INSTRUMENTAL TECHNIQUES IN FOOD ANALYASIS : NEAR INFRARED SPECTROSCOPY

 

Title: Study of Near Infrared Spectroscopy and its Applications in Food Industry

INTRODUCTION

Spectroscopy is the science of measuring the emission or absorption of different wavelengths of visible or non-visible light.

Spectroscopy is the study of the interaction between matter and electromagnetic radiation as a function of the wavelength or frequency of the radiation. It involves the use of a spectrophotometer, which is a photometer that can measure intensity as a function of the light source wavelength.

Based on the principle and the range of electromagnetic radiation spectroscopy is classified into several types:

Infrared spectroscopy (IR spectroscopy) is the spectroscopy deals with the infrared region of the electromagnetic spectrum, that is light with a longer wavelength and lower frequency than visible light. It covers a range of techniques, mostly based on absorption spectroscopy.

Used for Measurement of absorption of different frequencies of IR radiation by foods or other solids, liquids, or gases for both qualitative and quantitative analysis of ingredients and finished foods

Near-infrared (NIR) spectroscopy is based on the absorption of electromagnetic radiation at wavelengths in the range 780–2500 nm. NIR spectra of foods comprise broad bands arising from overlapping absorptions corresponding mainly to overtones and combinations of vibrational modes involving C-H, O-H and N-H chemical bonds. The concentrations of constituents such as water, protein, fat and carbohydrate can in principle be determined using classical absorption spectroscopy.

NIR spectroscopy is used routinely for the compositional, functional and sensory analysis of food ingredients, process intermediates and final products.

   

    BASIC PRINCIPLE OF NIR SPECTROSCOPY

• Near-IR (NIR) is a spectroscopic method is based on molecular overtones and combination vibrations of C-H, O-H and N-H. Combinations arise by interaction of two or more vibrations taking place simultaneously.
• NIR spectra arise from infrared spectroscopy causes vibrations, stretches, and rotations of atoms about a chemical bond.
• Absorption of light in the IR region causes molecules to vibrate and rotate. Absorption of light in the matter is usually not uniform and depends on molecular arrangement. At certain intervals, more intense absorption can be observed indicated by wide of absorption bands.
• The NIR region mainly contains overtones and combination bands that are due to hydrogen (C-H, O-H, N-H) vibrations. These overtones and combination bands are called secondary vibrations and are weaker than the fundamental vibrations.

Examples of molecular vibrations:

• 
  Symmetrical stretch     
• Asymmetric stretch
• Scissoring

INSTRUMENTATION OF NIR

• Light Source: for scanning the spectrum of an organic compound is light emitting diodes(LED) which emits the radiation at specific wavelength.
• Filters: filters are needed in order to eliminate visible radiation which prevent unnecessary sample heating
• Gratings: comprises metal or glass engraved surface with many fine parallel lines. When the light beam strikes the surface it divides into various wavelengths by diffraction
• Splitter: the light beam is split into two beams with a beam splitter. The two separated beams strikes the fixed and moving mirrors respectively and they are reflected back to beam splitter. They are then recombined and exit the interferometer in the direction of sample.
• Sample holder: This Cell is made up of quartz or glass to perform transmission with liquids. Depending on the design of the instrument the cells are of varied sizes and designs. For example, some instruments use round sample cups for dry solid and grained samples
• Detector: The choice of detectors depends on Wavelength range, Spectrometer design characteristics, detector characteristics such as photosensitivity and detectivity. Three different detectors are available: a silicon detector covers the range 400–1100 nm, an indium gallium arsenide covers the range 800–1700nm and a lead sulfide the range 1100–2500 nm.

Applications of NIR Spectroscopy

• Used for Analysis of moisture, fat, protein and starch content of food
• It can be used for determination of compositional analysis of Processed foods
• Determination of percent of fat in cheese spread,
• Determination of hardness of wheat and grains
• Also used to check the Freshness of meats
• It can directly measures the composition of solid foods

Major Applications in food sectors

• For analysis of Cereals and Cereal Products
• Milk and Dairy Products
• Meat and Meat products
• Fish
• Fruit and Vegetables
• Confectionery Products
• Beverages