Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
4853
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~ SCRIP~?IO~
"~CESS ~OR IOWERL~G l!HE OEILING q~E~ERATU~E OF W~
.
PRO~EINS OB~AINED ~ROM MI~En.
The present invention relates to a pro¢ess for
lowering the gelling temperature of whey proteins
obtained from milk, especially casein whey or cheese whey.
Eroteins are es~ential to the human diet because
of their ability to provide essential amino acids.
However, ma~y proteins are al~o used for their physical
properties as well as their nutritional properties, in
food systems where a gelling, foaming, emulsirication
or thickening function may be required and these
properties aro often collectively known as the functional
proporties Or a protein. Casein, egg white, gelatine
and ~luten are all examples Or proteins that are used
ror their functional properties, rather than the~r
nutritional properties. During recent years a ersat
d~al Or wor~ has been directed towards reco~ery of
~rotein~ Srom milk whey and whereas the nutritional
~uperiority of whey proteins is undisputed, the
~unctional use Or whey protein has been limited because
o~ the poor physical propérties of commercial product~.
Methods are now commercially a~ailable whereb~ whey
products containing up to 9~% or more whey protein may
- be produced, but these products tend to be rather limited
in their functional u~e, since the whipping and gelling
_properties are generally inferior to those of egg white,
.~ ~
J
`
~ 1~853G
and whole egg, and the viscosity properties are
inferior to thoqe o~ casein, gelatine or ~oya.
~ he whole whey proteins are globular protein~
and are capable of being utilised in a functional
mannor. ~he #pecific functional properties of whey
proteins in commer~ial products however, are at a level
which, at the present time do not, in general, comp~re
favourably with equivalent ~unctional propertie~ of
protein~ derived from othcr ~ource~.
It has besn proposed to effect a controlled break-
down of whey proteins into peptides and amino-acids by
~ydrolysi~ at a particular pH level whereby to improve
the whipping properties of such protein~q. &ch a
process, howevsr, has been found to have a deleteriou~
errect on the gelling properties of such proteins.
It has also been proposed to increase tho whipp~ng
properties Or aqueous solutions containing di~sol~ed
ch~ese whey prote~n e~poc~ally chee~e whey protein
~oncentratos obtained b~ gel filtration Or partially
delactosed cheese whey by heating the aqueouR protein
~olution to a temperature within the range of from at
lea~t 90~ to lower than 99C for not more tha~ about
5 minute~ and prererably for about 0.1 minute at a pH
Or from 5 to 8.5~ preferably 6 to 7.5 and cooling the
801ution to below 60C ~nd whipping the aqueous solution
within about 8 hours after heati~g. ~he aqueous
1148S3~
solutions thus produced are stated however not to be suit-
able for replacement of egg whites used in food systems
requiring the heat-set or coagulation property of egg
whites.
It is an object of the present invention to provide a
process whereby the gelling properties of whey proteins
may be modified such that the temperature at which gelling
thereof occurs is lower than that of the unmodified
proteins.
lG It has now been found that the structure of whey
proteins can be modified such that interaction between the
modified protein molecules occurs at a lower temperature
than between unmodified protein molecules thus causing
a lowering in the gelling temperature of the proteins.
It has been found that this modification occurs if the
proteins are held at an elevated temperature for a suf-
ficient time whilst the pH of the system is maintained
at a level which prevents precipitation coagulation or
gelling of the protein during the time the proteins are
maintained at the elevated temperature.
According to the present invention there is provided
a process for lowering the gelling temperature of whey
protein derived from milk which comprises maintaining an
aqueous solution of such whole whey proteins having a
concentration of proteins of from 0.5 to 10% weight/volume
at an elevated temperature of at least 70C and at an
1148S3~
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alkaline pH to effect an increase in the sulphydryle groups
available for reaction, the period of time over which the
proteins are maintained at the eLevated temperature and
the pH of the solution both being selected such that pre-
cipitation, gelling and coagulation of the proteins while
at the elevated temperature is prevented, and cooling the
resultant solution to a temperature at which no further
change in the protein occurs.
