Application of RADIAN ASAP-LiveID Platform in Flavor Type Discrimination of Chinese Baijiu and Authentication of Maotai

In this application note, Waters RADIAN ASAP System was employed to discriminate the flavor type of different Chinese Baijiu, while the authenticity of Maotai was identified.

Benefits

• Ease of operation – Little to no sample preparation and the and minimum instrument optimization.
• Fast and accurate results – Based on direct analysis and LiveID real-time recognition technology with easy data elucidation, analysis and results of identification can be done and generated in seconds.
• Compact design with excellent performance – the RADIAN ASAP System is designed with robust and reliable single quadrupole mass spectrometry technology in combination with Atmospheric Solids Analysis Probe (ASAP), featuring small footprint, ease of use, and the ability to provide high-quality MS data.

Being a traditional fermented beverage of China, Chinese Baijiu (liquor) as a long history and ranks among the top six distilled spirits in the world together with whiskey, brandy, rum, vodka, and gin. Chinese Baijiu differs from other distilled spirits in the aspects of brewing ingredients, production process, and flavor components. Chinese Baijiu is usually made from grains such as sorghum, wheat, rice, maize, etc. through saccharification, fermentation, distillation, aging, and blending. Daqu fermentation starter offers essential enzymes and microbes for saccharification and fermentation of the starch in the starting materials. The flavor components of Chinese Baijiu mainly include esters, ethanols, acids, aldehydes, ketones, pyrazines, and some trace components. Most of these components are metabolites produced by the brewing microbes during the fermentation process. There are 12 flavor types of Chinese Baijiu depending on the production ingredients and process, they are: sauce-flavor, strong-flavor, light-flavor, miscellaneous-flavor, feng-flavor, rice-flavor, medicine-flavor, sesame flavor, te-flavor, chi-flavor, laobaigan-flavor, and fuyu-flavor Baijiu. Where the sauce-flavor, strong-flavor and light-flavor Baijiu are the three basic flavor types, from which all the other flavor types are derived.^1–2

At present, flavor type discrimination of Chinese Baijiu is based on the brewing ingredients and process, and the authentication of Chinese Baijiu is mainly conducted through organoleptic evaluation. However, the development of mass spectrometry technology and chemometrics provides us with an additional way of flavor type discrimination and authentication. And these techniques in combination with the ambient ionization, which is a fast, scientifically proven, and real-time technology, can help us to further improve the studies in this area. In this experiment, Waters RADIAN ASAP System was employed to discriminate the flavor type of different Chinese Baijiu, while the authenticity of Maotai was identified.

Sample Source

The samples were provided by collaborating laboratories and purchased from supermarkets.

Sample Preparation

5 µL of Baijiu sample was pipetted into the ASAP sampling capillary to perform direct analysis.

LiveID chemometric model

In this experiment, MassLynx MS Software (v4.2) was used to acquire non-target full scan data, and multivariate statistical software LiveID (v2.0) was used for modeling and sample assignment and identification.

Discrimination of Different Baijiu Flavor Types

Establish the experimental model

The raw MS data of different Baijiu samples were acquired, the samples include: strong-flavor Baijiu (Wuliangye, Luzhou Laojiao, Yanghe, and Jiannanchun), light-flavor Baijiu (Fenjiu, Niulanshan, and Hongxing), sauce-flavor Baijiu (Maotai, Langjiu, and Baiyunbian), sesame-flavor Baijiu (Jingzhi, Qingzhi, Nongzhi, and Bandaojing), feng-flavor Baijiu (Xifeng), and laobaigan-flavor Baijiu (Hengshui Laobagan). The identification and study of Baijiu samples of different flavor types were conducted by performing multivariate statistical analysis based on Principal Component Analysis-Linear Discriminant Analysis (PCA-LDA) and then establishing an identification model based on the LDA results.

The chemometric model was established based on 20 PCA components and 5 LDA components. As shown in the PCA-LDA clustering scores plot (Figure 3), the qing xiang xing Baijiu, nong xiang xing Baijiu, jiang xiang xing Baijiu, feng xiang xing Baijiu, and zhima xiang xing Baijiu samples were well separated. However, the laobaigan xiang xing Baijiu sample was very close to the qing xiang xing Baijiu sample. This is very likely because that the laobaigan xiang xing flavor is derived from the qing xiang xing flavor and they are intrinsically very similar. In addition, one zhima xiang xing Baijiu sample was also very close to the qing xiang xing Baijiu sample. It was confirmed to be the Baijiu sample from the brand Qingzhi, which is a Baijiu of mixed-flavor combining both the qing xiang xing flavor and zhima xiang xing flavor. This further demonstrates that classification based on this model is scientific to some extent.

