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Applied Biological Chemistry
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Particle size of ginseng (Panax ginseng Meyer) insoluble dietary fiber and its effect on physicochemical properties and antioxidant activities

Applied Biological Chemistry volume 63, Article number: 70 (2020) Cite this article

Abstract

Dietary fibers (DFs) and associated phytochemicals in ginseng species are known to provide various functional and health benefits. The incorporation of ginseng insoluble dietary fiber (IDF) in food products often result in undesirable physicochemical properties. Thus, to overcome such demerits, micronization of IDF has been considered. This study investigated the effect of particle size on the physicochemical properties, antioxidant activities, structure and thermal analysis of ginseng IDF. Micronized IDF powder with median particle diameter of 15.83 μm was produced through fine grinding. Reduction of ginseng IDF resulted in increased brightness, water holding capacity and solubility. Decreasing particle sizes also lowered bulk, tapped density, Carr index and Hausner ratio. Reduction of particle size caused greater extractability of mineral and phenolic content and thereby increasing the DPPH radical scavenging activity and ferric reducing antioxidant power. Increased polyphenol extraction with smaller particle size also lowered the mice erythrocytes hemolysis percentage while the hemolysis inhibition rate was increased. Particle size also influenced the thermal stability of ginseng IDF powders. FTIR spectra revealed lack of impact on the major phenolic structures due to superfine grinding. Hence,micronized ginseng IDF powders with improved physicochemical properties and antioxidant activities possess the potential to be used in food and pharmaceutical industries.

Introduction

Several studies have elucidated various functional and health benefits of dietary fibers (DFs) including reducing postprandial glycemic index while maintaining gastrointestinal function and lowering the risk of cardiovascular diseases, diabetes and colon cancer [1]. The other functional effects of DFs include influences on water holding capacity (WHC) and oil holding capacity (OHC), which could be potentially utilized in the development or reformulation of food products. DFs are defined as carbohydrate polymers primarily derived from the cell walls of plants with two or more monomeric units [2]. DFs can be directly obtained from natural sources such as cereals, vegetables, and fruits. For the enrichment of foods, fibers with particular properties have been extracted, isolated and modified from various sources. Fibers are derived mainly from natural raw materials via chemical, physical and enzymatic methods [3]. DFs are classified based on some parameters that include major source, chemical structure and water solubility [4].

DFs are usually non-starch polysaccharides that possess the ability to withstand digestion and absorption in the small intestine, undergoing full or partial fermentation in the large intestine of humans [4]. DFs are also classified based on water solubility as water soluble DFs (pectin and some hemicelluloses) and water in-soluble DFs (cellulose or lignin). It is the insoluble dietary fibers (IDF) that regulate the intestinal function via improving the intestinal peristalsis and fecal volume and removing heavy metals, grease, and other unwanted substances [2, 5]. To achieve best activity of DFs, about 50–75% of IDF in daily meals is recommended [4]. Furthermore, soluble DF (SDF), which are higher in fruits and vegetables than cereals, are also required along with IDF. DFs can also act as prebiotics, which function as sources of carbon for the growth of gastrointestinal microbiota. Inulin, galactooligosaccharides and fructooligosaccharides, are the well-known prebiotics [6]. However, it is important to note that the functional benefits of DFs are contingent upon the structural and chemical composition of DFs [4].

