Evaluation Of Effects Of Different Drying Processes And Excipients On Hygroscopicity Of Scutellariae Radix And Coptidis Rhizoma Extracts Based On Physical Fingerprint Spectrum

Abstract: Objective Taking Huangqin (Scutellariae Radix, SR) and Huanglian (Coptidis Rhizoma, CR) extract powder as the research object, the effects of different drying methods and auxiliary materials on moisture absorption were investigated.

Methods The extract powder of SR and CR was prepared by conventional drying (CD), vacuum drying (VD), and spray drying (SD). Twelve secondary indexes, such as moisture content, moisture absorption rate, specific surface area, median diameter, span, width, Hausner ratio, angle of repose, bulk density, tapped density, gap rate, and Carr index, were used to establish the physical fingerprint of extract powder. The secondary indexes were converted into five primary ones: uniformity, pileup, compressibility, fluidity, and stability. Then the best drying process was selected. Principal component analysis (PCA) and partial least squares analysis (PLS) were used to analyze the correlation between the physical parameters and the moisture absorption behavior. The effects of five excipients, including dextrin, β-cyclodextrin, pre-gelatinized starch, anhydrous lactose, and microcrystalline cellulose, on the moisture sorption of the powder were optimized. The dynamic curve of the moisture sorption time of the powder was drawn, and the semi-equilibrium moisture sorption time (t1/2) and equilibrium moisture sorption time (F∞) were derived to form a two-dimensional evaluation index to evaluate the dynamic moisture sorption behavior of the powder and screen out the best moisture-proof excipients. Results Based on the physical fingerprint similarity study, the following results were obtained: SR: The best similarity of spray drying extract powder (SRSD) was 0.98, 0.99, 0.99, and the similarity of vacuum drying extract powder (SR-VD) was 0.87, 0.92, 0.89, which was better than that of atmospheric pressure drying. The similarity of vacuum drying, spray drying, and atmospheric pressure drying was 0.95, and 0.69, respectively. CR: There was no significant difference among the three drying methods. The best similarity of spray drying extract powder (CR-SD) was 0.99, 1.00, and 0.99, and the similarity of vacuum drying, spray drying, and atmospheric pressure drying was 0.94 and 0.61, respectively. According to the comprehensive evaluation of 5 first-level indicators, it can be concluded that the vacuum and spray drying modes are better. Through the matrix heat map, PCA and PLS, span, width, SSA and D50 had the most significant influence on H, followed by Dc and Da (P < 0.05). Through dynamic two-dimensional characterization technology, it can be observed that the excipients can improve the moisture absorption of the powder. The research shows that: SR: Under the three drying methods of extract powder, the samples belong to the second class, with a large equilibrium moisture absorption capacity and slow moisture absorption rate, and the medication-auxiliary mixture belongs to the third class, with a small equilibrium moisture absorption capacity and slow moisture absorption rate. Among them, the equilibrium moisture absorption of the atmospheric dried sample of SR and the medication-auxiliary mixture of β-cyclodextrin is the smallest, with F∞ = 9.12%. Vacuum-dried samples of SR and the drug adjuvant mixture of β-cyclodextrin had the lowest moisture absorption rate, t1/2 = 69.33 h, CR: The atmospheric pressure and spray extract powder belong to the second class, and the drug-auxiliary mixture belongs to the third class. The equilibrium moisture absorption of the drug-auxiliary mixture of the CR vacuum sample and lactose is the smallest, with F∞ = 7.72%, and the moisture absorption rate of the drug-auxiliary mixture of the CR vacuum sample and β-cyclodextrin is the smallest, t1/2 = 76.33 h. 

Conclusion Improving the drying method of traditional Chinese medicine extracts and selecting high-quality moisture-proof excipients can improve the moisture absorption of Chinese medicine extracts. 

