1. Introduction
Hemp (
Cannabis sativa L.), an annual herb of the
Cannabis family, has been used for thousands of years [
1]. The tetrahydrocannabinol (THC) content of industrial hemp is less than 0.3 wt%, which is different from medical marijuana and recreational marijuana [
2,
3]. Therefore, industrial hemp could be legally cultivated on a large scale. The chemical composition of industrial hemp is very complex, including cannabinoids, terpenoids, alkaloids, and flavonoids [
4]. The most bioactive compounds are cannabinoids that include more than 130 terpene phenolic compounds which mainly accumulate in the flower tops [
5]. The major cannabinoids are THC, cannabidiol (CBD), cannabinol (CBN), cannabigerol (CBG), cannabidivarin (CBDV), cannabitriol (CBT), and cannabicyclol (CBL) [
6]. Among them, THC, a psychoactive compound restricted in different countries, and CBD are the most studied cannabinoids for their significant bioactivities [
7], such as neuroprotective, antiepileptic, anticancer, and immunoregulatory activities [
8]. The existence of these compounds increases the importance of industrial hemp. At present, industrial hemp has been widely used in the fields of daily chemicals, materials, energy and medicine [
9]. The current treatment of industrial hemp residues (IHR) is directly discarding them, which not only pollutes the environment, but also causes a waste of resources [
10].
Polysaccharide is a polymer which consists of exceeding 10 monosaccharides [
11]. It is one of the most essential biological macromolecules. In recent years, many articles have reported that the natural polysaccharides from plants have good biological activities, including anticancer [
12], anti-inflammatory [
13], antioxidant [
14], immunomodulatory [
15], hypoglycemic [
16], and antiviral activities [
17]. The molecular composition and spatial structure of polysaccharides generally have significant effects on their properties and activities [
18]. With the development of separation, purification, and structural analysis technology of polysaccharide, it is generally accepted that polysaccharides have great application values in drug, cosmetics, and food fields [
19]. The content of polysaccharides from industrial hemp residues is about 10%–15%. Hemp polysaccharides have many excellent physicochemical properties because they contain lots of hydrophilic hydroxyls, such as strong water-absorption capability, emulsifying properties, and good film-forming ability. Meanwhile, hemp polysaccharides have moisture retention, antibacterial, and no-toxic effects. Therefore, they have extensive application prospects in the cosmetics field. The fermented products of hemp polysaccharides (oligosaccharides or some sugar alcohols), which are reported to have good antioxidant, anti-aging, and anti-fatigue activities, have been used to develop functional drinks [
20]. The composition of hemp polysaccharides is relatively complex and it ranges from monosaccharides to 5 × 10
4 Da polysaccharides.
There are few reports about the separation and extraction of hemp polysaccharides. Hillestad et al. isolated two glycoproteins from hemp. The linkage structure of glucoside chain and the connection between the chain and protein were analyzed by methylation and Smith degradation [
21]. J.W. Groce et al. measured the carbohydrate content of hemp grown in the United States, Thailand, and Vietnam respectively. It was pointed out that large differences existed in the type and content of compounds between the cultivars from different areas [
22]. Zheng et al. analyzed the monosaccharide composition and structure of HSP0 and HSP0.2, two components of hemp seed polysaccharide, by HPLC and FT-IR. It was found that HSP0 and HSP0.2 both contained sulfate radical [
23]. Bi et al. obtained two hemp seed polysaccharides HS1 and HS2 by gel filtration chromatography. The main monosaccharides were D-arabinose, D-xylose, D-mannose, D-galactose, and D-glucose, and their molar ratios were 0.12, 0.09, 0.15, 0.11, and 0.12, respectively [
24]. Guo et al. prepared polysaccharides from industrial hemp leaves and studied the effects of ultraviolet light, temperature, and pH on their antibacterial activity. It was found that the minimum bactericidal concentration and minimum inhibition concentration of the polysaccharides against
S. aureus were 6.25 and 3.125 mg/mL, respectively. Additionally, the antibacterial activity was the highest when pH was 7.
