Study on the correlation between moisture changes and color difference in Danshen processing based on LF-NMR/MRI
Low field nuclear magnetic resonance (LF-NMR) utilizes the spin relaxation properties of hydrogen atoms in a magnetic field to microscopically explain the distribution and migration of substances such as water, oil, and protein inside materials through changes in transverse relaxation time (T2). LF-NMR has the advantages of being fast, accurate, and non-destructive. Low field nuclear magnetic resonance technology is a magnetic resonance detection method that explains the presence of a large number of hydrogen atoms in water based on the principle of nuclear magnetic resonance. The transverse relaxation time of hydrogen in the sample varies with changes in the external chemical environment, and the corresponding T2 size reflects the degree of freedom of water. The longer the T2, the lower the water binding degree and the stronger the fluidity. It is often used to characterize the water migration law during the drying/rehydration process of the sample. Low field nuclear magnetic resonance technology can provide internal moisture information without interfering with the sample, and has been widely used in the industrial and food fields. It is mainly used to observe the changes in the form of moisture and oil in materials during the drying/soaking process, or to conduct adulteration identification research by measuring the moisture ratio. Previous studies have applied low field nuclear magnetic resonance technology to traditional Chinese medicine related fields, such as detecting during the drying process of Tianma, verifying that this technology can become a rapid method for determining the moisture content of Chinese medicinal materials; Using low field nuclear magnetic resonance technology and principal component analysis method to distinguish different brands of yellow gelatin as the detection object.

Fresh herbs are harvested and dried into Chinese medicinal materials, which are then processed into decoction pieces according to their intended use. The drying indicators and processing techniques affect the quality and efficacy of the decoction pieces. The drying index setting for the Chinese Pharmacopoeia and local processing standards in various provinces and cities is limited to “sun drying and shade drying”, and the specific parameters have not yet been determined. Previous studies have shown that drying process conditions and moisture content have an impact on the quality and appearance of medicinal materials, especially for root and stem Chinese medicinal materials. Due to their hard texture, moisture control is an important quality control indicator during processing. Salvia miltiorrhiza is the dried root and rhizome of Salvia miltiorrhiza Bge, a plant in the family Lamiaceae. It was first listed as a top-grade herb in the “Shennong Bencao Jing” and is known as the “One Ingredient Danshen Drink with the Same Function as Siwu Tang”. It plays an important role in the prevention and treatment of cardiovascular diseases. After the mature planting of Danshen, it is harvested and dried to form medicinal materials. The dried medicinal materials are washed, moistened, and cut into dried slices. The specific process is shown in Figure 1. In the traditional soaking process, water is required to enter the medicinal herbs. Improper soaking can easily result in loss of effective ingredient content, and incomplete soaking can make it difficult to cut and affect the appearance of the decoction pieces. Previous literature has shown that low field nuclear magnetic resonance technology can provide technical support for the rehydration conditions and endpoint determination of traditional Chinese medicinal materials, and provide intuitive reference for the water change pattern. Based on this, low field nuclear magnetic resonance technology is used to study the water change pattern during the infiltration process of Danshen medicinal materials. Given the cumbersome processing technology of traditional Chinese medicinal materials, integrated research on the processing and processing of Chinese medicinal materials in production areas has been conducted. Scholars have explored the feasibility of cutting fresh Danshen in production areas. Fresh Danshen medicinal materials were dried to a certain moisture content and cut, resulting in slices with similar appearance to traditional methods and higher active ingredient content than traditional methods. It is believed that cutting fresh Danshen in production areas is feasible. However, in this process, the moisture control is vague and the state is not intuitive, making it difficult to scientifically and reasonably define the endpoint indicators. It is urgent to adopt scientific technology for in-depth analysis. This experiment uses low field magnetic resonance imaging (MRI) technology to monitor the moisture changes during the infiltration and drying process of Danshen, providing technical methods and theoretical basis for further standardizing the processing procedures in the production area.

The color of traditional Chinese medicine is closely related to its medicinal properties and efficacy, and there is an important correlation between the appearance color and the quality of traditional Chinese medicine. The traditional evaluation of Danshen includes the saying “the color red is better” and “the skin and flesh are purple”, indicating that the color characteristics of its “skin” and “flesh” are particularly important. Research has shown that the appearance and color of Danshen are related to the Danshen red pigment it contains. Danshen red pigment, also known as total tanshinone, has a positive correlation with its lipophilic components. The depth of the skin color indirectly reflects differences in the quality of medicinal materials. Therefore, this study uses precision color difference analysis technology to compare the color difference values of Danshen samples in different processing processes, and conducts correlation analysis between moisture patterns and color difference values, providing scientific reference for ensuring the quality evaluation of Chinese medicinal materials.

