PROCESS FOR PRODUCING PROTEIN CONCENTRATE OR ISOLATE AND CELLULOSIC THERMOCHEMICAL FEEDSTOCK FROM BREWES SPENT GRAINS

Abstract

A process for treating brewers spent grains for producing a high value protein product and a cellulosic residue, both from brewers spent grains that have not gone through fermentation. The high value protein product is useful as a protein supplement for human consumption, or feed for livestock and poultry. The cellulosic residue has value as a feedstock for a thermochemical process unit, such as for the production of a biofuel.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application based on provisional application 62/447,383 filed Jan. 17, 2017.

BACKGROUND OF THE INVENTION

This invention relates to a process for treating brewers spent grains, that have not gone through fermentation, for producing a high value protein product and a cellulosic residue product. The high value protein product is useful as a protein supplement for human consumption, or feed for livestock and poultry. The cellulosic residue product has value as a feedstock for a thermochemical process, such as for the production of a biofuel.

BACKGROUND OF THE INVENTION

Brewers spent grains (BSG) is the major by-product left after the processing of steeped, germinated, dried cereal gains (malt) for the production of beer and other malt products. Though barley is the primary grain used for brewing, beers can also be made from other grains such as wheat, rye, maize, rice, oats, sorghum and millet. In general, BSG represents about 85% of the total by-products generated. BSG can generally be defined as a lignocellulosic material containing inter alia, water, cellulose, non-cellulosic polysaccharides, lignin, crude proteins, and crude fats. BSG is available in large quantities throughout the year, but its main application has been limited to animal feeding. Since BSG still contain proteins, there is a significant interest in the brewing industry to further process the BSG to obtain more valued products, particularly for human consumption.

Also, a substantial amount of research and development is undertaken in an effort to reduce our dependency on petroleum-based energy and to move us toward more sustainable and environmentally friendly energy sources, such as wind energy, solar energy, and biomass. The conversion of biomass into transportation and other fuels is of great interest for reducing reliance on fossil fuels. Various biomass conversion technologies employ thermochemical processes, such as pyrolysis and gasification, that have relatively high capital and operating costs. In particular, sourcing and preparing biomass feedstocks, such as wood and agricultural residues, such as corn stover and soybean hulls, for pyrolysis or gasification, typically result in marginal production economics.

Conventional processes have met with varying degrees of commercial success for obtaining higher value products from brewers spent grains, but there still exist a need for improving efficiency and economics of such processes. One such desired product is a high protein content product suitable for human consumption.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided a process for producing a protein product, and a cellulosic product suitable as a feedstock for thermochemical processing, from brewers spent grains having a starch and protein content, and which have not gone through fermentation, which process comprises:

a) introducing into a hydrolysis tank, with constant stirring, a mixture comprised of: i) brewers spent grains having a protein content and a starch content, and which has not gone through fermentation, and ii) an amount of water so that the ratio of water to grains is from about 8:1 to 11:1;

b) adding glucoamylase to the mixture in an amount that will convert at least about 90 wt. % of the starch to sugars;

c) heating said mixture to a temperature from about 30° to about 70° C.;

d) cycling said heated mixture to and from a particle size reduction stage wherein the average size of grain particles, in said mixture, is reduced to an average size less than 500μ;

e) maintaining the temperature of about 30° C. to about 70° C. for an effective amount of time to allow at least 95 wt. % of the starch of the grains to be converted to sugars;

f) adjusting the pH of the mixture to a level from about 7 to 10.5;

g) adding an alkaline protease enzyme to the mixture in an amount to solubilize 80 wt % to 90 wt % of the protein present;

h) passing the enzyme-containing mixture through a screen having 5 to 500μ openings thereby resulting in a permeate comprised of proteins of the grains, the alkaline protease enzyme, and solids having a particle size less than 5 to 500μ, and a retentate comprised of solids having a particle size greater than 5 to 500μ;

