Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to textured proteins. More
specifically, the present invention provides a new process for
preparing fibrous protein materials which can be used as, or in
the production of, fish analogs.
In recent years, considerable research efforts have
been focused upon developing new technology for producing meat-
like, protein-containing foods from various vegetable and animal
protein sources. Economics provides a major incentive. It
would clearly be advantageous to substitute, at least in part,
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the more efficient process of growing vegetable protein for the
rather inefficient process by which animals convert the protein-
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aceous vegetable materials into meat. This is especially true
where the ever-increasing human population is feared to be out-
distancing the availability of grazing land for meat-producing
animals. Additionally, recent efforts have also been directed
to avoiding certain natural products which may be undesirable
for religous, ethnic, or health reasons.
All natural meats, including fish and poultry, have
fibrous structures. The texture of the meat products is in-
herently dependent upon the fibrous nature of the meat. Likewise,the presence of a fibrous structure is an important factor in
; fabricated meat-like products. Thus, in producing these meat-
` like products, e.g~ meat analogs, much effort has been directed
~1 to creating a fibrous structure, similar to natural meat. Many
i~ workers have developed a ~ide variety of techni~ues for obtaining
` fibrous textures, and a good deal of published literature is
` available on the production of meat analogs with fibrous
structures.
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- One early worker, soyer, in U.S. Patent 2,682,466
disclosed the formation of synthetic meat products containing
quantities of vegetable protein filaments. These protein filaments
are made by forcing a colloidal protein dispersion through a
porous membrane, such as a spinnerette, into a coagulating bath
causing precipitation of the protein in filament form. The
filaments are assembled into a meat-like product by employing
binding materials, including cereals and protein. The use of
spun vegetable fibers enables the formation of a highly aligned
fibrous structure. Unfortunately, the manufacture of spun
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fibers is complicated and relatively high in cost. Moreover,
spun vegetable protein is generally poor nutritionally because
the starting material depends on soy isolate.
In view of the difficulties inherent in spun fiber
technology, other workers were encouraged to seek alternatives
to this technique. One alternative, disclosed in U.S. Patent
3,488,770, describes the production of a proteinaceous meat-like
product having an open celled structure with cell length greater
than cell width, and with the cells being substantially aligned.
This product is made by extruding a dough, substantially free of
non-proteinaceous filler, into an area of reduced pressure to
cause expansion. Another alternative process working with a
dough is disclosed in U.S. Patent 3,693,533. According to that
process, the protein containing dough is coagulated while being
passed through a set of converging conveyors. The resulting
stretching during coagulation produces what are described as
unidirectional fibers. While these processes are potentially
less costly than the spun fiber technology, they suffer a
penalty in the quality of the fibers produced.
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- ~everal workers, in Japanese published Specifications
48-21,502 and 48-34,228, and United States Patents 3,870,~08
and 3,920,853 describe the production of fibrous protein masses
`~ by processing including freezing a protein solution or dispersion
and heating the frozen mass to heat set the protein. These
fibrous products are described as being meat-like.
: Even taking the best of these teachings, however, the
. . ,
art has yet to closely reproduce the type of fibers normally
present in fish meats such as tuna. The fish fibers are well
ordered, but generally flake-like. This type of texture is
highly desirable when trying to simulate natural fish meat.
In view of difficulties with prior art techniques, it
would be advantageous to have a method which would be capable of
producing a textured protein material having a highly-defined,
`~ fish-like ~ibrous structure which would be both n~ltritious and
` economical.
Accordingly, the method of the present invention, in
its broad aspects, comprises freezing an aqueous mixture of
heat coagulable protein by cooling in a manner and at a rate
effective to create elongated ice crystals generally aligned
perpendicular to the surface of cooling, subjecting the frozen
mass to a temperature substantially different than that of the
frozen mass to cause a temperature stress in the material at
lines of weakness in the frozen mass perpendicular to the aligned
` ice crystals, stabilizing the protein in the frozen mass effec-
; tively to prevent loss of fibrous structure during heating, and
heating the stabilized material to coagulate the protein to a
fibrous, fish-like protein material.
