GB2326723A

GB2326723A - Monitoring the viscosity of gluten

Info

Publication number: GB2326723A
Application number: GB9813603A
Authority: GB
Inventors: Mark L Bason; Natalie E Turner; Robert W Sleigh
Original assignee: Newport Scientific Pty Ltd
Current assignee: Newport Scientific Pty Ltd
Priority date: 1997-06-27
Filing date: 1998-06-26
Publication date: 1998-12-30
Also published as: DE19828667A1; GB9813603D0; NL1009504A1; NL1009504C2; AUPO759697A0

Description

1 2326723 ASSESSING THE PROPERTIES OF FLOUR PROTEINS

BACKGROUND OF THE INVENTION

This invention relates to a method for assessing the properties of gluten or gluten-containing products and hence suitability for use in various. processes such as bread-making, or other uses such as noodle making, extrusion, etc.

DESCRIPTION OF THE PRIOR ART

Gluten is the name given to a mixture of proteins, primarily largemolecular- weight proteins called glutenins and smaller-molecular-weight proteins called gliadins, found in flour associated with the starch in the endosperm of the grain (e.g. wheat) from which the flour is milled.

Dough is a viscoelastic material comprising flour, water and, optionally, a leavening agent such as yeast or baking powder, kneaded together. In the process of kneading, the gluten proteins bond together to form a visco-elastic network weaving through the starch in the dough and it is this network which gives dough the ability to hold gas bubbles on the dough's rising. The strength of the dough is believed to be reliant on the quality of the glutenin proteins rather than the gliadins, although the combination of both is important.

The extent to which the gluten forms this visco-elastic network is known as its vitality, which depends on properties such as the gluten's molecular weight average and distribution, but also reflects the processing history of the gluten or glutencontaining products. For example, denaturing of the gluten proteins by heat damage or extraction using detergents will cause loss of gluten vitality.

Prior art methods for assessing gluten characteristics include preparing flour into a dough and assessing the physical properties, such as extensibility, of that dough. The molecular sizes of the gluten proteins may be determined using size-exclusion methods such as chromatography including high-performance liquid chromatography (HPLC), and gel electrophoresis. Other methods of determining the gluten's characteristics include sedimentation testing and baking sample batches of the dough and testing its properties.

2 Disadvantages of the known gluten assay methods are that they are timeconsuming, and require. the assays to be done in a laboratory environment. It would be advantageous for e.g. wheat farmers to be able to measure the gluten quality quickly, economically, accurately and without the need for a laboratory set-up.

SURY OF THE INVENTION The object of the present invention is to overcome the disadvantages of the prior art by providing a more convenient method for assessing the baking characteristics of glutencontaining material.

In a first form, the invention provides a method of assessing the properties of gluten, including the steps of taking a sample of a gluten-containing material, mixing the sample with a solvent and subjecting the mixture to conditions suitable for the gluten to be solubilised, stirring the mixture and assessing the viscosity of the solution.

A preferred solvent for use in the invention is a mixture of alcohol, preferably Cl - C4, with water.

Ethanol is most preferred, at concentrations preferably of about 5-50%, most preferably about 8-20%. Other solvents such as organic acids and bases and dimethylsulfoxide also may assist in the solubilisation process. The gluten solution preferably is heated to at least 500C most preferably to about 70-90'C, while the viscosity is measured.

Preferred apparatus for carrying out the assay method includes a sample container into which the gluten sample and solvent are placed, heat transfer means for controlled heating of the swnple, stirring means positioned within the container and means for analysing and recording the temperature and the viscosity of the solution.

BRIEF DESCRIPTION OF THE DRAWINGS

Further preferred embodiments of the invention now will be described with reference to the accompanying drawings, in which:

Fig. 1 is a schematic representation of viscometer apparatus suitable for use in the invention; and 3 Fig. 2 is a sample result graph in which both temperature and viscosity of two identical samples are plotted against time.