i) passing said permeate resulting from step h) above to an ultrafiltration stage comprised of a membrane having pores of 20 kDa to 40 kDA in size, resulting in a retentate comprised of proteins greater than 20 kDA to 40 kDA in size, the alkaline protease enzyme, and fiber material; and a liquid permeate comprised of proteins smaller than 20 kDA in size;

j) recycling the retentate from said ultrafiltration stage to the hydrolysis tank until there are no more proteins to hydrolyze, wherein during recycling the pH of 7 to 10.5 and the temperature of about 30° C. to 70° C. of the mixture are maintained;

k) conducting the resulting liquid permeate from said ultrafiltration stage to a nanofiltration stage wherein the resulting retentate has a solids content of from about 10 wt. % to about 50 wt. %; and

l) conducting the retentate having a solids content of about 10 wt. % to about 50 wt. % solids to an evaporation stage wherein at least a fraction of any remaining water is driven off thereby resulting in a product comprised of at least about 60 wt % to about 90 wt. % protein.

In a preferred embodiment of the present invention the brewers spent grain is barley grain.

In another embodiment of the present invention the mixture is conducted to solids separation stage prior to being conducted to the ultrafiltration stage, which solids separation stage to remove solids species of the mixture that could clog the ultrafiltration membrane.

In yet another embodiment of the present invention the permeate from the ultrafiltration stage is conducted to a heat treatment stage wherein it is subjected to temperatures capable of deactivating any remaining enzymes in the mixture.

In still another embodiment of the present invention the solids separation stage is comprised of microfiltration membrane.

BRIEF DESCRIPTION OF THE FIGURE

The FIGURE hereof is a flow diagram illustrating one preferred embodiment of the present invention. Dashed line in this FIGURE represent optional embodiments to the instant process.

DETAILED DESCRIPTION OF THE INVENTION

Any brewers spent grains can be used for the practice of the present invention as long as they have not been subjected to fermentation, as distillers grains have. Non-limiting examples of such grains include barley, wheat, rye, maize, rice, oats, sorghum and millet Preferred is barley.

The present invention can be better understood with reference to the FIGURE hereof. The instant process is generally practiced by introducing into hydrolysis tank HT brewers spent grains and an effective amount of water to achieve a ratio of water to grains, on a dry weight basis of 8:1 to 11:1. It is preferred that the ratio of water to grains be from about 9:1 to 10:1. Brewers spent grains received from a brewer are typically in a wet condition. The ratio of water to grains for wet grains received directly from a brewer will typically be from about 3:1 to about 6:1, more typically from about 3.5:1 to about 5:1. Thus, water will need to be added to achieve the desired ratio of water to grains for the process of this invention. Hydrolysis tank HT can be constructed from any suitable material, preferably a stainless steel. It can be open at the top, or enclosed with a suitable cover containing ports for allowing entry of water, grains, and any other ingredient, or reactant, needed for the practice of the present invention. Hydrolysis tank HT will also contain a stirring apparatus (not shown) of suitable corrosion resistant material. It is preferred that the mixture contained in hydrolysis tank HT be constantly stirred throughout the instant process.

The pH of brewers grains typically received form a brewer will normally be in the range of about 3.5 to about 6.5. If they are not in that pH range, the pH can easily be adjusted, usually with use of a suitable acid. The preferred pH range is from about 4.5 to 5.5. The acid used can be any suitable acid that is capable of achieving the desired pH range. The acid can be either an inorganic acid, preferably hydrochloric acid, or an organic acid, such as a carboxylic acid. The acidic mixture is then heated to a temperature from about 30° C. to about 70° C., preferably from about 40° C. to about 60° C. An effective amount of glucoamylase is added to the mixture in an amount that will convert at least about 90 wt. % of the starch to sugars About 0.1 wt. % to about 0.2 wt. %, preferably about 0.15 wt. % of glucoamylase, on a dry weight basis, is added. It will be understood that the terms “mixture” and “slurry” can be used interchangeably herein. It will also be understood that it is not critical to the instant process that the glucoamylase be added after the mixture is heated. For example, the glucoamylase can be added and then the mixture heated to 30° C. to 70° C.

