Detecting Maleic Anhydride in Starch using Line-Scan Hyperspectral Raman Chemical Imaging

Abstract. Maleic anhydride (MAN) is an illegal food additive found in production of starch powder. This study developed a macro-scale Raman chemical imaging method for direct inspection of MAN particles mixed in starch powder. A 785 nm line laser was used as an excitation source in a line-scan hyperspectral Raman imaging system, which was used to acquire Raman images in a wavenumber range of 103–2831 cm⁻¹ from corn starch mixed with MAN at eight concentrations (w/w) from 50 to 6,400 ppm. A sample holder with a sampling volume of 150x100x2 mm³ was used to present a large surface area and thin layer of the powdered mixture for image acquisition. The fluctuating fluorescence signals from the corn starch were removed by a baseline correction method based on adaptive iteratively reweighted penalized least squares. Single-band fluorescence-corrected images were extracted at a unique Raman peak wavenumber (i.e., 1839 cm⁻¹) preselected for the MAN detection, to which a simple thresholding method was used to generate chemical images for MAN detection and mapping. Limit of detection for the MAN was estimated at 100 ppm. The line-scan Raman chemical imaging method has great potential to authenticate the starch powder and also inspect other Raman-active illegal adulterants or additives mixed in different types of powdered foods and ingredients.