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- According to the present invention, a wide variety of
fish-like textures can be simulated using a wide variety o
protein materials. The common characteristic of all of these
products is the presence of well-defined, well-ordered fibers
separated by lines of cleavage generally perpendicular to the
direction of alignment of the fibers. The fibers are produced
by the present method from protein of vegetable or animal origin
used separately or in combination. In this manner it is possi-
ble to easily balance the textural, taste and nutritional
10 characteristics of the fibers to provide a textured protein
material having the desired characteristics. Among the features
: important to the present invention are: the need for cooling in
a direction and at a rate effective to produce the well-defined,
well-ordered ice crystals; the need for a shock temperature
stressing step to produce the lines of cleavage perpendicular to
the orientation of the fibers; and the need to stabilize the
protein prior to heat setting.
Any edible protein, or combination of proteins, can
~e employed in the process of the present invention, providing
that the sole protein or, in the case of combinations, at least
one of the proteins is soluble or partially soluble and can be
- stabilized by treatment according to this invention. In general,
proteins having excellent solubility provide excellent, distinct
fibrous structures probably because the ice crystals can grow.
freely, unrestricted by undissolved solidsO However, protein
solutions containing considerable insoluble material, such as
soy flour, meat homogenates, and fish homogenates, can also be
employed with good results to form fibrous structures according
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to the present invention. Representative of the protein mater-
ials which can be employed to give excellent results according
to the present process are soy milk, soy isolates, whole milk,
meat slurries, fish slurries, gluten, soy ~lour, wheat protein
concentrate, milk whey, egg protein, blood protein, single cell
protein and the like.
The final texture of the products depends in part on
the protein source employed, as well as the additives such as
flavoring, fillers, fat, carbohydrates, salts, and the like.
For example, the products prepared from soy milk have a juicy,
smooth, soft texture with good fiber tensile strength. The soy
milk produces a product having a desirable smoo~hness and softness,
probably due to the oil emulsified in the protein. Soy flour,
on the other hand, gives a product with lower tensile strength
than the soy milk, but this type of tenderness is desired in
some products either alone or as a component with another protein
material.
The protein, from whatever source, is admixed with
water to form an aqueous protein mixture wherein at least a
portion of the protein is dissolved in the water. The aqueous
protein mixture can be characterized as a solution, dispersion
or suspension of protein and water. To increase the degree of
solubility of the protein, which varies for different types of
protein, the pH of the mixture can be adjusted. To obtain the
optimum tensile strength and fiber integrity it is usually
desirable to adjust the pH of the aqueous protein mixture to the
point of maximum protein solubility. The pH of the mixture
appears to directly affect the tensile strength of the-final
textured product. Some protein materials such as soy flour,
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give better texture and tensile strength at high pH, e.g. pH lt
than at lower pH. This is probably because these proteins are
more soluble at higher p~I, and are partially dissociated and
denatured by the alkaline condition before texturization. At
high pH, the protein molecules tend to unfold, allowing more
complete dissociation and apparently allowing more freedom of
movement during freezing to form more perfect fibers. Some
proteins, such as egg white, have good solubility at their
natural pH and need not have their pH adjusted to alkaline
condition.
While high pH is sometimes useful in preparing the
textured product, excessively high pH values are not generally
desirable. The pH of the final product can be reduced during
rehydration, to be later explained in detail, by the use of an
acid in the rehydration bath. At times, however, reducing the
pH of the textured product to a level below the point at which
the particular protein is immobilized, may affect the texture of
the product. Depending on the particular end use contemplated,
this textural effect may be desirable or undesirable. For the
proteins which are solubilized at their natural pE of 6 to 8, no
neutralization will be needed.
The aqueous protein mixture is easily obtained by
mixing the protein in water. If necessary, the protein material
` can be finely divided or comminuted either before or after
mixing with the water; and, the pH can be adjusted to obtain the
optimum solubility. The presence of soluble and insoluble non-
coagulating materials is acceptable, and indeed in some cases
.
desirable so long as it does not adversely affect the desirable
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qualities of the fiber structure for a particular application.
In some cases, the presence of excessive amounts of fat would be
undesirable where it would reduce the tensile properties of the
fibers. However, in other cases, a reduced tensile strength
would be desirable as it would impart a more tender texture to
the product. Thus, those additives normally employed in forming
fibrous meat analog products can be employed according to the
present invention, it being realized that the process of the
present invention provides a process capable of widely modifying
the compositional features of the fiber forming material to
obtain a wide variety of textural and nutritional variations
from the single basic process. It is an added advantage of the
present invention that relatively high fat contents can be
employed and a good fiber structure obtained.