The mixture is continually cycled to and from particle size reduction zone M1 via lines 10, 12, and 16. A particle size reduction stage can also sometimes be referred to herein as a milling stage. Any suitable particles size reduction equipment can be used that is capable of reducing the size of particles in an aqueous mixture or slurry, preferably at a water to grains ratio of 8:1 to 11:1. It is preferred that a colloid mill or rotor stator type of mill be used. More preferred is high-shear rotor-stator wet milling equipment. Rotor-stator wet milling equipment is well known in the art and can be commercially obtained from such companies as Kady International having a facility in Scarborough, Me.; Custom Milling & Consulting Inc having a facility in Fleetwood, Pa.; and Chemineer having a facility in Dayton, Ohio. The aqueous mixture is milled for an effective amount of time. That is, for that amount of time that will result in an average particle size of grains in the mixture to be less than about 500 microns (μ). This amount of time will typically be from about 30 minutes to about 60 minutes, preferably for about 45 minutes. The temperature and pH are maintained for an effective amount of time in order to hydrolyze substantially all of the starch from the grains. By substantially all we mean at least about 90 wt. %, preferably greater than 95 wt. %, and more preferably at least about 98 wt. % hydrolyzed. It is most preferred that substantially all of the starch be converted to sugars. That is, wherein only a very small percent, for example less than about 1 wt. %, more preferably less than about 0.5 wt. % is left unconverted. This amount of time will typically be from about 20 minutes to about 60. The hydrolyzing process takes about 30 to 45 minutes which allows time to effectively mill the grain. The grains are most likely completely milled to the desired size in about 20 minutes, but extra time is preferred to allow the starch in the grains to be converted to sugar.

The pH of the resulting mixture in hydrolysis tank MV is brought to about 7 to 10.5, preferably from about 8 to 10, more preferably to about 8.5 to 9.5 with use of a suitable aqueous base solution. It is preferred that an alkali or alkaline earth metal aqueous solution be used, more preferred is the use of sodium hydroxide. The resulting treated mixture is then passed through a screen SN having 60μ openings resulting in an aqueous permeate containing proteins and solids having an average particle size less than 60μ and a retentate comprised of solids having a particle size greater than 60μ.

The permeate that passes through screen SN is then conducted via line 18, along with an alkaline protease enzyme introduced into line 18 via line 19, to ultrafiltration stage UF. The amount enzyme introduced into line 18 will be an effective amount that will be at least that amount to solubilize 80 wt % to 90 wt % of the protein present. Such an amount will be from about 0.1 wt. % to about 0.3 wt. %, preferably about 0.25 wt. %, on a dry weight basis. It is also preferred that the alkaline protease enzyme be alcalase. Ultrafiltration stage UF will be comprised of a suitable membrane having pores of a size of about 0.5 to 1.5 kDA. he term kDa is well known in the art and is used as a measure of molecular weight or mass. For example, one hydrogen atom has a mass of 1 Da. Proteins and other macromolecule molecular weights are usually measured in kDa or kilodaltons wherein 1 kDa is 1000 Da (daltons). The residence time of the mixture passing through the ultrafiltration membrane will be long enough to allow hydrolysis of both starch and larger size proteins to take place. It will be understood that hydrolysis of proteins takes place in both hydrolysis tank HT and ultrafiltration stage UF.

