ABSTRACT
Infrared (IR) and Raman spectroscopy provide detailed information about both the composition of foods and the molecular structure and the functionality of the components in food systems. Both techniques are based on molecular interactions with electromagnetic radiation that result in transitions between the vibrational energy levels of the ground electronic energy state of the molecule, corresponding to the excitation of various stretching and bending vibrations. However, the nature of these interactions is fundamentally different in these two types of vibrational spectroscopy, and hence they are regarded as complementary techniques. In general terms, as well as specifically in regard to applications to food systems, IR spectroscopy has found much more extensive use than Raman spectroscopy owing to the greater simplicity and
lower cost of the instrumentation as well as the greater utility of IR spectroscopy as a quantitative analysis tool. On the other hand, Raman spectroscopy offers certain advantages in relation to sample handling, the study of aqueous systems, and possibilities for on-line process monitoring. Thus, the selection of IR or Raman spectroscopy, or the combined use of both techniques, depends on the nature of the application. Near-infrared (NIR) spectroscopy combines the sample-handling advantages of Raman spectroscopy with the powerful multicomponent analysis capabilities of IR spectroscopy and thus has found widespread application for quality control and process monitoring in the food industry for several decades. However, by comparison with (mid-) IR and Raman spectra, NIR spectra are fairly uninformative, and NIR analysis is largely based on statistical treatment of the spectral data. Entire books have been devoted to NIR
I. Introduction............................................................................................................................................................44-1 II. Fundamental Principles of IR and Raman Spectroscopy......................................................................................44-2
III. Instrumentation ......................................................................................................................................................44-3 A. Infrared Spectroscopy ....................................................................................................................................44-3 B. Raman Spectroscopy......................................................................................................................................44-4
IV. Sampling Methods ................................................................................................................................................44-5 A. Infrared Spectroscopy ....................................................................................................................................44-5
1. Transmission Mode ................................................................................................................................44-5 2. Attenuated Total Reflectance..................................................................................................................44-6
B. Raman Spectroscopy......................................................................................................................................44-7 V. IR and Raman Spectroscopy of Food Components and Foods ............................................................................44-7
A. IR and Raman Spectroscopy of Food Proteins..............................................................................................44-9 B. Analysis of Foods by FTIR and Raman Spectroscopy................................................................................44-12
1. Milk and Dairy Products ......................................................................................................................44-12 2. Beverages ..............................................................................................................................................44-13 3. Edible Oil Analysis ..............................................................................................................................44-14 4. Syrups and Semi-Solids........................................................................................................................44-16 5. Solids ....................................................................................................................................................44-16
References ....................................................................................................................................................................44-17
considered in this chapter.