This experiment was calibrated using water quality and low field nuclear magnetic resonance signal. After fitting, there was a significant linear relationship between water quality and signal absorption peak area, with an r2 value of 0.999.6, indicating the reliability of the method. This study used low field nuclear magnetic resonance technology to investigate the moisture content and changes in Danshen during different processing stages. The T2 relaxation spectrum showed two peaks in different states, indicating that the internal moisture state of Danshen can be divided into two types: bound water and flowing water; The amplitude of the signal corresponding to different moisture content varies with the processing method, and the absorption peak shifts in different directions. After 6 hours of immersion, external water began to penetrate the interior of Danshen medicinal herbs, and free water and bound water began to merge and transform, ultimately increasing the moisture content to 88.76%; As the moisture content changes, the appearance and skin color of medicinal herbs also change, and they are easy to cut; After being dried at a constant temperature of 50 ℃ for 12 hours, the free water content of fresh Danshen medicinal herbs decreased to 46.69%. After about 24 hours, it approached the drying endpoint, and a small amount of bound water remained inside the tissue, which could no longer be recognized by MRI images. Studies have shown that the dehydration rate of Danshen under different drying methods is negatively correlated with the content of each component, which also indicates that water content control has a significant impact on drying. The traditional processing of Danshen is complicated, and some scholars have studied the optimization of Danshen’s fresh cutting technology, believing that it is feasible. However, the specific moisture content and process parameters of the medicinal material are not yet perfect. This study indicates that low field nuclear magnetic resonance technology can quickly detect the internal moisture changes during the drying or soaking process of Danshen, and also provide scientific evaluation for the endpoint control of medicinal material drying/soaking.

The color of traditional Chinese medicine is one of the important indicators of its quality. Since ancient times, people have relied on practical experience to summarize the method of identifying the authenticity and quality of traditional Chinese medicine based on color, which is called “color discrimination and quality analysis”. Danshen, also known as “skin, dan, flesh, and purple”, exhibits a strong red color due to its main content of red phenanthrenequinone derivatives. During the infiltration process of Danshen medicinal herbs, the color difference a value gradually increases with time, and the color of the outer skin of the herbs gradually deepens. Moreover, there is a significant negative correlation between water content and a value, indicating a certain relationship between water content and lipid soluble tanshinone components. During the drying process of fresh roots of Salvia miltiorrhiza, the values of a and b gradually decrease with time, and the color of the epidermis gradually becomes lighter. When dried for 24 hours, the value of a sharply decreases, and the proportion of flowing water is significantly positively correlated with the values of a and b, and extremely significantly negatively correlated with the L value, reflecting a significant decrease in the content of tanshinones in this state. The water-soluble component salvianolic acid B is a product of fresh Danshen harvested and dried, but its content gradually decreases over time. As a water-soluble component, this change is likely related to the moisture content of the sample. Can low field nuclear magnetic resonance be used to detect the critical point of moisture in medicinal materials to control the chemical component content? This has reference significance for the quality control of traditional Chinese medicinal materials.

Plants can be divided into two states of water based on their molecular states and environmental influences: bound water and free water. Bound water is adsorbed by large molecules in plant cells and cannot flow freely; Free water exists in the intercellular spaces of plants and can move or disappear freely. The root system is an important part for traditional Chinese medicine to obtain nutrients from the growth environment. Due to the complex and uneven internal structure of the root, it is difficult to control and distribute water. Plant roots and rhizomes are rich in a large amount of water, and hydrogen is highly abundant in water. Low field nuclear magnetic resonance spectra have strong signal values for hydrogen atoms, which has become a characteristic of the wide application of low field nuclear magnetic resonance in studying the water laws of root and rhizome medicinal materials. Low field nuclear magnetic resonance, as an emerging research method, has the advantages of intuitive results, accurate data, and fast detection compared to conventional traditional analysis methods, demonstrating unique superiority in moisture determination research. This study focuses on the root and rhizome medicinal herb Salvia miltiorrhiza, and elucidates the water content changes during the soaking and drying process of Salvia miltiorrhiza. It provides a more intuitive evaluation method for the processing of root medicinal herbs, as well as a fast and non-destructive visualization technique for studying water content changes during processing. At the same time, it provides scientific basis for controlling water content and optimizing processing technology in traditional Chinese medicine. The shortcomings were not comprehensively analyzed in combination with the content of chemical components. In the later stage, the differences in water content and chemical components of medicinal materials during processing will be scientifically and systematically explained based on changes in active ingredients, providing new ideas for the research and application of traditional Chinese medicine.