Identifying NuSun/mid oleic type sunflower seeds with the refractive index test as recommended by the National Sunflower Association

Recommended Equipment and Supplies

1. Handheld refractometer – There are many different handheld refractometers available, the make and model listed below was used to develop these standards.
   • Cole-Parmer Handheld Refractive Index Refractometer -
     Model SKU# EW-02940-10 (Cost is approximately $286)
     The specifications for this model are: an RI range of 1.435-1.520, resolution of 0.001 and an accuracy of ±0.001.
   • Contact information:
     Cole-Parmer
     625 E. Bunker Court
     Vernon Hills, Ill. 60061-1844
     1-800-323-4340
     1-847-549-7600
     Fax: 847-549-7676
     Web: www.coleparmer.com
     
2. Oil press – There are several oil presses available. The press listed below was specially designed for the NuSun project.
   • The Sun Oil Press is a 6 ton press with a stainless steel extraction cup and piston. Photos of the press can be viewed at graininspection.com (you can use the back button on your browser to return to this page).
   • Contact information:
     Ron’s Welding & Machine
     PO Box 83
     Onida, SD 57564
     1-605-258-2426
     1-605-258-2229
3. Standard NuSun Calibration Oil – upon request, North Dakota Grain Inspection Service, Inc. will provide this sample.
   • Contact information:
     N.D. Grain Inspection Service, Inc.
     PO Box 123
     Enderlin, ND 58027-0123
     1-701-437-3000 ext. 202
     1-800-553-6032 ext. 202
     E-mail request
4. Rubber spatula - called a “Rubber Policeman”, this tool or something very similar is essential to protect the lens of the refractometer from scratches or abrasions while applying oil.
   • Rubber Policeman
     Catalog # 14-105B
   • Contact information:
     Fisher Scientific
     1-800-766-7000
     Fax: 1-800-926-1166
     Web: www.fishersci.com
5. Kim wipes EX-L – delicate task, anti-static, low lint lens wipes are essential to protect the lens of the refractometer from scratches or abrasions while cleaning. This Kimberly-Clark product works well but any comparable lens paper can be substituted.
6. Isopropyl alcohol – can be purchased at most any drug or grocery store.
   • Placing the isopropyl alcohol in a mist type spray bottle makes it most convenient to apply to both the refractometer lens, oil press cup and piston.

1. Using the rubber spatula, place several drops of the Standard NuSun Calibration Oil on the lens of the refractometer. Always use a rubber spatula when placing any product on the lens. If that lens ever is scratched the refractometer may fail.
2. Close the cover and view the scale through the eyepiece of the refractometer. (Examples of the view through the refractometer are included here.) Record the reading to the nearest .001.
3. Keep a log of all your standard values and sample values for future reference. It should include the time the last standard value was recorded.
4. Clean the refractometer using the lens paper and isopropyl alcohol. Just as it is important that you use the rubber spatula, likewise the use of the lens paper will help insure that the lens is not scratched during cleaning.
5. Extract oil from the sample of sunflower seeds using an oil press. Utilize the entire volume of the extraction cup and piston, the larger the seed sample used the more likely it is that the oil will be representative of the lot.
   1. The higher the moisture content of the seeds, the more difficult it will be to extract oil from the sample. It may be necessary to dry the seeds before attempting to extract the oil. A hair dryer or microwave can be used to remove the excess moisture. For each 2% of moisture over 10%, microwave one cup of seed for approximately one minute. Remember that when this method is used the sample must be cooled to room temperature before proceeding with the refractive index test.
   2. To prevent contamination, before moving on to the next sample, clean the piston and the extraction cup thoroughly with isopropyl alcohol.
6. Using the rubber spatula, place several drops of the extracted oil from the unknown sample on the lens of the handheld refractometer.
7. Close the cover, wait two minutes to allow the sample temperature to equalize and view the scale through the eyepiece of the refractometer. Record the reading to the nearest .001.
   1. If there is not a clear line at the blue shaded area it could be because there is too much moisture in your sample. Use a hair dryer or microwave to remove the excess moisture from your seed sample.
8. Compare that reading from the unknown sample to the refractive index reading of the Standard NuSun Calibration Oil. The reading from the unknown oil sample must be equal to or less than that of the standard. If the reading of the refractometer for the oil from the unknown sample is higher than the reading of the standard oil, the sunflower seeds are of the traditional type or are NuSun contaminated with traditional sunflowers.
   1. There is no tolerance when reading a handheld refractometer. If the reading of the oil from the unknown sample is just a fraction higher than that of the standard oil, the lot should not be considered NuSun.
9. It is important that you run the Standard NuSun Calibration Oil sample often. The slightest change in the temperature of the room, sample or standard will affect the reading on your standard oil. When that value changes, so will the line where you consider accepting or rejecting a load of NuSun. If you are continually receiving NuSun loads throughout the day, the standard should be run at least every hour. If you are receiving NuSun less frequently, the standard should be run before each load.
10. To prevent the accidental rejection of a load of NuSun with an adequate level of oleic acid, the following precautions should be taken:
    1. Because of the possibility of an occasional erroneous reading from the refractometer, it is important that an oil sample be tested several times before it is rejected as NuSun.
    2. The natural variation in any lot of seeds can also be cause for a failure. A second sample should be drawn from the lot and retested before a load is rejected.
    3. As another precaution, before rejecting a load of NuSun, rerun the Standard NuSun Calibration Oil to be sure that the value has not changed.

Example of a possible reading of the NuSun Standard Oil
1.4720

Example of a possible reading of an unknown NuSun sample
1.4715

Example of a possible reading of a traditional sunflower
1.4730

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