Keywords: extracts; Coptidis Rhizoma; Scutellariae Radix; physical fingerprint; drying method; excipients; principal component analysis; partial least squares analysis; dynamic two-dimensional characterization technology; moisture absorption; conventional drying; vacuum drying; spray drying

NEW DRYING METHOD HERB EXTRACT-HIGH QUALITY CISTANCHE

Chinese medicine extracts (CMEs) are obtained from Chinese medicinal materials or Chinese medicinal compounds through extraction, separation, concentration, and drying. They have relatively clear efficacy and are important intermediates in the production process of Chinese medicine preparations. They are mostly used to prepare solid preparations such as Chinese medicine granules, tablets, and capsules [1]. Chinese medicine extracts are complex in composition and contain a variety of highly hygroscopic components, such as sugars, starch, protein, and tannin. They are very easy to absorb moisture when in contact with air, resulting in increased viscosity and difficulty in preparation molding. They are also highly hygroscopic after being made into solid preparations. During storage, they will cause a series of stability problems such as agglomeration of granules and capsules, and darkening of tablet color.

Refining the treatment of Chinese medicine extracts can reduce the hygroscopicity of extract powders, but the effective ingredients such as flavonoids, glycosides, and organic acids will also be lost to varying degrees, which does not meet the actual production process requirements. Selecting the appropriate drying method and reasonable process parameters has a great influence on the physical properties of Chinese medicine extract powders, which can increase the particle size of the powder, reduce the specific surface area, and significantly reduce the moisture absorption rate of the extract powder [2-5]. Adding appropriate excipients to Chinese medicine extract powder can not only reduce hygroscopicity and improve its stability, but also act as a diluent, adhesive, or lubricant, which is beneficial to the preparation molding [6-8]. The use of powder surface modification technology, moisture-proof coating technology, etc. can reduce the hygroscopicity of the material, and multiple methods can also be used in combination to improve the moisture-proof effect. In this study, the extracts of Scutellaria baicalensis and Coptis chinensis, which are commonly used traditional Chinese medicines with strong hygroscopicity, were selected as the research objects. A total of 12 powder science indicators, including water content, moisture absorption rate, specific surface area, median diameter, particle size distribution width, particle size range, Hausner ratio, angle of repose, bulk density, tap density, interstitial ratio, and Carr index, were determined. A physical fingerprint was established, and principal component analysis (PCA) and partial least squares analysis (PLS) were performed on each physical parameter to explore the correlation between each physical parameter and hygroscopic behavior. The effects of different drying processes and moisture-proof excipients on their hygroscopicity were optimized to provide a reference for the development of moisture-proof technology for traditional Chinese medicine preparations.

1 Instruments and Materials

1.1 Instruments

Bettersize 2600 laser particle size distribution analyzer, Dandong Better Instrument Co., Ltd.; HZ-D (III) circulating vacuum pump, Zunyi Sihua Instrument Co., Ltd.; DHG-9140A electric constant temperature blast drying oven, Shanghai Jinghong Experimental Equipment Co., Ltd.; LANYI-6000Y spray dryer, Shanghai Lanyi Industrial Co., Ltd.; D2F-6021 vacuum drying oven, Shanghai Yiheng Scientific Instrument Co., Ltd.; XL-10B high-speed Chinese medicine pulverizer, Guangzhou Xulang Machinery Equipment Co., Ltd.

1.2 Materials

Scutellaria baicalensis, batch number 210527, Jiangnantong Mitsukoshi Chinese Medicine Pieces Co., Ltd.; Coptis chinensis, batch number 211027, Jiangsu Chengkai Chinese Medicine Co., Ltd.; the pieces were identified by Professor Chen Jianwei of Nanjing University of Chinese Medicine, and they are the dried roots of Scutellaria baicalensis Georgi, a plant of the genus Scutellaria in the Lamiaceae family, and the dried rhizomes of Coptis chinensis Franch., a plant of the genus Coptis in the Ranunculaceae family, both of which meet the standards of the 2020 edition of the Chinese Pharmacopoeia; 95% ethanol (batch number 20220712), lactose (batch number 20220527), β-cyclodextrin (batch number 20201118), dextrin (batch number 20210309), Sinopharm Chemical Reagent Co., Ltd.; microcrystalline cellulose, batch number C2205104, Shanghai Shenmei Pharmaceutical Development Technology Co., Ltd.; pregelatinized starch, batch number Z22J8W40375, Shanghai Yuanye Biotechnology Co., Ltd.

