Method for Producing Extruded Puffed Protein

Abstract

Disclosed is a method for extruding protein, such as whey protein, for example, in a puffed form that can readily be ground, milled, or otherwise reduced in size to produce protein powder that can be used to reduce hardening in protein bars. The method uses acidification of the protein to modify its behavior during the extrusion process and produce extruded products (e.g., crisps) with improved properties.

Claims

1. A method for producing a high-protein, low moisture extruded protein product, the method comprising (a) acidifying at least one protein to provide an acidified protein having a pH of from below 6.0 to above the isoelectric point of the at least one protein; (b) processing the acidified protein by extrusion processing to produce an extrudate having a moisture content of about 35 percent or less; and (c) drying the extrudate to produce a mill-able extruded protein product, wherein the extruded protein product is a high-protein, low-starch product having a moisture content of from about 1% to about 12%.

2. The method of claim 1 wherein the pH of the acidified protein is from about 5.0 to about 5.8.

3. The method of claim 1 further comprising the step of cutting the extruded protein.

4. The method of claim 1 further comprising the step of milling the extruded protein product to produce a protein powder with particle of less than or equal to about 200 nm.

5. The method of claim 1 wherein the protein is selected from the group consisting of whey protein isolate, whey protein concentrate, serum protein isolate, milk protein isolate, milk protein concentrate, micellar casein concentrate, calcium caseinate, other specialized caseinates, egg protein isolate, collagen concentrate, pea protein concentrate, pea protein isolate, chia protein concentrate, flax protein concentrate, soy protein concentrate, wheat protein concentrate, rice protein concentrate, and combinations thereof.

6. The method of claim 1 wherein the protein is selected from the group consisting of whey protein isolate, whey protein concentrate, hydrolyzed whey protein, and combinations thereof.

7. The method of claim 1 wherein the step of processing the hydrated protein mixture using extrusion performed by using a twin-screw extruder.

8. The method of claim 1 wherein the protein mixture is made without added starch.

9. A method for producing extruded high-protein, low moisture whey protein products, the method comprising (a) admixing with water a whey product selected from the group consisting of whey protein isolate, whey protein concentrate, intact whey protein, and combinations thereof, and at least one acidulant to produce an admixture having a pH of from about 5.0 to about 5.8; (b) drying the admixture to produce an acidified whey protein product; and (c) processing the acidified whey protein product using extrusion at from about 120 degrees to about 185 degrees Celsius and from about 500 to about 700 psi, to produce an extruded protein product having a moisture content of about 35 percent or less; and

10. The method of claim 9 further comprising a step (d) drying the extruded protein product to moisture level from about 1% to about 12%.

11. A method for producing extruded protein products comprising the steps of (a) admixing at least one protein powder with at least one acidified protein powder to provide at admixture having a pH having an upper limit of pH 6.0 and a lower limit that is selected to be slightly above the isoelectric pH of the at least one protein; and (b) processing the hydrated protein powder using extrusion under conditions selected for the protein, wherein the extrusion process produces an extruded protein product having a moisture content of less than or equal to about 35%.

12. The method of claim 11 further comprising the step (c) of drying the extruded protein product to provide a moisture level of from about 1 percent to about 11 percent, thereby producing a protein crisp.

13. The method of claim 12 further comprising the step (d) of milling the protein crisp to produce a high-protein, low-starch protein powder.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] FIG. 1 is a photograph of two extrusion products made using a twin-screw extruder by hydrating the protein mixture to a moisture level of less than or equal to about 35 percent, and processing the hydrated protein mixture using extrusion at from about 120 degrees to about 185 degrees Celsius and from about 500 to about 700 psi, to produce an extruded protein product. The product on the left was made using WPI, while the product on the right was made by combining WPI with pre-acidified WPI to produce a protein/pre-acidified protein mixture having a pH of 5.3.

[0023] FIG. 2 and FIG. 3 are photographs illustrating the difference between extruded whey protein puffs produced at pH 6.0 under normal extruder output (FIG. 2) and extruded whey protein puffs produced at the same pH during extruder surging (FIG. 3).

[0024] FIG. 4 and FIG. 5 are photographs illustrating the difference between similarly-processed extruded whey protein puffs, but using pH 5.5 for the starting mix for the puffs in FIG. 4 and pH 6.5 for the starting mix for the puffs in FIG. 5.

[0025] FIG. 6 and FIG. 7 are photographs illustrating the difference between pea protein products extruded under similar conditions, with FIG. 6 representing the untreated product (control) and FIG. 7 representing a product processed according to the method of the invention.

