Particle Size Reduction and Mycotoxin Sample Testing

Grain inspection plays a critical role in food safety, especially when testing for mycotoxins such as aflatoxin, fumonisin, ochratoxin A, zearalenone, and deoxynivalenol (DON). Mycotoxins are toxic secondary metabolites produced by certain molds such as Aspergillus, Penicillium and Fusarium. They contaminate grains, nuts, dried fruit, spices and coffee, and can cause illnesses ranging from acute poisoning to liver cancer. Because these toxins are often distributed unevenly within grain lots—sometimes concentrated in just a few kernels—grain samples must be finely and uniformly ground before analysis.

The USDA’s Federal Grain Inspection Service (FGIS) emphasizes that samples should be reduced to a homogeneous blend, preventing false negatives (if contaminated kernels aren’t ground) and false positives (if over-powdered kernels skew results). Consistent particle size ensures that reagent extractions and immunoassay kits perform properly across all grain samples.

Current FGIS Standards for Particle Size

The 2023 Mycotoxin Handbook sets clear requirements:

• At least 60% of a ground sample must pass through a U.S. Standard No. 20 sieve (850 μm).

• Grinders must be checked periodically to ensure compliance.

• Grain moisture content must be ≤ 20% to avoid poor grinding and equipment overheating.

• Grinders must be cleaned or purged between samples to prevent cross-contamination.

Earlier standards, such as the 2003 Aflatoxin Handbook, recommended an optimum of 60–75% passing but allowed adjustment only when less than 50% passed. Over time, the USDA has tightened standards, prioritizing precision and consistency

Recent Regulatory Updates

FGIS, now part of the USDA Agricultural Marketing Service (AMS), has continued refining standards for particle size reduction and testing methods. While AMS considered expanding acceptable concentration ranges for certain mycotoxins in 2022, stakeholder concerns prevented changes from being implemented. Still, these discussions highlight the industry’s ongoing push for greater testing accuracy and reduced variability

How MPE’s GPX Grinder Exceeds Standards

Modern Process Equipment’s GPX disc-style grinder has been tested by USDA’s Technology & Science Division and verified as suitable for official grain and mycotoxin sample preparation. Its design features directly support compliance with each USDA/FGIS requirement:

• Particle size reduction: The GPX provides an adjustable grind range of 6–150 mesh (3,000–100 µm). Since a No. 20 sieve corresponds to 20 mesh (850 µm), the GPX can grind far below this threshold, ensuring that ≥ 60% of material consistently passes the required sieve size.

• Moisture handling: By cutting rather than hammering, the GPX’s diamond-hard discs minimize heat buildup, helping maintain grind quality even when processing near the 20% moisture limit.

• Verification consistency: The GPX’s dial-controlled adjustments allow operators to fine-tune output, ensuring repeatable sieve results during periodic compliance checks.

• Cross-contamination prevention: Its straightforward design facilitates rapid cleaning or purging, aligning with USDA’s requirement to eliminate carryover between samples.

• High-throughput capacity: With output ranging from 200–600 lb/hr (90–272 kg/hr), the GPX not only meets compliance standards but also supports the high sample volumes required in inspection and testing environments.

By delivering a consistent, uniform grind well below USDA’s minimum particle size requirement, operating reliably under moisture limits, and enabling efficient verification and cleaning, the GPX not only meets but exceeds USDA/FGIS standards for particle size reduction in mycotoxin sample testing.

Conclusion

As mycotoxin regulations and standards continue to evolve, reliable grain testing equipment is more critical than ever. MPE’s GPX grinder not only meets the USDA’s strict requirements but also provides precision, efficiency, and versatility that help grain inspectors and laboratories achieve greater accuracy in mycotoxin detection.

Modern Process Equipment’s GPX disc-style grinder is purpose-built to deliver the precision needed for grain and mycotoxin testing. Tested by USDA’s Technology & Science Division, the GPX has been deemed suitable for particle-size reduction across all regulated mycotoxins.