2 Methods and Results

2.1 Preparation of extract powder of Chinese herbal medicine extract

2.1.1 Preparation of extract

(1) Scutellaria baicalensis (SR): Take 300 g of Scutellaria baicalensis slices, add 10 times the amount of water and boil for 3 times, combine the decoctions, concentrate to an appropriate amount, add 70% ethanol to precipitate, stir evenly, let stand, take the supernatant to recover ethanol, and concentrate to a clear paste with a relative density of about 1.1 and 1.3 for use.

(2) Coptis chinensis (CR): Take 300 g of Coptis chinensis slices, add 12 times the amount of water, and boil for 2 times, combine the decoctions, concentrate to an appropriate amount, and concentrate to a clear paste with a relative density of about 1.1 and 1.3 for use.

2.1.2 Preparation of extract powder by different drying methods

(1) Conventional drying (CD) extract powder: Dry the thick paste with a relative density of about 1.3 at 75℃ under normal pressure, crush it with a high-speed Chinese medicine grinder for 90 seconds after drying, and pass it through an 80-mesh sieve to obtain the extract powder.

(2) Vacuum drying (VD) extract powder: Dry the thick paste with a relative density of about 1.3 at 75℃ under vacuum, crush it with a high-speed Chinese medicine grinder for 90 seconds after drying, and pass it through an 80-mesh sieve to obtain the extract powder.

(3) Spray drying (SD) extract powder: Spray dry the clear paste with a relative density of about 1.1, and pass it through an 80-mesh sieve to obtain the extract powder.

2.2 Construction of physical fingerprints

2.2.1 Determination of physical indicators of extract powder

The stability, uniformity, fluidity, stacking and compressibility of the extract powder are taken as the primary indicators of the physical fingerprint, and the moisture content (HR), moisture absorption rate (H), specific surface area (SSA), median diameter (D50), particle size distribution width (span), particle size range (width), Hausner ratio (IH), angle of repose (α), bulk density (Da), tapped density (Dc), gap rate (Ie), Carr index (IC) and a total of 12 parameters are secondary indicators [9-12].

2.2.2 Measurement methods and calculation formulas for each secondary index of extract powder

(1) α: Determined by fixed funnel method. Fix the funnel at a certain height above the coordinate paper, add materials from the funnel until the top of the piled cone is just in contact with the bottom of the funnel, measure the cone diameter, take the ratio of the funnel bottom height (h) to the cone radius (r) as the tangent value, calculate the angle of repose, and take the average value after three parallel measurements. The calculation formula is shown in formula (1).

tanα＝h/r (1)

(2) Da: Select a container with a fixed volume (V), and let the powder flow into the density container after vibration and sieving. After the powder fills the container, use a scraper to scrape off the excess powder, and weigh the mass of the container before and after adding the sample (m0 and m1), respectively. The calculation formula is shown in formula (2).

Da＝(m1－m0)/V (2)

(3) Dc: The determination method is the fixed volume method. Select a container with a fixed volume (V), weigh the empty cup mass (m0) before measurement, add the powder to be measured, and vibrate it continuously for 100 and 200 times. After vibrating, weigh the total mass of the container and powder (m). If the mass difference between 200 and 400 times of vibration is not greater than 2%, calculate Dc according to formula (3). If the mass difference between 200 and 400 times of vibration is greater than 2%, continue to vibrate for 100 times until the mass difference between two consecutive measurements is less than 2%. Scrape off the excess sample, weigh the mass of the measuring cup filled with the sample (m1), and measure three times in parallel. The calculation formula is shown in formula (3).

