Near infrared microscopy imaging o®ers the opportunity to explore not only what kinds of chemical species are present at micro-scale level but also where the chemical species would be present. By revealing the spectral and spatial information, the technique can identify and localize any interested component. This study investigates the feasibility of using Near infrared microscopy imaging to detect melamine in soybean meal. The results showed that 6805 cm À1 is very sensitive for melamine but not for soybean meal, so can be used for univariate analysis. Single wavelength image and peak integration image at 6805 cm À1 are simple and e®ective methods to detect the melamine in soybean meal. Furthermore, Principal Component Analysis is applied to detect the melamine in soybean meal.

Soybean meal was adulterated with melamine with the purpose of boosting the protein content for unlawful interests. In recent years, the near-infrared (NIR) spectroscopy technique has been widely used for guaranteeing food and feed security for its fast, nondestructive, and pollution-free characteristics. However, there are problems with using near-infrared (NIR) spectroscopy for detecting samples with low contaminant concentration because of instrument noise and sampling issues. In addition, methods based on NIR are indirect and depend on calibration models. NIR microscopy imaging offers the opportunity to investigate the chemical species present in food and feed at the microscale level (the minimum spot size is a few micrometers), thus avoiding the problem of the spectral features of contaminants being diluted by scanning. The aim of this work was to investigate the feasibility of using NIR microscopy imaging to identify melamine particles in soybean meal using only the pure component spectrum. The results presented indicate that using the classical least squares (CLS) algorithm with the nonnegative least squares (NNLS) algorithm, without needing first to develop a calibration model, could identify soybean meal that is both uncontaminated and contaminated with melamine particles at as low a level as 50 mg kg−1.