For the modification to occur within a reasonable time
the temperature must be maintained at or above 70C. For
a given degree of modification of the proteins the temper-
ature and duration of the treatment are inter-related, in
general the higher the temperature the shorter the period
of time required, and the lower the temperature the longer
the period required. The temperature should be high enough
to effect the necessary modification but not high enough
or be maintained for a sufficiently long period that it
effects coagulation, precipitation or the extensive break-
ing of primary structure peptide bonds although S-S or
other labile bonds, within the protein molecules may be
ruptured.
The effect of the above modification process on the
protein molecules is to open out the protein molecules and
thereby bring into a reactable state one or more of any
2s internal SH or S-S groups which in the natural condition
of the protein molecules are enclosed within the protein
molecule and unavailable for reaction. It
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~8536
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i8 belie~ed that the opening up of the protein molecules
also cauqes an increase i~ the di~ulphide groups which
are available for interaction with sulph~dryl group~
in other protein molecules and that this does play at
lcast some part in the lowering Or the gelling
temperature which result~. It is believed that the
extra sulphydryl groups and extra disulphide groups
rendered accessible, enable interaction of the protein
~lecule~ to be ;ncrea~ed and the gelling temperature
thereby decreased.
The modification treatment is effected on the
protei~s in ~olution i.e. in aqueous solution. ~he
¢oncentration of the proteins in the aqueous solution
may be from 0.5 to 10% weight/volume. Below 0.5%
concentration the solution may be uneconomical to process.
~bove 10% concentration it would be difficult or
impossible to prevent uncontrolled interaction o~ the
protein molecules, leading to insolubilisation,
precipitation or e~en gelling in the proce~sing
equipment. Preferably, the proteins are present in
the aqueous ~olution at a concentratio~ of from ~ to 5%
weight/volume.
It is essential that no precipitation, gelling or
heat coagulation of the protein occurs. In general, to
achieve this the pH of the solution needs to be slightly
alkaline, for example from 7.5 to 9. Preferably the
pH is maIntained at a level of substantially 8Ø
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-6-
For normal procedure~ the temperature should in
general be les~ than 90C to enable workable time period~
to be achieYed. If ultra high temperature techniques
are used, howe~er, much ~horter times are feasible and
tomperatures as high as 120C or more may be possible.
The period o~er which the elevated temperature
must be maintained for a given degree of modification,
i.e. a given lowering in the gellIng temperature, is
also dependant on the conc~ntration of the protein~
in the aqueous solution~ For any given elevated
temperature, the lower the concentration the longer the
~eriod of time required at that eleYated temperature to
~fect a given degree o~ modifi¢ation. ~hus using
~on-ultra high temperature techniques the time re~uired
~or a 3% weight/~olume con¢entration of whey proteIn ¢an
be as short as 30 soconds at 90C or as long as 30
~inutes at 70C. Preferabl~, ~or a 3% concontration
wei pt/~olume of whey proteins the temperatures a~d
other paramoters should be chosen to pro~ide a dwoll
time at tho ele~ated temperature Or from about 3 to 5
minutes~ Generally thi~ can be achie~ed by using a
temperature between 75 and 85C. ~t ¢on¢entrations
below 3% weight/Yolume longer times would be necessary
at a gi~en temperature for the same de OEee Or modification
and at concentrations greater than 3% e.g. 5~ or 10%,
shorter times will in ge~eral be necessary for a give~
temperatt~re to achie~e the same modif;cation.
11~853
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The modification process of the present inve~tio~
can be effected on unconcentrated milk whey but i~
preferably effected on whey which has been subjected to
an ultrafiltration treatment. Preferably the process
of the invention is carried out on concentrated separated
, whey in which the protein concentration i5 of the order
of 3% weight/volume. A fractionated milk whey may
also be used but if the fractionation i8 taken too far
~c~e individual fraction~ may not re~pond to the process.
Care should be exercised however, ~n any concentration
or fractionation technigue employed to avoid subjecting
the proteins to olevated temperatures which might cau~e
denaturation of the protein~ particularly where
concentrates ~rom dif~erent sources are to be used.
In a prsferred method of carrying out the process
Or the invention, a milX whey ha~ing a protein concen-
tration of about 3% weight/volume has its p~ ad~sted
to about pH 8.0 u~ing a dilute alkali metal hydroxide
colution 8uch as sodium hydro2ide. ~he temperature of
the whey is then raised to between 70C and 90C for a
re~idence time of between 30 m;m~tes and 30 seconds
e'ither i~ a continuous manner by means of heat exchangers
or u~ing a batchwise technique. ~t the end of the
appropriate re~idence time the whey i~ rapidly cooled
an,d optionally the p~ may be adJusted to 6.5 to 7.0 a~d
the whey then concentrated and dried to yield a dry
modified whey protein. Iow temperature concentra~ion and
~8536
~pray drying from fairî~ dilute solutions should be
ef*ected to avoid any denaturation of the proteins by
such tech~iques.