Panax ginseng Meyer, which usually refers to the root of the Panax genus, has long been widely used as a curative agent in Eastern Asia, North America, and Europe [7]. The utilization of ginseng root is more favored due to the presence of pesticide residue in other parts such as leaf or stem [8]. Ginseng has been shown to exhibit immunomodulatory properties that promote a wide range of antimicrobial functions. However, immunomodulatory properties are highly affected by factors such as type and source of ginseng, and extraction method [9]. The variation in such properties is attributed to the various phytochemicals that include ginsenosides, carbohydrates, phytosterols, polyacetylenes, polyphenolic compounds, sugars, acidic polysaccharides, organic acids, amino acids, vitamins, nitrogenous substances, and minerals. In particular, ginsenosides are known to provide various health benefits that include antioxidant, anti-inflammatory and immunity enhancing activities. Owing to the aforementioned bioactive agents along with dietary fibers, ginseng is used as nutritional supplement, herbal remedy [10] and adjuvants during vaccination [11]. However, acceptability of DFs in final product is dependent upon the interaction of DFs with components and ingredients utilized [4]. In particular, IDF has been shown to negatively impact the color, texture and flavor of the final product. To overcome such demerits, DFs have been modified using sulfuric acid (low concentration) and blasting extrusion. However, the most effective method was found to be with enzymatic treatment [12].

Micronization involves the reduction of average particle size of raw materials [13]. Particle size reduction of raw materials has been shown to modify structural characteristics and improve technological properties [14]. Particle size is known to influence physico-chemical properties such as water‐holding capacity, solubility and flowability. However, a major constraint in production of superfine powders is the nature of raw materials. Particularly, hardness and rough texture of materials can influence the average particle size of its powders [13]. Furthermore, health benefits derived from ginseng are dependent on dietary fibers, making it necessary to evaluate the impact micronization on ginseng IDF. In addition, functional properties, such as adsorption to cholesterol and oil, are mostly due to IDF than SDF [5]. As a result, micronization of IDF has gained increased attention [15]. Since studies pertaining to micronization of ginseng IDF are limited, this study focused on the structural characteristics and technological functionalities of micronized ginseng IDF. This study systematically analyzes composition, structure, physicochemical, and technological properties of IDF as influenced by micronization.

Materials and methods

Materials

Dried ginseng roots were purchased from a local supermarket in Jillin city (longitude 125° 40′ ~ 127° 56′, latitude 42° 31′ ~ 44° 40′), China. The ginseng roots cultivated for 5 years were collected in November 2019. All chemicals and reagents used in this study were of analytical grade. Trichloroacetic acid, hydrogen peroxide, ferric chloride, potassium ferricyanide, sodium carbonate, methanol were supplied by Zhengda Chemical Company, Jilin, China. α-amylase, amyloglucosidase, protease, gallic acid, 1,1-Diphenyl-2-picrylhydrazyl were obtained from Sigma-Aldrich (St. Louis, MO, USA).

Preparation of ginseng residue

Ginseng residue was prepared according to Hua et al. [5]. Briefly, Ginseng residue was formed after ginseng polysaccharides were extracted by boiling. The residue was then washed with ethanol and distilled water for the removal of water-soluble oligosaccharide and inorganic salts. The residue was dried (60 °C for 24 h), sieved (60 mesh), packaged in a self-sealing bag, and stored at − 20 °C until further analysis.

Extraction of ginseng IDF

The obtained ginseng residue was then used for the preparation of the IDF as described by Bunzel et al. [16] with some modification. Ginseng residue (60 g) was treated with 1.8 mL heat-stable α-amylase in 1.5 L of buffer (pH 6.0) using a water bath at 95 °C for 20 min. The pH of reactants was adjusted to 7.5, protease (3.0 mL) was added at 60 °C and incubated for 1 h. Later, amyloglucosidase (1.2 mL) was added to the reaction mixture with pH adjusted to 4.5 at 60 °C for the removal of starches and proteins. Finally, the reaction mixture was centrifuged at 5000 rpm for 20 min, and the residue was then washed twice with distilled water and 95% ethanol. Precipitate was dried at 50 °C for 24 h to yield IDF. The ginseng IDF was then packaged in an aluminum-laminated bag and stored at − 20 °C until further analysis.

