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Physicochemical and functional properties of extruded dietary fiber from mushroom Lentinula edodes residues
Food Bioscience 32 (2019) 100452
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Physicochemical and functional properties of extruded dietary fiber from mushroom Lentinula edodes residues
T
Zihan Xue, Qiqi Ma, Qingwen Guo, Ramesh Kumar Santhanam, Xudong Gao, Zhongqin Chen, Cong Wang, Haixia Chen∗ Tianjin Key Laboratory for Modern Drug Delivery & High-Efficiency, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, 300072, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Dietary fiber Lentinula edodes Mushroom
Dietary fiber from Lentinula edodes (LEDF) residues were obtained using various extrusion conditions and their physicochemical and functional properties, such as glucose adsorption capacity (GAC), water holding capacity, oil holding capacity, glucose retardation (GRI) and bile acid retardation index (BRI) were measured. Based on principal component analysis, the optimal extrusion conditions were determined, i.e., extrusion temperature 130 °C, moisture content 40% and screw speed 125 r/min. The dietary fiber contained 3.6% soluble and 88% insoluble dietary fiber and the major components were cellulose (26%) and hemicellulose (42%). Compared with untreated fibers, GAC and BRI of LEDF with optimal extrusion conditions increased 0.46 mg/mg and 28%, respectively. Regression analysis suggested that GRI and hemicellulose showed a significant positive correlation (p≤0.05). Overall, it could be suggested that the LEDF obtained with the optimized extrusion condition might be used as a potential ingredient in functional foods.
1. Introduction Dietary fiber (DF) is an indigestible food material obtained from plant sources. These fibers are classified into two types based on their solubility in water, i.e., soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). DF passes through the digestive system, absorbs water, ease bowel movements and gets fermented by the bacteria in the colon that produce short-chain fatty acids ( Khor, Ng, Chan, & Dong, 2017). It has several health benefits such as helping with weight control, preventing hyperglycemia and hyperlipidemia, and reducing the risk of cardiovascular diseases and cancer (Fuller, Beck, Salman, & Tapsell, 2016; Sawicki et al., 2017). The biological activities of DF are determined by their physical and chemical properties (Requena et al., 2016). To improve the microstructure and composition of DF, many studies implemented various pretreatment techniques such as high-speed homogenization, high-pressure homogenization (Hua et al., 2017), hot air drying (Talens, Arboleya, Castro-Giraldez, & Fito, 2017) and shear emulsifying assisted enzymatic hydrolysis (Ma et al., 2015). Extrusion is one of the commonly used physical pretreatment techniques in the food processing industry due to its high efficiency and convenience. It has the ability to reduce the size of solid particles and change the physicochemical characteristics through high shear rate, efficient heat transfer and rapid mixing of materials (Duque,
∗
Manzanares, & Ballesteros, 2017). Several studies reported that the extrusion had a role in the modification and quality improvement of starch, lipids and proteins (Guo et al., 2018; Philipp, Oey, Silcock, Beck, & Buckow, 2017; Zhang et al., 2013). Extrusion can be done using single-screw extrusion or twin-screw extrusion. The factors affecting extrusion include screw speed, extruder temperature, solid-liquid ratio in the extruder, etc. (Duque et al., 2017). Due to the influence of these multiple factors, the microstructure and macrostructure of the products will be altered. Duque et al. (2017) reported that the viscosity and retention time of the material in the extruder will be reduced by increasing the temperature of the barrel which also avoids the excessive degradation of cellulose and lignin. Different water contents contribute to the softening of cellulose and influence the shear force on the microstructure of fibers (Karunanithy & Muthukumarappan, 2010). Screw speed affects the structure of the DF by changing the residence time and influencing mechanical energy on the materials (Karunanithy & Muthukumarappan, 2013). Lentinula edodes (Berk.) Pegler is an edible and medicinal mushroom, that has a role in nutrition and health. It has been used in Japan, Korea, eastern Russia and China as a medicinal fungus (Lull, Wichers, & Savelkoul, 2005). Several studies reported the medicinal value of L. edodes. Most of the studies focused on culture media extracts, L. edodes mycelium, polysaccharides and isolated compounds such as eritadenine
Corresponding author. E-mail address: [email protected] (H. Chen).
https://doi.org/10.1016/j.fbio.2019.100452 Received 25 September 2018; Received in revised form 29 August 2019; Accepted 4 September 2019 Available online 06 September 2019 2212-4292/ © 2019 Elsevier Ltd. All rights reserved.
