Note: Descriptions are shown in the official language in which they were submitted.
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Background of the Invention
This invention relates to a process for the
preparation of a high protein content product from brewer's
spent grain (hereinafter referred to as BSG).
BSG is a saccharification residue of brewer's malt
(optionally containing rice, corn grits, corn grits, corn
starch, etc.) and is obtained as a by-product in the
production of beer. Usually, the BSG is separated from wort
in a wet state by means of a solid-liquid separator such as a
lauter tub or a mash filter, and has a water content of about
80 ~ by weight and contains about 25 ~ of proteins on dry
basis.
United States patent No. 3,846,397 discloses a
process of recovering proteins from BSG, in which BSG is
heated in an alkaline solution. One serious problem of this
process is deterioration of the quality of the product due to
the heat and alkali treatments.
United States patent No. 5,1135,765 (Kish et al)
discloses a process for producing a protein-rich product from
BSG, in which BSG in a wet state is passed through a roll
mill and is then sieved to recover a protein-rich product.
Since this process uses only physical treatments such as roll
milling and sieving without resorting to a chemical treatment
such as an alkali treatment, the protein-rich product is
quite safe for feed and food, and has a very high protein
content. In this process, the protein-rich product as sieved
is dried in vacuum to produce a dried product. Since the as
sieved product has a very high water content, the vacuum
evaporation method is not industrially applicable for reasons
of economy.
Summary of the Invention
It is, therefore, the primary object of the present
invention to provide an economical process which can produce
a dry high protein content product from BSG on a large scale.
Another object of the present invention is to
provide a process of the above-mentioned type which can
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produce a high quality product with a high yield.
In accomplishing the above objects, there is
provided in accordance with the present invention a process
for the preparation of a high protein content product from
brewer's spent grain containing husks and a proteinaceous
material adhering to the husks, comprising the steps of:
(a) pressing the brewer's spent grain having a water
content of at least 65 % by weight to separate said
proteinaceous material from said husks with simultaneous
grinding of said proteinaceous material;
(b) dispersing the product obtained in step (a) in water
to obtain a slurry having a solid matter content of 3-5 % by
weight;
(c) filtering said slurry with a sieve having a mesh
size of 30-60 mesh to obtain a filtrate containing said
ground proteinaceous material and a solid residue;
(d) separating said filtrate into a condensed slurry
containing 0.5-2 % by weight of said ground proteinaceous
material and a supernatant;
(e) separating said condensed slurry into a solid-rich
phase having a water content of 70-95 ~ by weight and a
liquid phase;
(f) contacting said solid-rich phase with a hot gas
while maintaining said solid-rich phase at a temperature not
higher than 100C such that said solid-rich phase is dried to
have a water content of 15 % by weight or less within 60
seconds, thereby obtaining said high protein content product.
Brief Description of the Drawing
Other objects, features and advantages of the
present invention will become apparent from the detailed
description of the preferred embodiments of the invention
which follows, when considered in light of the accompanying
drawing, in which:
the sole FIGURE is a schematic flow diagram showing
an apparatus suitable for carrying out the process according
to the present invention.
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Detailed Description of the Preferred
Embodiments of the Invention
BSG is constituted by husks, germs and other
particles having protein contents of about 5 ~ by weight, 50
% by weight and 50 % by weight, respectively. The germs and
other particles are bound to or adhered to the husks. In the
present specification, the germs and other particles are
commonly referred to as "proteinaceous material". BSG
separated from wort and having a water content of about 70-80
% by weight may be used as such for the purpose of the
present invention. The BSG concentrated or dried for
easiness in storage and transportation may also be used for
the purpose of the present invention after addition of water
to have a water content of at least 65 ~ by weight.
Referring now to FIGURE, BSG is fed through a line
21 to a pressing zone 1, preferably a roll mill, where BSG is
subjected to pressing and shearing forces so that the
proteinaceous material is scraped and separated from the
husks with simultaneous grinding of the proteinaceous
material. When a roll mill is used, it is preferred that the
gap between rolls be 0.05-2 mm, more preferably 0.1-0.3 mm.
The BSG treated in the pressing zone 1 should contain at
least 65 % by weight of water, since otherwise part of the
husks which have a low protein content will be also
pulverized and incorporated into the final product, so that
the protein concentration of the product is lowered.
The press-ground product obtained in the pressing
zone 1 is then introduced through a line 22 into a mixing
zone 2, where the press-ground product is dispersed in water
supplied through a line 41. The dispersing operation is
performed with stirring by any suitable means such as a
propeller-type stirring apparatus for a period of time
sufficient to form a slurry, generally for 5-30 minutes,
preferably 10-20 minutes. The water is used in an amount so
that the resulting slurry has a solid matter content of 3-5
by weight, preferably 4-5 % by weight.