Preparation of ginseng IDF powders

The ginseng IDF was milled coarsely using a disc-mill (FZ102, Taisite Instrument Co., Ltd., Tianjin, China), and then the powders were passed through 20–60 mesh, 60–80 mesh and 100–160 mesh sieves, such that three different particle size ginseng IDF were obtained. The superfine powders passed through mesh sized less than 400 mesh was prepared using a superfine mill (HMB-700S, Hongquan Machinery Co., LTD, Taiwan) by regulating the grinding time. The particle size of samples between 20 and 60 mesh, 60 and 80 mesh, 100 and 160 mesh and less than 400 mesh were designated as M20, M60, M100 and M400, respectively. All samples were sealed in aluminum-laminated bags and stored at − 20 °C until use.

Particle size and microstructure measurement of ginseng IDF

Particle size distributions of the ginseng IDF powders were analyzed using a Matersizer 3000 laser diffraction instrument (Malvern Instruments Ltd., Malvern, UK). The powder was dispersed in methanol prior to measurements. Dv 50 is considered the median particle diameter, which is the equivalent volume diameter at 50% cumulative volume. Correspondingly, Dv 10 and Dv 90 denote the volume diameter at 10 and 90% cumulative volume, respectively. Powder morphology was observed using an environmental scanning electron microscopy (ESEM; Quanta 250 FEG, FEI Company, USA) at 15 kV. Powders were coated with gold, attached to a double-sided adhesive tape, and observed at 200× magnification.

Hydration properties

WHC and water solubility index (WSI) were determined according to a method reported by Phat et al. [17]. For WHC quantification, 0.5 g (H) of sample was added to 10 mL of distilled water and mixed in a 15 mL centrifuge tube (W1). Afterwards, the reaction mixture was subjected to incubation in a water bath (DK500, Jing Hong Laboratory Instrument Co., Ltd., Shanghai, China) at 60 °C for 30 min and subsequently centrifuged at 3000 rpm for 15 min (TD5A-WS, Xianglu Centrifuge Apparatus Co., Ltd., Changsha, China). The sediment tubes were then weighed (W2) and WHC was calculated based on the formula:

$$ {\text{WHC }}({\text{g}}/{\text{g}}) = ({\text{W}}_{ 2} - {\text{W}}_{ 1} )/{\text{H}} $$
(1)

For WSI quantification, About 10 mL of distilled water was mixed with 0.2 g of powder in a tube, which was placed in a water bath at 80 °C for 30 min. After centrifugation at 3000 rpm for 10 min, the supernatant was transferred to a pre-weighed dish (S1) and dried at 105 °C to constant weight (S2). WSI was calculated using the formula:

$$ {\text{WSI }}\left( \% \right) = ({\text{S2}} - {\text{S1}}) / {\text{S}} $$
(2)

Color values

Ginseng IDF samples of color properties (L*, a* and b* values) were measured by colorimeter (CM-3600A, Konica Minolta, Osaka, Japan). The sample (powder) was placed on a glass plane and the colorimeter was placed directly on to the sample to measure the color values. The calibration of the equipment was performed by a white tile prior to recording sample color values and standard values were these: L* = 86.90, a* = 0.3170, and b* = 0.3240.

Bulk density, tap density, flowability, and cohesiveness

The bulk and tapped densities were measured according to the method described by Ramachandraiah and Chin [18]. The flowability and cohesiveness of the samples were evaluated by the Carr index (%) [19] and Hausner ratio [20], respectively. The Carr index and Hausner ratio were calculated as shown below;

$$ {\text{Carr index }}\left( \% \right) \, = \, ({\text{Tap density}} - {\text{Bulk density}})/{\text{Tap density}} \times 100 $$
(3)
$$ {\text{Hausner ratio}} = {\text{ Tap density}}/{\text{Bulk density}} $$
(4)

Samples with Carr index values < 15% very good, 15–20% were considered good, 20–35% fair, 35–45% bad, and very bad if > 45% [21]. Hausner ratio values < 1.2 were considered to have low cohesiveness, Hausner ratio values 1.2 to 1.4 were intermediate, and the Hausner ratio value > 1.4 were considered to have high cohesiveness [21].

