Fourier transform infrared photoacoustic (FTIR-PAS) characterization of food systems

Fourier transform infrared (FTIR) spectroscopy has been widely used for qualitative and quantitative characterization of biological and agricultural materials. Most of the FTIR spectroscopic methods involve a minimal amount of sample preparation; the photoacoustic option, however, has the potential for non-destructive examination. The major focus of this research is to apply FTIR with photoacoustic spectroscopy (PAS) and other FTIR accessories, such as attenuated total reflectance (FTIR-AIR) and diffuse reflectance (DRIFTS) to elucidate the structures and chemical characteristics of a variety of food and agricultural materials. In this study, FTIR spectroscopy with a major emphasis on the PAS technique was used to analyze cheese and its polymer packages, edible oils and fats, meats, particle sizes of food powders, edible coatings, and microorganisms on the food surfaces.; Photoacoustic spectroscopy (PAS), in conjunction with the step-scan and digital signal processing function, was used to perform depth profile studies of the intact sample and package. Well separated bands of fat and protein were displayed in FTIR-PAS spectra of cheese samples with minimum sample preparation. The depth profile of intact cheese polymer package indicated that there is a diffusion of cheese component into its package. The potential of generalized two-dimensional (G2D) correlation analysis to enhance the resolution and interpretation and differentiate overlapping spectral peaks was demonstrated. Step-scan FTIR-PAS spectra also showed a moisture variation in meat samples.; Distinctive peaks corresponding to starch, protein, and polyethylene in multilayer films were obtained from step-scan FTIR-PAS spectra. The analysis was confirmed by comparing peaks from the composite layers with peaks of the individual components. Overlapping peaks that correspond to protein and starch in the mid-infrared region were resolved using the G2D correlation analysis for spectral enhancement. FTIR-PAS magnitude and phase angle spectra obtained from edible coatings on the surface of an apple effectively distinguished the coating surface and the food substrate by examination of magnitude, phase angle, and G2D correlation spectra. Without elaborate sample preparation, the FTIR-PAS technique successfully differentiated apple and honeydew melon surface with/without microorganisms. Compared to the more commonly used FTIR-ATR technique, FTIR-PAS spectra of edible oils and fats (vegetable oil and lard) were very similar, indicating that the FTIR-PAS can be an alternative non-destructive analysis tool. DRIFTS and FTIR-PAS were used to study the particle size and distribution of sucrose powders. Both DRIFTS and FTIR-PAS methods successfully predicted the mean particle size and constituent concentration in binary and quaternary mixtures.; The very first application of the depth profile analysis on selected food products was accomplished. Qualitative and quantitative analysis of a wide range of food products was successfully demonstrated, indicating that this technique has excellent future potential in non-destructive characterization of foods and biomaterials.