There may be an occasion to provide a coarser filtering step prior to ultrafiltration stage UF. One occasion to use a course filter prior to ultrafiltration is when the mixture is such that it begins to clog the ultrafiltration membrane, thereby preventing a suitable flow-through and preventing the ultrafiltration membrane from adequately performing its intended function. If the mixture is to be filtered prior to ultrafiltration stage UF, then the mixture flowing through line 18 is diverted through line 100 to first separation stage S1. Any suitable solids separation equipment can be used for S1 as long as it is capable of filtering out solids greater than about 100 kDA. Non-limiting examples of such suitable equipment include a microfiltration membrane, a hydrocyclone, and a decanting centrifuge. Preferred is a microfiltration membrane having pores of about 100 kDA in size. The permeate from this first separation stage will be sent, via line 110 to ultrafiltration stage UF. The retentate from S1 will be recycled to hydrolysis tank HT via lines 120 and 16.

The permeate from ultrafiltration stage UF, which contains substantially all of the lower molecular weight proteins is preferably conducted to nanofiltration stage NF via line 20. It is within the scope of this invention that the permeate from ultrafiltration stage UF be heat treated prior to nanofiltration stage NF in the event there are still alkaline protease enzymes remaining in the permeate. If heat treatment is desired the permeate is passed via line 200 through heat treatment stage H which is operated at an effective temperature to deactivate any remaining enzymes. This temperature will be an effective temperature to cause deactivation of the enzyme. This temperature will typically be from about 75° C. to 100° C., preferably from about 80° C. to 85° C. The mixture is then held at that temperature for an effective amount of time to ensure that the enzyme is deactivated. This effective amount of time will be from about 2.5 to about 30, preferably from about 5 to 20 minutes, more preferably about 15 minutes. Any suitable heat treatment equipment can be used. One heat treatment type of equipment preferred for the practice of the present invention is pasteurization equipment. The heat treated permeate is then passed to nanofiltration stage NF via lines 210 and 20.

The retentate from ultrafiltration stage UF, which may still contain high molecular weight proteins, fiber material and fats, is recycled via line 21 and 16 to hydrolysis tank HT until there are no more proteins to hydrolyze. High molecular weight proteins, for purposes of this invention, those that stay in the retentate of the UF membrane, are >20 kDA. The molecular weight of the proteins passing through the UF membrane are less than 20 kDA. At the NF stage, proteins and any other species that are <1 kDA, which include amino acids and very low molecular weight proteins are removed.

Nanofiltration is well known in the art and is a membrane filtration-based method that uses nanometer sized cylindrical through-pores that pass through the membrane at 90°. Nanofiltration membranes have pore sizes from 0.5 to 1.0 kDa, which is smaller than that used in microfiltration and ultrafiltration, but typically larger than reverse osmosis. The retentate from the nanofiltration stage will typically be comprised of about 20 to 50 wt. % solids and is passed via line 22 to evaporation stage VE which is preferably performed under a vacuum wherein the solids content of the stream is increased to about 50 to 60 wt. % solids. The stream exiting evaporation stage VE is passed via line 24 to first drying stage D1 to drive off at least a fraction of the water and to concentrate the protein. It is preferred that substantially all of the water be driven off by the use of a spray drier to result in a powdered protein product. It is also within the scope of this invention that an ultrafiltration membrane be used that has pores large enough to allow the enzyme to pass through. Such a membrane would be those whose pores are greater than about 20 kDA, particularly those having pores in the range of about 30 to 100 kDA. In such a case, the use heating treatment stage H is preferred.

The permeate from the nanofiltration stage NF can optionally be sent via line 300 to a reverse osmosis unit RO so that clean, low solids water can be recycled back to the hydrolysis tank HT via line 310 for water conservation purposes. The clean water is the permeate from reverse osmosis unit RO. The retentate from reverse osmosis RO is preferably disposed of as wastewater via line 320. The RO membrane will have pores from about 100 to 500 daltons, so everything larger than that will be removed from the water stream.