The solids concentration of the mixture can affect
both product texture and processing efficiency. It is generally
desirable to maintain low solids concentrations. One reason is
that there is a tendency to diminish the distinct fibrous struc-
ture by increasing the concentration of solids. Typically, the
solids will not exceed about 40%, and preferably not more than
about 35% of the mixture on a weight basis. When the solids
concentration increases, the efficiency of the stabilizing
treatment is decreased. However, processing at excessively low
concentrations loses economy due to the increased costs of
removing the water. The costs for energy, vessels, transfer and
storage equipment increase rapidly as concentration is reduced.
However, the quality of the fibers produced at low concentrations
is high. It is therefore necessary to determine the optimum
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concentration ~or each particular system, understanding that
there are many influences which must be considered. In a very
broad sense it can be said that the optimum concentration for
freezing will be anywhere from 3% to about 35% protein, with
concentrations of from 10 to 30~ being preferred, based upon the
total weight of the aqueous protein mixture. It is clear however
that the optima for particular protein and additive materials,
may vary widely within this range and at times extend beyond
this range.
; 10Those skilled in the art will be able to determine the
optima for the particular systems employed, especially with a
knowledge of the economics of their particular processing equip-
ment and procedures. Reference to the examples below will
provide those skilled in the art with working examples of a
number of different systems. Any concentration effective to
` produce substantially independent, oriented fibers is acceptable
according to the present invention. The particular concentration
must be determined in each case for the balance of product
physical properties and processing efficiency which is desirable
and justified. It is noted that a gelled protein material of
; the type employed in forming Tofu, where the watér is restricted
fxom forming long crystals by the gel structure, cannot be
employed according to the present invention.
Once prepared, the aqueous protein mixture is frozen
by cooling according to a de~ined directional pattern to provide
a well-defined, well-ordered fibrous structure produced by the
ice crystals. As the water is frozen to ice crystals, the
remaining protein mirture becomes more concentrated. The for-
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mation of the ice crystals separates the protein material intodistinct, generally parallel aligned zones. Any means capable
of accomplishing this result is suitable according to the present
invention. The ice crystals form in a lattice-work entrapping
protein in orderly fiber-like portions between the elongated ice
crystals. The zones of protein material are separated from each
other almost completely --- forming substantially independent
fibers of protein when coagulated. However, the zones of protein
are not completely independent of each other and are joined at
sufficient locations to bind the individual zones into a branched
or cross-linked structure. The degree of binding achieved is
just sufficient to provide a cohesiveness to the final product
similar to cooked meat, and does not destroy the substantially
independent fibers. This binding, achieved during the formation
of the fibers, eliminates the need for added binder materials.
` Freezing is obtainable by cooling at least one surface,
preferably one surface or two opposed surfaces, of the mixture
to below the freezing temperature of the mixture. The cooling
or refrigerating preferably causes freezing to take place through-
20 out the thickness of the mass to produce generally parallel
fibers, aligned generally perpendicularly to the cooling sur-
.,
faces. Desirably, the cooling surface or surfaces will beplanar; however, they can have any other, regular or irregular
configuration~ For example, a single cooling surface can be
employed having a hemispherical, spherical or cylindrical con~
figuration in contact with the aqueous protein mixture. In
these exemplary situations, the ice crystals, and thus the pro-
tein fibers, would form generally perpendicularly to tangents to
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the surface, radiating generally toward the center. During
freezing, a boundary between the frozen mixture and the liquid
mixture appears and moves in the direction of cooling. At
typical freezing temperatures employed according to the present
invention, and where the cooling surface is not highly irregular,
the boundary will generally conform to the shape of the cooled
surface of the protein mixture. However, under other conditions
according to the present invention, the boundary will assume a
somewhat modified shape. It is to be understood that after an
initial thickness of the mixture has been frozen, the moving
boundary of freezing becomes the cooling surface through which
heat transfer takes place. It is this moving boundary, which
then controls the pattern of the formation of ice crystals and,
therefore, fibers. The important consideration in all cases is
the production of well-defined fibers having an orderly alignment
similar to natural meat. If needed, the surfaces of the mass
not in contact with the cooling source can be insulated to
reduce heat transfer at these surfaces. It is observed, in most
; cases, that the surfaces not in contact with the one or the two
opposed cooling surfaces exhibit a thickness of somewhat randoml~
oriented fibers. This is because directional cooling at these
edges is difficult to obtain due to heat transfer with external
sources. This edge portion can be either retained in the final
product or severed therefrom such as by cutting with a knife,
heated wire or the like. It is also noted that where cooling is
effected from two opposed surfaces, horizontal surfaces of
discontinuity appear, bisecting the thickness of the frozen
mass. This is apparently due to the independent crystal growth
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from each of the opposed surfaces toward a plane of contact in
the middle of the mass.
