Comprehensive Quality Evaluation of American Ginseng for Different Parts and Abnormal Trait Based on the Major Ginsenoside Contents and Morphological Characteristics

The demand for American ginseng, a famous traditional medicine and high-grade healthy food, has increased dramatically over recent years. However, only the main root is popular among consumers, whereas other parts of American ginseng are rarely available in the market. In this study, the contents of 5 major ginsenosides (Re, Rc, Rg1, Rd, and Rb1) were determined through high-performance liquid chromatography. Our study showed that all these 5 major ginsenosides are found in different parts of American ginseng plants, and the total content in different parts varied significantly in the following order: fibrous root > flower > branch root > main root > leaf > stem. Interestingly, the total content in the fibrous root was approximately 2.24 times higher than that in the main root. Further research indicated that the ginsenoside content in American ginseng with abnormal characteristics (physical deformity caused by disease and discolouration) is similar to that in the normal plant. Interestingly, a positive correlation was observed between the main root diameter and total ginsenoside content, whereas a negative correlation was observed between the main root length and total ginsenoside content. Our comprehensive study revealed that all parts of American ginseng, including the main root with abnormal characteristics, possess medicinal or economic value. Therefore, our results provide feasible evidence to further explore the potential application of American ginseng.


Introduction
American ginseng (Panax quinquefolius L.) is native to North America and has been widely used as a traditional medicine and in health tonics [1]. Recent studies have reported that American ginseng exhibits immunomodulatory [2], antitumour [3], antioxidative [4], antiinflammatory [5], and antidiabetic [6] effects, prevents ovarian ageing [7], and helps in expediting recovery from common cold [8]. Ginsenosides, as the main secondary metabolites of American ginseng, are the main bioactive components [9,10]. Because of its multiple biological activities, American ginseng has been widely adopted as a fundamental ingredient in functional foods, pharmaceutical products, cosmetics, and nutraceuticals. Currently, artificial cultivation of American ginseng is encouraged to satisfy the ever-increasing market demands [11,12]. However, further application of American ginseng is still restricted because of its slow growth rate, high price, and complicated quality evaluation criteria.
So far, considerable efforts have been made to resolve these problems, and one of the main strategies is to increase production and quality. For example, a small seedling size is known to be associated with a high ginsenoside content in the main root (MR) [13]. Some studies have reported that the quality of American ginseng differs considerably depending on the age and cultivation region [14,15]. In addition, the application of biofertilisers has also shown to decrease the rate of rotten roots, thus enhancing the yield and quality [16][17][18]. However, most researches are focused on the root, and only the MR is popular among consumers [19]. In fact, the remaining parts such as flower, leave, stem, branch root (BR), and fibrous root (FR) are not considered a good source of ginsenoside. Thus, these parts have been rarely studied and are not available in commercial markets.
Compared with American ginseng, every part of Asian ginseng has been fully explored and medicinally utilised [20][21][22]. For example, the MR in the form of Chinese patent medicine is commonly used to treat cancers, fatigues, and cardiovascular diseases. The BR and FR are generally ground into powder and used as a food additive or in tonics, whereas the flower, stem, and leaf extracts are used as raw materials in cosmetic manufacturing. However, for the American ginseng, previous studies have only focused on the ginsenoside content of the MR, and therefore, the systematic profiles of the total ginsenoside contents of other parts are unknown. Additionally, the American ginseng plant is susceptible to disease, invasion by insect pests, and harsh environment during its growth, which may lead to the development of abnormal characteristics, such as physical deformity caused by disease and discolouration [23]. Normally, these abnormal roots are discarded. Therefore, it is necessary to comprehensively investigate the ginsenoside content of different parts including abnormal roots of the American ginseng, which will provide an effective solution to the complete utilisation of all the parts of this plant. Additionally, there is also lack of a simple criterion for assessing the intrinsic quality of American ginseng, which would further limit the classification according to different purposes. To date, numerous methods have been developed to determine the quality of American ginseng; however, only a few studies have focused on the correlation between the morphological characteristics of its roots and the ginsenoside content. Previous studies have reported that thin roots tend to contain a high ginsenoside content [19]. However, this finding is inconsistent with the evaluation criteria in the market, where thicker roots are costlier than thinner roots. Therefore, to conclude the debate on the relationship between quality and morphological features, further comparison of the ginsenoside content and MR morphotypes is required.
In this study, we performed a comparative analysis using the high-performance liquid chromatography (HPLC) method to investigate the possible commercial worth of 6 different parts including the abnormal root of the American ginseng plant and establish simple quality evaluation criteria for the MR. Our analysis attempts to present an overview of the ginsenoside content of American ginseng, which would serve as a reference for further research and development of potential applications of American ginseng. Moreover, the correlation between ginsenoside content and MR shapes might provide a scientific and practical standard to evaluate the quality of American ginseng based on morphological characteristics.

