Infrared Spectroscopy for Food Quality Analysis and Control

Da-Wen Sun

• Publisher: Academic Press
• Year: 2009
• eBook ISBN: 9780080920870
• Topic: Technology & Engineering
• Subtopic: Spectroscopy & Spectrum Analysis
• Index: Technology & Engineering

Written by an international panel of professional and academic peers, the book provides the engineer and technologist working in research, development and operations in the food industry with critical and readily accessible information on the art and science of infrared spectroscopy technology. The book should also serve as an essential reference source to undergraduate and postgraduate students and researchers in universities and research institutions.Infrared (IR) Spectroscopy deals with the infrared part of the electromagnetic spectrum. It measure the absorption of different IR frequencies by a sample positioned in the path of an IR beam. Currently, infrared spectroscopy is one of the most common spectroscopic techniques used in the food industry. With the rapid development in infrared spectroscopic instrumentation software and hardware, the application of this technique has expanded into many areas of food research. It has become a powerful, fast, and non-destructive tool for food quality analysis and control.Infrared Spectroscopy for Food Quality Analysis and Control reflects this rapid technology development. The book is divided into two parts. Part I addresses principles and instruments, including theory, data treatment techniques, and infrared spectroscopy instruments. Part II covers the application of IRS in quality analysis and control for various foods including meat and meat products, fish and related products, and others.- Explores this rapidly developing, powerful and fast non-destructive tool for food quality analysis and control- Presented in two Parts -- Principles and Instruments, including theory, data treatment techniques, and instruments, and Application in Quality Analysis and Control for various foods making it valuable for understanding and application- Fills a need for a comprehensive resource on this area that includes coverage of NIR and MVA

Part I

Fundamentals And Instruments

Chapter 1

Principles of Infrared Spectroscopy

Éric Dufour

Publisher Summary

Major food components are generally complex molecules resulting from the polymerization of monomers such as amino acids or carbohydrates. These monomers exhibit specific chemical groups such as carboxylic and amine functions in amino acids. As each chemical group may absorb in the infrared region, it appears useful in a first step to clearly identify the characteristic absorption bands of these groups in the near- and mid-infrared regions. C–H bonds, which are found in large quantities in organic molecules, show stretching vibrations between 2750 and 3320 cm^–1 in the mid-infrared (MIR) region. The location of these bands is related to carbon hybridization. In the near-infrared (NIR) region, the first and second harmonics for C–H stretching vibrations are observed at about 1700 nm and 1200 nm, respectively. Combination bands involving stretching and bending of the C–H bond may be identified between 2000 and 2500 nm and, with a lower intensity, between 1300 and 1440 nm. In the NIR region, the second harmonics assigned to the stretching of C–H bonds give a weak absorption band at about 1200 nm. In this region, hexane shows two bands at 1186 and 1208 nm, whereas dodecane is characterized by a band at 1208 nm and a shoulder at 1186 nm.

Introduction

The development of rapid analytical methods for food products relies mainly upon two approaches: the use of physical properties of substrates as an information supply and the automation of chemical methods. Most rapid analytical methods based on the physical properties of food products are spectroscopic methods. Spectroscopy can be split into two large groups (Wilson, 1994): photonic spectroscopy, which is based on the study of the interaction of an electromagnetic wave with matter, and particle spectroscopy. The first group comprises spectroscopic methods exhibiting an analytical potential for rapid control. The second group is represented by mass spectrometry and derived methods.

All the spectroscopic methods, except mass spectrometry, can be classified according to the energy involved during measurement. Electromagnetic radiation, of which visible light forms a tiny part, exists as waves that are propagated from a source and move in a straight line if they are not reflected or refracted. The undulatory phenomenon is a magnetic field associated with an electric one. The speed of the electromagnetic wave is a universal constant “c,” equal to 3×10⁸ m/s. This wave can be represented as a sinusoidal function of time:

$y=Asinw.t$

(1.1)

where A is signal amplitude, w is the pulsation expressed in radians per second (rad/s), and t is the time in seconds. In a second, the shape of the wave is repeated w/2π times. This value is the frequency, υ, in cycles per second (s⁻¹, or Hertz, for which the symbol is Hz). The above equation represents a wave as a temporal phenomenon. A wave can also be represented as a function of the covered distance, x, expressed by the following equation, which takes into account the relation between time and distance:

$x=c.t$

(1.2)

Combining equations (1.1) and (1.2) gives:

$y=Asin2\pi \upsilon t=Asin(2\pi \upsilon x)/c$

(1.3)

Wave can then be characterized by another value, the wavelength, which is the distance covered by light during a full cycle. Considering that the speed of the wave is “c” meters per second and that there are “υ” cycles per second, we get the following relation:

$\lambda =c/\upsilon$

(1.4)

In spectroscopy, the wavelengths are expressed using different units, aiming to avoid the manipulation of large number in the considered spectral region. Usually centimeter, millimeter, micrometer (1 μm=10⁻⁶ m), nanometer (1 nm=10⁻⁹ m), angström (1Å=10⁻¹⁰ m) are used. Another unit is generally used in the mid-infrared spectral region, the wavenumber, υ¯

. Wavenumber is defined as the inverse of the wavelength expressed in centimeters:

$\overline{\upsilon }=1/\lambda$

(1.5)

As the wavenumber is proportional to the frequency:

$\upsilon =c\cdot \overline{\upsilon }$

(1.6)

The conversion relationship is υ¯

(cm⁻¹)=10⁷/λ, with λ expressed in nanometers; and λ (nm)=10⁷/υ¯

, with υ¯

expressed in centimeters⁻¹.

In this chapter, wavelength expressed in nanometers will be used for the near-infrared spectral region and wavenumber for the mid-infrared spectral region. Spectral regions, several of them being of interest for analytical purposes, can be defined as a function of wavelength (Figure 1.1):

Figure 1.1 Spectral regions of interest for analytical purposes.

• X-ray region (wavelengths between 0.5 and 10 nm) is involved in energy changes of electrons of the internal layers of atoms and molecules.

• Far-ultraviolet region (10–200 nm) is the zone corresponding to electronic emission from valence orbitals. In the near-UV region (200–350 nm), electronic transitions of the energetic levels of valence orbitals are observed. This spectral region is characterized by the absorption of peptidic bonds in proteins and of molecules presenting conjugated double bonds such as aromatic amino acids of proteins or vitamins such as vitamins A and E. In this wavelength range, luminescence (fluorescence and phosphorescence) may also be observed.

• The visible region (350–800 nm) is another zone where electronic transitions...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• About the Editor
• Contributors
• Preface
• Part I: Fundamentals And Instruments
• Part II: Applications
• Index