WO2008019429A1

WO2008019429A1 - Methods and apparatus for measuring water absorbance in multi-phase systems

Info

Publication number: WO2008019429A1
Application number: PCT/AU2007/001137
Authority: WO
Inventors: Ian John Wesley
Original assignee: Grain Foods CRC Ltd
Current assignee: Grain Foods CRC Ltd
Priority date: 2006-08-14
Filing date: 2007-08-13
Publication date: 2008-02-21
Anticipated expiration: 2009-02-14

Abstract

A method and apparatus for measuring water absorbance in multi-phase systems are disclosed. The apparatus comprises a container and a mixer for mixing water and a material at a constant rate to form a multi-phase system, such as dough, and a pump for adding water to the container at a constant rate. A source of a range of wavelengths of light energy in the NIR spectrum irradiates the multi-phase system, which reflects the light. A detector uses NIR spectrophotometry to detect the reflected light at a plurality of time points during the mixing to obtain a plurality of reflection spectra. A processor coupled to be in communication with the pump, the source of light energy and the detector plots peak height values of the reflection spectra with respect to time, which are indicative of the water absorption of the multi-phase system over time.

Description

TITLE

METHODS AND APPARATUS FOR MEASURING WATER ABSORBANCE IN

MULTI-PHASE SYSTEMS

FIELD OF THE INVENTION

The present invention relates to methods and apparatus for measuring water absorbance in multi-phase systems. In particular, but not exclusively, the present invention relates to methods and apparatus for measuring water absorbance in ground grain and other foodstuffs.

BACKGROUND TO THE INVENTION

Water absorbance is a critical property of many materials in a wide range of disciplines. For example, water absorbance is a critical property of ground grain because it affects the performance of the ground grain in processing and the quality of the final product. Typically, the water absorbance of a ground grain product, such as wheat flour, is measured using a Farinograph instrument. In the Farinograph, typically 20Og of flour is mixed in a mixing bowl that is attached to a torque measuring device. The torque measured by the Farinograph is measured in Farinograph Units (FU) and water is added until the resistance to mixing, as measured by the torque measuring device, reaches a predetermined arbitrary level. The water absorbance is the amount of water added expressed as a percentage of the original flour weight.

Other parameters such as Development Time, Stability and Degree of

Softening are also measured using the Farinograph. With reference to FIG 1 , the Development Time is the time taken to reach the peak maximum torque under standardised conditions, which is 1.8 minutes for the example shown in FIG 1. The Stability is the time taken for the curve to fall to the 500 FU level under standardised conditions, which is 2.5 minutes for the example shown in FIG 1. The Degree of Softening is the fall from the 500 FU level under standardised conditions (12 minutes in Figure 1), which is 135 units in the example shown in FIG 1.

The Farinograph is also commonly used for the analysis of other food and non-food multi-phase systems that involve the redistribution of water during a mixing or other processing step. There are however a number of problems with the Farinograph. Firstly, the torque target is purely arbitrary. This means that the water addition has little relation to the water addition required when manufacturing a food product, nor the water absorbing capacity of the flour. Secondly, the Farinograph relies on the sample forming a visco-elastic dough so that the torque measurement can be made. However, not all grain types possess this property. Thirdly, the test is operator and equipment dependent and consequently a wide range of results for the same sample between different operators of the same instrument and different instruments are often exhibited. Despite these problems, the Farinograph is widely used in the wheat flour product industry. It is known that near infrared (NIR) spectroscopy can be used to measure the chemical properties of materials. It is particularly applicable to the measurement of water in materials and a specific application is the measurement of bound and unbound water in materials. United States Patent No. 6,342,259 entitled Monitoring of Dough Properties, for which the present Applicant is a co-patentee, and recent publications, such as Non-invasive Monitoring of Dough Mixing by Near Infrared Spectroscopy, I. J. Wesley, N. Larsen, B. G. Osborne and J. H. Skerritt, Journal of Cereal Science, 27, 61-69 (1998), demonstrate that NIR spectroscopy can be used to measure the mixing time of wheat flour doughs by measuring the bound and unbound water in the dough. In these applications the water is added at the beginning of the mixing process and the NIR spectrum recorded as mixing progresses. A simple calculation from the spectral data (peak area at 1160nm) is all that is required to estimate the bound water at any point during the mixing process and a plot of these values against time can be used to determine the optimum mixing time.