In this study, the IHR after cannabidiol extraction were used as the raw material for polysaccharides extraction. The extraction and purification process of industrial hemp residue polysaccharides (IHRPs) were optimized. Then the structure and composition of IHRPs were analyzed. Besides, the ABTS and DPPH scavenging ability of IHRPs was evaluated. Its anti-aging activity was also studied at the cellular level. It is hoped that IHRPs could be widely used in cosmetics and functional food fields.
3. Materials and Methods
3.1. Materials and Reagents
IHR was provided by Yunnan Hempmon Pharmaceuticals Co., Ltd. (Kunming, China). Phenol, α-naphthol, sulfuric acid, carbazole, Coomassie blue G-250, phosphoric acid, ethanol, chloroform, and monosaccharide control were supplied by Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Galacturonic acid, glucuronic acid, guluronic acid, and arbutin were bought from Sigma-Aldrich Co., Ltd. (St. Louis, MO, USA). Human dermal fibroblast (HDF), human epidermal keratinocytes (HEK), and complete cell medium were bought from Sciencell Co., Ltd. (Carlsbad, CA, USA). 12-well plates and 96-well plates were offered by Corning Co., Ltd. (Corning, NY, USA). CCK-8 cell viability assay kit was bought from DOJINDO Biology Co., Ltd. (Tokyo, Japan) and other detection kits were offered by Takara Co., Ltd. (Takara, Japan).
3.2. Optimization of IHRPs Extraction
3.2.1. Comparison of Different Extraction Methods
Percolation extraction: 100 g IHR was added into 2000 mL deionized water. The extraction was performed with a flow rate of 150 ± 50 mL/h after 2 h. Heating extraction: 100 g IHR was added into 2000 mL deionized water. The extraction was performed at 98 °C for 1 h and the process was repeated twice. Ultrasonic-assisted extraction: 100 g IHR was dissolved in 2000 mL deionized water. The extraction was conducted for 0.5 h at 60 °C and the process was repeated twice.
The filtrates were concentrated using a vacuum rotary evaporator. Then the solution was dried by a vacuum drier. The polysaccharide content was determined to choose an appropriate method.
3.2.2. Single-Factor Experiments
For the extraction of IHRPs, 100 g IHR was added into a certain amount of deionized water. Extraction temperature (40, 60, 80, and 98 ± 2 °C), solid–liquid ratio (1:6, 1:8, 1:10, and 1:15), extraction time (0.5, 1.0, 1.5, and 2 h), pH (3, 5, 7, 9, and 11), and number of successive extractions (1, 2, 3, 4) were studied separately to evaluate the influence of individual factors on IHRPs extraction.
3.2.3. Orthogonal Experimental Design
Extraction conditions were further optimized by orthogonal experimental design. As shown in
Table 7, the four selected variables were extraction temperature (60, 80, and 98 ± 2 °C), R
S/L (1:6, 1:8, and 1:10), number of successive extractions (1, 2, and 3), and pH (4, 7, and 10). The orthogonal experiments were divided into 9 groups. The weight of polysaccharides was considered as the target to estimate the extraction conditions.
3.3. Screen of IHRPs Alcohol Precipitation Conditions
The extraction solution was obtained by the optimum condition according to 3.2 and 400 mL ethanol was added. The experiments were conducted based on the different rate of adding alcohol, stirring method, and cooling rate in
Table 8. The precipitate was obtained after centrifugation and dried. Then the weight and polysaccharide content were acquired to determine the suitable alcohol precipitation conditions.
3.4. Determination of Polysaccharide Yield and Chemical Composition of IHRPs
The protein content was calculated based on the Bradford method and the bovine serum albumin (BSA) was employed as a standard [
42]. The total sugar content of IHRPs was acquired according to the phenol-sulfate method and the glucose was used as a standard [
43]. The uronic acid content was obtained by a carbazole-sulfuric acid method [
44]. Polysaccharide yield was obtained by the Equation (1).
where
YP refers to the polysaccharide yield,
mA refers to the weight of IHRPs, and
mB represents the weight of IHR employed for polysaccharide extraction.
3.5. Purification of IHRPs
First, 100 g crude IHRPs was prepared by the optimum condition determined in
Section 3.2 and
Section 3.3. The crude IHRPs were further purified by different methods.