Sample Preparation.
To compare differences in ginsenoside contents among different parts of American ginseng, we randomly selected 10 American ginseng (four-year-old) plants. Each plant was further divided into 6 parts: MR, BR, FR, flower, stem, and leaf. Subsequently, each part from the 10 plants was combined to form a single sample. Sixty MRs with various abnormal characteristics were collected and classified according to the abnormal characteristics into 3 grades: mild, moderate, and severe. In addition, 19 MRs (MR1-MR19) were selected to analyse the correlation between ginsenoside content and MR shapes. Sample information is listed in Table 1. The samples were washed with water, blot dried with gauzes, and placed in individual paper bags. All the samples were authenticated by the authors according to the Chinese Pharmacopoeia.

Preparation of Sample Solution.
The samples were dried to a constant weight at 50°C and were ground, blended, and passed through sieves (50 mesh) to obtain homogeneous powder. For the 6 parts of the American ginseng and abnormal MRs, 6 powder samples from each part were prepared, and each sample weighed 1.0 g. Because of the availability of a large number of samples for the correlation analysis between ginsenoside content and MR shape, 3 copies of each sample were selected and each copy weighed 1.0 g. These samples were ultrasonically extracted for 30 min at room temperature with 50 mL of 50% methanol (Xilong Scientific Co, Ltd, Guangdong, China). The temperature of the samples increased because of ultrasonic energy. After they were cooled to room temperature, the weight loss was replenished with the same solvent. Extraction solutions were then filtered. Subsequently, 10 mL of the solutions was transferred into an evaporating dish, and the solutions were allowed to evaporate to obtain dry powder. Finally, the dried extract was dissolved in 5 mL of 50% methanol and filtered through a 0.45 μm membrane before HPLC analysis [24].

Statistical Analysis.
Ginsenoside content is presented as the mean ± standard deviation (n = 6). The analysis of variance was performed using the program SPSS 20.0, and Duncan's multiple range test was employed to analyse differences between the means. P value of <0.05 was considered statistically significant. For analysing correlations between the length, diameter, and ginsenoside content, the Pearson correlation coefficient test was used, and a two-tailed P value with a 95% confidence interval was calculated for each correlation.

Results and Discussion
3.1. Method Validation. HPLC chromatograms of the mixed standards are shown in Figure 1(a), and all the 5 ginsenosides can be effectively distinguished on the basis of these chromatograms. The reliability of the method was validated by checking its linearity, limits of detection (LODs), limits of quantification (LOQs), precision, repeatability, stability, and recovery. All the results are listed in Table 2. To get the linear equations of the 5 ginsenosides (Rg 1 , Re, Rb 1 , Rc, and Rd), 6 levels of mixed standard solutions were obtained by diluting their stock standard solutions with 50% methanol. That is, 2, 5, 8, 10, 12, and 15 μL of former standard solution and corresponding 50% methanol were taken to make 1 mL of standard solution. Then, the linearity for each component was determined by plotting the peak area (Y) versus the concentrations (X) of ginsenoside. The values of the correlation coefficient (r = 0:9995 0:9999) indicated a strong correlation between the measured ginsenoside contents and peak areas within test ranges. The LODs and LOQs were determined when the signal-to-noise (S/N) ratios were 3 and 10, respectively. The obtained LODs were 0.012, 0.002, 0.021, 0.027, and 0.023 μg/mL for the 5 ginsenosides, respectively, while the values of LOQs were 0.022, 0.007, 0.041, 0.055, and 0.049 μg/mL for the 5 ginsenosides, respectively. Precision was evaluated by analysing the peak area variations of the mixed standard solution with 6 replicated analyses. Repeatability testing was performed by analysing 6 individual samples. Stability was examined on a sample solution at time intervals of 0, 2, 4, 6, 10, and 12 h. All the RSDs of precision, repeatability, and stability were found to be less than 3.000%. Recovery assessment was evaluated using spiked samples by adding 200 μL of the standard mixture into 200 μL of the sample solution. This process will be repeated 6 times with 10 μL for each injection. The average recovery rate was 98.522%, 100.847%, 105.009%, 104.507%, and 105.424% for Rg 1 , Re, Rb 1 , Rc, and Rd, respectively, with the RSDs of