DETAILED DESCRIPTION

[0026] The inventors have developed a method for making extruded, puffed protein products (e.g., puffed whey protein products, puffed pea protein products), which may also be referred to as “crisps,” that are easily milled and have excellent properties-both as crisps and as powders—for use as ingredients in products such as nutritional bars, which are shelf-stable for extended periods of time. The invention provides a method for producing extruded protein products, wherein the extruded protein products are high-protein, low-starch, and low-moisture products. The method comprises acidifying at least one protein with at least one acid to provide an acidified protein in the pH range of from about 6 as an upper limit to just above the isoelectric point of the at least one protein as a lower limit. The pH is targeted in a range that is acidic, but higher than the isoelectric point of the protein, and the protein/acid admixture is processed using extrusion processing to produce an extruded protein product generally having a moisture content of about 35% or less (e.g., less than or equal to 35%). The innovative method allows the protein to increase in structure and viscosity through gelation, while still providing protein that does not clog the die or impede throughput. This can decrease or eliminate extruder surge, and provide products that are extruded at a significantly more consistent rate. The puffed form can readily be ground, milled, or otherwise reduced in size to produce protein powder that can be used to reduce hardening in protein bars when incorporated as ingredient in those bars. The product produced by the method of the invention is a milled high-protein crisp, not to be confused with a product such as texturized vegetable protein (TVP). Crisps of the invention are low-moisture, high-protein products that are expanded without relying on the use of starch to produce the expansion., and are referred to herein as “low-starch” products because they will comprise no more than 5% starch (i.e., less than or equal to about 5% starch), and preferably no appreciable levels of starch, at all.

[0027] The invention provides a method for producing extruded protein products, and is especially useful for producing extruded whey protein products. Acidification of the protein can be achieved by various means known to those of skill in the art, such as, for example, combining at least one protein with at least one pre-acidified protein to produce a protein/pre-acidified protein mixture having a pH of from about 6.0 to about the isolectric pH of the at least one protein, from about 5.0 to about 5.8, etc. The protein thus acidified is processed by extrusion under conditions known to those of skill in the art to be appropriate for the selected protein(s). For example, for whey protein extrusion at from about 120 degrees to about 185 degrees Celsius and from about 500 to about 700 psi provides good results. In various aspects of the method, the pH of the protein/pre-acidified protein mixture is from about 5.0 to about 6.0, from about 5.0 to about 5.9, from about 5.0 to about 5.8, from the isoelectric point of the at least one protein to about 6.0, from the isoelectric point of the at least one protein to about 5.9, from the isoelectric point of the at least one protein to about 5.8, from 5.0 to about 5.5, from the isoelectric point of the at least one protein to about 5.5, etc. It will be understood by those of skill in the art, given the disclosure herein, that selection of a pH in a range that falls slightly above the isoelectric point of the at least one protein is desirable for use in the method. The pH range should be also understood to encompass sub-ranges thereof.

[0028] In another aspect of the invention, the method for producing extruded whey protein products comprises admixing with water a whey product selected from the group consisting of whey protein isolate, whey protein concentrate, intact whey protein, and combinations thereof, and an acidulant to produce an admixture with a pH of from about 5.0 to about 5.8, drying the admixture to produce an acidified whey protein product, and processing the hydrated protein mixture using extrusion at from about 120 degrees to about 185 degrees Celsius and from about 500 to about 700 psi, to produce an extruded protein product. In various aspects, the extruded protein product has a moisture content of less than about 35 percent.

[0029] The method can also comprise the steps of reconditioning a dried acidified protein powder, and processing the reconditioned protein powder using extrusion at from about 120 degrees to about 185 degrees Celsius and from about 500 to about 700 psi, to produce an extruded protein product.

[0030] In various aspects of the invention, the extruded protein product is cut with a knife such as, for example, an inline knife (i.e., inline cutting system) to reduce the size and provide smaller pieces of protein product. Those pieces can then be dried to produce protein puffs. Once dried and cooled, the protein puffs can be milled to produce power having a particle size of less than about 200 nm, for example. Suitable milling/grinding equipment is commercially available. One option for milling extruded protein puffs is the Comitrol® 1700 Processor. Generally, it is advisable to cut the protein puffs to a length of about 2.5 inches or less before drying in order to produce puffs of suitable size for such a milling device.