OBJECT OF THE INVENTION

It is an object of the present invention to provide a method and/or apparatus for measuring water absorbance in multi-phase systems, such as ground grain and the like, that addresses or at least ameliorates one or more of the aforementioned problems of the prior art.

SUMMARY OF THE INVENTION

In one form, although it need not be the only or indeed the broadest form, the invention resides in a method of measuring water absorbance in a water- containing multi-phase system including the step of analyzing the multi-phase system using near infrared (NIR) spectroscopy.

In another form, although again not necessarily the broadest form, the invention resides in a method of measuring water absorbance in a multi-phase system comprising water and a material using near infrared (NIR) spectroscopy, said method including the steps of: (i) adding the water to the material at a constant rate; (ii) mixing the water and the material at a constant rate to form the multiphase system;

(iii) irradiating the multi-phase system with a range of wavelengths of light energy in the NIR spectrum, said light being reflected from the multi-phase system;

(iv) detecting the reflected light over the range of wavelengths using NIR spectrophotometry at a plurality of time points during the mixing to obtain a plurality of reflection spectra; and (v) plotting the peak height values of the reflection spectra with respect to time, said peak height values indicative of the water absorption of the material over time.

Preferably, the method includes the following step: (vi) calculating the second mathematical derivative of the reflection spectra.

Preferably, the method includes the following step: (vii) correcting the peak height values of the reflection spectra by subtracting a minimum peak height value from the peak height values to obtain a plurality of corrected peak height values. Suitably, the range of wavelengths over which the reflected light is detected is 400 - 1700nm and preferably the range is 1100 - 1250nm.

The material may be a material to which water binds, ground grain, wholemeal, flour, or a product derived therefrom or another foodstuff or non- foodstuff. In another form, the invention resides in an apparatus for measuring water absorbance in a multi-phase system comprising water and a material, said apparatus comprising: a container and a mixer for mixing the water and the material to form the multi-phase system; a pump for adding water to the material in the container at a constant rate; a source of a range of wavelengths of light energy in the NIR spectrum for irradiating the multi-phase system, said light being reflected from the multi-phase system; a detector for detecting the reflected light over the range of wavelengths using NIR spectrophotometry at a plurality of time points during the mixing to obtain a plurality of reflection spectra; and a processor coupled to be in communication with the pump, the source of light energy and the detector for plotting the peak height values of the reflection spectra with respect to time, said peak height values indicative of the water absorption of the multi-phase system over time.

Preferably, the pump is a peristaltic pump to control the rate of water addition to a high degree of accuracy.

Preferably, the detector is a diode array detector to achieve a high data acquisition rate. Alternatively, a fixed filter or light emitting diodes can be used. The multi-phase system may be a food product or non-food product.

Further features of the present invention will become apparent from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, preferred embodiments of the invention will be described more fully hereinafter with reference to the accompanying drawings, wherein: FIG 1 shows a typical torque vs. time curve obtained using a prior art

Farinograph and the parameters that can be determined therefrom;

FIG 2 is a schematic representation of an apparatus according to an embodiment of the present invention;

FIG 3 is a general flow diagram illustrating a method according to an embodiment of the present invention;

FIG 4 shows the variation of water absorbance values of a material with respect to time;

FIG 5 shows the variation of corrected water absorbance values of the material with respect to protein corrected water absorbance values for the same material obtained with the prior art Farinograph;

FIG 6 shows the variation of peak area with respect to time obtained by stopping water addition at peak values of the spectra;

FIG 7 shows the variation of the water binding parameter obtained with the present invention with respect to the development time parameter obtained with the prior art Farinograph; and

FIG 8 shows the variation of the gradient parameter obtained with the present invention with respect to the stability parameter obtained with the prior art Farinograph. DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the method and apparatus of the present invention will now be described with reference the water absorbing capacity of materials commonly found in the baking industry. However, it will be appreciated that embodiments of the present invention are applicable to measuring water absorbance in other materials found beyond the baking industry and are applicable to measuring water absorbance other foodstuffs and non-foodstuffs.

