Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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The present invention relates to a method for
sterilizing milk.
Milk gives rise to serious preservation problems,
both when it is to be used as such, and when it is to be
converted into other produces, such as cheeses, yogurt and
the like.
The preservation problems are essentially related
to the pollution by bacteria, which, on account of the chemical
composition of milk, find therein an excellent culturing
medium in which they multiply at a very fast rate. As a
matter of fact, milk is a highly valued produce for human
feeding but, just for this reason, it is one of the most
perishable foodstuffs. Bearing this circumstance in mind, a
number of treatments have been studied and applied in the
industry, such as sterilization, pasteurization and uperization,
which enable milk to keep for average and long periods of time
without substantially modifying its nutritional value.
All of these treatments are mainly heat-treatments
- and require expensive installations, which are, of necessity,
centralized, and often remote from the production centers.
The problem of milk keeping is, at any rate, still
- left outstanding in the time span between milking and the
heat treatment, that is, during shlpping and storage preliminary
to such treatment.
Refrigeration solves this problem only in part, both
because it is not always practicable, and because it merely
moderates the bacterial growth-rate. It is apparent that the
period of time between milking and the heat-treatment must
be as short as practicable.
Conversely, there is a sterilization treatment which
is extremely simple and cheap and does not require any
special installations, and which can be carried out immediately
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upon milking. It would suffice to add to the freshly drawn
milk hydrogen peroxide in a concentration of from 500 to
2,000 ppm (parts per million) to have an absolutely sterile
produce without any need of further treatments. In addition,
the presence of hydrogen peroxide would keep the produce
sterile during shipping and storage, the refrigeration problem
and the requirement of minimizing the times taken by these
operations being thus offset.
Regrettably enough, this so simple and efficient
treatment cannot be carried out because hydrogen peroxide,
due to its toxicity, must be driven off, but this cannot be
done, in its turn, without adding chemicals which would
modify both the chemical and organoleptic properties of the
milk.
It has now been ascertained that it is possible to
carry out a simple treatment which enables hydrogen peroxide
to be converted to water and oxygen and therefore to be
eliminated without modifying the chemical composition of milk, --
by employing a catalase enæyme immobilized in fibers of a
polymeric material according to the procedure disclosed in
the Italian Patent 836,462, and permitting this enzyme to
exercise its catabylic activity on the residual hydrogen
peroxide of the milk for a time sufficient to remove any traces
of this residual hydrogen per~xide.
As a matter of fact the enzyme catalase, which
catalyzes the conversion of hydrogen peroxide into water and
oxygen, can simply be removed, on completion of the reaction,
by merely separating the fibers, by which the enzyme is immobil-
ized, from milk. It is apparent than, by so doing, the
overall treatment of sterilization and driving off of hydrogen
peroxide involves, as regards the chemical composition of
milk, but a slightest increase of the quantity of water. -
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It is also apparent that such a treatment can be
applied to any foodstuff whatsoever which is composed by a
solution, or also by a suspension.
At any rate, the invention is illustrated in more
detail in the ensuing examples. -
E X A M P L E 1
75 g (grams) of cellulose triacetate have been
dissolved in one litre of methylene chloride at room temperature.
To the polymeric solution, which had been cooled to 1C, there
have been added 150 g of a solution of catalase at the concen-
tration of 12.5 mg (milligrams) of proteins per ml, equivalent
to 625~000 IU/ml in a potassium phosphate 0.01 M, pH 7.0
buffer which contained glycerol (30% wt/wt). By stirring,
an emulsion has been obtained which is composed by a fine
dispersion of the enzymic solution in the solution of the
polymer.
The emulsion has then been extruded through a
spinneret immersed in a coagulation bath composed by toluene.
The filament thus formed has been collected on a takeup drum
and dried in air to drive off the spinning solvents.
To one litre of milk in which, by the bacterial
count made according to the APHA standards (" Standard
Methods for the Examination of Dairy Products" , 13th Edition,
- American Public Health Association, Inc., New York, 1972?,
120.103 colonies per ml had been found, hydrogen peroxide
has been added in a concentration of 1,000 ppm. The milk
has been held for one hour at 35C in a closed container.
Then, to the milk has been added 1 g of the catalase-occluding
fiber and the whole has been kept for one hour at 25C with
a bland stirring. The fiber has been removed and the bacterial
count on the treated milk was nil.
The determination of hydrogen peroxide has been
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made with the polarograph AMEL* Mod. 463 with mercury drop
electrode after having added to 10 mls of milk and equal
volume of phosphate buffer 0.05 M, pH 7.0 as the supporting
electrolyte and after having reduced the oxygen level by
flushing with nitrogen for 5 mins.
The concentration of hydrogen peroxide in the
treated milk, calculated with the aid of a calibration curve
obtained with milk samples of known H2O2 concentrations, was
nil.
E X A M P L E 2
20 g of the fiber described in Example 1 have been
introduced in a tubular reaction vessel (dia. 12 mm, height
1,000 mm), the temperature of which was thermostatically kept
25C. The fibres were arranged so as to have their axis
parallel to the axis of the reactor. The reactor has con-
tinuously been fed with 10 litres an
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hour of milk which has been stored at 35C for 12 hrs with 800
ppm of hydrogen peroxide in a sealed container. Prior to the
addition of hydrogen peroxide, there had been found, as in Example
1, 150.10 3 bacteria per ml.
After that the milk had flown through the column, no hydrogen
peroxide has been found and the bacterial concentration was 7
bacteria per ml.
E X A M P L E 3
To a cheese whey having a pH of 6.8 and a bacterial concen-
tration of 108.103 bacteria per ml hydrogen peroxide has been ad-
ded up to a concentration of 500 ppm. After 12 hours of storage
at 35C in closed container the solution has been caused to flow
through the reactor described in Example 2 at the rate of flow of
10 litres an hour and no hydrogen peroxide has been found in the
eluate. The bacteria in the eluate were 6 per ml.
E X A M P L E 4
To one litre of milk hydrogen peroxide has been added at the
concentration of 4,500 ppm. To the milk, thermostatically kept
at 25C, there have been added 250 mg of a fiber containing catalase
occluded therein and prepared according to the procedure detailed
in Example 1. After 60 mins the fiber has been withdrawn from
the milk and 2,000 ppm of hydrogen peroxide have been found in the
milk. After 2 additional hours, during which the milk has still
been kept at 25C but out of contact with the fibers, 2,000 ppm
of hydrogen peroxide have been found again. Then the fibers have
been introduced in the milk mass again and, after 1 hour of reaction,
the level of hydrogen peroxide had dropped to 950 ppm. The fiber
has been removed from milk once more and, after 2 further hours,
950 ppm of hydrogen peroxide had still be found. These facts are
3 an evidence that the separation of the fibers from milk ensures
also the complete removal of the catalase enzyme.
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