**2. Near infrared spectroscopy: A rapid analytical tool in cereal quality control**

In the 60s, the initial application of the NIRS technique in routine analysis was demonstrated and it was related to the determination of moisture and protein in cereals. The first stage of commercial application of the NIRS technique, during the 1970s, was predominantly related to the prediction of protein, moisture and oil content in cereals. In the second stage, during the 1980s, the NIRS prediction of more complex constituents such as complex carbohydrates was enabled. The third stage of NIRS application in cereal technology has been related to the prediction of functional properties of grains. The success of this technique lays in numerous advantages it offers over wet chemical analysis such as:


However, the application of NIR spectroscopy is characterized by the relevant restrictions, which are primarily related to the nature of NIRS as an indirect method (Dowell et al., 2006; Jirsa et al., 2008; Miralbés, 2008; Pierce et al., 1996; Pojić et al. 2002; Pojić et al., 2003). To

Fig. 1. NIR reflectance spectrum of wheat flour (1100-2500 nm) recorded by FOSS's

Also, the application of NIRS technique has been extended to determination of certain functional properties of tested samples which do not represent the unique chemical entities which manifest absorption in NIRS spectral region, but manifest relationship with certain constituents that can be used as a basis for calibration model development. So far, a number of applications of the NIRS technique have been demonstrated having commercial and/or scientific significance that was developed on the basis on different NIR spectral ranges, different ways of recording and processing of spectra, different sample presentations, various chemometrics techniques used for calibration development and different use of

**2. Near infrared spectroscopy: A rapid analytical tool in cereal quality control**  In the 60s, the initial application of the NIRS technique in routine analysis was demonstrated and it was related to the determination of moisture and protein in cereals. The first stage of commercial application of the NIRS technique, during the 1970s, was predominantly related to the prediction of protein, moisture and oil content in cereals. In the second stage, during the 1980s, the NIRS prediction of more complex constituents such as complex carbohydrates was enabled. The third stage of NIRS application in cereal technology has been related to the prediction of functional properties of grains. The success of this technique lays in numerous advantages it offers over wet chemical analysis such as:

NIRSystem 6500

validation statistics.

Significant reduction of testing time,

No requirement for the sample preparation

No requirement for the use of chemicals and their preparation,

No requirement for additional technical expertise to carry out examination

However, the application of NIR spectroscopy is characterized by the relevant restrictions, which are primarily related to the nature of NIRS as an indirect method (Dowell et al., 2006; Jirsa et al., 2008; Miralbés, 2008; Pierce et al., 1996; Pojić et al. 2002; Pojić et al., 2003). To facilitate the application of this method, it is necessary to develop the calibration model by which the obtained spectral data are translated into the required result – the content of the selected compound of interest, and it is often necessary to check and update the calibration models due to changes in the sample matrix. However, this restriction has been significantly overcome by development and application of calibration models based on artificial neural networks that handle very large data set and proved to be very accurate, stable, transferable and therefore globally applicable (Büchman et al, 2001).

The potential of wheat to be processed in wide range of different final products gives it the significance of upmost grain of commerce (Williams, 2002). Application of the NIRS technique in wheat quality control has been characterized by rapid development from prediction of major constituents in wheat grains (moisture, protein, oil starch, cellulose) to prediction of functional properties of wheat that define its capability to meet the requirements of the intended purposes (production of bread, pastry, cookies, pasta). Since the functionality of the commodity is strongly affected by its physico-chemical properties which do not manifest characteristics absorption in NIR spectral region, the use of NIRS to predict functionality is based on the relationship between physico-chemical properties and certain constituent having absorptions in NIR region (protein, oil, starch etc) (Williams, 2007). The value of wheat grain is dependent on its composition, functionality and safety, that all have an equal importance in wheat breeding, trade and processing (Fig. 2) (Williams, 2002).

#### **2.1 The role of NIRS in cereal breeding**

The breeding purposes require the knowledge on both composition and functional properties of grain, whilst the functionality of wheat grain has always been an issue of a great concern for wheat breeders. Functionality in wheat includes prediction of milling yield, kernel texture, rheological parameters of dough, loaf volume, product appearance,

The Application of Near Infrared Spectroscopy in Wheat Quality Control 171

above mentioned purposes, special attention must be paid to demonstrate that it generates technically valid results satisfying the regulatory requirements for analytical procedures. Stand-alone bench type instruments, designed for testing whole grains by measuring the intensity of transmission of NIR radiation from the spectral range 850-1050 nm are the most suitable for cereal trade purposes. Moreover, the measurement infrastructure comprised of

A significant advance in the application of the NIRS technique in cereal trade has been achieved by the development of global ANN calibration models, and by the establishment of measurement infrastructure composed of multiple NIRS devices interconnected in the network. Operation of the NIRS instruments through the network significantly improved the routine application of NIRS method, eliminated specified shortcomings and significantly facilitated the application of the NIRS method for the end-users. Hence, the independent measurements of protein content that are internationally equivalent have triggered off the establishment the NIRS networks in many countries around the world (Büchman, 1996;

Establishing a network of NIRS devices allows achieving of the same level of accuracy of determining the protein content regardless of location of devices. In addition, the NIRS networks ensure reliability and uniformity of quality control of grain crops as well as simplification of procedures for calibration model monitoring and their improvement.

