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Team TFS
Team TFS
leather proteinThis morning as I was drinking my glass of milk and taking some notes in my leather portfolio I recalled a case of food adulteration (link to community page) that took place a few years back. The headlines stated that leather protein was detected in milk products. How in the world does leather end up in milk? Why would anyone put leather in a milk product?

The reason: economic adulteration!

To learn more about economic adulteration, I suggest reading the FDA/Law blog post on GAO Says FDA Needs to do More to Address “Economic Adulteration” by Kurt R. Karst.

Some corrupt manufacturers were taking hydrolyzed leather protein, which is made from hydrolyzing the scraps of animal skin or even animal hairs, and adding them to milk products to increase the protein content. The amino acid or protein content is greatly improved after hydrolysis. This illegal attempt to artificially increase the protein levels also presents a food safety concerns for consumers.

Hexavalent Chromium Contamination Concerns

During the manufacturing of leather products, the products are sometimes colored or tanned with dyes containing trivalent chromium (Cr III). It is possible that some of the trivalent chromium oxidizes to hexavalent chromium (Cr VI). Chromium is an odorless and tasteless metallic element. It’s found naturally in rocks, soil, plants, humans and animals. Chromium can find its way into our food and water supplies by many routes. The most common forms of chromium that occur in natural waters in the environment are trivalent chromium (Cr III), and hexavalent chromium (Cr VI). Hexavalent chromium is a known carcinogen and can irritate or damage the respiratory tract, gastrointestinal tract, and skin. Trivalent chromium is harmless if present in small quantities in food, however, higher amounts of Cr (III) can be toxic. Cr (III) and Cr (VI) can transform each other by oxidation and reduction, therefore both need to be monitored in milk and milk products to determine if they have been adulterated.


Methods for Detecting Leather Protein Adulteration in Milk

Testing for chromium or hydroxyproline in milk and milk products can determine the presence of leather proteins.

Determination of Hexavalent Chromium in Dyes

In our application brief 107, Determination of Hexavalent Chromium in Dyes, (link to downloadable PDF) we analyze two dyes for Cr (VI) using a sensitive ion chromatography (IC) method with post column reaction to produce a colored complex detected by visible absorbance. Figure 1 shows that Cr(VI) was not found in a 1:100 dilution of the Fast Red dye while 56.1 μg/L Cr(VI) was found in a 1:100 dilution of the Metal Complex Black. Spiking both diluted dye samples with 30 μg/L Cr (VI) yielded recover­ies of 99.3 and 101% for the red and black dyes, respectively, demonstrating method accuracy. This IC method delivers an easy, fast, sensitive, and accurate determination of Cr (VI) in dyes.


Hydroxyproline Testing

Another way to determine if milk and milk products have been adulterated with leather protein is by looking for amino acid hydroxyproline, which is formed from the hydrolysis of connective tissue protein such as collagen. Hydroxyproline is not found in lactoprotein, so it could be used to determine if the product is adulterated with animal hydrolyzed protein. Application Note 163, Determination of Protein Concentrations Using AAA-Direct™, (link to downloadable PDF) describes a study to measure hydroxyproline by AAA-Direct™ Amino Acid Analysis System. You can also use a precolumn-labeling method coupled to reverse-phase HPLC (RP-HPLC).

Hexavalent chromium is the most toxic form of chromium found in the environment. It can also be present in our drinking water, and it requires regulatory monitoring as a primary drinking water contaminant in the U.S. The Environmental Protection Agency (EPA) oversees the monitoring of drinking water in the U.S and has a dedicated webpage for chromium (link to web page). The page states that the EPA has an enforceable drinking water standard of 0.1 milligrams per liter (mg/L) for total chromium, which includes hexavalent chromium and trivalent chromium. This standard was established in 1991.

Hexavalent chromium, does this word sound familiar to you? The movie Erin Brockovich (link to Wikipedia page) highlighted this chemical compound in its story line and how it affected the community of Hinkley, California.


Additional Resources

To learn more about our solutions for detecting hexavalent chromium in drinking water, visit the resources below.


Has your lab encountered hexavalent chromium? If so, I’d like to hear about your experience.