Many cooling sources can be employed according to the
present invention. For example, the aqueous protein mixture can
simply be placed in a pan and the pan set on a piece of dry ice
or submerged to a slight depth (e.g. 1/8 inch) in a cold liquid
such as liquid nitrogen, ethylene glycol, brine, or the like.
Alternatively, a container of the aqueous protein material can
be placed on a plate fxeezer or between two opposed plate
reezers. Also suitable would be a moving belt type freezer of
the kind illustrated in U.S. Patents 3,253,420 and 3,606,763.
The temperature employed can be any temperature effective to
yield substantially independent, aligned ice crystals. It is
noted that, while the rate of cooling is generally not a factor
with regard to the formation of well defined, well-ordered,
. .
elongated fibers where the cooling is substantially unidirec-
tional, the rate of cooling does definitely affect the size and
shape of the crystal. Rapid cooling rates result in the forma-
tion of minute, microscopic ice crystals. Slower cooling or
fxeezing rates result in the formation of long, needle-like ice
crystals. Preferred cooling rates, defined in terms of the rate
of advance of the freezing boundary, range from about 0.02 to
about 1.0 ft/hr, more preferably from about 0.03 to about 0.5
ft/hr.
While there is nothing presently believed critical in
the temperature of the protein solution or slurry prior to the
freezing step, it is considered preferable to reduce the tem-
perature of the solution or slurry to as close to the freezing
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point as possible prior to subjecting it to free~ing. This is
preferred at the present time solely on the basis of economics.
It is less expensive to cool a liquid by conventional means with
turbulence and high surface contact with the heat transfer media
than to cool by means of the single or two opposed heat transfer
elements employed for freezing. It is cautioned, however, that
the liquid mixture should not be supercooled prior to the freez-
, .ing operation as this will result in too rapid, random cooling
and will produce an undesirable, random fiber structure in the
product.
Unexpectedly, when this frozen material is immersed in
a liquid, such as liquid nitrogen, substantially colder than the
frozen mass, cleavage planes are produced perpendicular to the
direction of fiber formation. A similar effect is noted when
the frozen mass is immersed in a substantially warmer liquid.
After stabilizing the protein, and heating as will be hereinafter
discussed, the product can be rehydrated to givé a surprisingly
fish-like texture. While not wishing to be bound by any theory,
a plausible explanation of what is occurring during this process
is based on the manner in which the material reacts during
freezing. During the unidirectional freezing step, a concentra-
tion gradient of the dissolved solids (e.g. salts, aminoacids,
polypeptides etc.) is generated along the fiber axis. This
gradient occurs repeatedly as the ice crystal front moves upward
and away from the cooling surface. As a result, planes of high
and low solids concentration are generated along the fiber axis.
Corresponding to these planes are weak regions (planes) perpen-
dicular to the fiber axis. When the frozen material is subse-
quently immersed in a bath at a substantially warmer or colder
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temperature, (e.g. liquid N2), the expansion of the ice crystals
along the fiber axis causes the fiber to crack along the weak
planes thereby giving a structure similar to tuna fish muscle
upon freeze-dr~ing and heat setting~ In the exemplary situation
where the minimum dimension of the frozen mass is about two
inches, the temperature during immersion is preferably at least
50C colder or warmer than the frozen mass, and more preferably
at least 100C different. Where the minimum dimension is greater,
the temperature difference must also be greater; where lesser,
the temperature difference can be lesser.
