed the
maximum temperature suggested by the manufacturers of filtration
membranes.
The filtration system used was Tetra PakT^^ with RomiconTM PM50
filtration membranes and the filtration parameters were the following:
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Temperature z50 C
Transmembrane 1.0 Bar
pression
Velocity _ 7 meters/second
Permeation speed 30 Um2/hre
During the ultrafiltration step, the retentate is submitted to diafiltration
by
addition of water so as to decrease the lactose content from about 4.6 -
4.9% to about 3%. At this concentration, the content ratio of lactose to
protein is about 1:1. The reduction of the lactose content or ratio is a key
feature of the present invention. When the lactose content is reduced to
about 3% and the protein content is of about the same percentage value
(on average, about 3.1 - 3.3%), and further, when the fatty matter content
is of about 3.25%, the conversion of the residual lactose into
monosaccharides will result in the production of a milk with an
unnoticeable change in sweetness.
As may be seen from Figure 1, the order of the subsequent fourth
and fifth steps comprising thermal treatment and enzymatic hydrolysis
may be interchanged. In both cases, the objective of the thermal
treatment is to destroy pathogens and is based upon the intensity and the
time selected for the heat treatment. The heat intensity influences the
organoleptic and nutritional properties of the finished product and its
conservation time. For example, a low temperature/long time process
(LTLT) consists of heating at 65.6 C for 30 minutes. The high
temperature/short time (HTST) process consists of heating at about
72.8 C for about 16 seconds. The ultrahigh temperature process (UHT)
consists of heating at 120 C for only a few seconds. In the present
example, the heat treatment UHT was selected to ensure sterility for
commercial purposes (see above parameters). It is worthwhile noting that
LTLT and UHT have a more pronounced denaturing effect on proteins
than the HTST heat process. The HTST heat treatment was combined
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with known methods of multicentrifugation and microfiltration in order to
avoid denaturing the milk without compromising on acceptable microbial
quantities. A sterile, agreeable milk product having a long shelf life was
obtained.
When the heat treatment is performed before the enzymatic
hydrolysis, the advantage is that it takes a longer time for the heat
exchanger to become clogged.
As stated above, the heat treatment may follow enzymatic
hydrolysis.
The enzymatic hydrolysis step itself has as an object the
conversion of the residual lactose (about 3%) of the diafiltered milk into
glucose and galactose.
Should the enzyme be added after the heat treatment, it should be
in a sterile form if the finished product is to have a lengthy conservation
time. If heat treatment follows enzymatic hydrolysis, the enzyme 0-
galactosidase (or lactase) will be denatured and will lose its activity, and
the sterility of the final product will be ensured.
The quantity of enzymes and the reaction temperature should be
adjusted to ensure complete hydrolysis of the lactose. Lactose hydrolysis
was performed with (3-galactosidase in accordance with the manufacturer's
directives. Many commercial enzymes are available, such as those sold
under the following trade names: LactaidTM, LacteezeTM, DairyaidT"" and
PMS-prolactaseTM.
For the heat treatment and enzymatic hydrolysis steps, the
conditions that were chosen are summarized in the following Table.
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TABLE
1) Heat treatment 1) Enzymatic hydrolysis
2) Enzymatic hydrolysis 2) Heat treatment
Incubation time 24 - 48 hres 24 - 48 hrs
Temperature * < 5 C < 10 C
*The incubation temperature is decreased when the product is non-sterile
after heat treatment because of the introduction of the enzyme.
The last step of the above process is a usual conditioning step
which is performed in accordance with available equipment. In the
present case, the EQ5 process was used.
Homogenization ensures proper dispersion of fatty matter in the
aqueous phase. The diameter of fat vesicles resulting from
homogenization should be less than about 1 micron in order to avoid
separating the lipidic and aqueous phases.
The final product may be aromatized by adding any flavor, or
further processed.
EXAMPLE 2
Evaluation of organoleptic properties of the milk product made following
the procedure of Example 1
The organoleptic properties of the milk produced by the process of
Example 1 were evaluated using a taste test. Individuals who tasted the
milk did not discern an unpleasant taste.
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EXAMPLE 3
Improvement of the organoleptic properties of a fat-free, lactose-free milk
The steps of Example 1 were reproduced starting with an original
milk having a fatty matter standardized to about 0%. The watery and
sweet taste of the skimmed milk so-treated may be greatly improved by
increasing the concentration of protein from about 3% (i.e., 3.1 to 3.3%)
to about 3.8-4.0% or greater. This increase was achieved during the
ultrafiltration/diafiltration step performed on the original milk (i.e., by
concentrating milk proteins). Alternatively, proteins may be added at any
step, such as after diafiltration or after complete hydrolysis of lactose.
This
simple increase in proteins rendered the fat-free and lactose-free milk
significantly more acceptable to consumers involved in taste trials.
EXAMPLE 4
Dairy products derived from the lactose-free milk
A plurality of dairy products may be derived from the milk produced
in accordance with the present invention. "Derived" should be construed
as "obtained by milk transformation or as a milk-comprising food product".
Any such dairy product (cream, ice cream, yogurt, butter, cheese,
beverage etc.) is contemplated as being under the scope of the invention.
This invention has been described with reference to specific
embodiments. It is well within the ability of the skilled artisan to make
modifications without departing from the above teachings. These
modifications are within the scope of this invention as defined in the
appended claims.