Dc＝(m－m0)/V (3)

(4)Ie： Calculated from Da and Dc, the calculation formula is shown in formula (4). Ie＝(Dc－Da)/DaDc (4)

(5)IC： Calculated from Da and Dc, the calculation formula is shown in formula (5). IC＝(Dc－Da)/Dc (5)

(6)IH： Calculated from Da and Dc, the calculation formula is shown in formula (6).

IH＝Dc/Da (6)

(7)HR： According to the 2020 edition of the Chinese Pharmacopoeia [13], 1 g of powder sample is accurately weighed and evenly spread in a weighing bottle (m2) with a constant mass, with a total mass of m3 and a thickness not exceeding 5 mm. The bottle cap is opened and dried at 100-105℃ for 5 h. The bottle cap is closed and placed in a dryer. It is cooled for 30 min and accurately weighed. It is then dried at the above temperature for 1 h, cooled, and weighed until the difference between the two consecutive weighings does not exceed 5 mg. The constant mass is m4. The water content of the sample is calculated based on the lost mass. Three samples are measured in parallel and the water content is calculated. The calculation formula is shown in formula (7).

HR＝(m3－m4)/(m3－m2) (7)

(8)H: Take the weighing bottle, dry it, place it in a desiccator containing saturated sodium chloride solution for 24 hours, and weigh its mass (m5). Take about 1 g of powder spread it evenly in the weighing bottle, and accurately weigh the total mass (m6). Uncover the weighing bottles and place them in a desiccator for 24 hours, cover them with the caps, and then take out and weigh the mass (m7). Measure each powder three times in parallel and calculate H. The calculation formula is shown in formula (8). H＝(m7－m6)/(m6－m5) (8)

(9)Particle size (D10, D50, D90), span, SSA, and width: measured by laser particle size distribution analyzer, with air as the medium, add the sample into the feed hopper of the dry dispersion system, and measure the particle size D10, D50, D90 and particle size SSA corresponding to the cumulative particle size distribution number reaching 10%, 50% and 90% respectively. The calculation formulas of span and width are shown in formulas (9) and 10).

span＝(D90－D10)/D50 (9)

width＝D90－D10 (10)

2.2.3 Measurement results of each secondary index of extract powder

Take 3 batches of extract powder of Scutellaria baicalensis and Coptis chinensis dried in 3 different ways, measure and calculate the actual value of each index according to the method under "2.2.2", and use the average value as the control. The results are shown in Table 1.

The data showed that the α values of all samples were between 42.20° and 48.80°, all greater than 40°, indicating poor fluidity; the average values of SR-Da of atmospheric pressure samples were 0.49 g/mL, SR-Dc was 0.95 g/mL, CR-Da was 0.44 g/mL, and CR-Dc was 0.78 g/mL; the average values of SR-Da of vacuum samples were 0.58 g/mL, SR-Dc was 0.99 g/mL, CR-Da was 0.49 g/mL, and CR-Dc was 0.78 g/mL; the average values of SR-Da of spray samples were 0.41 g/mL, SR-Dc was 0.64 g/mL, CR-Da was 0.31 g/mL, and CR-Dc was 0.61 g/mL. It was found that the Da and Dc values of atmospheric pressure dried and vacuum-dried samples of Scutellaria baicalensis extract powder were different. The values are close, and the Da and Dc of the spray-dried samples are significantly reduced; the HR of all samples is 4.39%~5.29%, and H is 9.35%~12.04%. According to the hygroscopicity requirements of the 2020 edition of the Chinese Pharmacopoeia [13], when 2%＜H＜15%, it has hygroscopicity. Combined with the observation of the determination process of H, it can be seen that Scutellaria baicalensis and Coptis chinensis have obvious hygroscopicity; the particle size D50, span and width of the atmospheric pressure samples range from 36.17 to 44.99 μm, 2.79 to 3.78 and 113.70 to 143.15 μm, the range of D50, span and width of the vacuum samples range from 45.39 to 54.31 μm, 3.05 to 3.26 and 145.74 to 166.13 μm, respectively, and the particle size D50, span and width of the spray samples range from 45.39 to 54.31 μm, 3.05 to 3.26 and 145.74 to 166.13 μm, respectively. The ranges are 5.02-6.02 μm, 1.46-1.71, and 7.26-10.61 μm, respectively. It can be found that the normal pressure samples and vacuum samples of Scutellaria baicalensis and Coptis chinensis have similar particle sizes, large span and width, and uneven particle size distribution, while the D50, span and width of the spray-dried samples are significantly reduced, indicating that the extract powder obtained by spray drying has a small and uniform particle size.