.,~
After freezing, and shock temperature treating as
described above, the crystalline structure of the material can
be easily observed, if desired, by fracturing the frozen mass
and observing it visually. To retain the integrity of the
individual protein fibers thus formed, the protein is stabilized
according to the present invention by freeze drying or by immers-
ing the frozen mass in an a~ueous solution, comprising an edible,
water-soluble material capable of lowering the freezing point of
water and stabilizing the protein. If the substantially soluble
protein is not stabilized prior to heating, such as for heat
setting, the heating will result in excessive bonding of the
individual ibers due to melting of the ice crystal lattice
separating them. As the fibers are then heat set, they tend to
form a less dintinctly fibrous mass. For fish analo~s especially,
` this excessive bonding of the protein material is undesired.
Also in this regard, the frozen mass should not be stored at
temperatures which are only slightly below the freezing point of
the mass for extended periods of time. Storage under these
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conditions will cause recrystallization of the ice and randomi-
zation of the fibrous structure. While this may be desirable to
some extent as a means o~ effecting the texture of a final fish
analog, it must only be done with the knowledge that reorienta-
tion is occurring, and it must be allowed to proceed only to
the extent that would be desirable for a particular application.
The frozen mass can be freeze dried in conventional
manner using conventional equipment. The product can be sub-
divided either before or after freeze drying. It should be
dried sufficiently to reduce the moisture content to the point
where the structure does not collapse. The details of freeze
drying are well known to those skilled in the art and form no
part of the present invention. In an exemplary freeze drying
situation a laboratory freeze dryer is employed to freeze a one
inch thick slab having a total volume of 3 liters. The drying
.
takes approximately two days to reduce the moisture content to
~ a level of from about 3~ to 5%. In this specific set-up, the
; plate temperature is about 20 to 30C, preferably about 25C;
t~e condenser temperature is from about -40 to -7QC, pre~erably
about -50C; and the pressure of the freeze drying chamber is
from about 20 to 50 microns, preferably from about 30 to 40
microns of ~g. This set of conditions is merely exemplary of
those which can be employed and is not to be taken as limiting
of the present invention. Any freeze-drying technique which is
capable of drying the fibers to self-sustaining form, preferably
to a moistuxe content of less than about 10%, while not allowing
substantial melting of the ice crystals to allow excessive
`- bonding of the fibers and does not maintain the temperature at
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723~4
too high a level for a period o~ time which would cause randomi-
zation of the fibrous structure, would be effective and appro-
priate according to the present invention.
Alternatively, the frozen mass can be immersed in a
stabilizing solution in any convenient manner using conventional
equipment. The product can be subdivided either before or after
immersion. Water miscible organic solven~s have been previously
used to precipitate proteins, and any of these known materials
can be used as the stabilizing material in aqueous solution so
long as they decrease water availability to the protein, decrease
the hydrophillic potential of the protein by causing conforma-
tional changes in the protein, lower the freezing point of the
water and lower the surface tension of the water. The amount of
water available to the protein is reduced simply by the reduced
mole fraction of water in the presence of these stabilizing
- materials. Thus, the water is less available for dissolving the
protein. The effective stabilizing materials also enhance the
displacement of the equilibria;
- helix + water
hydrated random protein coil
- conformation + water
to the right, thereby adversely affecting the solubility of the
proteins. The most effective stabilizing materials which can be
employed, reduce the surace tension of the water and thereby
reduce the contribution of the water to protein hydrophobic
group adherence. The most noticeable adherence e~fective in
decreasing protein solubility is noticed, in the case of organic
solvents, where the molecules have short, straight-chained
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hydrophobic groups. Reducing the freezing point of the water is
essential because the stabilizing material must be able to
penetrate the ice in the frozen product mass.
'! Among the suitable stabilizing materials are the polar
organic solvents such as alcohols, with ethanol and propanol
being preferred on the basis of their lack of toxicity even
where large residual amounts of these solvents remain in the
product. Ethanol is particularly preferred; however, any solvent
can be employed so long as it has the indicated functionality
and is not toxic at the reasonable levels which may remain in
the product after removal of the solvent by known techniques
such as extraction and drying. Also suitable as the stabilizing
or coagulating materials are the known acids and salts having
the necessary functionality in aqueous solution. If desired,
these known salts and/or acids can be employed in combination
; with an alcohol, such as ethanol, or other non-toxic organic
solvent. Such combinations are desirable from the standpoint
that it allows a balancing of the benefits and liabilities of
the various stabilizing agents for a particular processing or
product application. Among the suitable acids are hydrochloric~
sulphuric, phosphoric, acetic and other edible acids. Among the
suitable salts are the edible ammonium, alkali metal and alkaline
earth salts of these acids as well as other salts having the
` indicated functionality.