Activated carbon adsorption: 10 g crude IHRPs was added into 200 mL deionized water. The activated carbon of 1%, 2%, 4%, and 8% IHRPs weight was mixed with the solution, respectively. Then, the solution was agitated at 60 °C for 1 h and filtrated. After washing by deionized water, the filtrate was concentrated and dried.
Membrane filtration: 10 g crude IHRPs was added into 500 mL deionized water. Subsequently, the solution was filtrated by membranes with different molecular weight (30,000 Da, 10,000 Da, 1000 Da, and 500 Da) continuously. The filtrate and retentate were both collected and dried. Finally, IHRPs with different molecular weight were obtained.
Sevage method: 1 g crude IHRPs was added into 100 mL deionized water. Then the solution was blended with Sevage reagent (n-butanol: chloroform = 1: 5 (v/v)). The mixture was stirred for 15 min and transferred to the separatory funnel for stratification. The above process was repeated for 5 times. Subsequently, the organic phase and the aqueous phase were both dried.
Column chromatography: 10 g weakly-basic anion exchange resin was immersed in deionized water for 2 h, then loaded into a glass column (2 × 30 cm). 10 g crude IHRPs was added into 200 mL deionized water. Subsequently, the solution was slowly passed through the resin layer. The column was rinsed with 100 mL 30% ethanol. The eluent was concentrated and dried.
3.6. Monosaccharide Composition Analysis
The monosaccharide composition test was performed according to the previous method with slight modifications [
45]; 5 mg IHRPs was hydrolyzed with 1 mL trifluoroacetic acid (TFA, 2 M) for 6 h at 105 °C. Subsequently, the solution was dried under nitrogen atmosphere. The dried hydrolysate was added into 5 mL deionized water after TFA was removed by methanol. Afterwards, 0.5 mL of 0.3 M NaOH solution and 1 mL of 0.5 M 1-phenyl-3-methyl-5-pyrazolone (PMP) methanol solution were added into the hydrolysate. The obtained solution was kept in a water bath for 2 h at 70 °C for derivatization. Then, 0.5 mL HCl solution (0.3 M) was added for neutralization. The solution was mixed with 1 mL chloroform for HPLC analysis. Several monosaccharides were used as references. Chromatographic conditions: Mobile phase A (82%): 0.1 M KH
2PO
4 solution. Mobile phase B (18%): acetonitrile. Column: C18 (5 μm, 4.6 × 250 mm). Injection volume: 10 μL. Flow rate: 1.0 mL/min. Detection wavelength: 245 nm. Column temperature: 30 °C.
3.7. Fourier Transform Infrared Spectroscopy (FT-IR)
The samples for FT-IR analysis were prepared by mixing 5 mg IHRPs with 125 mg KBr. The FT-IR spectra of samples were obtained between 4000 and 500 cm−1.
3.8. Antioxidant Activity Study
3.8.1. DPPH Radical Scavenging Activity
The DPPH free radical scavenging activity of IHRPs was evaluated based on a reported method with a few modifications [
46]. In short, 2 mL sample solution (0.2, 0.4, 0.6, 0.8, and 1.0 mg/mL) was blended with 2 mL DPPH solution (0.1 mM). The mixture was kept for 30 min in the dark, and then the absorbance (Abs) was obtained at 517 nm. The DPPH scavenging rate was estimated with the following equation (Equation (2)) and the 50% effective concentration (EC
50) was counted.
where
represents the free radical scavenging rate,
refers to the Abs of the reaction system (DPPH with the sample),
is the Abs of the sample background (solvent with the sample); and
is the Abs of the negative control (DPPH with solvent).
3.8.2. ABTS Radical Scavenging Activity
The ABTS scavenging activity of IHRPs was evaluated based on a previous method [
47]. In short, potassium persulfate solution (2.45 mM) was blended with the ABTS solution (7 mM) in dark for 12 h. The obtained ABTS solution was diluted 50 times to the Abs of 0.70 ± 0.02 at 734 nm. Subsequently, 1 mL sample solution (0.2, 0.4, 0.6, 0.8, and 1.0 mg/mL) was added into 4 mL ABTS solution. The mixture was shaken rapidly for 1 min and placed in the dark for 6 min. Then the Abs was measured at 734 nm and Vc was used as a positive control. The ABTS scavenging rate was calculated with Equation (2).