Comparison of the 5 Major Ginsenosides in Different
Parts of the American Ginseng. By using the aforementioned HPLC method, we determined the ginsenoside content in MR, BR, FR, flower, stem, and leaf ( Figure 2). Because the major ginsenosides (Rg 1 , Re, Rb 1 , Rc, and Rd) typically account for more than 70% of the total ginsenoside content in the American ginseng plant, these 5 major ginsenosides were considered quality indicators in this study [25,26]. Table 3 presents the ginsenoside content of different parts. Surprisingly, all the 5 ginsenosides were detected in the 6 studied parts of the American ginseng plant. Nevertheless, a significant difference between these parts was observed in the ginsenoside content. As illustrated in Figure 3, the total ginsenoside content of different parts ranked as follows: FR > flower > BR > MR > leaf > stem. The FR had the highest level of 117.62 mg/g, which was about 1.74, 1.87, 2.24, 2.86, and 8.98 times higher than those in the flower, BR, MR, leaf, and stem, respectively. Moreover, the total ginsenoside contents in the FR and BR were more than 2.24 and 1.20 times higher than those in the MR, which is inconsistent with traditional experience. This result might be attributed to the fact that the FR is much thinner than the MR, and thus, the more periderm contributes to a higher ratio in the FR. In general, consumers believe that the MR is more effective than the BR and FR, which leads to a significant price difference among these 3 parts. However, our analysis suggests that the American ginseng plant with a thin root is of superior quality for medicinal use.
Similar to the total ginsenoside content, a large variation in individual ginsenoside amounts was observed among the 6 parts of the American ginseng. For example, the contents of Rb 1 in the MR, BR, and FR were obviously higher than those in the flower, stem, and leaf; thus, this could be used as a major indication to identify the roots of American ginseng plants. The flower contained the highest ginsenoside contents of Rc, Re, and Rg 1 , whereas the FR contained the highest level of Rb 1 . Because the individual ginsenoside exhibits specific effects on different diseases, these 6 parts of the American ginseng can be used purposefully [27].
We noticed a similar trend in the Panax ginseng, wherein the FR had a higher ginsenoside content than the MR [28,29]. However, compared with the American ginseng, obvious differences were found in the flower, leaf, and stem of the Panax ginseng. The decreasing order of the total ginsenoside content in these 3 parts of the Panax ginseng was as follows: leaf > flower > stem. Additionally, not all the 5 individual ginsenosides could be detected in the stem and leaf. The Rb 1 contents in the stem and leaves were considerably low, and Rc was almost not detected in the stem of the Panax ginseng. Nevertheless, the contents of the ginsenoside Rc in leaf and stem were compared to the ones in the root for the American ginseng. These results indicated that the American and Panax ginsengs should be used differently according to the requirement.
The sum of the individual ginsenoside (Rg 1 , Re, and Rb 1 ) content in the American ginseng, which is the index stipulated in the Chinese Pharmacopoeia (2020), has also been reported. As presented in Figure 3 and Table S1, the total of Rg 1 , Re, and Rb 1 content in different parts, except for the stem, was higher than the Pharmacopoeia standard (>20 mg/g). The result indicated that not only the MR but also the BR, FR, flower, and leaf can be used as traditional Chinese medicine. Although the sum of Rg 1 , Re, and Rb 1 in the stem was lower than the pharmaceutical standards, it could also be used as a raw material in cosmetic manufacturing. In the past, these parts were often discarded, which resulted in great losses. We can fully utilise the flower, stem, and leaf as raw materials for extracting active ingredients and for developing means to maximise the utilisation of traditional Chinese medicine resources. Moreover, although the FR is not as popular as the MR in the medicinal material market, it had the highest ginsenoside content among the 6 parts of American ginseng that were investigated, which means that more attention should be paid to its medicinal value in the future. Therefore, all 6 different parts of the American ginseng could be effectively used in various products according to different needs, and our study could provide an important visual standardisation for quality evaluation and classification of American ginseng plants.