: While only exemplary of suitable stabilizing materials
: which can be employed, ethanol will be employed as the stabiliz-
ing material in the following discussion for conciseness. When
a frozen mass of protein and ice prepared in the ~anner described
above is brought into contact with ethyl alcohol in a coagulation
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bath, a diffusional interchange occurs between the two phases,
water in the protein and the ice crystals, and ethyl alcohol.
The ice crystals melt and water leaves while alcohol enters the
protein phase. As soon as protein comes into contact with
alcohol, it is insolubilized and the fibers stabilized. In
order to insolubilize the protein completely, alcohol has to
diffuse into the protein phase thoroughly. After a sufficient
length of time, no more exchange takes place: hence, a state of
equilibrium is achie~ed between the two phases. The final
equilibrium concentration of alcohol in the coagulating bath is
dependent on the ratio of alcohol to water in the frozen protein
mass. The concentration of alcohol in this coagulating bath
affects the freezing point of solution as well as the diffusion
rate and coagulation rate of protein which are important factors
to control in this process.
When the unidirectionally frozen protein mass is
immersed in the alcohol bath to stabilize the freeze-aligned
fibrous structure! the temperature of the bath mus~ be lower
than freezing point of the protein solution. This immobilizes
free water and thereby minimizes rehydration of the protein and
dissolution of the freeze-aligned structure by water. At the
freezing temperature, water exists as ice crystals in the protein
mass. When ice crystals contact with alcohol, the ice melts and
water diffuses out; at the same time the protein also contacts
with a sufficient concentration of alcohol and is insolubilized.
If the temperature of alcohol bath is close to freezing point of
water, higher than -5C, recrystallization takes place in the
frozen protein block, and the unidirectional fibrous structure
disappears and a random structure is formed.
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Freezing point depression is dependent on the con-
- centration of solute added in solution. Therefore, the freezing
point of the coagulating bath can be regulated b~ changing the
concentration of alcohol. In order to prevent ~reezin~ the
alcohol bath, the freezing point must be lower than the process-
ing temperature.
While any effective concentration of stabilizing
.: .
` material can be employed, in the case of ethanol, it is found
that the concentration should be maintained at above about 10~,
and preferably above 20~. With one particular sample using 5
ethanol, the protein was completely solubilized and fibrous
~ structure was disintegrated. At 10%, thP protein was partially
`~ solubilized and fibers were very soft. However, the fibers did
not fall apart. At 20~ alcohol, the protein was not solubilized.
- The texture was soft due to partial hydration. At higher than
~ 30% alcohol, the protein was completely insoluble and the texture
:~ of the fibrous material was hard. When the final equi~ibrium
concentration of alcohol in this coagulation process was higher
than 70%, the fibers were very fragile due to excessive de-
hydration of protein. It appears that optimum concentration at
equilibrium was about 60~ of eth~l alcohol.
Ethanol soluble pigments, carboh~drates, oil and fat
`~ in protein materials are diffused out during this process. This
~ is desirable from the standpoint of removing pigments and flatu-
. ~ ., .
` lents from the products. Fat and oil can be reco~ered and used
~`~ in foods.
`~ Once stabilized by freeze drying or immersion as
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i described above, the fibrous mass can be dried, stored for
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indefinite periods of time and later heat set; or heat set
immediately and then stored for subsequen~ use. It is possible
through the proper selection of the particular type of heat
treatment, to effect the texture, color, toughness, tensile
stren~th, rehydra~ion and water retention properties of the
final product. Textured materials receiving severe heat treatment
tend to retain less water upon rehydration. However, all tex~ured
materials according to the present invention preferably receive
an amount of heat treatment sufficient to increase the structural
integrity of the fibers. Materials receiving mild heat treatment
tend to be softer and more pliable than those which receive
severe heat treatment. Moist heat treatment is highly efficient
and gives an extremely good fish flesh-like texture to the final
product.