The retentate of that does not pass through 60μ screen SN situated down the bottom of hydrolysis tank HT remains in extraction tank and continues to be recycled to and from first particle size reduction stage M1. Of course, as grain particles become less than 60μ in size they will eventually pass through screen SN and be conducted to ultrafiltration stage UF. Those particles greater than 60μ that are left in the upper section of hydrolysis tank HT are conducted via line 26 as an aqueous slurry to second liquid/solids separation stage S2 wherein the solids are separated, sent via line 28 to second dryer D2, then via line 30 to second milling stage M2 to result in a fiber flour product.

Alternative hydrolysis conditions can include: temperatures from about 10° C. to about 100° C., preferably from about 20° C. to about 80° C., more preferably from about 30° C. to about 70° C. and most preferably from about 40° C. to about 60° C.; and times from about 30 minutes to 180 minutes, preferably from about 60 minutes to about 150 minutes, and more preferably from about 90 minutes to about 130 minutes.

In a preferred embodiment, the treated spent brains be subjected to an effective amount of ultrasonic energy to improve the efficiency of the protein extraction portion of the process. The preferred effective ultrasonic energy input is from about 3 to about 30 Joules/gram of grains with a frequency of about 40 kHz with about 3 to about 10 Joules/gram being preferred.

The following additional embodiments are also within the scope of this invention; i) the use of a debittering exo-peptidase prior to the drying step at a pH between 6.5-9 and a temperature of 45° C. to about 65° C. for 30 to 120 minutes to reduce protein bitterness; ii) the use a debittering exo-peptidase during the alcalase addition step to reduce protein bitterness; iii) performing the milling step prior to the addition of glucoamylase, iv) include the addition of alpha-amylase and/or beta-amylase during the glucoamylase addition step to increase starch hydrolysis of branched chains; v) separate the water and from grains immediately following the glucoamylase addition step which removes the glucose from the process prior to solubilizing the protein, then add additional water to the grains to bring the water to grains ratio back to 9:1 and continue the process as normal; vi) the use of a mild milling to separate the husk from the rest of the grain, then separate from the grain and continue the process as normal after husk removal; and vii) during the glucoamylase addition step, add an effective amount of glucose oxidase, which will oxidize the glucose to form hydrogen peroxide which will lighten the color of the end products and reduce the glucose content, then continue the process as normal.

Also within the scope of this invention is a brewery process wherein a cereal grain is processed to produce a beer and leaving a substantial amount of spent grains as a by-product. The spent grains are then processed in accordance with the process herein described for obtaining a concentrated protein product and a cellulosic product from the spent grains. Conventional beer making steps typically require that a cereal grain, preferably barley, be prepared for brewing by a process involving malting, heating, drying out, and cracking open the husks of the kernels of the grains, which helps expose the starches during the mashing process. In mashing, the grains are steeped in hot, but not boiling water for an effective amount of time, typically about an hour. This activates enzymes in the grains that cause it to break down the starch into sugars. Once this is done the water is drained from the mash, which is now rich in sugar from the grains. A sticky, sweet liquid referred to as “wort” is produced and it is often referred to as unmade beer. The wort consists primarily of sugars and water resulting from mashing. At this point lautering can be used to separate the wort from spent grains as efficiently as possible. Once the wort has been separated from the grains in the lautertun, the process described herein can be performed using the lautertun as the extraction tank. The lautertun has a false bottom with a screen that can act as the 60 micron screen previously described. It also contains a stirring mechanism.

The wort is boiled for an effective amount of time then hops and other spices are added. Hops provide bitterness to balance out the sugar in the wort and provide flavor. Once the wort is cooled, strained, and filtered and put into a fermentation vessel wherein yeast is added. At this point the brewing is complete and fermentation begins. The beer is stored for a few weeks at cold temperatures in the case of lagers, while the yeast works its magic by eating up the sugar and producing carbon dioxide and alcohol and waste products. The resulting beer can then be conditioned so it can mature and become smooth and by-products of fermentation diminished. The beer can be subjected to secondary fermentation.

