Raman scattering refers to the inelastic scattering generated by light mapping onto a substance. Raman scattering includes Stokes scattering and anti Stokes scattering, with Stokes scattering being commonly monitored. Each substance has a characteristic Raman spectrum, and the number of Raman spectral lines, displacement values, and band intensity are related to molecular vibration, which can be used as a basis for identifying substances. Raman spectroscopy in Baijiu quality control is mainly applied to online real-time detection of Baijiu flavor identification, food safety indicators detection, etc. Surface Enhanced Raman spectroscopy (SERS) technology is often used to control food safety in Baijiu. The main process is to collect the spectra of Baijiu samples with known components, establish standards for the spectra and sample components, verify and optimize the model, and substitute unknown samples into the model verification.
1. Detection of alcohol blending in Baijiu
The Raman spectral peak intensity of ethanol is directly proportional to the concentration of ethanol, and the microstructure of ethanol solutions at different concentrations varies, resulting in different positions of Raman spectral peaks. Measure ethanol concentration using the correlation between the peak intensity and peak position of the C-C-O stretching vibration spectrum of ethanol. Scholars have used absolute Raman difference spectroscopy to present the differences in C-C-O stretching vibration Raman peaks under different ethanol concentrations, calculated the spectral offset, and determined the ethanol content in the sample through the relationship between the offset and ethanol concentration. In addition to the determination of ethanol content, Raman spectroscopy technology can also be used to distinguish between grain fermented liquor and alcohol blended liquor, as the Raman spectral characteristic peaks of grain fermented liquor and ethanol are roughly the same, with a shift of 1-10 cm − 1.
2. Determination of pesticide residues in Baijiu
The brewing raw materials are affected by the environment during the planting process, which brings some pesticide residues of carbofuran, dimethoate and dichlorvos into Baijiu. At present, the commonly used methods and techniques for detecting pesticide residues are gas chromatography and liquid chromatography. There are few reports on the detection of pesticide residues by Raman spectroscopy. Some scholars have established a qualitative detection method of carbofuran, a pesticide residue in Baijiu, by SERS technology, which can detect trace carbofuran in Baijiu. Most of the existing methods for the detection of pesticide residues in Baijiu need pretreatment such as extraction. Raman spectroscopy has the advantages of simple operation and time-saving. It is believed that Raman spectroscopy has great potential in the application of pesticide residue detection in Baijiu.
3. Detection of food additives in Baijiu
Saccharin sodium and sildenafil are common illegal additives in Baijiu, and their side effects threaten human health. Therefore, it is of great significance to accurately detect and identify saccharin sodium and sildenafil in Baijiu. Scholars have established a SERS method based on novel core-shell nanoparticles to detect saccharin sodium in Baijiu. In order to obtain strong Raman signals during the modeling process of detection models, gold colloids are often prepared for enhancing substrate optimization. Based on the solvent extraction method, scholars extracted saccharin sodium in Baijiu with dichloromethane, prepared gold sol and concentrated it, and optimized the enhancement bottom to obtain the best Raman signal for rapid detection of saccharin sodium in Baijiu, with the detection limit of 0.5 mg/L. Some scholars used OptoTraceRaman202 as the gold sol of SERS to accurately detect the content of sildenafil in alcoholic beverages such as Baijiu. The application of Raman spectroscopy to the detection of illegal additives in Baijiu provides an effective means for the relevant detection departments and the quality and safety monitoring in the production process of Baijiu.
4. Detection of endogenous pollutants in Baijiu
Biological amines (BAs), methyl carbamate (MC) and ethyl carbamate (EC) have been detected as endogenous pollutants in Baijiu. BAs in Baijiu come from the metabolism of lactic acid bacteria or the formation of amino acid decarboxylation; MC and EC react with ethanol in grain fermented wine using cyanide precursors such as urea and cyanate. All three are carcinogens, and their content detection is of great significance to the food safety of Baijiu products. In 2015, SERS began to be used in the detection of food BAs, and most of the previous studies focused on the detection of histamine in fish. The application of SERS in Baijiu has not yet been reported. The main limitations of SERS based BAs detection in food analysis lie in the expensive price of Raman spectrometers and the need for precious metal nanoparticles for quantification. Xu Chenxi et al. [62 − 63] established a laser Raman spectrum database of MC and EC standard samples based on laser Raman spectroscopy technology, and used Raman sensitizer to enhance the sample signal, thus realizing the qualitative and quantitative determination of MC and EC residues in Baijiu. Research and Application of Raman Spectroscopy in Food Safety in Baijiu Multi focus on the determination of various indicators of finished liquor. There is less research on the traceability and tracking of endogenous pollutants in the production process. Further discussion can be made on the application of Raman Spectroscopy in the determination and tracking of endogenous pollutants in the brewing process of Baijiu.
Raman spectroscopy has various applications in the field of brewing, providing important information about the brewing process and products. Here are some typical application scenarios:
1.Raw material analysis: Raman spectroscopy can be used for the analysis and identification of raw materials. By scanning Raman spectroscopy of grape, barley, yeast and other brewing materials, their composition and quality characteristics can be determined, including sugars, proteins, organic acids, and other components. This helps winemakers evaluate the quality and suitability of raw materials and select the best ones for brewing.
2. Fermentation process monitoring:Raman spectroscopy can monitor the metabolic activity and product accumulation during yeast fermentation in real-time. By collecting and analyzing Raman spectra in fermentation broth, information about yeast growth, carbohydrate utilization, and alcohol generation can be obtained. This has guiding significance for controlling the temperature, pH value, and nutritional conditions of the fermentation process, as well as adjusting brewing strategies.
3. Analysis of brewing products: Raman spectroscopy can be used for the analysis and quality control of brewing products. By scanning Raman spectroscopy on samples such as wine and beer, components such as alcohol, sugars, acidity, polyphenols, etc. can be detected and identified. This helps evaluate the quality, flavor characteristics, and health and safety of the wine, as well as carry out quality control and brand protection.