The amount of heat treatment, with or without pressure,
to stabilize the product varies with the type of protein materials
used. By way of example, dry soy milk fibers are preferably
heat ~reated in an autoclave under a 15 psig pressure for from
about 5 to 10 minutes to stabilize the structurer and fibers
from soy flour, on the other hand, are preferably heat treated
for from 20 to about 25 minutes under the same conditionsO Any
; combination of time, temperature, and pressure effective to heat
set the protein into substantially independent fibers can be
employed according to the present invention. It appears that
heat treatment at a temperature ranging from about 100 to
about 120C for a time of from about 5 to about 30 minutes i5
adequate depending upon the texture desired in the final product.
The exact times, temperatures, and pressures employed will be
~ easily determinable by those skilled in the art for a wide
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variety of products. Reference to the examples below will show
a number of specific heat treatment operations which will guide
those skilled in the art.
Typical of the heating means which can be employed are
conventional autoclave or steam chamber devices capable of
producing pressures of up to about 20 psig and temperatures of
up to about 130C. ~lso suitable would be electric or gas-fired
infrared ovens capable of operating under conditions of high
relative h~lmidity. The use of moist heat in such devices, or in
the autoclave or steam chambers previously mentioned, aids in
providing a more complete coagulation or immobilization of the
protein materials. The specific heating means employed is not
critical to the present invention. All that is necessary is
that the heat be sufficient in time and intensity to coagulate
or immobilize the protein sufficiently to substantially prevent
loss of the individual protein fibers upon rehydration.
. ~.~
~ After heat setting, the fibrous protein material can
,:
` be marketed as is, or rehydrated immediately to obtain a more
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meat-like texture. The product is easily rehydrated by soaking
in water for a period of time effective to obtain a desired
water content. The rehydrating solution can contain acids for
neutralizing any residual alkali, or flavorings, emulsified
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fats, flavor enhancers, condiments, sugars, heat coagulable or
soluble proteins, amino acids, and the like. In this manner,
the product can be modified to have the taste as well as the
texture of fish. Of course, as indicated previously, these
ingredients can also be employed in the aqueous protein mixture
` before freezing. Experience with particular recipes will dictate
at what point these additives are employed.
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The following examples are presented or the purpose
of further explaining and illustrating the present invention,
and are not to be taken as limiting in any regard. Unless
otherwise indicated, all parts and percentages are by weight.
EXAMPLE I
~ To prepare a texturized soy protein product having
i~ highly-oriented, well-defined fibers in a fish-like texture, a
soy milk is used as a protein source. The soy milk is prepared
by soaking 600 grams of soy beans for 16 hours in water, changing
the water several times. The soaked beans are then ground in
boiling water, the water being present at a 10:1 ratio with
regard to the soy beans. The resulting slurry is heated to
boiling and held for 15 minutes, and filtered through a double
layer of cheesecloth. The residue on the cheesecloth is dis-
carded and the level of solids in the supernatant is determined.
The pH of the supernatant is then adjusted to 7.5 using 2N sodium
hydroxide, and an antioxidant is added to the superna~ant at a
level equivalent to 0.02% of the fat content. Because full fat
soy beans are employed, the fat content of the supernatant is
about 1/4 the weight of the solids present. The soy bean milk
is then placed in an aluminum pan to a depth of about one inch.
The pan is placed on a block of dry ice (~76C) which extends
~" across the entire bottom surface of the pan. Unidirectional
ice crystals, substantially perpendicular to the bottom of the
'` pan, are generated. The mass is completely frozen in about 30
minutes. The frozen mass is then placed in liquid nitrogen for
about one minute during which time this shock cooling causes
planes of fractures transverse to the direction of alignmen-t of
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; the fibers. The frozen mass is removed ~rom the pan and immersed
in 95% ethanol at the weight ratio of 1:4 for 8 hours with stir-
ring at a temperature ranging from -5 to -10C. The stabilized
` fibrous material is pressed by applying force perpendicular to
the direction of fibers to hasten the release of ethyl alcohol
trapped in the spaces between the fibers. The pressed product
is then air dried to remove water and residual ethanol. This
drying process strengthens the structure. This dried material
is autoclaved at 15 psig for 10 minutes to strengthen the struc-
ture. The heat set material is then rehydrated by soaking in
water or about 20 minutes to yield a product having discrete,
soft, chewy, fish-like fibers.