[0031] Under the same extrusion conditions, WPI will generally gel, burn, and clog up in the extruder, or in the best case scenario, produce a product that consists of browned hardened nuggets, while the whey protein/acidified whey protein combination of the method of the invention will smoothly process and produce an extruded product that can readily be dried to produce a whey protein puff having a lighter color and more pleasant texture and flavor that is more reminiscent of the whey crisp products that can be produced using a combination of whey and carbohydrate. It should be clear to those of skill in the art that using starch or other carbohydrates in high protein products such as bars can be undesirable, particularly in regard to nutritional needs and protein/carbohydrate interactions. The present method allows a formulator to produce a protein puff that is readily mill-able to produce a protein powder that has the improved properties that can be provided by extrusion processing. Small amounts of acidification are occasionally used to improve viscosity in extruded products, however in protein applications, acidification will encourage even more gelling and hardening. Thus, acidifying high-protein products can increase the already high risk of gelation, clogging the extruder, and browning. Because of this, high levels of acidity are typically seen as something to avoid in high protein extrusion, with some choosing to add alkali treatments to improve extrusion in high protein (75-95%) blends (see WO2016/054657, Erie Foods Intl.). However, the inventors have discovered that when tightly controlled, the molecular interaction of the protein molecules, gelling and hardening induced by acid can encourage useful structural changes to the resulting extruded crisp itself. Starch often performs a roll in gel/gelatinized starch matrices in crisp recipes, and the inventors have discovered that encouraging some amount of protein gelling by acidification of the protein can actually reduce the need for starch.

[0032] Although acidification of WPI chemically generally promotes more gelling, this change in rheological properties actually helps the whey protein/acidified whey protein combination move through the extruder without gelling to a level that would clog the extruder and stop the product flow. Promoting a consistent flow rate and pressure allows the product to puff, which can be important for proper drying and eventual milling. The method of the invention provides a means by which protein can be extruded without requiring the addition of starch to facilitate extrusion. The method therefore can be practiced without the addition of starch to the protein mixture, and products made by the method can comprise little to no starch. The method also enables those of skill in the art to extrude whey protein, a protein that has traditionally proven to be more challenging for extrusion processing and crisp production, providing whey protein products made at least about 90 percent whey protein, at least about 95 percent whey protein, and/or exclusively whey protein.

[0033] “Acidified whey protein,” or “pre-acidified whey protein,” as used herein, is a whey protein product such as that described in U.S. Patent Number 8,637,102 (Petersen, B., et al.). It can be produced by combining whey protein (e.g., whey protein isolate) with a sufficient amount of acid in solution to give a solution with an acidic pH (i.e., below pH 6). The acidified protein is then dried to form an acidified protein powder. Acidified whey protein is commercially available from Glanbia Nutritionals, Inc. (Monroe, Wis.) as Bevwise® A-102W.

[0034] Starting material(s) for use in the method of the invention can include, for example, whey protein isolate, whey protein concentrate, serum protein isolate, milk protein isolate, milk protein concentrate, micellar casein concentrate, calcium caseinate, other specialized caseinates, egg protein isolate, pea protein concentrate, pea protein isolate, chia protein concentrate, flax protein concentrate, and combinations thereof. The method is especially useful, however, for producing mill-able puffed whey protein, as it overcomes problems that have been associated especially with whey protein extrusion, and particularly for extrusion of whey protein under lower moisture (i.e., 35% or less) conditions.

[0035] “Extrusion,” as used herein, generally refers to the process of processing the protein mixture using either a single-screw or twin-screw extruder (with the twin-screw extruder being preferred). Both types of machines are well known to those of skill in the art, and are readily available from a variety of equipment manufacturers. Briefly, a twin-screw extruder is a machine having two relatively identical screws that are mounted on shafts and rotate in the same direction in a fixed, closed, housing referred to as a “barrel.” Suitable extruders for use in the method of the invention are available from a variety of manufacturers such as, for example, the Buhler Poly-Twin™ (Bühler AG, Uzwil, Switzerland), a line of extruders from Entek (Lebanon, Oreg. USA), MPX30, MPX40, MPX50, MPX65, and MPX80 extruders from Baker Perkins (Baker Perkins Limited, Peterborough UK), etc. Conditions for extrusion, known to those of skill in the art, are disclosed, for example, in WO2016/054657 (Erie Foods International, Inc.). However, that publication discloses the extrusion of whey protein, acid casein, and alkali, rather than acidified whey protein, the pH produced by that method as compared to the present method being significantly different. The present method also provides a means by which all the protein can be whey protein, which can be significantly more desirable in many product formulations.

