Study on the Differences between Microwave Processing and Traditional Processing of Glycyrrhiza uralensis Based on HPLC Fingerprint and Chemometrics
Glycyrrhiza uralensis Fisch is a leguminous plant The dried roots and rhizomes of Glycyrrhiza uralensis Bat. or Glycyrrhiza uralensis L. have the effects of tonifying the spleen and qi, clearing heat and detoxifying, expectorant and cough relieving, slowing down and relieving pain, and harmonizing various medicines. They are mainly used for spleen and stomach weakness, fatigue, palpitations and shortness of breath, coughing and phlegm accumulation, abdominal and limb spasms and acute pain, abscesses and sores, relieving drug toxicity and high potency. With a long history of medicinal use in China, there is a saying that “there are ten prescriptions and nine herbs, and no herb can make a prescription”, known as the “old man of the country”. According to relevant literature, the main processed products of licorice include honey roasted licorice, stir fried licorice, and microwave heated licorice processed using modern methods. Microwave heating processing refers to the simultaneous heating of materials from the inside and outside through dipole rotation and ion conduction after absorbing microwave energy, while traditional heat treatment is carried out from the outside to the inside through thermal conduction and radiation, with a slow temperature rise. The advantage of microwave heating processing is that the absorbed microwave energy of the processed drug rapidly increases the temperature inside the cell, creating a pressure difference between the inside and outside of the cell that causes the cell wall to rupture, making it easier for the components inside the cell to dissolve. In addition, microwave heating processing is not only easy to control in terms of firepower and time, but also simple to operate. After processing, the medicinal pieces have a beautiful and clean appearance, which makes up for the shortcomings of traditional processing methods in terms of craftsmanship. The main purpose of traditional Chinese medicine processing is to change the nature, taste, and function of Chinese medicine, achieving the effects of relieving drug properties, reducing toxicity, and increasing efficiency. After processing, licorice enhances the effects of tonifying the spleen and stomach, relieving pain in a slow and urgent manner, and detoxifying sores, in order to facilitate rational clinical use and ensure therapeutic efficacy. Research has shown that licorice contains more than 400 compounds, mainly divided into five categories: flavonoids, triterpenoids, triterpenoid saponins, stilbenes, coumarins, etc. Among them, triterpenoid saponins are mainly glycyrrhetinic acid, glycyrrhetinic acid, etc., while flavonoids are mainly glycyrrhizin, isoliquiritigenin, glycyrrhizin, isoliquiritigenin, etc. Chemometrics is an emerging counting analysis method that can quickly and comprehensively identify and classify a large amount of sample data obtained by chromatography, spectroscopy, gas chromatography-mass spectrometry, and other methods in traditional Chinese medicine chemistry. Its methods mainly include cluster analysis (CA), principal component analysis (PCA), partial least square discriminant analysis (PLS-DA), orthogonal partial least squares discriminant analysis (OPLS-DA), etc. This article compares the differences between microwave processing and traditional processing of licorice using high-performance liquid chromatography (HPLC) fingerprinting and chemometric methods such as CA, PCA, PLS-DA, OPLS-DA, etc., providing a reference for the feasibility of modern microwave heating processing methods.

The development of traditional Chinese medicine cannot be separated from inheritance and innovation. The use of modern processing techniques to prepare traditional Chinese medicine is an innovation in traditional Chinese medicine processing technology, which is conducive to the modernization of traditional Chinese medicine. The modern processing method of microwave heating is not only simple to operate but also time-consuming, which can effectively improve energy utilization. It requires low temperature and short drying time during drying, and has significant advantages over traditional processing methods. This experiment establishes HPLC fingerprint spectra of raw and processed licorice, and compares the differences between microwave processing and traditional processing of licorice using chemometric methods. From the fingerprint spectrum, it can be intuitively seen that the chemical components of raw licorice are the same as those of honey processed licorice, but after stir frying and microwave processing, peaks 4, 5, and 11 are missing, indicating that some components of raw licorice may have changed during stir frying or microwave heating processing. After comparison with the reference standard, it cannot be identified and further research is needed; The similarity evaluation shows that the similarity between batches of raw and processed licorice is high, indicating that the processing technology is stable and feasible. CA shows that licorice honey processed products can be clearly distinguished from other processed products, indicating that the addition of auxiliary honey during the honey processing has a significant impact on the chemical composition content of licorice; Raw licorice and honey roasted licorice can be clustered separately, while stir fried licorice and microwave processed licorice cannot be clustered separately, indicating that the chemical characteristics of stir fried licorice and microwave processed licorice are similar, suggesting that microwave heating processing methods have certain feasibility. PCA and OPLS-DA showed that the raw and processed licorice products could be clustered independently, while there was a small overlap between stir fried and microwave products, which was consistent with the CA results. After further pairwise comparison between stir fried and microwave products using OPLS-DA, the clustering effect was good, making OPLS-DA analysis more suitable for discriminant analysis of licorice and its processed products; PCA identified peaks 4, 5, 11, and 8 as components closely related to different processed licorice products. OPLS-DA differential component analysis showed that the main differential chromatographic peaks between microwave processed licorice and raw licorice were peaks 2, 1, and 8. The differential chromatographic peaks between microwave processed licorice and stir fried licorice were peaks 7, 2, 9, 15, 6, 13, 17, 16, and 14. The main differential chromatographic peaks between microwave processed licorice and honey processed licorice were peaks 8, 13, 7, and 16. These components may be the material basis for the differences in efficacy between microwave processed licorice products and raw and other processed licorice products.

Overall, it can be concluded that the chemical composition of licorice has indeed undergone changes after microwave heating and processing, and it has its unique advantages. Although the analysis results of CA, PCA, and PLS-DA show that licorice is closer to each other after microwave processing and stir frying, there is a certain degree of commonality, which may be due to the fact that both processing methods involve heating licorice without adding auxiliary materials; However, the VIP results in OPLS-DA analysis showed that there were significant differences in the chemical composition between microwave processed licorice and stir fried licorice compared to honey fried and raw licorice, indicating a difference in the principles of microwave heating and ordinary heating. The application of modern processing techniques plays a driving role in the modernization of traditional Chinese medicine, and studying and elucidating its processing principles can have a profound impact. The chemical composition of licorice is complex, and whether changes in its chemical composition and content can cause differences in efficacy remains to be verified by subsequent pharmacological experiments.