Identification by microscopy and MS-based electronic nose of a fraudulent addition to maize gluten

Abstract

Classical and chemometric methods have been used to detect falsified maize gluten products. Microscopic observations (numerous starch grains, seed envelopes and wheat bran fragments) clearly showed the presence of atypical maize gluten particles in samples with otherwise normal crude protein levels (≥ 60%) and the usual gold-yellow color. Chemical analyses in a few samples confirmed the presence of urea (19 to 174 g.kg-1), melamine (0 to 20 g.kg-1), and cyanuric acid (0 to 10 g.kg-1) coping for the low levels of methionine (0 to 13 g.kg-1) in incriminated products (genuine maize gluten methionine level ≥ 16 g.kg-1). Furthermore, a fast technique (an electronic nose based on mass spectrometry detection) also proved to be reliable for the identification of falsified maize gluten products: 100% correct classification of model and unknown samples was achieved with principal component analysis. As a consequence of these results, the Swiss feed-inspection authority blocked the import, or restricted the use, of 2,500 tons of the falsified products.

Keywords

• electronic nose
• maize gluten
• melamine
• microscopy
• urea