2.2.4 Establishment of the physical fingerprint spectrum of extract powder and similarity analysis

Since the measured values of the secondary physical quality indicators have different dimensions and ranges, each secondary indicator is normalized and converted to the same scale, i.e. 0-10, through the formula. The conversion formulas of each secondary indicator are shown in Table 2, and the conversion results are shown in Table 3. Then, the conversion means of each secondary indicator representing the primary indicator are added together, and the average value is calculated to obtain the value of each primary indicator [14-15]. The results are shown in Table 4. The physical fingerprint of the extract powder is quantitatively and intuitively displayed in the form of a radar chart. The radar chart is drawn for the data in Table 3 using Origin software, and the similarity is calculated using the Pearson correlation of SPSS. Compared with the control charts of each group, the closer the similarity is to 1, the more similar the physical properties of the powders are, as shown in Figure 1. The similarities of the normal pressure dried extract powder of Scutellaria baicalensis are 0.76, 0.85, and 0.94, the similarities of the vacuum dried extract powder of Scutellaria baicalensis are 0.87, 0.92, and 0.89, and the similarities of the spray dried extract powder of Scutellaria baicalensis are 0.98, 0.99, and 0.99. The similarities of vacuum-dried, spray-dried, and normal pressure-dried Scutellaria baicalensis are 0.95 and 0.69, respectively. It is concluded that the normal pressure dried similarity of Scutellaria baicalensis is not high, the vacuum-dried similarity is higher than the normal pressure, and the spray-dried similarity is the highest. The similarities of atmospheric pressure drying extract powder of Coptis chinensis were 0.89, 0.97, and 0.93, the similarities of vacuum drying extract powder of Coptis chinensis were 0.98, 0.99, and 0.98, and the similarities of spray drying extract powder of Coptis chinensis were 0.99, 1.00, and 0.99. The similarities of vacuum drying, spray drying, and atmospheric pressure drying of Coptis chinensis were 0.94 and 0.61, respectively. The results showed that atmospheric pressure drying, vacuum drying, and spray drying of Coptis chinensis were all similar.

The difference in fingerprint spectra of different drying methods of Scutellaria baicalensis and Coptis chinensis may be due to the different chemical compositions of Scutellaria baicalensis and Coptis chinensis. During the experiment, Scutellaria baicalensis and Coptis chinensis under the same drying method were placed in the same environment, and Scutellaria baicalensis quickly absorbed moisture and clumped; the high similarity of fingerprint spectra of atmospheric pressure drying samples and vacuum drying samples of the two may be because both of them have undergone the same crushing and sieving process, while the spray-dried sample has not undergone this process, but its particles are finer and more uniform.

