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United States Department of Agriculture

Agricultural Research Service

Related Topics

Research Project: Sensing Methods & Instrumentation for Rapid Determination of Moisture Content... and Other Quality Attributes of Grains, Seeds, & Nuts

Location: Quality and Safety Assessment Research Unit

2011 Annual Report


1a.Objectives (from AD-416)
1. Develop cost-effective systems and sensors for rapid and nondestructive measurement of moisture content and density of cereal grains, oilseeds and nuts that can be used in static and dynamic situations (on line and in process applications). 2. Develop a portable system for moisture measurements of shelled and unshelled peanuts that can be used in the field and at peanut grading stations.

3. Improve peanut grading processes by developing a rapid system for nondestructive determination of peanut kernel moisture from measurements on pre-cleaned samples and samples consisting of a mixture of pods and foreign materials.

4. Develop methods for monitoring water migration in almonds and other nuts and its effect on their quality by dielectric and spectroscopic methods.


1b.Approach (from AD-416)
Developing a cost-effective microwave system for rapid moisture measurement will require analysis of existing dielectric properties data to determine the optimum frequency and measurement parameters. From these results, microwave components will be specified, assembled into a low-cost rapid prototype, compared to a network analyzer, then calibrated and validated for moisture content of wheat, corn, soybeans, almonds, oats, sorghum, and barley.

For peanuts, dielectric properties from 2 to 18 GHz on Runner, Spanish, Valencia, and Virginia will first be collected on shelled and unshelled peanuts. As with the other grains above, these data will then be analyzed to determine the optimum dielectric properties parameters and associated algorithms for a density- and variety-independent measure of peanut moisture content, and a prototype low-cost rapid peanut moisture measurement system will be developed. From these measurements and system development for peanut moisture content of shelled and unshelled peanuts, further development of a system to measure the moisture content of peanut kernels without shelling will be developed. Additional dielectric properties of both the unshelled and shelled kernels will be collected as needed, along with the moisture content of both the shells and the kernels. From these data, moisture algorithms will be developed. Additional dielectric properties measurements on unshelled peanuts with and without foreign material will also be collected for development of moisture models that are also independent of foreign material (trash). Models will be developed for both pod and kernel moisture contents. Besides kernel moisture content, meat content and percentage of foreign material are also important grading parameters. Attempts to correlate the dielectric properties data with these parameters will also be made.

For almonds, since no dielectric properties data exists, fundamental dielectric properties measurements of almonds of varying varieties, growing locations in California, and moisture contents will be collected with a network analyzer. Correlations between moisture content and dielectric properties data will be developed. To investigate the dynamics of water migration in the almond kernels, known amounts of water will be sprayed on almond kernels of known moisture content, mixed, and then sealed in a Styrofoam box. The sealed box will then be placed between two horn-lens antennas for free-space measurement of the dielectric properties between 2 and 18 GHz at room temperature. Changes in the dielectric properties will be recorded over time as water moves from the almond surface to water in equilibrium inside the kernels. The next stage will be the use of these dielectric spectroscopic methods to monitor water migration inside the almonds under controlled conditions of humidity and temperature. In this instance, the water will permeate the almonds from the atmosphere for varying relative humidities from 20 to 80% in a controlled environmental chamber. Additionally, measurements will be repeated over varying temperatures from 0 to 50 oC in 5 oC increments.


3.Progress Report
In developing dielectric-based methods and sensors for rapid and nondestructive moisture content and other quality attributes of grains, seeds, and nuts, there is need for a database comprising dielectric properties of these materials measured over a broad frequency range for samples of different moisture content, bulk density, and temperature. The databases of the dielectric properties of grain sorghum, oats, barley, almonds, and unshelled and shelled peanuts were completed. For unshelled peanuts, dielectric measurements were also taken with varying percentages of foreign material.

At the request of the Georgia Federal State Inspection Service and USDA, Agricultural Marketing Service, several of our prototype microwave moisture meters for in-shell kernel moisture determination were field tested at different buying points in Georgia, Mississippi, North Carolina, and Texas for the third season. The prototype microwave moisture meter provides instantaneously and nondestructively the peanut kernel moisture content while still in the pod. Both peanut inspectors and peanut growers have been very pleased with the performance and consistency of the meter year after year. Also, for the second harvest season, a comparative study of our prototype microwave moisture meter and two official moisture meters against the standard oven-drying technique revealed a better performance for the prototype microwave moisture meter, particularly for samples with moisture contents above 12%. The samples came from 10 different States and consisted of different types and varieties. Note that both official meters require the pod samples to be cleaned and shelled before the kernel moisture content can be determined while the prototype microwave meter did not and still was more accurate.

Evaluation of poultry meat quality requires measurement of different parameters including pH, water holding capacity, color, moisture content, drip loss, and cooking yield. Measurement of these parameters often involves lengthy procedures and various types of instrumentation. Since up to 70% of poultry meat is water, radiofrequency dielectric spectroscopy can be used for rapid and nondestructive assessment of meat quality from measurement of its dielectric properties. Dielectric measurement of fresh chicken breast meat were performed with coaxial-type probe over a broad range of frequencies (200 Megahertz to 20 Gigahertz) and temperatures (-20 +25 deg. Celsius). For each chicken breast sample, the pH, water holding capacity, water content, and protein content were also determined. Initial graphical and statistical analyses of the dielectric spectra indicate the prominence of the binding modes of water over the entire frequency range and ionic conductivity in the lower frequency region (between 200 Megahertz and 2 Gigahertz). These features will be used in correlating the dielectric spectra with the quality attributes of chicken meat.


4.Accomplishments
1. Integrated standalone microwave moisture meter for in-shell peanut kernel moisture determination. Peanut grading is a labor-intensive and time-consuming procedure in which kernel moisture content is critical. A microwave moisture meter for determining peanut kernel moisture content while still in the pod was developed, prototyped, and field tested successfully for the third consecutive harvest season at different buying points in Georgia, North Carolina, Texas, and Mississippi with samples representing different peanut types and varieties. Originally, the microwave moisture meter was operated externally through a laptop computer which sometimes was subject to malfunctions and resulted in miscommunication with the meter causing unexpected interruptions. This year, all the meter functions were executed through a microcontroller and a keypad that were integrated into the original sensor making it more portable and less prone to interruptions and malfunctions. Routine use of the microwave meter will result in significant reduction in costs associated with drying/grading of peanuts and improvement of the peanut quality and hence improved competitiveness in the global market.


Review Publications
Guo, W., Zhu, X., Nelson, S.O. 2013. Permittivities of watermelon pulp and juice and correlation with quality.. International Journal of Food Properties. 16:475-484.

Nelson, S.O., Trabelsi, S. 2011. Models for the microwave dielectric properties of grain and seed. Transactions of the ASABE. 54(2):549-553.

Trabelsi, S., Nelson, S. 2011. Sensing Grain and Seed Moisture and Density from Dielectric Properties. International Journal of Agricultural and Biological Engineering. 4(1):75-81.

Guo, W., Zhu, X., Nelson, S.O., Yue, R., Liu, Y., Liu, H. 2011. Maturity Effects on Dielectric Properties of Apples from 10 to 4500 MHz. Journal of Food Engineering. 44(201):224-230.

Last Modified: 11/28/2014
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