Miller Magazine Issue 108 / December 2018

55 MILLER / DECEMBER 2018 COVER STORY tein concentrations between 8 and 15%. The nature and the concentration of the protein in the flour are major determinants of the dough making and baking characte- ristics of the finished food. The type and variety of the wheat used to produce flour determine the application for the flour. Protein in wheat is a major quality parame- ter that determines the strength of the dough and there- by the application of the flour. Starch and water content also affect the application of the flour. As such measure- ment of these and other parameters in wheat and flour are very important to the milling industry. This article describes the use of Near Infrared Spectroscopy (NIRS) as a means of performing rapid quality measurements in wheat and flour. Near Infrared Spectroscopy: In the mid 1960’s, an agricultural engineer, Karl Norris, USDA, Beltsville, Maryland, USA, was given the challenge to develop a rapid me- ans of measuring protein, oil and moisture in soybeans. Mr. Norris is credited as being the father of NIR because he was the first person to use multiple linear regression analysis to de- velop mathematical models to relate the Near Infrared Reflectance spectra ground soybeans to the protein, moisture and oil concentrations. In the last 50 odd years, Near Infrared Spect- roscopy has evolved to become a mainstay me- asurement tool for many food and agricultural products. Almost all of the world grain is traded based on the use of NIR analysers to rapidly measure protein and moisture in wheat, corn, barley, rice, pulses, oats, rye, sorghum and pro- tein, oil and moisture in oil seeds such as canola, soybe- ans, sunflower, safflower, linseeds and others. Figure 1. shows a schematic of the basic optics that is used in NIR analysers to generate spectra of flour and whole wheat grains. Light from a tungsten halogen lamp passes through a sample of either flour or whole grains. Energy is absorbed at specific frequencies by the che- mical bonds in protein (N-H), water (O-H), oil (C-H) and carbohydrates (C-O-H). An optical element called a Diffraction Grating separates the light into individual frequencies from 720-1100nm. The dispersed light is detected by a silicon photodiode array detector, similar to that used in a flat bed scanner or a laser printer. The amount of light absorbed by the sample at the resonant frequencies that correspond to protein, moisture, oil and carbohydrate is proportional to the concentration of each component in the sample. Figure 2. shows the NIT spect- ra of wheat, durum, flour and semolina. Figure 2. NIT Spectra of Wheat and Flour Applications for NIR Spectroscopy in the Flour and Wheat Milling Industry: The starting point for the pro- duction of flour and semolina is wheat and durum. Typi- cally NIR analysers measure the protein and moisture in whole grains of wheat and durum as basic trading para- meters, however for millers the measurement of gluten, falling number, hardness, sedimentation and Zeleny are important. Gluten is the major group of protein found in wheat. Gluten consists mostly of two protein, i.e., Glutenins and Gliadin. The question is whether the NIR spectra contains specific information that al- lows the analyser to measure gluten as part of the total protein compliment. The answer is no. The spectra of wheat grains are made up of a few broad absorption bands which are related to N-H bonds that are common to all proteins. The correlation between glu- ten and total protein is generally high and as such, the measurement of gluten using NIR is simply a proportional relationship to the total protein. Nonetheless, calibrations for gluten are commonly found in NIR analysers supplied to the flour milling industry. Likewi- se the physical parameters such as falling number, hardness, sedimentation and Ze- leny are not directly measured form the NIR spectral but moreover indirect correlations to one or several of the chemical parame- Figure 1. Near Infrared Transmission Spectroscopy Figure 2. NIT Spectra of Wheat and Flour