Infrared and Raman Spectroscopy

Infrared (IR) spectroscopy is currently widely used in the food industry for both qualitative and quantitative analyses of ingredients and finished foods. Mid-IR, near-IR, and Raman spectroscopy requires much less time to perform quantitative analysis than do many conventional wet chemical or chromatographic techniques. This chapter describes the techniques of mid- and near-IR and Raman spectroscopy, including the principles by which molecules absorb IR radiation, the components and configuration of commercial IR spectrometers, sampling methods for IR spectroscopy, and qualitative and quantitative applications of these techniques to food analysis. Infrared (IR) spectroscopy refers to measurement of the absorption of different frequencies of IR radiation by foods or other solids, liquids, or gases. IR spectroscopy measures the absorption of radiation in the near- (λ = 0.8–2.5 μm) or mid-IR (λ = 2.5–15 μm) regions by molecules in food or other substances. By using multivariate statistical techniques, infrared instruments can be calibrated to measure the amounts of various constituents in a food sample based on the amount of IR radiation absorbed at specific wavelengths.