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(Matsuhisa et al., 2015; Morales et al., 2018; Ren, Xu, Lu, & Yin, 2018). Akram, Shahbaz, Kim, Farooq, and Kwon (2017) reported that the exposure of this mushroom to gamma rays could increase the yield of soluble polysaccharides. Lu, Guo, Yao, and Jian (2016) characterized the moisture transformation and distribution of L. edodes with hot-air drying. Bach, Helm, Bellettini, Maciel, and Haminiuk (2017) showed that after extraction of the bioactive constituents from L. edodes, the remaining residues were rich in DF. However, little information was available on the biological activities and functional properties of DF from L. edodes (LEDF) obtained from the residue using different extrusion conditions. The purpose of this study was to determine the physicochemical and functional properties of DF from L. edodes residues using various extrusion conditions. Principal component analysis (PCA) was used to determine the relationship of the conditions, and physicochemical and functional properties.
Table 1 Design of extrusion process parameters for L. edodes. Group
Barrel temperature (°C)
Moisture content (%)
Screw speed (r/min)
1 2 3 4 5 6 7 8 9
100 100 100 130 130 130 160 160 160
20 40 60 20 40 60 20 40 60
100 125 150 100 125 150 100 125 150
2.3. Extraction and preparation of DF from L. edodes residues The DF extraction procedure was done using the method of Ma et al. (2015) with some modifications. Briefly, extruded L. edodes powders were soaked in water (1:20, w/v) and hydrolyzed with cellulase (0.9%, w/w, pH 5.0) in a water bath at 60 °C. After 4 h, the enzymatic hydrolysis was terminated by heating to 95 °C for 10 min. The resulting solutions were allowed to cool to room temperature (22 to 25 °C) and centrifuged (Heal Force Neofuge 15 R, Shanghai Lishen Scientific Equipment Co. Ltd., Shanghai, China) at 7000×g for 20 min. The resulting precipitate was air dried to constant weight. Finally, LEDF was obtained. The extraction efficiency of LEDF was calculated using the following equation.
2. Materials and methods 2.1. Materials Dried L. edodes were purchased at Qingguang Vegetable Base (Tianjin, China) and identified by Prof. Haixia Chen and a voucher specimen (No. TJC201001) was deposited in the herbarium of the School of Pharmaceutical Science and Technology, Tianjin University (Tianjin, China) for further reference. They were sliced into pieces of approximately uniform size (about 1 cm in length) with a knife and then treated with 75% ethanol (1:20, w/v) at 85 °C for 2 h to remove most of the pigments and fats (Ma et al., 2018). After repeating three times and drying in air for about 3 d, the raw materials were obtained. Glucose assay kits (glucose oxidase-peroxidase method) were obtained from Shanghai Rongsheng Biotech Co. Ltd. (Shanghai, China) and the glucose content was determined using a UV spectrometer (UV-9200, Shimadzu, Kyoto-fu, Japan) with a glucose calibration curve (0 to 10 mg/mL). α-Amylase (source: Aspergillus oryzae; enzyme activity: 30 U/mg) and protease (source: Bacillus licheniformis; enzyme activity: 200 U/mg) were purchased from Solebo Biotech Ltd. (Beijing, China). Cellulase (source: Trichoderma; enzyme activity: 10 U/mg) was purchased from Tianjin Nuoao Enzyme Preparation Technology Co. (Tianjin, China). All chemicals and reagents used were of analytical grade and purchased from Jiangtian Chemical Technology Co. Ltd. (Tianjin, China).
Y = W1 × 100% / W0
(1)
where Y (%) is the extraction efficiency of LEDF, W0 is the weight (g) of samples, and W1 is the DF weight (g) of the precipitate. Total dietary fiber (TDF), IDF and SDF were measured using AOAC official method 991.43 (2000). LEDF was digested with α-amylase and protease to remove starch and protein. The residue was washed with warm distilled water to obtained IDF. SDF was obtained from the supernatant by precipitation with 4 vol of 95% ethanol. The TDF content was the sum of the IDF and SDF (Huang & Ma, 2016).
