Bead Beating: A Primer (continued)
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
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.
||Prepare samples according to the following table:
||4 ml Vials
||15 ml Vials
||Up to 5 gm
| Grinding Balls
||1 x 3/8”
||2 x 7/16”
| Processing Time
| Bead Beater Speed
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
||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.
||Sample can be processed as needed.
|| 3/8” Stainless Steel Grinding Balls (GBSS
375-1000-02), 7/16” Stainless Steel Grinding Balls (GBSS
||24 Well PC Vial Set (PCVS
04-240-03), 15 ml Polycarbonate Vials (PCVS
||See Appendix A
||See Appendix A