~ nalysis of modified whey proteins produced by the
5 method of the invention has shown that the available
8ulphydryl content has been increased over that obtaining
in the unmodified whey proteins. Determination Or the
gelling temperature of reconstituted unmodified and
mo~ified protein solutions containing 15% weight/~olume
10 of protein has shown that the modified protein gells
at a lower temperature but that there is no sign~ficant
decrease in the gel strength as between a gel produ¢ed
~rom unmodi~ied protein and a gel produced from modified
protein.
The degree of lowering in the gelling temperature
will depend on the combined effect of temperature a~d
dwell time for a given concentration of whey pro~ei
~ tho aqueou~ solution being treated. For a given
con¢entration of whey protein and a given temperature of
20 treatment, the lowering in gelling temperature i8
OEeater with increasing time and for a give~ concen-
tration of whe~ proteins and a given time the lowering
in the gelling temperature i8 greater the hi~her the
temperature.
~he in~ention will be further illu~trated by
reference to the following examples -
3S36
_ 9 _
F~4~D~LE 1.
~ whey protein concentrate powder prepared by an
ultrafiltration and low temperature spra~ drying
technique (containing 85% protein, 8.~% fat and 3%
5 lactose) was reconstituted in water to give a ~olution
containing 3% protein. ~he pH of this solution was
ad~usted to p~ 8.0 using dilute sodium hydroxide and the
temperature of the solution increased to 90C for 30
se~onds after which time, it was rapidly cooled in a~
10 i~e/water bath. ~he solution was then dried by means
of a spray drier. ~nalysis of the dried product showed
that the sulphydryl content had i~creased from 2 x 10 6
moles ~g to 20 x 10-6~ moles /g. When a solution
¢ontaining 15% weight/~olume protein was prepared, a
15 firm gel was formed at 25C whereas the llnmodified whey
protein required a temper~ture o~ 72C berore a rirm gel
would form.
} 2,
Tho procedure described in Example 1 wa~ repe~ted,
20 except that the whey protein solution was held at 80C
for 3 minutes. As a result of this treatment the ~ree
~ulphydryl content was increased to 8.0 x 10 6j~ mole~/g,
~nd the gelling temperature wa~ lowered to approxImately
50C.
25 EXAMEIE 3.
~ he procedure of Example 1 was repeated except that
the whey protein solution had a concentration of 1~
~1~8536
-10-
weight/volume and wa~ held at 80C for 10 minutes. As
a result of this treatment thè face sulph~dryl co~tent
was increased to 9.0 x 10 6~ moles/g. A 15% weight/
volume aqueous solution of the treatod proteins had a
gelling temperature of ~0C.
E~MPLE 4.
~ he procedure of Example 1 was repeated except
that the whey protein solution had a concentration
o~ 5% woight/volume and was held at 80C for 10 minutes.
10 ~s a result of this treatment the free ~ulphydryl content
wa~ increased to 16.2 x 10-6ju moles/g. A 15% weight/
volume aqueous solution of the treated protein had a
gelling temperature of 42C.
The procedure of Example 1 was repeated except
that the whey prote~n solution had a concentration of
10% weight/Yolume and was held at 80C for 10 mi~utes.
~8 a rosult o~ this treatment tho freo sulphydryl content
Wa8 increased to 22 x 10 6~ moles/g. ~ 15% weight/
20 volume aqueous solution of the treated protein had a
gelling temperature of 36C.
By ~arying the parameters of concentration temperaturo
and time a range of product3 can be prepared with
gelling temperature~ varying between 25C and 72C thu~
25 greatly increasing the number of applications and the
efficiency with which the whey proteins could be used in
food systems. Further~ore product~ having consist.ent
~ ' t.
~8536
_11-
gelling temperatures and gelling strength become possible.
The product produced ~y the method of the in~entio~ can
of course be used in admixture with untreated whe~
protoins or with materials from other sources.