Fig. 3 is a further sample result graph in which both temperature and viscosity of different samples are plotted against time.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A viscometer apparatus suitable for use in preferred embodiments of the invention is the Rapid Visco Analyser (RVA) manufactured by Newport Scientific Pty Ltd of Sydney, Australia. Fig. I is a schematic illustration of that apparatus. A more complete description of its construction and operation may be found in U. S. Patent

No. 4,879,897, the contents of which are incorporated herein by reference.

The apparatus of Fig. I includes a cylindrical sample canister 10 having a side wall of heat-conductive material such as aluminium and a stirrer 12 including a stem 13 and a paddle 14. At the top of the stirrer 12 there is provided a plate 15 and coupling pins 16.

An electric motor 17 and drive coupling 18 arrangement is movable from a position allowing insertion and removal of the canister 10 to the position shown in Fig. 1, in which the motor 17 is positioned directly over the canister 10 and the drive coupling 18 engages the coupling pins 16 to drive rotation of the stirrer 12.

Heating blocks 19 clamp into contact with the side wall of the canister 10 to transfer heat through the canister 10 to its contents. Heating of the blocks 19 is controlled by a microprocessor 20 to create a desired temperature profile over the test cycle.

A temperature sensor (not shown) in the vicinity of the canister 10 provides an input signal to the microprocessor 20 and the temperature data is recorded, for example by outputting the value to a plotter 22.

Simultaneously with the commencement of heating, the stirrer 12 is rapidly rotated at approximately 800- 1 OOOrpm to mix the sample in the canister 10. The stirrer 12 thereafter is run more slowly, at a fixed speed in a range of about 100 200rprn, for assessment of the viscosity by measuring the current of the stirrer 12.

The viscosity output also is sent to the plotter 22 by the microprocessor.

4 In a preferred assay method, a sample of gluten or of gluten-containing product (e.g. flour) is placed in the canister 10. Ethanol and water are added at room temperature and the mixture is agitated to form a slurry. The stirrer 12 is placed in the canister 10, which then is placed in the RVA apparatus as shown in Fig. 1.

Alcohol, or alcohol/water mix, are preferred solvents as it is believed that these achieve solution of the gluten without cleavage of the protein molecules, which would affect its characteristics. The alcohol or alcohol/water solvent becomes effective to solubilise the gluten upon heating in the RVA. Reduction of pH, usually to the range 4.0 to 6.0, but covering the range 3.0 to 7.0, along with addition of ethanol also may facilitate estimation of gluten quality: lower levels of pH assist in solubilising the gluten protein and also are beneficial in dough development.

The initial rapid stirring of the sample places the gluten in homogeneous suspension. As the temperature increases, the gluten is solubilised sufficiently for the stirring to cause entanglement of the gluten proteins, forming a protein network within the solution and increasing the viscosity of the solution. The viscosity profile and temperatures of these for the mixture are believed to indicate the ability of the gluten sample to form networks, and thus of its functional characteristics as required for its end use.

Further information of the gluten characteristics may be gained by addition of enzymes such as alpha-amylase to remove the viscous effects of non- protein polymers such as starch.

Example 1

Into a canister of an RVA apparatus was placed 6g gluten. To the gluten was added, at room temperature, 3.5g ethanol and 20.5g water, and the sample mixture was agitated to form a slurry.

A stirrer was placed into the canister, which was then placed into the RVA apparatus as shown in Fig. 1.

The RVA apparatus commenced heating and initial rapid stirring of the sample mixture at 960rpm to place the gluten into homogeneous suspension. The microprocessor controlled gradual heating of the sample mixture to about 85C, held at that temperature, and then allowed cooling, over a 20minute test cycle.

Concurrently, the stirrer was run at 160rpm and the viscosity of the solution calculated from measuring the current.