: EXAMPLE II
To prepare a texturized soy protein product having
` highly-oriented, well-defined fibers in a fish like texture, a
` soy milk is used as a protein source. The soy milk is prepared
by soaking 600 grams of soy beans overnight in water, changing
" the water several times. The soa~ed beans are then hot ground
:
with boiling water, the water being present at a 10:1 ratio with
regard to the soy beans. The resulting slurry is heated to
boiling and held there for 15 minutes, and filtered through a
double layer of cheesecloth. The residue on the cheesecloth is
discaxded and the level of supernatant is then adjusted to 7.5
- using 2N sodium hydroxide, and an antioxidant is added to the
supernatant at a level equivalent to 0.02% of the fat content.
Because full fat 50y beans are employed, the fat content of the
supernatant is about 1/4 the weight of the solids present. The
soy bean milk is then poured into a two inch cellulose sausage
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casing to a height of about one foot. The casing is lowered in
1/2 inch intervals into a bath cooled to -40C. The soy milk is
allowed to freeze to a height of about 1 1/2 inches above the
surface of the bath each time before further lowering the casing
until the ice-liquid interface is about 1 inch above the surface
of the bath. Unidirectional ice crystals, substantially per-
pendicular to the surface of the bath, are generated. Lowering
the casing from the air above the bath in~o the bath causes
shock stressing of the mass and fracturing at planes of weakness
due to the temperature differential between the mass as maintained
above and below the surface of the bath. The frozen mass is
removed from the pan and immersed in 95% ethanol at the weight
ratio of 1:4 for 8 hours with stirring at a temperature ranging
from -5 to -10C. The stabilized fibrous material is pressed
by applying force perpendicular to the direction of fibers to
hasten the release of ethyl alcohol trapped in the spaces between
the fibers. The pressed product is then air dried to remove
water and residual ethanol. This drying process strengthens
the structure. This dried material is autoclaved at 15 psig for
` 20 10 minutes to strengthen the structure. The heat set material
`' is then rehydrated by soaking in water for about 20 minutes to
yield a product having discrete, soft, chewy, fish~like fibers.
EXAMPLE III
The procedure of Example II is repeated, but this time
the material is freeze dried instead of immersing it in the
ethanol. The freeze dried material is then treated with moist
heat at 15 psig for 10 minutes to stabilize tha structure.
EXAMPLE IV
A fibrous 50y protein product is prepared from soy
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protein isolate. Here lOOg of soy protein isolate (91% protein)
was mixed with 900g of water to make 10% solution and pH was
adjusted to 7.0 -8Ø This solution is placed in a pan to a
depth of about 1 inch and ~rozen and stabilized as described in
Example I.
EXAMPLE V
A fibrous protein product is prepared from peanut pro-
tein isolate. Here 150g of peanut protein isolate (93~ protein)
was mixed with 850g of water to make 15~ solution and pH was
adjusted to 7.0 - 8Ø This solution is placed in a pan to a
depth of about 1 inch and frozen and stabilized as described in
Example III.
EXAMP~E VI
A fibrous egg albumin product is prepared from fresh
egg white. The whites of several eggs are separated from the
~` yolks, placed in a pan, frozen and stabilized as described in
Example I. Here 10% egg albumin solution prepared from egg
white powder can be successfully used.
EXAMPLE VII
`.`! 20 A fibrous fish protein product is prepared from a 15
aqueous mixture of fresh fish meatO To prepare the aqueous
~; mixture, 150g of lean fish meat is homogenized with %50 ml of
cold 3~ NaCl aqueous solution in a Waring Blendor* at high
speed for about 5 minutes under vacuum. The resulting homogen-
ate mixture is then placed in a pan, fxozen, and stabilized as
described in Example II.
'``
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EXAMPLE VIII
The procedure of Example I iS again repeated, but this
time the soybean milk is concentrated as follows: The pH of the
`. soybean milk is adjusted to 4.5 by adding HCl (lN). The result-
ing precipitate is separated by centrifugation at S,000 x G for
20 minutes. The supernatant is discarded. The precipitate is
transferred to a mixer and mixed with water for 20 minutes to
get a smooth and concentrated (18 to 20% solids) soybean milk.
The soybean milk slurry is then adjusted to a pH of about 7.5
using 2N sodium hydroxide and the resulting solution is placed
in a pan, frozen and further processed as in Example I.
Many modifications and variations of the present
,~
invention will be apparent to those skilled in the art upon
reading the above disclosure. It is intended that all such
modifications and variations be included within the scope of the
~ .
~ present invention which is defined by the following claims.
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