In order to measure the water absorbing capacity of a material, such as flour, it is necessary to add water at a known rate. As the water is added to the dry flour and mixed, the water is initially completely absorbed. As more water is added, a dough is gradually formed, the rate of water absorbance decreases, and the amount of unbound water increases. At some point, the maximum amount of water that the flour can absorb will be reached. The inventor has identified that NIR spectroscopy can be used to monitor the amount of unbound water as the mixing process occurs. The NIR method and apparatus of the present invention rely on measuring the unbound water in the system by monitoring the intensity of a range of wavelengths, and a specific wavelength within that range, as water is added to the system at a constant rate.

Referring to FIG 2, in accordance with embodiments of the present invention, there is provided an apparatus 20 for measuring water absorbance in a multi-phase system, such as dough and other food and non-food multi-phase systems that involve the redistribution of water during a mixing or other processing step. Apparatus 20 comprises a container 22, such as a bowl or other vessel, comprising a z-arm Farinograph-type mixer for mixing the multi- phase system, as would be familiar to one skilled in the relevant technical field. A pump 24 adds water to the container at a known constant rate. In a preferred embodiment, pump 24 is a peristaltic pump because the rate of water addition needs to be controlled to a high degree of accuracy. Peristaltic pumps also eliminate, or at least minimize the likelihood of, contamination, which could skew the results.

Apparatus 20 comprises a spectrometer 26 comprising a source 27 of a range of wavelengths of light energy in the NIR spectrum for irradiating the multiphase system in the container 22. The spectrometer 26 comprises a detector 29 for detecting the light reflected from the multi-phase system over the range of wavelengths. The spectrometer 26 must have a high data acquisition rate to enable many measurements to be made per second. Therefore, in a preferred embodiment, the detector is a diode array detector, various suitable models of which are available from a number of manufacturers.

In an alternative embodiment, instead of the diode array detector, a simple fixed filter device using transmission filters suitable for the desired wavelengths can be employed and one or more additional filters to correct for the effects of scatter can be used. In another alternative embodiment, light emitting diodes of the correct wavelength according to the wavelengths measured could be used. Apparatus 20 also comprises a processor 28, such as a standard computer, coupled to be in communication with the pump 24 to monitor the rate of water addition. Processor 28 is also coupled to be in communication with the source 27 and the detector 29 of the spectrometer 26 for receiving, storing and processing the spectral data. It will be appreciated that the processor will include a memory for storing computer readable program code components, some or all of which will be retrieved from memory for executing some of the steps of the method described herein, such as steps (v), (vi) and (vii).

The method 300 of measuring water absorbance of multi-phase systems using NIR spectroscopy according to embodiments of the present invention will now be described with reference to the general flow diagram in FIG 3.

At step 310, the method includes adding water to a material, such as grain or other foodstuff or non-foodstuff being analyzed. Water is added at a constant rate and controlled to a high degree of accuracy using pump 24. At step 320, the method includes mixing the water and the material at a constant rate to form a multi-phase system whilst the water is added at the constant rate. At step 330, the method includes irradiating the multi-phase system with a range of wavelengths of light energy in the NIR spectrum from spectrometer 26. According to one embodiment, the range of wavelengths is 400-1700nm. In a preferred embodiment the range of wavelengths is 1100-1250 nm and the measurement is centred on the absorbance peak at 1160nm, which is the water O-H stretch-bend combination band in the spectrum. The light is reflected from the multi-phase system and at step 340, the method includes detecting the reflected light over the range of wavelengths using NIR spectrophotometry at a plurality of time points during the mixing to obtain a plurality of reflection spectra. It should be appreciated that whilst FIG 3 shows steps 310-340 as separate steps, the steps 310-340 of adding the water to the material at a constant rate, mixing at a constant rate, irradiating the mixture and detecting the reflected spectra occur simultaneously. At step 370, the method includes the processor 28 plotting the peak height values of the reflection spectra with respect to time, the peak height values being indicative of the water absorption of the material over time.