The calculation results of each primary index are shown in Table 4. When the primary index is greater than 5, the performance can be considered good. The atmospheric pressure and vacuum-dried samples of Scutellaria baicalensis have excellent stacking, good stability, and uniformity; the spray-dried samples have good uniformity, but relatively poor stability. Combined with the secondary indexes, it can be seen that its moisture absorption rate (H) is also relatively high; considering the stability of the vacuum-dried extract powder of Scutellaria baicalensis, the secondary indexes HR and H closely related to moisture absorption are the best in each group. In addition, its stacking, fluidity, and uniformity are good, which is convenient for the subsequent process development of solid preparations such as capsules and granules. The stability and uniformity of the Coptis chinensis extract powder with different drying methods are good, while the atmospheric pressure and vacuum-dried samples have good stacking, but poor compressibility. The compressibility secondary indexes IC, Ie, and SSA of the spray-dried sample are large, and its compressibility is the best. Combining D50, IC, Ie, and SSA, it is concluded that the spray-dried extract powder of Coptis chinensis is stable and uniform, with good compressibility, which is convenient for subsequent process development.

The 12 physical parameters of different batches of extract powders of Scutellaria baicalensis and Coptis chinensis dried in different ways were normalized by SPSS data and the correlation between the parameters was obtained by Pearson correlation coefficient method. On this basis, a correlation matrix hotspot map was drawn, and the results are shown in Figure 2. The darker the color and the closer the color, the higher the similarity of each sample and each physical parameter. Conversely, the lighter the color or the greater the color difference, the weaker the correlation. Figure 2-A reflects the correlation of each sample in 12 physical attributes. It is found that the extract powder has a high similarity in Da, Dc, Ie, IH, HR, span, and SSA, and there are obvious differences in α, particle size D50, and width. Figure 2-B is the two-dimensional matrix correlation between various physical parameters. The results show that H is significantly correlated with SSA, span, and width (P < 0.05), SSA is significantly correlated with Dc, Ie, D50, span, and width (P < 0.05), and Dc is significantly correlated with Da, D50, width, and SSA. If SSA changes significantly, H, Dc, and other related parameters will also change significantly accordingly, indicating that the hygroscopicity of extract powder is affected by multiple physical properties.

Fig. 1 Physical fingerprint of extract powder of SR and CR in different drying methods

A-correlation of physical indicators of different extract powders; B-2D matrix correlation of powder indexes. 

 Fig. 2 Hotspot map of similarity matrix among sample indexes

2.2.5 PCA based on Powder Science

The 12 physical parameters of the extract powder of Scutellaria baicalensis and Coptis chinensis under different drying methods were analyzed in the PCA model using SIMAC software. The results showed that the variance contribution rate of principal component 1 was 53.46%, the variance contribution rate of principal component 2 was 26.86%, and the variance contribution rate of principal component 3 was 7.24%. The cumulative explanatory variables of the first two principal components reached 80.32%, which met the statistical requirements [16]. Therefore, the experiment selected the first two principal components for statistical analysis. Based on the load dispersion diagram obtained by PCA, the horizontal axis represents principal component 1 and the vertical axis represents principal component 2. The farther the parameter index is from the origin, the greater the contribution rate to the corresponding principal component. Main components 1 have the largest contribution rate from IH, HR, H, Da, Dc, and particle size D50; Main component 2 is composed of α, IC, Ie, SSA, and width, and span. Some physical parameters have a clustering trend. The clustered parts indicate that the correlation between each other is stronger. Among them, SSA is close to span and width, indicating that the particle size distribution width and particle size range have a greater impact on the specific surface area. The results are shown in Figure 3. The PCA model analysis score chart shows that the distribution of the extract powders of Scutellaria baicalensis and Coptis chinensis under normal pressure and vacuum drying is relatively dispersed, reflecting the large differences in physical properties between batches; the distribution of the extract powders of spray drying is relatively concentrated, and the fluctuation is small due to the influence of physical properties. In addition, the distribution of the extract powders obtained by spray drying of Scutellaria baicalensis and Coptis chinensis is relatively independent, which also reflects the significant difference between the spray drying method and normal pressure drying and vacuum drying, which is consistent with the results of the physical fingerprint similarity comparison, see Figure 4.

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