Nine Key Points for Quality Control of New Corn for Feed: From Moisture and Test Weight to Mycotoxins

This article outlines nine key points for quality control of new corn. New corn for feed must meet basic requirements such as appearance, moisture (≤16%), test weight (≥680 g/L), and impurities (≤2.0%). Special attention should be given to controlling damaged kernels (≤5%) and moldy kernels (≤2%, recommended ≤1%), while strengthening the detection of fatty acid value (KOH ≤60 mg/100g) and crude protein. Finally, mycotoxin testing during storage and warehousing must be emphasized to ensure safe use. 

1. Appearance Requirements  

The appearance of corn should generally be light yellow to golden yellow or slightly reddish, with plump kernels and a fresh odor, free from musty, sour, or other off-odors.  

2. Moisture Requirements  

Newly harvested corn typically has high moisture content and should generally be controlled within 16%. The testing method should follow GB/T 6435—2014 "Determination of Moisture in Feed."  

To improve efficiency during raw material acceptance, feed mills may use rapid moisture meters for quick determination, with periodic calibration using the oven method to ensure accuracy.  

3. Test Weight Requirements  

Test weight refers to the mass of corn kernels per unit volume, positively correlated with starch content, reflecting kernel plumpness and uniformity, and serves as an indicator of corn grade.  

Studies show: when corn moisture is between 15.0% and 18.0%, test weight increases by 2 g/L for every 1% decrease in moisture; when moisture is between 14.0% and 15.0%, test weight decreases by 2 g/L for every 1% decrease in moisture.  

When test weight is near the borderline for grading, moisture changes can affect the corn grade. For feed corn, test weight should be ≥680 g/L.  

4. Impurity Requirements  

Impurities refer to materials that can pass through a 3.0 mm round-hole sieve, as well as corn without feed value and other substances. The impurity content for feed corn is required to be ≤2.0%.  

5. Damaged Kernel Requirements  

Damaged kernels refer to kernels that are defective or damaged but still have feed value, including insect-damaged, diseased, broken, sprouted, moldy, and heat-damaged kernels. Currently, corn harvesting involves high levels of mechanization, with threshing often completed directly by machinery.  

New corn with high moisture content is more prone to mechanical damage, resulting in an increased proportion of broken kernels and a certain percentage of damaged kernels. Mechanical damage compromises the kernel's natural protective layer, significantly impacting its nutritional value and increasing the likelihood of mold contamination. Therefore, damaged kernels should be controlled below 5%.  

6. Moldy Kernel Requirements  

Moldy kernels refer to kernels with obvious mold on the surface that has penetrated the endosperm, rendering them inedible. Moldy kernel detection methods include counting, weighing, and sensory evaluation.  

The national standard requires moldy kernels to be ≤2%. To ensure raw material quality and safety, feed production enterprises with large storage capacities may raise the standard to ≤1%.  

7. Fatty Acid Value (KOH) Testing  

During storage, grains undergo chemical changes such as fat hydrolysis into fatty acids and protein decomposition into amino acids, producing acidic substances. Therefore, monitoring changes in fatty acid value (KOH) can effectively assess corn quality changes.  

KOH testing for corn should follow GB/T 15684—2015 "Determination of Fatty Acid Value of Milled Cereal Products." Enterprises should control the acceptance limit for corn KOH within 60 mg·100g⁻¹ to ensure storage stability.  

8. Crude Protein Testing  

Corn is an energy feed, and its crude protein content is often overlooked. However, crude protein levels in corn vary significantly, with corresponding variations in amino acid composition, and are negatively correlated with starch content. Therefore, crude protein should also be tested, following GB/T 6432—2018 "Determination of Crude Protein in Feed" using wet chemistry methods, or using near-infrared spectroscopy (NIRS) as per GB/T 18868—2002 "Rapid Determination of Moisture, Crude Protein, Crude Fiber, Crude Fat, Lysine, and Methionine in Feed by Near-Infrared Spectroscopy." When using NIRS, periodic calibration of the NIRS database using national standard methods is necessary to ensure accuracy.  

9. Enhanced Mycotoxin Testing  

Corn during warehousing and storage should undergo increased mycotoxin testing frequency. Rapid test strips or enzyme-linked immunosorbent assay (ELISA) methods can be used for quantitative detection to improve the safety of corn use.