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Corn Export Cargo Quality Report 2011/2012

Contents

  1. Export Cargo Quality Highlights
  2. Survey Overview
  3. Grade Factors and Moisture
  4. Chemical Composition
  5. Physical Factors
  6. Mycotoxins
  7. Corn Export System
  8. U.S. Export Corn Flow
  9. Impact of the Corn Market Channel on Quality
  10. U.S. Government Inspection and Grading
  11. Survey Design and Sampling
  12. Statistical Considerations
  13. Corn Grading Factors
  14. Chemical Composition
  15. Physical Factors
  16. Grade Requirements and Conversions
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Physical Factors

100-Kernel Weight, Kernel Volume and Kernel True Density

The 100-kernel weight is determined from the average weight of two 100-kernel replicates using an analytical balance with a minimum of four decimal places. The averaged 100-kernel weight is reported in grams. The kernel volume is calculated using a helium pycnometer to determine the volume (displacement) of the two replicates and is expressed in cm3/100. Kernel volumes usually range from 0.18-0.30 cm3 per kernel for small and large kernels, respectively. True density is calculated as the mass (or weight) of the two replicates of 100 externally sound kernels by the volume (displacement) of the same 100-kernels. The replicate results are averaged. True density is reported in grams per cubic centimeter (g/cm3). True densities typically range from 1.20 to 1.35 g/cm3 at “as is” moistures of about 12 to 15%.

Stress Crack Analysis

Stress cracks are evaluated by using a backlit viewing board to accentuate the cracks. A sample of 100 intact kernels with no external damage is examined kernel by kernel. The light passes through the horneous or hard endosperm so the severity of the stress crack damage in each kernel can be evaluated. Kernels are sorted into four categories: (1) no cracks; (2) 1 crack; (3) 2 cracks; and (4) more than 2 cracks. Stress cracks, expressed as a percent, are all kernels containing one, two or more than two cracks divided by 100 kernels. Lower levels of stress cracks are always better since higher levels of stress cracks lead to more breakage in handling. If stress cracks are present, singles are better than doubles or multiples. Some corn end users will specify the acceptable level of cracks based on the intended use.

Stress crack index (SCI) is a weighted average of the stress cracks. This measurement indicates the severity of stress cracking.

  1. SCI is calculated as SCI = [SSC x 1] + [DSC x 3] + [MSC x 5]

Where

  1. SSC is the percentage of kernels with only one crack,
  2. DSC is the percentage of kernels with exactly two cracks, and
  3. MSC is the percentage of kernels with more than two cracks.

The SCI can range from 0 to 500, with a high number indicating numerous multiple stress cracks in a sample, which is undesirable for most uses.

Whole Kernels

In the whole kernels test, 50 grams of cleaned (BCFM-free) corn are inspected kernel by kernel. Cracked, broken, or chipped grain, along with any kernels showing significant pericarp damage are removed, the whole kernels are weighed, and the result is reported as a percentage of the original 50 gram sample. Some companies perform the same test, but report the “cracked & broken” percentage. A whole kernels score of 97% equates to a cracked & broken rating of 3%.

% Horneous Endosperm

The % horneous (or hard) endosperm test is performed by visually rating 20 externally sound kernels, placed germ facing up, on a light table. Each kernel is rated for the estimated portion of the kernel’s total endosperm that is horneous endosperm. Soft endosperm is opaque and will block light, while horneous endosperm is translucent. The rating is made from standard guidelines based on the degree to which the soft endosperm at the crown of the kernel extends down toward the germ. The average of horneous endosperm ratings for the 20 externally sound kernels is reported. Ratings of horneous endosperm are made on a scale of 70-100%, though most individual kernels fall in the 70-95% range.

Mycotoxin Testing

The Export Cargo Quality Report official aflatoxin results are provided by FGIS. For the aflatoxin testing, a sample of at least 10 pounds of shelled corn was used according to FGIS official procedures. The 10-pound sample is ground using a FGIS-approved grinder. Following the grinding stage, two 500-gram ground portions are removed from the 10-pound comminuted sample using a riffle divider. From the 500-gram ground portion, a 50-gram test portion is randomly selected for testing. After adding the proper chemicals to the 50-gram test portion, aflatoxin is quantified or qualified. For the quantitative tests, one of the following FGIS-approved test kits may have been used: Aflatest, Fluoroquant, Veratox-AST, Myco, RIDASCREEN Fast Aflatoxin Total, or RIDASCREEN Fast Aflatoxin SC test. The FGIS-approved qualitative test kits that may have been used were: Rosa Aflatoxin P/N 20 ppb, ROSA Aflatoxin P/N 10 ppb, ROSA BEST Aflatoxin P/N, Reveal for Aflatoxin (MeOH or EtOH), and Romer AgraStrip.

For the DON testing, the FGIS-approved Romer AgraQuant test method was used. An approximately 1350-gram portion was ground by a Romer Mill to a particle size which would pass through a number 20 wire mesh sieve and divided down to a 50-gram sample using a riffle divider. The sample was then processed as the FGIS DON (Vomitoxin) Handbook requires. The DON was extracted with 250 ml of distilled water, and the extracts were tested using the Romer AgraQuant micro well test kits. The DON results were read using the StatFax Reader.