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The slurry is fed through a line 23 to a first
sieving zone 3 and is filtered with a sieve having a mesh
size of 30-60 mesh (0.213-0.567 mm) to obtain a filtrate, in
the form of a slurry, containing the ground proteinaceous
material and a solid residue containing the husks. The sieve
used in the sieving zone 3 is preferably of a vibrating-type.
The ground proteinaceous material generally has a protein
content of 50-52 % by weight on dry basis.
The filtrate is fed through a line 30 to a first
separation zone 6. Preferably, the solid residue obtained in
the first sieving zone 3 is fed to a second mixing zone 4,
where the solid residue is dispersed in water supplied
through a line 42 to obtain a mixture, in the form of a
slurry, having a solid matter content of 3-5 % by weight,
preferably 4-5 % by weight. As a result of this treatment,
the ground proteinaceous material remaining, in a small
amount, in the solid residue is separated therefrom. The
mixture is fed through a line 25 to a second sieving zone 5
and is filtered with a sieve having a mesh size of 30-60 mesh
(0.213-0.567 mm) to a first phase (filtrate) which has passed
through the sieve and which contains a small amount of the
ground proteinaceous material and a second phase (solid
residue) which has remained on the sieve and which is
substantially free of the ground proteinaceous material. The
first phase (filtrate) obtained in the second sieving zone 5
is fed to the first separation zone 6 through a line 26
together with the filtrate from the first sieving zone 3.
In the first separation zone 6, the filtrate from
the sieving zones 3 and 5 is separated into a condensed
slurry containing 0.5-2 % by weight of the ground
proteinaceous material and a liquid phase. In one preferred
embodiment, the separation zone 6 is a sedimentation tank or
settler having a discharge port at the bottom thereof. The
filtrate fed to the sedimentation tank 6 is allowed to
quiescently stand for 5 minutes to 2 hours, preferably 10-20
minutes, until a condensed slurry containing 0.5-2 % by
weight, preferably 1-2 % by weight, of the ground
215S0~2
proteinaceous material is formed as a result of the
sedimentation. During the sedimentation, the fats (vegetable
oils and fats) contained in the ground proteinaceous material
is dissolved into water so that the protein concentration of
the ground proteinaceous material is increased. The slurry
is discharged from the sedimentation tank 6 through the
bottom discharge port and is introduced into a second
separating zone 7 through a line 27. The supernatant
obtained in the sedimentation tank 6 is fed to the water tank
13 through lines 31 and 39.
In the second separating zone 7, the slurry is
separated into a solid-rich phase having a water content of
7-95 ~ by weight, preferably 80-90 ~ by weight, more
preferably 80-85 ~ by weight, and a supernatant phase by any
suitable dehydrating device such as a centrifuge, a drum
filter, a leaf filter or a filter press. The use of a
continuous centrifuge is preferred. The protein-containing
solid-rich phase is fed to a drying zone 8, whereas the
supernatant is fed to the water tank 13 through lines 38 and
39.
In the drying zone 8, the solid-rich phase is
brought into direct contact with a hot gas to obtain a dried
product. The drying should be carried out under specific
conditions, since otherwise the product is discolored or
deteriorated; i.e. the product becomes dark and shows a
reduced digestibility by the enzyme pepsin. Thus, it is
important that the solid-rich phase should be maintained at a
temperature not higher than 100C, preferably 80-90C, and
should be dried so that the water content of the solid-rich
phase is reduced to 15 % by weight or less, preferably 10-12
~ by weight, in a period of 60 seconds or less, preferably in
a period of 30-60 seconds. The hot gas is preferably hot air
and preferably has a temperature of 300-500C, more
preferably 400-450C. The drying is suitably carried out
with a rotary kiln-type dryer or a drum dryer.
The dried product is discharged from the drying
zone through a line 29 and is recovered. The dried product
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generally containing lumps is preferably ground into a
particle size of 0.1-1 mm and is packaged. If desired, an
anti-oxidant such as ethoxyquin (for animal feeding) or
Vitamin E (for food purposes).
The solid residue (husks) obtained in the sieving
zone 5 is fed to a dehydrating zone 9 through a line 32. The
solid residue generally has a water content of 85 % by weight
or more, typically about 91 % by weight, is thus dehydrated
in the zone 9 so that the dehydrated product has a water
content of less than 75 ~ by weight, typically 65-70 % by
weight. A screw press, a centrifuge or a filter may be used
to effect the dehydration.
