Corn gluten meal is rich in amino acids and the natural pigment lutein, making it an important feed ingredient, especially widely used in chicken feed. For this reason, the market has been flooded with various inferior and counterfeit corn gluten meals in recent years. Most feed mills have limited testing conditions and cannot test for lutein and amino acids in every batch. They usually only judge the quality based on three indicators: appearance, moisture, and crude protein. This allows these counterfeit products to take advantage of the loopholes, making counterfeiting and selling of fake products an increasingly serious issue, which directly affects the quality of feed. Based on years of testing experience and market research, the author has summarized some simple and easy-to-use methods to identify fakes for everyone's reference. Composition and Hazards of Inferior Corn Gluten Meal
Authentic corn gluten meal is the remaining product after the raw corn is treated by the wet process for corn starch or corn syrup, with the starch, germ, and pericarp removed. It has a golden yellow appearance, a roasted corn smell, and a special fermented corn odor. It comes in two specifications: one with over 60% protein and another with over 50% protein. Generally, only three indicators—appearance, moisture, and crude protein—are routinely tested, while the probability of testing for amino acids and lutein is very low.
Counterfeiters exploit the shortcomings (loopholes) in routine testing to produce fake corn gluten meal. The composition of fake products typically includes protein concentrate, corn flour, millet flour, pigment, and a small amount of real corn gluten meal. Their functions are: using dyed yellow protein concentrate (urea-formaldehyde polymer) to impersonate crude protein, using millet flour and corn flour as fillers, and adding a small amount of real corn gluten meal. According to the quality requirements of feed mills, the proportions are adjusted to produce low-quality corn gluten meals of different specifications, which are then sold to feed mills at low prices, passing off inferior goods as superior and fakes as authentic, causing a significant decline in feed quality.
It is particularly important to note that the substance used in this inferior corn gluten meal to increase crude protein content is euphemistically called "protein concentrate" or "protein powder." It is a light yellow powder that contains no protein at all; it is a polymer of urea and formaldehyde, with a nitrogen content of about 30%. Adding a small amount can significantly increase the crude protein content. It not only has no nutritional value but is also toxic because it can decompose in acidic conditions (such as gastric acid) to release formaldehyde, causing chronic poisoning in livestock and poultry and leading to a series of unexplained symptoms. Therefore, feed mills should take this issue seriously and prevent inferior corn gluten meal containing protein concentrate from entering their premises to ensure feed safety. Methods to Identify Inferior Corn Gluten Meal
Inferior corn gluten meal contains large amounts of millet flour, corn flour, and protein concentrate, so the composition and total amount of amino acids, as well as the lutein content, vary greatly. A well-equipped laboratory can easily distinguish the genuine from the fake by testing the sample for amino acids, ammonia, and lutein content. Ordinary laboratories can adopt the following methods to identify authenticity.
Observe the appearance and check the sample's solubility in water
Pure corn gluten meal does not dissolve in water and settles quickly. Its aqueous solution is colorless, clear, and transparent (lutein is insoluble in water). Inferior corn gluten meal will suspend in water and settle very slowly. Its aqueous solution is turbid, and may even be yellow (due to the addition of water-soluble pigments). Check the changes in corn gluten meal in dilute acid and dilute alkali
Place about 5 grams of the sample in a beaker, add 50 ml of water, and stir for a moment. Then slowly add 10 ml of dilute hydrochloric acid (1+3). If the surface of the sample turns red, slowly add 10 ml to 15 ml of sodium hydroxide (30%). If the red turns to yellow, the sample is an inferior product. This is because a certain protein concentrate reacts with a dye during its synthesis to form a new substance. This substance undergoes a molecular rearrangement under the action of acid or base, and the resulting isomers show different colors in acid and base. Pure, authentic corn gluten meal, however, shows no significant change in appearance when acted upon by acid or base at room temperature. Check the color change of corn gluten meal in chromotropic acid
Protein concentrate (urea-formaldehyde polymer) decomposes in sulfuric acid to produce formaldehyde. Formaldehyde then reacts with chromotropic acid to form a purple substance. Starch, protein, sugar, and ammonium do not interfere with this reaction.
Take 0.1 grams to 0.2 grams of the sample in a dry 50 ml beaker, add about 1 ml of chromotropic acid solution (1 gram/liter in concentrated sulfuric acid), and carefully heat it on an electric stove until it just starts to smoke slightly. Remove the beaker and add 10 ml of water. If the solution turns purple, the sample contains protein concentrate and is therefore an inferior product. Microscopic examination
Place the sample under a stereoscopic microscope, magnified 10 to 20 times. If yellow, brittle particles are found, carefully pick out a few and place them in a 50 ml beaker. Add about 0.5 ml of chromotropic acid solution (1 gram/liter in concentrated sulfuric acid)