Mineral content

Each ginseng IDF (0.5 g) was added with 10 mL deionized water and boiled for 15 min. Each sample was then centrifuged at 3500 rpm for 10 min and filtered using Whatman filter paper no. W1. After that, liquid solution (1 mL) was transferred to a 50 mL volumetric flask with deionized water and analyzed. An atom absorption spectrophotometer (AFS-8230, Titan Instruments Co., Ltd, Beijing, China) was used to determine the elemental composition (K, Ca, Na, Mg, Zn, Fe, Mn and Cu) in ginseng IDF samples.

Preparation of phenolic extracts

The ginseng IDF samples were extracted according to a method by Jiang et al. [22]. The samples (2 g) were homogenized with 20 mL methanol (80%) for 5 min and then extracted by sonication for 20 min. Homogenization and sonication treatments were performed repeatedly followed by filtration with a No 1. filter paper (Whatman Ltd., Cambridge, UK). The supernatant of each sample was collected, concentrated in vacuum, and stored at − 20 °C before being analyzed.

Total phenolic content (TPC)

TPC was determined for each sample based on the method described by Eghdami and Sadeghi [23]. Diluted extract (200 μL) was added to Folin-Ciocalteu reagent (800 μL) and 7.5% sodium carbonate (2 mL). Distilled water used to dilute the mixture before being incubated at room temperature under dark condition for 2 h. The absorbance values were measured at 765 nm using a UV spectrophotometer (UV-1800, Shimadzu Instruments Mfg. Co., Ltd, Kyoto, Japan). The TPC was expressed as gallic acid equivalents (mg GAE 100 g−1) on dry weight (DW) basis.

1,1-Diphenyl-2-picrylhydrazyl radical-scavenging activity (DPPH-RSA)

The DPPH-RSA of the samples was determined using the method described by Kang et al. [24]. Methanolic extract (50 μL) was added to 80% methanol (50 μL), and mixed with 0.2 mM DPPH radical solution (2 mL). The vortexed mixture (30 s) and stored at 25  °C for 30 min. Sample absorbance of the mixture was measured at 517 nm using a spectrophotometer.

Reducing power (RP)

RP was determined as described by Huang et al. [25]. Methanolic extract (0.3 mL) was added with 1.1 mL phosphate buffer (0.2 M, pH 6.6) and mixed. To this mixture, 0.6 mL of 1% potassium ferricyanide was added and incubated at 50 °C for 20 min. Following incubation, 10% trichloroacetic acid (1 mL) was added and centrifuged at 2016×g for 15 min. The supernatant was separated and mixed with distilled water (1 mL) and 0.1% ferric chloride (0.5 mL). Sample absorbance was measured at 700 nm; increased absorbance corresponded to higher RP.

Hemolysis of mice erythrocytes

The maintenance of mice was carried out using a laboratory diet and water ad libitum until they were 6 weeks old. Experimental female mice weighing 18–20 g were fed in an environment of temperature 20–24 °C, humidity 50–70%, and 12 h alternate light and dark. All of the animal procedures were conducted in adherence to the animal welfare guidelines and ethical committee compliance. Whole blood collected from experimental mice was added with anticoagulant heparin sodium and then centrifuged at 5000 rpm for 10 min. The plasma was discarded, and the erythrocytes isolated were washed with cold phosphate-buffered saline three times. Each phenolic extract (0.3 mL) from the different particle sizes (M20, M60, M100 and M400) was added with 0.1 mL mice erythrocytes suspension (0.5%), followed by the addition of 0.1 mL of 100 mmol/L H2O2. The test tubes were incubated at 37 °C for 1 h, and then added with 5.2 mL normal saline [26]. The samples were then centrifuged at 4000 rpm for 10 min, and the absorbance measured at 415 nm (Optizen 2120 UV; Mecasys Co., Daejon, Korea).