Fig. 2 is a copy of the resultant plots of temperature (top line, right hand axis) and viscosity (bottom line, left hand axis) against time. As the temperature sensor in the RVA is located outside the canister, there is some time-lag between the temperature reading and the sample temperature. As can be seen from Fig. 2, as the sample mixture was heated to and held at around 85'C, the viscosity of the sample mixture rose and reached a plateau as the protein formed a network in solution. The viscosity rose fiirther to a peak then fell rapidly as the sample mixture was cooled and the gluten in the sample mixture formed a ball around the stirrer in the RVA machine.

The dual lines for viscosity indicate the test results for two samples from the same source. It can be seen that the results were highly reproducible.

The test also may be carried out using a 2 - 6g sample of flour in place of 3 8g of gluten.

Example 2

Into a canister of an RVA apparatus was placed 6g vital gluten. To the gluten was added, at room temperature, 3.5g ethanol and 20.5g water, and the sample mixture was agitated to form a slurry.

The RVA apparatus commenced heating and initial rapid stirring of the sample mixture at 960rpm to place the gluten into homogeneous suspension. The microprocessor controlled gradual heating of the sample mixture to about 85'C, held at that temperature, and then allowed cooling, over a 30minute test cycle.

The above protocol was repeated using 6g non-vital (heat-darnaged) gluten in place of the 6g vital gluten.

Fig. 3 is a copy of the resultant plots of temperature (top line, right hand axis) and viscosity (bottom line, left hand axis) against time. As the temperature sensor in the RVA is located outside the canister, there is some time-lag between the temperature reading and the sample temperature. As can be seen from Fig. 3, as the 6 sample mixture was heated to and held at around 85'C, the viscosity of the sample mixture rose and reached a plateau as the protein formed a network in solution. The viscosity rose further to a peak then fell rapidly as the sample mixture was cooled and the gluten in the sample mixture formed a ball around the stirrer in the RVA machine for the vital sample, whereas there was no dough ball formed in the heat-damaged sample and thus the viscosity did not drop at the end of the test. - The two lines for viscosity are for two different samples, a vital sample and a heat-damaged sample. It can be seen that there are large differences between a vital and a non-vital gluten sample.

While particular embodiments of this invention have been described, it will be evident to those skilled in the art that the present invention may be embodied in other specific forms without departing from the essential characteristics thereof. The present embodiments and examples are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

7

Claims

1. A method of assessing the properties of gluten, including the steps of taking a sample of a gluten-containing material, mixing said sample with a solvent and subjecting the mixture to conditions suitable for the gluten to be solubilised, stirring said mixture and assessing the viscosity of said solution.

2. A method according to claim I wherein the gluten proteins become entangled and the gluten forms a protein network during said mixing and stirring steps.

3. A method according to claim I wherein changes in viscosity of said solution over time are assessed and recorded.

4. A method according to claim 3 wherein said changes in viscosity are compared to known standards.

5. A method according to claim I wherein said solvent is a mixture of alcohol with water.

6. A method according to claim 5 wherein said alcohol is a C, - C4 alcohol.

7. A method according to claim 6 wherein said C, - C4 alcohol is ethanol.

8. A method according to claim 7 wherein the concentration of ethanol employed is within the range 5-50%.

9. A method according to claim 8 wherein said concentration of ethanol employed is 8-20%.

10. A method according to claim I wherein said solvent contains an organic acid, organic base or dimethylsulfoxide.

11. A method according to claim 1 wherein said gluten solution is heated to at least 50'C while the viscosity is measured.

12. A method according to claim 11 wherein the temperature of said gluten solution is increased to approximately 85'C, held at that temperature and then decreased while the viscosity is measured.

13. A method of assessing the properties of gluten, including the steps of providing a sample container into which a sample mixture of a glutencontaining material and a solvent are placed, heat transfer means for controlled heating of said 8 sample, stirring means positioned within said container and means for assessing and recording the temperature and the viscosity of the gluten- containing solution, and heating said sample mixture, stirring said mixture and assessing and recording the changes in said temperature and viscosity.