Claims

1. A process for producing a protein product, and a cellulosic product suitable as a feedstock for thermochemical processing, from brewers spent grains having a starch and protein content, and which have not gone through fermentation, which process comprises:

a) introducing into a hydrolysis tank, with constant stirring, a mixture comprised of: i) brewers spent grains having a protein content and a starch content, and which has not gone through fermentation, and ii) an amount of water so that the ratio of water to grains is from about 8:1 to 11:1;

b) adding glucoamylase to the mixture in an amount that will convert at least about 90 wt. % of the starch to sugars;

c) heating said mixture to a temperature from about 30° to about 70° C.;

d) cycling said heated mixture to and from a particle size reduction stage wherein the average size of grain particles, in said mixture, is reduced to an average size less than 500μ;

e) maintaining the temperature of about 30° C. to about 70° C. for an effective amount of time to allow at least 95 wt. % of the starch of the grains to be converted to sugars;

f) adjusting the pH of the mixture to a level from about 7 to 10.5;

g) adding an alkaline protease enzyme to the mixture in an amount to solubilize 80 wt % to 90 wt % of the protein present;

h) passing the enzyme-containing mixture through a screen having 5 to 500μ openings thereby resulting in a permeate comprised of proteins of the grains, the alkaline protease enzyme, and solids having a particle size less than 5 to 500μ, and a retentate comprised of solids having a particle size greater than 5 to 500μ;

i) passing said permeate resulting from step h) above to an ultrafiltration stage comprised of a membrane having pores of 20 kDa to 40 kDA in size, resulting in a retentate comprised of proteins greater than 20 kDA to 40 kDA in size, the alkaline protease enzyme, and fiber material; and a liquid permeate comprised of proteins smaller than 20 kDA in size;

j) recycling the retentate from said ultrafiltration stage to the hydrolysis tank until there are no more proteins to hydrolyze, wherein during recycling the pH of 7 to 10.5 and the temperature of about 30° C. to 70° C. of the mixture are maintained;

k) conducting the resulting liquid permeate from said ultrafiltration stage to a nanofiltration stage wherein the resulting retentate has a solids content of from about 10 wt. % to about 50 wt. %; and

l) conducting the retentate having a solids content of about 10 wt. % to about 50 wt. % solids to an evaporation stage wherein at least a fraction of any remaining water is driven off thereby resulting in a product comprised of at least about 60 wt % to about 90 wt. % protein.

2. The process of claim 1 wherein the brewers spent grains are spent barley grains.

3. The process of claim 1 wherein the ratio of water to grains is about 9:1 to about 10:1.

4. The process of claim 1 wherein the particle size reduction is performed with a rotor stator mill.

5. The process of claim 1 wherein at least 95 wt. % of the starch is converted to sugars in step e)

6. The process of claim 7 wherein at least 98 wt. % of the starch is converted to sugars.

7. The process of claim 1 wherein the alkaline protease enzyme is alcalase.

8. The process of claim 1 wherein the pH is adjusted during step a) to about 3.5 to about 6.5.

9. The process of claim 1 wherein pasteurization is performed at a temperature from about 70° C. to about 90° C.

10. The process of claim 1 wherein the membrane used in the nanofiltration stage contains pores in the range of 500 to 1000 daltons.

11. The process of claim 1 wherein the enzyme-containing mixture from step h) herein is first passed through a separation stage capable of separating out solids greater than about 100 kDA in size prior to being passed to said ultrafiltration stage.

12. The process of claim 11 wherein the separation stage is microfiltration stage containing a microfiltration membrane having pores of about 100 kDA in size.

13. The process of claim 1 wherein the permeate from said ultrafiltration stage is passed to a heat treatment stage wherein it is subjected to an effective temperature of deactivating any enzymes present in the permeate.

14. The process of claim 1 wherein the permeate from said nanofiltration stage is conducted to a reverse osmosis stage wherein particles greater than about 200 daltons will be removed.