Differential scanning calorimetry

Ginseng IDF powder samples (10–20 mg) were weighted accurately, sealed in aluminum pans and analyzed using DSC (Cph60, Netzsch, Germany). Temperature scans were conducted from 20 to 200 °C at a heating rate of 10 °C/min. Each sample was measured at least in triplicate. The Universal Analysis 2000 software (TA Instruments Co., New Castle, USA) was applied to analyze the curve of each sample.

Fourier-transform infrared (FT-IR) spectroscopy

The organic functional groups of ginseng IDF samples were analyzed using a FT-IR spectrophotometer (FTIR/NIR 400, Perkin–Elmer Inc., Waltham, MA, USA). The spectrum wavelength was 400–4000 cm−1 at 4 cm−1 resolution with 4 scans at a scan speed of < 10 s.

Statistical analysis

All analyses were performed in triplicate and values were presented as mean ± standard deviation. One-way analysis of variance (ANOVA) was used to determine differences between treatments and were carried out in SPSS version 18.0 (Chicago, IL, USA). The differences in means were evaluated using the Duncan’s multiple-range tests for means with 95% confidence limit (p ≤ 0.05).

Results and discussion

Particle size reduction

It is known that the reduction in particle size and increased surface area could influence several powder properties. Particle sizes of ginseng IDF as affected by disc mill and superfine grinding are shown in Table 1. Although the difference in the average particle size of M20 and M60 was large, the specific surface was not (p > 0.05) affected. However, when ginseng IDF was subjected to vibrating superfine mill treatment, powder with highly (p ≤ 0.05) reduced particle size and increased specific surface area was formed. This is because vibrating superfine mill treatment caused greater breakage of the physical structure than disc mill. Similar reduction in particle size was observed in a study by Wen et al. [12], wherein rice bran dietary fibers were modified using enzyme-ball mill treatments. In another study, superfine powder was formed when rice bran IDFs were milled in a vibrating superfine mill [15]. However, the span values, which indicate the width of the particle size distribution was increased upon superfine grinding. Similar increases in span values were also observed in rice bran IDF [15]. On the other hand, decreased span values were observed in Lentinus edodes mushroom powder [14]. Apart from the nature of the materials, the milling method and time also influence span values. It is important to note that micronization is a dynamic process that encompasses physical forces of fracture, breakage, and aggregation [27].

Table 1 Particle size distribution of ginseng IDF powders
Full size table

ESEM

Changes in the microstructure of ginseng IDF powders are illustrated in Fig. 1. As shown in Table 1, the particle size of M20, M60, and M100 are considerably larger than M400. Superfine powders (M400) show smaller particles of varying sizes as opposed to large blocky particles in the other three powders. Smaller particles that seem to have broken off from larger particles indicate the impact of superfine grinding on ginseng IDF. Large particles of ginseng IDF with porous surface was also shown in another study [5]. The lack of smooth surface is attributed to the loss of water soluble components during processing [3].

Fig. 1
figure 1

Environmental scanning electron microscopy (ESEM) images of ginseng IDF with different particle sizes

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Hydration properties and color values of ginseng IDF powders

Hydration properties of ginseng IDF powders with different particle sizes are shown in Table 2. Although disc milling of ginseng IDF reduced the particle size, it had no impact on WHC. However, superfine grinding resulted in increased WHC. Increased WHC of superfine powders was also seen with rice bran IDF [13]. Likewise, WSI increased significantly only for superfine powders. Improved hydration properties of superfine powders are due to increased surface area, which causes higher exposure of polar groups to water. Increased polar groups present as binding sites for water. Studies have indicated the increased porosity of particles could also affect its ability to hold water via hydrogen bonding [15]. Particle size reduction resulting in increased solubility was also seen in other study with Hericium erinaceum powders [17]. Increased solubility has been attributed to shorter cellulose chains and higher exposure of hydrophilic cellulose and hemicellulose groups as a result of superfine grinding [28]. When products such as instant food are developed, the hydration property, WSI, is a major consideration.