Cross validation of the PCA-LDA classification model of the 6 Baijiu flavor types was performed with the method of “Leave 20% Out”. It can be seen from the validation results shown in Figure 4, the correctness score was as high as 93.59%.

After construction of the classification model of Baijiu flavor type, the flavor type of several Baijiu samples (Luzhou Daqu, Niulanshan, Xijiu, and Xuanjiu) purchased from the supermarkets was determined. LiveID Software generated the identification results in a near instantaneous way (Figure 5), and the results were exactly correct.

Authentication of Maotai

Because of its extremely high market value and collection value, Maotai is currently the most counterfeited product in Chinese Baijiu market. In this experiment, an identification model for Maotai was constructed and used to perform Maotai authentication tests on different Baijiu samples purchased from the market. The results showed that all non-Maotai Baijiu samples were recognized as Outliers.

The mass spectral information of the sample acquired by the RADIAN ASAP System was analyzed. It has been reported that more and higher concentration of pyrazines present in jiang xiang xing Baijiu compared with Baijiu of other flavors types. These pyrazines mainly include tetramethylpyrazine (m/z 137), trimethylpyrazine (m/z 123), dimethylpyrazine (m/z 109), and methylpyrazine (m/z 95), while the tetramethylpyrazine (m/z 137) concentration in Maotai is the highest.^3–5 By comparing the mass spectra in Figure 2 (6 Baijiu samples of different flavor types) with those in Figure 7 (3 Baijiu samples of jiang xiang xing flavor), we found the results highly consistent with what has been reported in the above studies. The contents of these four pyrazines in the three Baijiu samples of jiang xiang xing flavor were significantly higher than those in other Baijiu samples. And the content of tetramethylpyrazine (m/z 137) in Maotai sample was significantly higher than in the other two Baijiu samples of jiang xiang xing flavor. In addition, Baiyunbian Baijiu is nong jiang jian xiang xing Baijiu which has a mixed flavor combining both nong xiang xing flavor and jiang xiang xing flavor, and its mass spectrum also showed the characteristics of both nong xiang xing Baijiu and jiang xiang xing Baijiu.

The RADIAN ASAP System features a simple and flexible design as well as ease of use and fast speed to results, enabling mass detection without the need for any sample preparation or chromatographic separation. By combining the system with LiveID Software, model identification can be done in a near instantaneous way. It is ideal for chemical reaction monitoring, raw material quality control, and food authentication.

In this experiment, the RADIAN ASAP-LiveID System was used to successfully discriminate different flavor types of Baijiu, which provides scientific rationale for the characteristics of different Baijiu flavor types. In addition, an identification model enabling quick authentication of Maotai was constructed. According to the mass spectrum information acquired by the system, pyrazines, the flavor components commonly found in jiang xiang xing Baijiu, were also detected. Based on the data information, we have gained a more straightforward understanding of the differences in contents of the pyrazines among Baijiu of different flavor types, as well as between Maotai and other Baijiu. This provides a fast way of food authentication for the regulatory authorities and a new idea of food research and quality control for academic institutions and related industries.

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2. Wang D, Chen L, Yang F, Wang H, Wang L. Yeasts and Their Importance to the Flavour of Traditional Chinese Liquor: A Review [J]. Journal of the Institute of Brewing, 2019, 125(2):214–221.)
3. Chen M Z, Qiu S Y, Hu B D, et al. Research Progress on Yeasts in the Brewing System of Maotai-flavor Liquor[J]. China Brewing, 2015, 34(6): 5–10.
4. Wu J F. Study on the Full-process Metabolism Mechanism of Tetramethylpyrazine in Chinese Liquors[J]. Wuxi: Doctoral Dissertation of Jiangnan University, 2013.
5. Sun D, Zhao G B, Yang B. Detection and Characteristics of Pyrazine Compounds in Maotai-flavor Liquor[J]. China Brewing, 2015, 34(12): 162–166.