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Bead Beating: A Primer (continued)

PLANTS

Seed Homogenization

Seeds are best homogenized via dry grinding by using a disproportionally large grinding ball to crack these hard samples. Some protocols call for freeze drying the seeds prior to bead beating, but this is not always necessary. If seeds are air dried before homogenization, then water content may be sufficiently low to allow for the generation of a fine meal.

The choice of grinding vessel is very important when bead beating seeds. Most plastics tend to soften as the tube heats during processing; therefore polycarbonate should be used to ensure a hard grinding surface during homogenization. In almost all instances, 5/32” grinding balls are too small to effectively process seeds. For instance, a single grain of rice requires no less than a 3/8’’ stainless steel grinding ball and polycarbonate vial. Single seeds are commonly processed in 4 ml grinding vials with one 3/8” grinding ball to ensure that the seed is pulverized. Multiple seeds should be processed in 15 ml polycarbonate vials with two 7/16” stainless steel grinding balls. Up to fifteen corn kernels (about 5 gm) can be ground in a 15 ml vial. In the event that stainless steel balls do not have enough energy to pulverize a seed, tungsten carbide grinding balls can be substituted. Some seeds, such as palm nuts, are virtually impossible to process by bead beating.

Procedures

1. Seeds should be dry ground. Extraction buffers can be added after grinding. Grinding should be done in 4 or 15 ml polycarbonate vials with larger grinding balls.
2. Prepare samples according to the following table:
4 ml Vials 15 ml Vials
Sample Size One seed Up to 5 gm
Grinding Balls 1 x 3/8” 2 x 7/16”
Processing Time 2-3 minutes 3-5 minutes
Bead Beater Speed high speed high speed
3. Process the samples as stated in the table. Usually heat is not a big issue in dry grinding. However, should it become a problem, sample processing can be divided into short bursts followed by a cooling period.
4. Samples should be processed until a powder is generated.  Ideally the powder will be fine in texture, but moisture present in the seed may make the powder mealy.
5. Sample can be processed as needed.

Suggested Products

Balls: 3/8” Stainless Steel Grinding Balls (GBSS 375-1000-02), 7/16” Stainless Steel Grinding Balls (GBSS 412-1000-03)
Vial Sets: 24 Well PC Vial Set (PCVS 04-240-03), 15 ml Polycarbonate Vials (PCVS 15-050-22)
Homogenization Vessel: See Appendix A
Homogenizers: See Appendix A