The dehydrated product is then fed to a combustion
zone 10 through a line 33 and is combusted. The combustion
zone 10 may be, for example, a fluidized bed incineration
furnace or a rotary incineration furnace. The combustion
waste gas is introduced through a line 34 into a heat
exchanger where the heat of the combustion waste gas is
recovered by indirect heat exchange with a suitable gas
medium such as air. The heated medium is fed to the drying
zone 8 through a line 50 as at least part of the hot gas.
The water separated in the dehydrating zone 9 is
fed to a separating zone 12, preferably a sedimentation tank,
through a line 35, and is allowed to quiescently stand for 5
minutes to 2 hours, preferably 10-20 minutes, so that solids
contained in the water in a small amount are separated by
sedimentation to form a slurry in the bottom of the
sedimentation tank. The slurry, which generally contains
0.5-1.5 ~ by weight of solid matters (husks and trace amount
of the proteinaceous material), is discharged through a line
36 and recycled to the dehydrating zone 9. The supernatant
obtained in the sedimentation tank 12 is fed to the water
tank 13 through lines 37 and 39.
The water from the separating zones 6, 7 and 12 is
collected in the water tank 13 and is recycled to the mixing
zones 2 and 4 through a line 40 and the lines 41 and 42.
Excess water is discharged from the tank 13 through a line
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43, while make up water is supplied to the tank 13 through a
line 44.
In the above embodiment, the second mixing zone and
the second sieving zone may be omitted, if desired. In this
case, the solid residue separated in the sieving zone 3 is
fed to the dehydrating zone 9.
The following examples will further illustrate the
present invention. Parts and percentages are by weight.
Example 1
BSG (water content: 78 ~, protein content: 25.5 %
on dry basis) was treated using the system shown in the
FIGURE. Thus, 100 Kg of the BSG (dry weight 22 kg) were
pressed and ground with a roll mill 1 having a roll aperture
of 0.1 mm.
The ground mass was then placed in a mixing tank 2
together with 447 liters of water and stirred for 10 minutes
with a propeller stirrer. The resulting slurry (solid matter
content: 4 ~) was filtered with a 55 mesh sieve 3 (wire net,
opening: 0.250 mm) of a vibrating type to obtain 189 kg of
solid residue constituted of husks (water content: 91 %, dry
weight: 17 kg) as a plus fraction and 358 liters of a
filtrate in the form of a slurry (solid matter content: 1.4
%, dry weight 5 kg, protein content: 52 % on dry basis) as an
under-size fraction.
The solid residue was placed in a mixing tank 4
together with 236 liters of water and stirred for 10 minutes
with a propeller stirrer. The resulting slurry (solid matter
content: 4 ~) was filtered with a 55 mesh sieve 5 (wire net,
opening: 0.250 mm) of a vibrating type to obtain as a plus
fraction and 258 liters of a filtrate in the form of a slurry
(solid matter content: 1 ~, dry weight 2 kg, protein content:
47 ~ on dry basis) as an under-size fraction.
The under-size fractions (total 616 liters, protein
content: 50.0 ~ on dry basis) obtained by the sieving steps 3
and 5 was fed to a settler 6 and allowed to quiescently stand
for lO minutes. The sediment (condensed slurry, solid matter
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content: 2 ~) was discharged from the bottom of the setter 6
and recovered. The amount of the recovered sediment was 370
liters. The supernatant (amount: 246 liters, solid matter
content: 0.1 %) was also recovered.
The sediment was found to have a protein content of
52.5 ~ on dry basis. Thus, the protein content is increased
by the sedimentation. The increase is considered to be
ascribed to the dissolution of lipids contained in the
proteinaceous material in water during the sedimentation
stage.
The condensed slurry obtained in the settler 6 was
dehydrated using a centrifuge 7 (3,600 G) to obtain 38 kg of
protein-containing solid-rich phase (water content: 85 ~).
The solid-rich phase was fed to a rotary hot air dryer 8 and
dried for 60 seconds by contact with the hot air to obtain 6
kg of protein-rich product (water content: 10 ~). The hot
air had a temperature of 440C. The solid-rich phase was
maintained at a temperature below 100C throughout the drying
step.
The product was then ground and sieved with a 30
Tyler mesh sieve to obtain 6 kg of a pulverized product.
This was mixed with an anti-oxidant (ethoxyquin) to obtain a
mixture having an ethoxyquin content of 90 ppm. The mixture
was packed in plastic bags.
The solid residue (167 kg, water content: 91 %)
obtained in the sieving step 5 was dehydrated with a screw
press 9 to obtain 50 kg of a dehydrated product (water
content: 70 ~). The dehydrated product was burned in a
rotary incinerator with kerosene oil.