NIRS network consists of two to several hundred or even thousands of NIRS devices that are controlled and configured from the central so-called master device. The initial idea of operation of NIRS instruments through the network came from FOSS Analytical AB, and currently the most impressive networks worldwide consist of FOSS's instruments - scanning monochromator Infratec 1241 Grain Analyzer. The success of such measurement infrastructure is highly dependent on the network organization and procedures and tasks

reference laboratory that analyze samples using the reference (wet chemical) tests and

administrative center, which manages databases, communication between devices in

network management body for the decision-making on the organization of network and

Procedures that enable undisturbed functioning of the NIRS network and confirm compliance of results obtained by wet chemical tests on the one hand and consistency of results of individual devices with the central (master) device on the other hand is achieved

the network and performs the standardization of network devices

the network of NIRS instrument significantly improved the cereal testing in trade.

 ensure metrological traceability of results of measurement of grain quality define the common interests of entities involved in the network system

distribute costs and improve network operation domain

monitor performance of the used calibrations

calibration center that develops new calibration models

**2.2.1 The role of NIRS networks** 

Pojić & Mastilović, 2006).

NIRS networks are formed in order to:

proposed and divided between:

calibrations updates.

through the following activities:

etc. Most of these parameters are dependent on the protein-proteinase complex of wheat grain and the condition of carbohydrate complex as well (Williams, 2007).

First attempt to determine the functional properties of wheat was made by Rubenthaler and Pomeranz (1987) by development of NIRS model for prediction of water absorption, mixing time and loaf volume. The following work presented by Williams et al. (1988) showed the potential of NIRS to predict Farinograph stability, Extensigraph energy and Alveograph deformation energy. Further research reported by Pawlinsky and Williams (1998), Hrušková et al. (2001), Hrušková and Šmejda (2003), Miralbés (2003, 2004), Dowell et al. (2006) and Vázquez et al. (2007) were carried out by using analyzers of higher generation – scanning monochromators. The efficiency of the models developed were affected by the form of the samples used (whole grain, ground grain or flour), by the composition of the sample sets which were insufficiently variable and by the inherent variability of the reference rheological methods.

One of the first attempts to develop NIRS calibration model for prediction of protein composition was made by Delwiche et al. (1998). It was possible due to the fact that the main fractions of gluten - glutenin and gliadin, exhibit some differences in their NIR spectra which enable them to be determined in mixtures with starch (Wesley et al., 1999) Total glutenin, insoluble glutenin and gliadin contents can also be measured in whole wheat kernel by NIRS against HPLC as a reference method (Delwiche et al., 1998; Dowel et al., 2006; Wesley et al., 1999; Seabourn et al., 1998; Wesley, 2001) with sufficient accuracy for screening purposes in breeding programs. Although some authors has recommended the use of instrument with a monochromator in reflectance mode over the range of 2000 to 2300 nm for these application (Wesley, 2001),it has been proved that use of instruments in transmittance mode with narrower spectral range below 2000 nm could also be applicable (Dowell et al., 2006; Scholz et al., 2007). Concerning the carbohydrate complex of grain, the NIR spectra of amylose and amylopectin are very similar since they consist of the same glucose unit. Therefore, very little progress has been made in estimating the quality of carbohydrate components in wheat. Scanning visible–NIR spectrophotometers are often applicable for research and development purposes, since this application requires wider spectral ranges such as 400-2500 nm, 400-1700 nm, 1100-2500 or 1000-2600 nm. Also, since breeders commonly face with insufficient quantity of samples, the development of NIRS single kernel characterization systems has been initiated.

#### **2.2 The role of NIRS in cereal trade**

Methods based on near infrared spectroscopy are accepted worldwide for cereal quality control in trade, especially according to the fact that it is capable of generating results for several quality parameters rapidly and in a non-destructive way. Although different countries established their own systems for classifying wheat on the basis of different quality parameters, wheat grading systems is commonly based on the wheat protein content (Williams, 2007; Hulasare et al., 2003; Váradi et al., 1999). The price of wheat is dependent on the protein content, often with substantial price increments between grades. Measuring protein content in wheat and wheat flour has been demonstrated as successful NIRS application due to its strong and broad absorption bands in the NIR region which affect easy calibration model development. Therefore, the segregation or blending grain prior to delivery is inconceivable without the use of NIR technology. When using NIR analysis for above mentioned purposes, special attention must be paid to demonstrate that it generates technically valid results satisfying the regulatory requirements for analytical procedures. Stand-alone bench type instruments, designed for testing whole grains by measuring the intensity of transmission of NIR radiation from the spectral range 850-1050 nm are the most suitable for cereal trade purposes. Moreover, the measurement infrastructure comprised of the network of NIRS instrument significantly improved the cereal testing in trade.