According to a preferred embodiment, the method includes step 350 of calculating the second mathematical derivative of the reflection spectra. Since the calculations are performed on the second derivative spectra, data points either side of the peak, for example, about 50 points either side, are required to accurately calculate the derivative function. Use of the second derivative has a number of advantages. Baseline shifts between the spectra, caused by the position of the multi-phase system in the container 22, are largely removed and overlapping absorbances are separated, making analysis easier.

According to a preferred embodiment, the method includes step 360 of correcting the peak height values of the reflection spectra by subtracting a minimum peak height value from the peak height values to obtain a plurality of corrected peak height values. Processing of the NIR spectrophotometry data can take place in real time as the data is collected or once some or all of the data has been collected.

Example 1

Standard bakers control flour was mixed in the apparatus of the present invention as described above and spectral data was acquired and processed in accordance with the aforementioned method of the present invention. Pump 24 was delivering water at a rate of 10ml per minute to achieve repeatable results and the mixer was running at 100 rpm. However, alternative rates of water addition and/or alternative mixing speeds could be used. One spectrum was acquired every 1.25s and spectra were recorded over the wavelength range 400- 1700 nm at 5 nm intervals. A 4 point (20nm) gap was used to calculate the second derivative of the spectrum and the peak area of the 1160nm band was plotted. A 30 second running average was then calculated. The results are shown in the graph in FIG 4, which illustrates the variation of the peak heights of the reflection spectra with time. Variations in the aforementioned parameters are envisaged. For example, in alternative embodiments, one spectrum can be acquired every 1-2s and alternative wavelength intervals can be employed.

The critical parameter is the corrected maximum height, given by equation 1: Hc = Hmax - H_min (eqn. 1)

The plurality of corrected peak height values were plotted against protein corrected water absorbance values obtained using the prior art Farinograph and the results are shown in FIG 5. There is a clear relationship between the NIR spectroscopy measurements obtained in accordance with embodiments of the present invention and the prior art Farinograph measurements, indicating that the NIR spectroscopy method and apparatus can provide useful information on the water absorbing properties of materials, in particular flours. However, it is also envisaged that the NIR spectroscopy method and apparatus can also provide useful information on the water absorbing properties of other food or non-food multi-phase systems that involve the redistribution of water during a mixing or other processing step. Example 2

The experimental set up and method employed were the same as those in Example 1 described above, except that water addition was stopped at a time i.e. when a maximum water absorption is reached, but mixing is continued. The results are shown in FIG 6, which show the variation in the area of the spectral peak with time. In FIG 6, the drop 600 in the peak area is due to water binding to the dough as it develops. The gradual increase 610 in the peak is due to the dough breaking down.

FIG 7 shows the relationship between the water binding values obtained with the method and apparatus according to embodiments of the present invention with the development time values obtained with the prior art Farinograph.

FIG 8 shows the relationship between the gradient values obtained with the method and apparatus according to embodiments of the present invention with the stability values obtained with the prior art Farinograph.

