application

1 Overview

UV visible spectrophotometer is one of the most useful analytical tools for analysts. Almost every analytical laboratory cannot do without UV visible spectrophotometer, and the same is true in food testing. It can be used for various types of food analysis

Component analysis and detection have a wide range of applications.

1. 1 UV visible spectrophotometry

UV visible spectrophotometry is an instrument analysis method that utilizes the absorption of radiation in the UV visible spectral region by material molecules for analysis. This type of molecular absorption spectrum is generated by the transition of valence electrons and electrons on molecular orbitals between electronic energy levels, and it is widely used for qualitative and quantitative analysis of inorganic and organic substances.

Lambert Beer's law is the fundamental law of light absorption, commonly known as the law of light absorption, and serves as the basis and foundation for quantitative analysis using spectrophotometry. When the wavelength of the incident light is constant, the absorbance A of the solution is a function of the concentration C of the absorbing substance and the thickness l (absorption path length) of the absorbing medium. The commonly used expression is: A=E × l × C (where ∈ is the coefficient)

1. 2 UV visible spectrophotometer

UV visible spectrophotometer is a conventional analytical instrument based on the principle of UV visible spectrophotometry. According to different optical path designs, UV visible spectrophotometers can be divided into single beam spectrophotometers, dual beam spectrophotometers, and dual wavelength spectrophotometers. Various models of UV visible spectrophotometers, in terms of their basic structure, are composed of five basic parts: light source, monochromator, absorption cell, detector, and signal indication system.

1Characteristics of UV visible spectrophotometer

13.1 Widely applicable

Among the analytical papers published internationally, photometry accounts for approximately 28%. Due to the absorption of various inorganic and organic substances in the UV visible region, they can be measured using this method. In the food industry, UV visible spectrophotometers are widely used in food testing and are receiving increasing attention.

13.2 The instrument price is relatively low and the analysis cost is low

UV visible spectrophotometers are relatively inexpensive, with low analysis costs and minimal instrument wear and tear during use. Most food enterprises are small and medium-sized enterprises with thin profits. Reducing food testing costs is particularly important. Using UV visible spectrophotometers as the main testing instrument can greatly reduce the testing costs of enterprises.

13.3 Easy and fast operation

For some foods with a short shelf life, simple and fast operation is required for testing. For example, fresh milk has a short shelf life (only 1 day), and its testing must be simple and fast. UV visible spectrophotometer can meet this requirement well.

13.4 High accuracy

For general spectrophotometry, the relative error of concentration measurement is within the range of 1% to 3%. If differential spectrophotometry is used for measurement, the error can often be reduced to a few thousandths.

2 Application of UV Visible Spectrophotometer in Food Testing

When a molecule contains one or more chromophores (i.e. atomic groups with unsaturated bonds), radiation can cause changes in the electron energy of the molecule. Common chromophores include:

>C=0N=N, N=O, C; N,>C=S

If only one carbon atom is separated between two chromophore groups, a conjugated group will be formed, which will shift the absorption band towards longer wavelengths (i.e. red shift) and significantly increase the intensity of the absorption band; When the molecule contains chromophores (0), a red shift effect will also occur. Common color enhancing groups include:

One OH, one NH2, one SH, one C1, one Br, one I

These functional groups are widely present in food and food additives, so UV spectrophotometers are widely used in food detection, with the following main applications.

21 photometric measurement

In order to ensure colored beverages in food production (such asColaThe color of products such as fruit juice and tea beverages is consistent, and their absorbance values can be measured using a UV visible spectrophotometer in the visible light range to ensure that the color difference meets the product requirements. In the fermentation industry, the degree of fermentation completion of a product can also be determined by measuring the absorbance value. For products with relatively single components, the qualification of the product can also be determined by measuring the absorbance value. For example, to determine the quality of the nutritional enhancer vitamin B1, its absorbance value can be measured at 400nm. When its value does not exceed 0.020, it can be determined as a qualified product.

2-2 Qualitative analysis of ingredients

The absorption spectrum of a substance essentially refers to the absorption of specific wavelengths of light energy by molecules and atoms in the substance, resulting in molecular vibrational and electronic energy level transitions. Due to the different molecules, atoms, and molecular spatial structures of various substances, their absorption of light energy will not be the same. Therefore, each substance has its own fixed absorption spectrum curve, and the presence of a substance can be determined based on the maximum absorption peak (peak) and waveform at certain characteristic wavelengths in the absorption spectrum. In food production, some food additives are used. In order to determine the quality of food additives, a UV visible spectrophotometer can be used for spectral scanning. For example, a UV visible spectrophotometer can be used to conduct a comprehensive scan of some complex sweeteners, preservatives, and umami compounds involved in food to exclude the use of prohibited additives. In addition, this method can also serve as an auxiliary tool for infrared spectroscopy (IR), nuclear magnetic resonance (NMR), mass spectrometry (Ms) and other methods in material structure analysis.

2Quantitative analysis of components

Some ingredient items that require strict control of content in food hygiene and safety testing can be accurately detected using a UV visible spectrophotometer. The items commonly measured by UV visible spectrophotometers in food are shown in Table 1. Table 1 Items that can be detected by UV visible spectrophotometer in food

Determination of Composition Method Absorption Wavelength (nm)

Pb Dithiazone 510

As Diethylaminodithioformate silver 510

Fe Phenanthroline 510

Cu Sodium diethylaminodithiocarbamate 440

Cd Dithiazone 518

Hg Dithiazone 485

Free chlorine/total chlorine, 4-phenylenediamine 510

Nitrite N - (naphthyl) ethylenediamine 540

Fluoride reagent 620

cyanide Isonicotinoid I pyrazolone 638

Formaldehyde Acetylacetone 414

Sulfur dioxide, formaldehyde, hydrochloric acid, mesh I, rose aniline 548

Pectin Carbazole Shrinkage Reaction 530

Hexitol condensation reaction 490

Pentose phenol condensation reaction 480

Methyl pentose phenol condensation reaction 480

Fructose anthrone method 620

Glucose ortho toluidine 625

Fat copper trial win integration 700

2. 4 DNA/protein analysis

DNMProteins are biomolecules, and the UV absorption they produce is often caused by small functional groups within their molecules, such as purine bases, pyrimidine bases, tyrosine, phenylalanine, tryptophan, and peptide bonds. Purine bases, pyrimidine bases, and nucleosides, nucleotides, and nucleic acids composed of them have strong absorption of ultraviolet light, with the highest absorption value at the absorption wavelength of 260nm. In protein molecules, the benzene rings of tyrosine (T), phenylalanine (Phe), and tryptophan (Trp) residues contain conjugated double bonds,

The conjugated double bond absorbs ultraviolet light (with the largest absorption Tyr at an absorption wavelength of 274fiB); Phe absorbs at a wavelength of 257nm, while Trp absorbs at a wavelength of 280Flm, resulting in protein absorption of ultraviolet light. The maximum absorption of ultraviolet light by peptide bonds occurs at an absorption wavelength of 238nm. This characteristic can be used to accurately and reliably determine the protein content in dairy products.

3 Conclusion

In short, UV visible spectrophotometers can almost meet the needs of food testing and analysis for a large number of small and medium-sized food enterprises. With the development of science and technology, UV visible spectrophotometers can also be connected to other analytical instruments, making their application scope more extensive and able to play a role in more fields.