Comparison of the 5 Major Ginsenosides in the American
Ginseng with Various Abnormal Characteristics. To date, only a few studies have focused on determining the correlation between abnormal characteristics and the quality of American ginseng. Although the parts of Salvia miltiorrhiza with abnormal characteristics, such as physical deformity caused by disease and discolouration, still contain comparable active components compared with the healthy parts [30], the same cannot be concluded for the American ginseng. Therefore, the 5 major ginsenosides were also detected in the abnormal MRs. The results are listed in Table 3.     BioMed Research International Surprisingly, no significant difference was observed in the ginsenoside content among the 4 grades of the American ginseng, as shown in Figure 4. The total ginsenoside content of these MRs was ranked as mild > normal > moderate > severe, where the values were 58.00, 52.45, 49.78, and 39.30 mg/g, respectively. A similar trend was also observed for the individual ginsenoside content. Notably, the abnormal American ginseng of the mild grade displayed the highest ginsenoside content. This phenomenon may be caused by the change in metabolism due to diseases, insect pests, and adverse environmental conditions, and it has also been reported in other plants such as Salvia miltiorrhiza [30], Panax notoginseng [31], and Glycyrrhiza uralensis [32].

BioMed Research International
The sum of individual ginsenoside (Rg 1 , Re, and Rb 1 ) contents was 34.35, 42.83, and 50.79 mg/g for the severe, moderate, and mild ones, respectively. Obviously, the sum of individual ginsenoside (Rg 1 , Re, and Rb 1 ) contents was higher than the Chinese Pharmacopoeia standard (20 mg/g) (2020). Therefore, the American ginseng with abnormal characteristics should be effectively used rather than being discarded.

Correlation between Morphological Characteristics and
Ginsenoside Contents. Presently, the MR is the most common part of the American ginseng plant that is sold in the market. Thus, the exploration of the relationship between its quality and morphological features is essential. In this study, we analysed 19 MR samples of the American ginseng, as shown in Figure S2. Among the morphological characteristics, the diameter and length of the MR were determined as a simple and objective measurement index. The quantitative results between the 5 major ginsenoside contents and their morphological characteristics are listed in Tables 1 and 3.
The diameter of all the MRs ranged from 1.10 cm to 1.92 cm, whereas the length ranged from 5.4 cm to 13.2 cm. The 5 ginsenoside contents varied significantly in the MRs with different diameters and lengths. The total ginsenoside contents ranged from 35.15 to 69.88 mg/g, and the average value was 53.16 mg/g. This result was consistent with that reported in Section 3.2, which confirms the accuracy of the method adopted in the present study. The correlation between the total ginsenoside content and morphological characteristics is shown in Figure 5. Interestingly, an opposite trend was observed for the diameter and length. The Pearson correlation coefficient was 0.701 for the diameter, whereas the value was −0.683 for the length. These results indicate that the MRs with thicker and shorter morphology contain higher levels of ginsenosides, which is consistent with the evaluation criteria in the market where thicker MRs have higher prices. It indicates that the diameter and length of the MR are key morphological characteristics and can be used by consumers and retailers to roughly estimate the quality of the American ginseng. Consequently, dividing the MR of the American ginseng plant into specific grades and optimising the utilisation of each grade will greatly enhance the production value and improve economic benefits rather than mixing them together.

Conclusion
In summary, this study provides an overview of the inherent qualities of the American ginseng using the HPLC method. Our findings indicate that the ginsenoside content of the American ginseng has a strong correlation with the parts, degree of abnormal characteristics, and morphological characteristics. The MR, BR, FR, flower, stem, and leaf are all rich in the 5 major ginsenosides, namely, Rg 1 , Re, Rb 1 , Rc, and Rd. Moreover, the ginsenoside contents in all the parts, except for the stem, meet the pharmacopoeia standard. The ginsenoside contents in the abnormal MRs were compared to those in the normal MRs, and no obvious difference was found. In addition, our results indicate that a thicker MR contains greater amounts of ginsenosides, but a longer MR contains lower amounts of ginsenosides. Our study provides scientific 30 1.0 1.4 Diameter of main root (cm)   BioMed Research International evidence for further development and for the effective and economic use of every part of American ginseng plants.

Data Availability
All data generated or analysed during this study are included in this published article. The datasets used or analysed during the current study are available from the corresponding authors on reasonable request.