Application of Near Infrared Spectroscopy in Food Analysis

Abstract: This paper introduces some applications of modern near-infrared spectroscopy in quantitative analysis and quality inspection in the food industry. As a simple, fast, efficient, non-destructive, green detection method, NIR spectroscopy has unique advantages in the authenticity of raw materials, the detection of active ingredients, toxic components and industrial online monitoring, and thus in the food industry. Get more and more applications.
Key words: near-infrared spectroscopy; food analysis; application

Near-infrared light is an electromagnetic wave between visible light (VIS) and mid-infrared light (IR), which is defined by the American Society for Testing and Materials (ASTM) as a spectral region with a wavelength of 78O to 2526 nm. Near infrared spectroscopy (NIR) was first applied to the analysis of agricultural and sideline products in the mid and late 50s of the 1950s, but due to technical difficulties, development was slow. Until the mid-1980s, with the development of computer technology and the deepening of chemometrics research, coupled with the increasingly perfect manufacturing technology of near-infrared spectroscopy, the measurement signals of near-infrared spectroscopy were digitalized and promoted. In addition, due to the weak absorption of the near-infrared spectrum, the sample can be directly subjected to diffuse reflection analysis after simple pretreatment, thereby avoiding damage to the sample during pretreatment and achieving non-destructive testing. At the same time, the chemical operation is required to make the analysis operation green, thereby becoming The most compelling spectral analysis technique of the 1990s. Due to the good transmission of near-infrared spectroscopy in optical fibers, it has been widely used in industrial online analysis in many developed countries in recent years. Near-infrared quantitative analysis has been listed as one of the world's food analysis standards by its rapid and accurate classification, which has been listed by the World Grain Chemical Technology Standards Association and the American Grain Chemistry Association.

1 Application of near-infrared spectroscopy in food industry

NIR has been widely used in the following areas:

1.1 Food and feed

Agriculture is the foundation of the national economy, the source of our food and clothing, and the basis of survival. The use of NIR technology to detect the nutrient composition and quality of agricultural and sideline products is an indispensable task in finding reasonable plant cultivation and animal feeding methods. It guides farmers to adjust industrial structure, develop agriculture, forestry, animal husbandry, fishery, and develop food and The deep processing of other agricultural products has a very important significance.

At present, NIR combined with diffuse reflection technology can quickly and accurately determine the moisture content, protein and other important indexes of wheat, barley and other agricultural products, as well as water content, protein, ash and granularity in flour, so that online monitoring can be realized in the production process. The quality of rice was evaluated on the basis of establishing a certain training set by using near-infrared spectroscopy. China Agricultural University has also established a mathematical model for near-infrared quantitative analysis of some agricultural products (including wheat and barley, corn, puerarin, Eucommia, etc.), and developed and developed a near-infrared corn quality analyzer for analyzing moisture and protein in samples. And the chemical value of starch.

At present, the NIR method is widely used in the oil and fat industry to measure protein, fat (residual oil), moisture, ash and other indicators in soybean, rapeseed, sunflower seeds and other cakes. NIR can also be used as a non-destructive method to determine the oil content of peanuts and to obtain similar results to Soxhlet extraction. For the first time, Shandong Xiangchi Cereals and Oils Co., Ltd. has successfully tested the residue urease in soybean meal with NIR, which is faster and easier than other methods. . .

1.2 Meat and dairy products

Foreign people have successfully used the near-infrared fiber optic probe to detect the change of moisture in the heating process, which provides an effective new way for the meat industry to effectively and rationally control the processing. The application of NIR in liquid milk quality testing rose in the 1980s and gradually matured. There are many related research reports in foreign countries. Domestic researchers use this technology to quickly determine the fat, protein, lactose and other majors in milk. The ingredients have also achieved satisfactory results.

1.3 Alcoholic beverages

Using NIR, the content of ethanol in alcoholic beverages (including beer, fruit wine, rice wine) and the content of ethanol, fructose and glucose in aqueous solution can be quickly determined. The sample can be obtained without satisfactory pretreatment, which is better than traditional gravity method and heavy chromium. Acid oxidation, spectrophotometry, gas chromatography and ultraviolet detection high performance liquid chromatography, enzymatic, nuclear magnetic resonance and flow injection analysis methods proposed by foreign scholars are faster, more accurate, simpler and cheaper.

1.4 Fruits and Vegetables

The use of NIR can nondestructively determine the total sugar, sucrose, glucose and fructose in the whole apple and the sugar and acid content in the juice, and the composition analysis efficiency is high, which provides a new method for judging the quality of apple. In the processing of grape juice, pear juice, etc., NIR can continuously measure the changes of soluble solids, total solids and total moisture, and then monitor the quality of processed products.

1.5 Condiments

Because vinegar contains acid, sugar and other ingredients, the main components of vinegar can be detected by NIR method to judge its quality. At the same time, the content of various components of the same product of different manufacturers is different. NIR can detect this difference and judge the origin of raw materials. To prevent infringement. Lizuka K achieves the identification of soy sauce by measuring the near-infrared spectrum of the soy sauce product and analyzing the soy sauce with LDA (Linear discriminates analysis) PLS (Partial least squares) to distinguish the origin of the soy sauce.

1.6 Determination of VE

Using NIR to measure vitamin E at a concentration of 93% to 97.4%, it achieves better results and is more time-saving than traditional spectrophotometry, fluorescence spectroscopy, gas chromatography and high performance liquid chromatography, and the cost is greatly reduced. .

2 Method characteristics

2.1 Advantages

2.1.1 Simple and convenient There are different sample devices that can directly measure liquid, solid, semi-solid and gel samples, and the detection cost is low.
2.1.2 Non-damaged samples can be referred to as non-destructive testing.
2.1.3 Analysis speed is fast. General samples can be completed in 1min.
2.1.4 High resolution allows simultaneous qualitative and quantitative analysis of multiple components of a sample.
2.1.5 Green analysis technology is environmentally friendly from sample pretreatment to analytical testing.
2.1.6 Optical fiber suitable for near-infrared analysis is easy to obtain, so it is easy to realize on-line analysis and monitoring, which is very suitable for sample analysis in production process and harsh environment.
2.1.7 The requirements for testers are not high, and it is easy to train and promote.
2.2 Disadvantages 2.2.1 Not suitable for trace analysis (content <0.1%) and analysis of dispersive samples.
2.2.2 The sensitivity is low due to the measurement of the frequency doubling and the combined frequency absorption.
2.2.3 is an indirect method to establish a relevant model library (training set).

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