Measuring Flour Using Novel Sample Packing and Presentation with an IM 9500 Near-Infrared Instrument

Wes Shadow, Simon Sverkel, Yong Ni, Jory Harris, Jeanette Purhagen, Bo Allvin
Perten Instruments
wshadow@perten.com; ssverkel@perten.com; yni@perten.com; jharris@perten.com; jpurhagen@perten.com

Introduction

Grains and seeds belong to one of the most important staple food categories in the world. They are used in a wide variety of products and processing industries including food, feed brewing, and vegetable oil production. The composition of seeds and grains is very important as farmers, elevators, and processors use the information for critical purchasing, processing, and formulating decisions. Grains are often segregated based on compositional differences to optimize price and maximize the value during processing.

The Inframatic 9500 (IM 9500) is a grain analyzer based on industry standard Near-Infrared (NIR) technology transmittance technology. The instrument passes a monochromatic light beam through a sample. The sample interacts with the light dependent upon several factors, including molecular composition. The light passing through the sample is therefore modified in some form. A detector on the far side detects the transmitted light. The detector signal is amplified and processed. The instrument uses advanced chemometric calibrations to convert the signal into constituent results such as moisture, protein, oil, and ash. The IM9500 is also standardized to a National Institute of Standards and Technology (NIST) reference material for wave-length scale accuracy. It is officially approved for grain analysis in several countries (1-4).

In addition to measuring grains and oilseeds, many processors need to measure samples in powder and meal form. A new flour module was developed to enable flour measurements for millers and bakers using the IM 9500. Calibrations were developed for data collected using the flour module for moisture, protein, ash, and wet gluten in flour. The calibrations were further validated with independent samples. The results are presented in this paper.

Material and Methods

Sample presentation
Sample handling and presentation can affect results. For samples such as flour, packing a sample cell or cuvette differently can affect the density and therefore the amount of light transmitted through the sample. The new module and packing method are designed to minimize these differences. Multiple operators of varying degrees of training performed the measurements to include normal operator variation in the studies. The new flour module, Figures 1 and 2, was used for the measurements. The packing procedure of the module is described in a video (5).

 

 Figure 1: Flour module and preparation kit  Figure 2: Flour module

Calibration development
0ver 900 wheat flour samples from eight countries on three continents were used as a calibration set. The calibration set includes both hard and soft wheat flours. Note that reference data was not available for all samples on all parameters.

The samples were analyzed in replicate on several IM 9500s using multiple operators. In addition, samples were also sent to an external qualified analytical lab for reference analysis. These measurements were performed in duplicate. Data on samples at varying temperatures were collected to inoculate the calibration to temperature variation. The resulting data was combined and partial least squares (PLS) regression was used to generate the calibrations for moisture, protein, ash, wet gluten, and L*.

Validation of the calibrations
For the validation of the calibrations, 300 wheat flour samples from China were analyzed using the calibrations as described in the previous section for prediction. Each sample was analyzed in duplicate to measure re-pack reproducibility. The validation was made for moisture, ash, and wet gluten.

Calibration transferability
Thirty-three wheat flour samples from the USA were analyzed for test calibration transferability across five IM 9500 instruments. The sample cell was re-packed for each instrument. The comparison was performed using the ash results predicted by the globally developed calibration.

Results

Calibration
The summarized results from the calibration measurements are displayed in Table 1.

Table 1: Summarized results from calibrations measurements, dry basis


As can be seen in Table 1, the ranges for the measured parameters are wide and encompass both hard and soft wheat flour. As demonstrated in Figures 3 and 4, the samples are well distributed across the ranges as well. The Lab to NIR correlations are better than 0.99 for moisture, protein, and wet gluten. Ash and L* have correlations of 0.97 and 0.96 respectively.


Figure 3: Correlation for protein in wheat flour


Figure 4: Correlation for ash in wheat flour


Validation

The validation of the calibrations was performed on moisture, ash, and wet gluten, and the results are presented in Table 2.

Table 2: Validation results in dry basis

The validation samples were all within the ranges of the calibration samples.

Ash has the highest correlation followed by wet gluten and moisture. As can be seen in Table 2, the Repack Standard Deviation (Repack SD) indicates that packing of the flour module adds little error to the system.

Transferability

The transferability of the global calibrations was measured by using predicted results from five different IM 9500 instruments. The results for ash prediction from the five instruments are displayed in Table 3. All results are on dry basis.

Table 3: Instrument ash prediction, dry basis

Instrument A was used as the reference instrument. The results from instrument B – E were plotted against the results from instrument A, Figure 5.

In Table 3 and Figure 5 it is clear that the correlation and performance amongst the five instruments is very good. The small standard deviations further demonstrate that the sample preparation and presentation can be performed by different operators with negligible effects on the results.


Figure 5: Ash in flour prediction, instruments B – E versus instrument A

Conclusions

Stable calibrations for measuring flour samples using the IM 9500 equipped with the new flour module were developed. The calibrations were validated for moisture, ash, and wet gluten and effect of sample re-pack was tested. High lab to NIR correlations and very small standard deviations for the sample re-packs demonstrate the stability of the calibrations and sample presentation method. Minimal differences were observed between five instruments predicting the same samples. The calibration, validation, and transferability data indicate that the IM 9500 can measure flour accurately, for a wide range of flour sample types, and that the new flour packing and presentation method nearly removes all operator effects on the measurements.

References

  1. Australian Government – National Measurement Institute (NMI), Certificate of Approval NMI 15/1/5 (2012)
  2. Bundesamt für Eich- und Vermessungswesen, Amtsblatt für das Eichwesen (BEV), Edited 27 June 2014 – Wien, Nr. 2, Approval number 3904/2013
  3. Physikalisch- Technische Bundesanstalt (PTB), Approval number 11.26/13.01
  4. National Type Equipment Program (NTEP), Certificate of Conformance, Approval number NTEP CC No. 13-112, 2014. http://www.ncwm.net/resources/dyn/files/1226934zd93446cf/_fn/13-112A1.pdf
  5. Sample preparation video
    http://www.perten.com/im9500flourus