3.9. Anti-Aging Activity Study
3.9.1. Cell Culture
Human dermal fibroblast (HDF) and human epidermal keratinocytes (HEK) were purchased from ScienCell Co., Ltd. The cells were cultured with DMEM medium containing 10% FBS. The culture condition was 37 °C with 5% CO2.
3.9.2. Cell Viability
Cell Counting Kit-8 (CCK-8) assay was carried out to determine the cytotoxicity of IHRPs against HDF and HEK cells. The cells were cultured in 96-well plates with a concentration of 2 × 104 cells/well for 48 h. Afterwards, 100 μL fresh medium containing samples was added and the wells were incubated for 24 h. Then CCK-8 solution was added to wells according to the instruction of test kits and the plate was incubated for 2 h. The Abs at 450 nm was obtained to calculate the cell viability.
3.9.3. Scratch Assay
HDF was cultured at 37 °C with 5% CO
2. Then the cells were seeded into a 12-well plate at a concentration of 1 × 10
5 cells/well. After incubated for 48 h, the scratch was created on the HDF cellular layer by the syringe needle. The cell fragments were cleaned by PBS and the samples with different concentrations were added. Subsequently, the healing of cell layer scratches was observed after 24 h to evaluate the effect of IHRPs on proliferation of HDF. The obtained images were quantified by image J software [
48]. Transforming growth factor-β (TGF-β) was used as the positive control. Healing rate was calculated according to Equation (3).
where
A1 represents the initial scratch area and
A2 refers to the final scratch area.
3.9.4. Quantitative RT-PCR (qRT-PCR) Analysis
Then the cells were seeded into 12-well plates with the concentration of 1 × 105 cells/well. After incubated for 48 h, the samples were mixed and cultured for another 24 h. Total RNA was extracted and cDNA was synthesized. The qRT-PCR analyses for aquaporin gene (AQP-3), collagen gene (COL1A1 and COL3A1), elastin gene (ELASTIN), and matrix metalloproteinase (MMP-1) were performed using a real-time PCR system (Applied Biosystems Life Technologies, Inc., ABI StepOnePlus). Relative quantification was conducted with the comparative CT method (2-ΔΔCt method). Hyaluronic acid (HA), Vc, and TGF-β were employed as the positive control.
3.10. Statistical Analysis
Results were displayed as the mean ± SD (n = 3). Statistical significance was performed by ANOVA. Values of p < 0.05 were considered to be statistically significant.
4. Conclusions
In this work, the polysaccharide extraction from IHR was optimized by single-factor experiments and orthogonal experimental design. The optimum heating extraction conditions were extraction temperature was 98 °C, solid–liquid ratio 1:10, extraction time 1 h, number of successive extractions 2, and pH 4. The extraction ratio and the polysaccharide content were 20.12% and 12.35% respectively at the conditions. Additionally, the suitable alcohol precipitation conditions were pumping with 2 L/h, stirring continuously, and ice-water bath for 4 h. The crude IHRPs was further purified by column chromatography and the polysaccharide/protein contents of purified IHRPs were 34.44% and 1.61%. The monosaccharide composition of IHRPs was: fucose (1.33%), arabinose (19.60%), rhamnose (10.41%), galactose (20.87%), glucose (27.42%), xylose (4.23%), ribose (3.12%), galacturonic acid (6.22%), guluronic acid (0.28%), and glucuronic acid (2.37%). The FT-IR demonstrated the polysaccharide skeleton of IHRPs. Besides, the EC50 values of ABTS and DPPH radicals were 0.34 and 0.47 mg/mL, showing the great antioxidant activity of IHRPs. IHRPs also could promote the cell proliferation of HDF and HEK and healing of cell scratches. Moreover, IHRPs could significantly promote the expression of MMP-1. Therefore, it is believed that the polysaccharides from industrial hemp residues could be developed as potential antioxidant and anti-aging products for cosmetics or functional foods.