Table 2 Hydration properties and color values of ginseng IDF as affected by different particle sizes
Full size table

The color values of ginseng IDF powders as affected by different particle sizes are given in Table 2. The L* (lightness) and b* (yellowness) values of powders showed significant (p ≤ 0.05) increases with corresponding rises in powder mesh sizes from M20 to M400. It was found that reduction of particle size conferred more degree of brightness to powder product. On the other hand, the a* (redness/greenness) values showed significant decreases with increases in mesh sizes. This implied that superfine grinding led to decreasing tendency of redness in powdered products. The increases in degree of yellowness might be attributed to the aggregation phenomenon of phenolic compounds after exposure to superfine grinding. These results are in correspondence with the findings of previously reported study in which decreases in particle sizes led to increases in lightness and yellowness during superfine grinding of celery stalk powders [18].

Bulk and tapped densities, and flowability

Bulk and tapped densities as well as flowability are also shown in Table 3. Decreasing particle sizes resulted in decreasing bulk and tapped density. This is contrary to other studies wherein particle size reduction caused increased bulk density [17]. However, decreased bulk and tapped density indicates open packed structures of powders subjected to superfine grinding. Studies show that bulk density is associated with particle size distributions, surface weighted mean D (3, 2), and fineness. Lower surface weighted mean is associated with higher cohesiveness [29]. However, in this study, D (3, 2) values of M20, M60, M100 and M400 were 583.3 ± 4.6 µm, 555.0 ± 4.3 µm, 87.2 ± 2.7 µm and 8.0 ± 0.02 µm, respectively. As shown in Table 3, reduced particle sizes resulted in increased cohesiveness of ginseng IDF powders. This is based on the Hausner ratio, which increased with reduced particle size indicating higher cohesiveness. Nonetheless, particles within cohesive superfine powders tend to aggregate and form larger particles that are held together by inter‐particle forces. Cases in which external force is unable to break such inter‐particle forces between larger particles can cause loose packing of powders, which in turn decreases the bulk density [30]. Bulk and tap densities are considered in the development of aqueous food products, such as instant beverages or soup mixes [17]. However, in this study, lower particle size increased the Carr values, which in turn lowered the flowability of ginseng powders from very good to fair to poor. Carr index values should be considered when powders are poured, sieved, and mixed during processing [31].

Table 3 Density, flowability, and cohesiveness of ginseng IDF as affected by different particle sizes
Full size table

Mineral element, TPC and antioxidant activities

The results of mineral content analysis for ginseng IDF with different particle are shown in Table 4. Ginseng residue insoluble dietary fibers have been shown to contain mineral elements such as calcium, sodium, magnesium, potassium, copper, manganese, and zinc etc. [3]. Mineral and inorganic components are essential for several purposes and play a vital role in metabolism [32]. However, in this study, the mineral elements detected were calcium, potassium, magnesium, manganese, zinc, copper and iron. Powders with the largest particle size contained Ca, K and Mg. However, as the particle size reduced, the mineral content of Ca, K and Mg were increased. The particles with the smallest size was found to contain Mn, Zn and Fe. These results indicate that particle size reduction caused higher extraction of mineral content.