Whilst there is a considerable amount of scatter on the graphs of FIGS 7 and 8, there is a general trend and the inventor envisages that improvements may be achieved by careful tuning of the dough mixing parameters, such as the mixer speed and rate of water addition. Hence, the method and apparatus according to embodiments of the present invention thus provide a solution to the aforementioned problems of the prior art because the water addition required is more related to that required in the production of a food product. The method and apparatus of the present invention also do not rely on the sample forming a visco-elastic dough to enable a torque measurement to be made as with the prior art Farinograph. It is further envisaged that the present invention is more robust than the prior art in that the results are less dependent on the operator and more repeatable results can be achieved. The method and apparatus of the present invention can be used to measure water absorbance in any multiphase system in which water binds to a material resulting in a change in the spectral data.

In this specification, the terms "comprises", "comprising", "including" or similar terms are intended to mean a non-exclusive inclusion, such that a method, system or apparatus that comprises a list of elements does not include those elements solely, but may well include other elements not listed. Throughout the specification the aim has been to describe the invention without limiting the invention to any one embodiment or specific collection of features. Persons skilled in the relevant art may realize variations from the specific embodiments that will nonetheless fall within the scope of the invention.

Claims

CLAIMS:

1. A method of measuring water absorbance in a multi-phase system comprising water and a material using near infrared (NIR) spectroscopy, said method including the steps of:

(i) adding the water to the material at a constant rate;

(ii) mixing the water and the material at a constant rate to form the multi-phase system;

2. The method of claim 1 , further including the following step: (vi) calculating the second mathematical derivative of the reflection spectra.

3. The method of claim 1 , further including the following step: (vii) correcting the peak height values of the reflection spectra by subtracting a minimum peak height value from the peak height values to obtain a plurality of corrected peak height values.

4. The method of claim 1 , further including acquiring a reflection spectrum every 1-2s.

5. The method of claim 1 , further including detecting the reflected light over wavelengths in the range 400 - 1700nm.

6. The method of claim 1 , further including detecting the reflected light over wavelengths in the range 1100 - 1250nm.

7. The method of claim 1 , further including centering the range of wavelengths over which light is detected on 1160nm.

8. The method of claim 1 , further including detecting the reflected light at 5nm intervals over the range of wavelengths.

9. The method of claim 1, further including detecting data points up to 50 data points either side of the peaks of the spectra.

10. The method of claim 1 , wherein the material is one of the following: a material to which water binds, ground grain, wholemeal, flour, a product derived therefrom, a foodstuff, a non-foodstuff.

11. An apparatus for measuring water absorbance in a multi-phase system comprising water and a material, said apparatus comprising: a container and a mixer for mixing the water and the material at a constant rate to form the multi-phase system; a pump for adding water to the material in the container at a constant rate; a source of a range of wavelengths of light energy in the NIR spectrum for irradiating the multi-phase system, said light being reflected from the multi-phase system; a detector for detecting the reflected light over the range of wavelengths using NIR spectrophotometry at a plurality of time points during the mixing to obtain a plurality of reflection spectra; and a processor coupled to be in communication with the pump, the source of light energy and the detector for plotting the peak height values of the reflection spectra with respect to time, said peak height values indicative of the water absorption of the multi-phase system over time.

12. The apparatus of claim 11 , wherein the pump is a peristaltic pump.

13. The apparatus of claim 11 , wherein the detector is a diode array detector.

14. The apparatus of claim 11 , wherein the detector is a fixed filter device.

15. The apparatus of claim 11, wherein the detector comprises light emitting diodes.

16. The apparatus of claim 11 , wherein the wherein the material is one of the following: a material to which water binds, ground grain, wholemeal, flour, a product derived therefrom, a foodstuff, a non-foodstuff.

17. The apparatus of claim 11 , wherein the processor calculates the second mathematical derivative of the reflection spectra.

18. The apparatus of claim 11 , wherein the processor corrects the peak height values of the reflection spectra by subtracting a minimum peak height value from the peak height values to obtain a plurality of corrected peak height values.

19. The apparatus of claim 11 , wherein the processor detects the reflected light over wavelengths in the range 400 - 1700nm.

20. The apparatus of claim 11 , wherein the processor detects the reflected light over wavelengths in the range 1100 - 1250nm.