(13g) Microstructure Analysis of Heterogeneous Foods: Chemical Imaging Using MicroFTIR

Food microstructure can be investigated at the molecular level by vibrational spectroscopic techniques, such as IR and Raman. In this study, a microscope coupled FTIR was employed to investigate food microstructure, providing a spatial distribution and interactions between major food constituents, namely protein, lipid and carbohydrates. Imaging with FTIR microscopy is a nondestructive technique to study chemical composition of spatially heterogeneous environment. The technique requires almost no sample preparation step and fast enough to acquire FTIR images without spoiling. A linear array of imaging detector helps acquire chemical images at spatial resolution down to 10 microns in a few minutes. Cheddar cheese and salami are two good examples of complex heterogeneous food. These samples were investigated at the microscopic level to acquire chemical imaging and distribution of major chemical constituents within the food matrix. Chemical imaging of complex food samples were studied using a MicroFTIR with an ATR accessory to scan 150x150 micron area. Spectral data from the preseleceted region was acquired on an automated microscope stage at 6.5 and 1.65 micron spatial resolution parameters. Using either chemimap or band ratio data processing techniques, chemical distribution of protein and lipids in different cheddar cheese and salami matrices was demonstrated in a map. Figure1 shows a chemical map of cheddar cheese acquired at 1.65 micron spatial resolution from a 100X2000 micron sized area. The spatial distribution of lipids (lowest scale, violet) and protein (highest scale, red) in the cheddar cheese was obtained by integrating the protein related amide I band (1600 ? 1700 cm-1) of FTIR spectra. As seen in the figure, protein is more like a continuous phase and fat globules are distributed in the matrix. Two points in the map (point 73 and 74) were chosen from fat and protein rich region and the associated spectra were given in Figure1. The talk will present one of the very first results of food microstructure analyses by means of microFTIR and cover the techniques to and difficulties of chemical imaging of complex food matrices that can be used to investigate the important quality indices of commercial foods.