Table 4 Mineral content of ginseng IDF with different particle sizes (Unit: μg/g)
Full size table

Effect of particle size on TPC is shown in Fig. 2a. Decreasing particle size resulted in increasing TPC. Particles of superfine ginseng powders had the highest TPC. Increased TPC due to superfine grinding has also been reported in other studies on wine grape pomace [33] and rice bran IDF [15]. Ginseng has been reported to contain a variety of phenolic compounds. In a study, 23 different types of phenolic compounds were identified. Particularly, gentisic acid, rutin, p- and m-coumaric acid, and chlorogenic acid were reported to be the main phenolic compounds present in Panax ginseng [34]. In a previous investigation, 12 different free, esterified, and insoluble-bound forms of phenolic acids were identified. The predominant free phenolic acid was trans-Ferulic acid, esterified phenolic acids were cis-ferulic acid and trans-ferulic acid and the main insoluble-bound phenolic acid was Ferulic acid (cis and trans isomers) [35]. However, in this study, smaller particles due to increased surface and improved extraction caused an increase in TPC. DPPH-RSA, which relates to the antioxidant activity of ginseng IDF is shown in Fig. 2. Similar to the trend of TPC values, DPPH-RSA also increased with decreasing particle size. DPPH-RSA for M20, M60, M100 and M400 was 13.29%, 23.88%, 25.54% and 39.21%, respectively. The smallest particle size IDF exhibited the highest RSA. Elevated levels of RSA could be directly associated with increased TPC. These results are consistent with another study on rice bran IDF [15]. However, higher DPPH-RSA is not always related to increased TPC. Despite the decrement in particle size, DPPH RSA was not increased, as seen in other studies [33]. Likewise, RP assay is also employed to measure the antioxidant activities of ginseng IDF. RP, as shown in Fig. 2, was also consistent with the TPC. Ginseng IDF with the largest particle size had the lowest activity. When compared with M20, reducing power increased by 28.8%, 36.6% and 90% for M60, M100 and M400, respectively. The antioxidant potential of ginseng has been demonstrated in a clinical study, wherein level of serum ROS and methane dicarboxylic aldehyde activity were reduced in healthy volunteers [36]. However, in this study, with decrement in particle size, increases in surface area could have caused greater exposure and release of phenolic contents from fibrous matrix, which in turn could have improved antioxidant activity. Since several traditional materials have been adopted as modern medicines, it is likely that ginseng powders can also be utilized in the development of new therapeutic agents [37].

Fig. 2
figure 2

Total phenol content (TPC), DPPH radical scavenging activity and reducing power (antioxidant activities) of ginseng powders (A) and hemolysis of mice erythrocytes (B) by ginseng powders as affected by different particle size. Mean ± SD (n = 3) with different letters (a–d) indicating significant difference (p ≤ 0.05)

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Hemolysis of mice erythrocytes

It is known that oxidative damage by reactive oxygen species occurs through the peroxidation of erythrocyte membranes. Oxidative damage induced by H2O2 can elevate erythrocyte hemolysis and the inhibition rate [26]. In this study, RBC hemolysis percentage decreased with decreasing particle size (Fig. 2b). Contrarily, hemolysis inhibition rate increased with decreasing particle size. This is likely due to the increased extraction of polyphenols with the decreasing particle size of ginseng powders. Studies have shown that polyphenols binding to RBC membrane matrix, particularly to tryptophan residues, can inhibit oxidation of lipids and induce antihemolytic activity [38]. In this study, the smallest particle size (M400) had the highest erythrocyte hemolysis inhibition rate of 86.6%, which was higher than other ginseng IDFs. As shown in Fig. 2a, increased TPC with decreasing ginseng particle size could have contributed to such inhibition rates. A similar effect of the concentration of polyphenols from mulberry fruit on the hemolysis rate and inhibition rate of red blood cells from mice induced by H2O2 was observed in another study. Increasing polyphenol concentration decreased the mice erythrocytes hemolysis rate and increased the inhibition rate [26].

Thermal analysis of ginseng IDF

The transition temperature (Tp1) and melting peak temperatures (Tp2) of ginseng IDF with different particle sizes in shown in Table 5. The transition temperature (Tp1) tended to reduce with decreasing particle size. The smallest particle size powder (M400) had the lowest Tp1. Endothermic peaks (Tp2) for all the samples were observed to be between 80 and 125 °C. The peak temperatures also decreased with decreasing particle size. Similar results were observed for sugar beet pulp powders [39]. These results are in contrast with another study on white winter wheat bran, wherein decreasing particle size resulted in a decreasing tendency for peak temperatures [40]. In this study, it is likely that the reducing particle size could have caused greater exposure of polysaccharide and protein groups, thereby lowering the peak temperatures.