[0036] Whey proteins have been extruded for many years under high (>35, up to 90%) moisture levels, in a process widely known as functionalization, to create gelatinized products usable as meat replacers. Milk protein concentrate, which is less prone to gelation and has better pasting properties, being a combination of casein and whey in a ratio of 4:1 casein/whey, has been successfully extruded under low-moisture conditions. However, the inventors are unaware of similar results being produced using isolated whey protein in the form of whey protein isolate or whey protein concentrate. Generally, it has been thought that increasing protein concentrate in an extruded product significantly increases the density and breaking force of the extruded product, so extruding products comprising all, or substantially all, whey protein can be challenging and can result in dense, brittle, products that are not amenable to milling to produce protein powders (Allen, K. E., et al., Influence of Protein Level and Starch Type on an Extrusion-Expanded Whey Product, Int. J. Food Sci. Technol. (2007) 42(8): 953-960).

[0037] Brnčić et al., (Influence of Whey Protein Addition and Feed Moisture Content on Chosen Physicochemical Properties of Directly Expanded Corn Extrudates, Food and Bioprocess Technology, October 2011, 4(7):1296-1306) demonstrated that whey protein can be used in traditional extruded products, but increasing concentrations can impact the product, with increasing protein concentrations impacting both the water solubility index and water absorption index. These differences were particularly pronounced in acidic conditions. Day and Swanson (Functionality of Protein-Fortified Extrudates, Comprehensive Reviews in Food Science and Food Safety, September 2013 Vol. 12(5), p. 546-564) noted that “WPC . . . in excess of 20% resulted in decreased expansion and low sensory scores.” Others have disclosed undesirable absorption characteristics, textural characteristics, and color in whey protein crisps having high levels of whey protein. noting that the changes were most pronounced in whey protein crisps with low pH. Most importantly, gelling and cross-linkage of whey protein typically made products more difficult to extrude at lower pH. Progress has been made to increase the protein content in high protein crisps (e.g., 90% protein has been disclosed in WO2016/054657). However, that method was performed used an alkalizing agent to increase the pH.

[0038] To address the problem of hardening in the extruder, some have used low temperature supercritical carbon dioxide assisted production for extruded whey having a range of from about 50 to about 75 percent whey protein. Obviously, measures such as these can significantly add to the cost of production, which is not the case with the present invention.

[0039] The previous observations reported by others in the field has made it counterintuitive to suggest that the solution to processing of extruded whey protein products having high levels of whey protein (e.g., at least about 80%, by weight) would be to acidify the product. One would expect a decrease in water absorption, higher viscosity earlier in the barrel, and significant cross-linkage and gel formation at the temperatures and pressures used. However, the inventors have discovered that these developments can actually be manipulated to perform a useful purpose under the controlled conditions which are disclosed herein.

[0040] The invention also provides protein products made by the method of the invention. Protein products made by the method of the invention can also include protein powders having excellent color, flavor, wettability, etc., which make the protein powder an excellent ingredient for use in nutritional bar formulations.

[0041] While a method and/or composition may be described herein as “comprising” a series of steps, it should be understood that such a method can also more narrowly “consist of” the recited steps, and such a method can additionally be described as “consisting essentially of” the recited series of steps.

[0042] The invention can be further described by means of the following non-limiting examples.

EXAMPLES

Production of a Mill-Able Extruded Puffed Whey Protein

[0043] WPI (Provon® 190, Glanbia Nutritionals, Monroe, Wis. USA) powder and an acidified WPI (Bevwise® A-102W, Glanbia Nutritionals) powder were admixed at a ratio that should result an estimated pH 5.3 for the admixture (i.e., 17% Bevwise® A-102W, 83% Provon® 190). The dry mixture was then fed into the extruder with enough water to achieve an approximate 27% moisture content. The addition of water was the only “pretreatment” performed on the admixture. The mixture was then fed into a twin-screw extruder.

[0044] Temperature was adjusted to produce multiple runs for comparison, and observations indicated that lower temperatures yielded a more uniform “puffed” product, but it was more prone to surging and inconsistency in the result. Higher temperatures yielded slightly less puffing and product cohesion, which was selected as the target result. Product runs were therefore conducted at higher temperatures within the range of 120 degrees to about 185 degrees Celsius. As product exited the extruder, it was cut with a rotating knife, then fed into an oven to be dried.

Production of a Mill-Able Extruded Puffed Pea Protein

[0045] Extrusion of pea protein was performed in substantially the same manner as that described above for whey protein. Citric acid was blended into pea protein concentrate (“treated”) and the mix was extruded under typical extrusion conditions. The protein extrudate was more easily extruded, more expanded, and more porous than that produced with untreated protein.