Introduction

Soya bean products are a common protein source in animal feed. These products are subject to adulteration with melamine, a plasticizer that mimics protein in routine quality tests. Standard testing determines nitrogen content but cannot distinguish between protein and non-protein nitrogen. In 2007, a high-profile adulteration incident with pet food made in China resulted in the deaths of thousands of dogs and cats. There were strong consequences in the Chinese food market and changes in regulations because of this incident. NIR spectroscopy offers one potential method for fast, non-invasive testing for melamine adulteration in pet food and the results of one study are presented below.

Analytes

• Products: Soya Bean Meal
• Adulterants: Melamine

Scientific References and Statistics

The Application of Near-Infrared Reflectance Spectroscopy (NIRS) to Detect Melamine Adulteration of Soya Bean Meal – Haughey, Graham, Cancouet, Elliott, Food Chemistry (2013) 1557-1561

Soya bean products are widely used in the animal feed industry as a protein-based feed ingredient and have been found to be adulterated with melamine. Melamine fraudulently increases the apparent protein content of products as standard protein determination assays cannot differentiate between protein nitrogen and non-protein nitrogen. It is not permitted to be added directly to foods or feeds nor can it be used as a fertilizer. A number of high-profile incidents, including a scandal in China with adulterated milk and infant formula which led to illnesses in over 300,000 children and six deaths, have highlighted the need for monitoring melamine adulteration in food products. A similar incident with pet food in China also resulted in deaths of dogs and cats and had worldwide consequences for food safety and regulations. Current reference methods for melamine detection are effective but have drawbacks. They are expensive, time-consuming, often require the use of both skilled labor and toxic chemicals, and cannot be implemented on a large scale as a quality control tool. NIR spectroscopy was examined as a method for detecting melamine adulteration in soya bean animal feed. Four different types of soya bean meal samples were procured for the study: dehulled soya genetically modified (GM), dehulled soya non-GM, soya hulls, and toasted soya. All samples were ground and spiked with melamine at w/w concentrations from 0% to 2% at 0.25% intervals. NIR spectra were collected from 12000 cm^-1 to 3800 cm^-1 at 8 cm^-1 resolution. Sixty-four scans were collected per reading and averaged into one spectrum. This process was repeated three times for each sample. Various pre-processing methods were applied to the NIR spectra before chemometric analysis. Partial Least Squares (PLS) regression models were created for each type of soya bean meal sample correlating the NIR spectra to melamine concentration.

PLS

Dehulled Soya GM	R² = 0.963	RMSEP= 0.169%
Dehulled Soya Non-GM	R² = 0.986	RMSEP= 0.102%
Soya Hulls	R² = 0.965	RMSEP= 0.163%
Toasted Soya	R² = 0.996	RMSEP= 0.059%

The results of this study were excellent with correlation coefficients above 0.96 and RMSEP well below 0.2% for all models. NIR spectroscopy has the potential to replace the current time-consuming and expensive methods used to detect melamine adulteration in soya bean meal animal feed. It can be used for routine tests of shipments and if melamine is detected, samples can be sent for further and more detailed analysis. Potential future work could include transferring the lab-based methods created in this study for use in an industrial setting where incoming batches of feed material can be screened before processing.

https://www.sciencedirect.com/science/article/pii/S0308814612001045