Table 5 The transition temperature (Tp1) and melting peak temperatures (Tp2) of ginseng IDF as affected by different particle sizes
Full size table

FT-IR analysis of ginseng IDF

FT-IR spectra of ginseng IDF with different particle sizes are shown in Fig. 3. Functional groups such as OH, NH, and CO can be qualitatively evaluated via FT-IR analysis [41]. The OH group stretching at 3300–3500 is associated with phenolic structures [41]. In this study, the peaks formed at 3301 cm−1 correspond to –OH stretch vibration, which indicates the presence of phenolic structures. The FT-IR spectra in this study was similar to that of ginseng IDF [5]. However, the decrease in intensity in this region of spectra for different powders could be attributed to the breakdown of intermolecular bonds due to the physical force of milling [42]. Similar bands formed at these frequency ranges were also observed in another study [43]. The major absorption peak at 2923 cm−1 is due to the C–H stretching indicating the presence of cellulose [42, 44]. Similarly, in an earlier study, peak at 2924 cm− 1 was assigned to C–H stretching of grape pomace powders [13]. The major peak at 1619 cm−1 can be attributed to the esterified and ionized carboxyl groups of galacturonic acid [3]. The peak corresponding to CH bonds indicate the presence the aromatic molecules as also shown in another study [13, 43]. The weak peaks at 1317 cm−1 and 1239 cm−1 can be ascribed to the cellulose and hemicellulose structures, respectively. The peaks formed around 1027 cm−1 for ginseng IDF with different particle size distributions indicated stretching vibration of C–O [43]. Furthermore, the decrease in absorbance intensity of peaks is associated with the changes in the surface properties of the finer powders. Similar decrement in the intensity associated with lower particle size was also observed in a recent study on Moringa Oleifera leaf powders [45]. The lack of disappearance of the major phenolic compounds in the profiles of different ginseng powders suggested that the particle size reduction did not affect the major structure of phenolics.

Fig. 3
figure 3

FT-IR analysis of ginseng IDF as affected by different particle sizes

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Availability of data and materials

The datasets used and/or analyzed during the current study are available from the first and corresponding author on reasonable request.

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Acknowledgements

This study was financially supported by Jilin Medical University (Project Number: JYBS2019010), Jilin Province, China.

Funding

This study was financially supported by Jilin Medical University, Jilin Province, China (Project Number JYBS2019010).

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Author notes

  1. Guihun Jiang and Zhaogen Wu contributed equally to this work

Authors and Affiliations

  1. School of Public Health, Jilin Medical University, Jilin, 132013, China

    Guihun Jiang, Zhaogen Wu & Shanji Li

  2. Department of Food Science and Biotechnology, Sejong University, Seoul, 05006, South Korea

    Karna Ramachandraiah

  3. Department of Food Science and Technology, Graduate School of Chonnam National University, Gwangju, 61186, Republic of Korea

    Kashif Ameer

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  1. Guihun Jiang
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  2. Zhaogen Wu
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  3. Kashif Ameer
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  4. Shanji Li
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Contributions

Project administration & experiment & writing, GJ; Writing & experiment, SL; Experiment, ZW; Analysis, KA; Writing—review & editing, KR. All authors read and approved the final manuscript.

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Correspondence to Shanji Li or Karna Ramachandraiah.

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Jiang, G., Wu, Z., Ameer, K. et al. Particle size of ginseng (Panax ginseng Meyer) insoluble dietary fiber and its effect on physicochemical properties and antioxidant activities. Appl Biol Chem 63, 70 (2020). https://doi.org/10.1186/s13765-020-00558-2

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