2.4. Proximate composition of LEDF The content of crude protein was determined using the Kjedahl method with a nitrogen-to-protein conversion factor of 6.25 (AOAC 955.04, AOAC, 2000). The content of ash was determined using incineration in a muffle furnace at 550 °C (AOAC Method 940.26, AOAC, 2000).
2.2. Extrusion treatment on L. edodes residues L. edodes residues were extruded using a DS56-X twin-screw co-rotating, self-wiping extruder with length/diameter ratio of 25 (SYSLG32II, Jinan Saixin Machinery Co., Jinan, Shandong province, China). The die has a 3 mm diameter hole and feed rate was maintained at 300 g/ min. The parameters used were based on previous studies (Duque et al., 2017; Haghighi-Manesh & Azizi, 2018; Yan, Ye, & Chen, 2015). The barrel temperature was adjusted to 100, 130 and 160 °C. The moisture content of raw materials was kept at 20, 40 and 60%. The screw speed was maintained at 100, 125 and 150 r/min. An orthogonal test method was used to optimize the conditions (Yan et al., 2015) and the experimental design is shown in Table 1. Nine groups of samples with different extrusion conditions were collected, air dried for about 3 d and ground into fine powder using a universal high-speed smashing machines (Tianjin City Taisite Instrument Co. Ltd., Tianjin, China). Then it was passed through a 50-mesh sieve and stored in a sealing bag (22 × 34 cm, Haimen Lihua Laboratory Equipment Sales Department, Haimen, Jiangsu province, China) at −20 °C for a maximum of two wk prior to analysis. The group without extrusion was taken as the control group.
2.5. Chemical composition analysis of LEDF The content of cellulose and hemicellulose were estimated using the method of Chylińska, Szymańskachargot, Kruk, and Zdunek (2016). Briefly, LEDF (100 mg) was placed into a glass crucible and boiled in 100 mL neutral detergent solution (3% sodium dodecyl sulphate) for 1 h. The neutral detergent fraction (NDF) was obtained by washing with boiling water and acetone, and drying at 105 °C. Similarly, the acidic detergent fraction (ADF) was obtained through boiling in acidic detergent solution (2% cetyltrimethyl ammonium bromide). The hemicellulose and cellulose yield were estimated as: Hemicelluloses (g/100 g) = (MNDF – MADF) / MLEDF × 100
(2)
Cellulose (g/100 g) = MADF / MLEDF × 100
(3)
where M is the mass of the respective compounds. 2
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Table 2 Protein, ash, insoluble, soluble and total dietary fiber and cellulose and hemicellulose in modified and unmodified LEDF. Chemical constituents (g/100g) SDF (g/100g) UDF LEDF1 LEDF2 LEDF3 LEDF4 LEDF5 LEDF6 LEDF7 LEDF8 LEDF9
2.3 1.8 2.2 2.0 2.5 3.6 2.4 2.3 2.2 2.0
± ± ± ± ± ± ± ± ± ±
a
0.2 0.1a 0.2a 0.3a 0.3a 0.1b 0.2a 0.4a 0.1a 0.2a
IDF (g/100g) 88 91 90 92 86 88 88 88 87 89
± ± ± ± ± ± ± ± ± ±
a
0.1 0.2b 1b 0.4c 0.4a 0.3a 0.4a 0.2a 0.3a 0.2a
TDF (g/100g) 91 94 92 94 89 91 90 91 89 91
± ± ± ± ± ± ± ± ± ±
Protein (g/100g)
a
f
1 2a 1a 1a 0.1a 0.4a 1a 0.2a 0.2a 0.4a
11 ± 0.03 11 ± 0.03f 12 ± 0.03c 11 ± 0.03d 11 ± 0.03d 9.5 ± 0.03a 11 ± 0.1d 10 ± 0.03b 11 ± 0.03f 11 ± 0.1e
Ash (mg/100g) g
300 ± 10 160 ± 10f 80 ± 3c 110 ± 3d 70 ± 2c 50 ± 1b 30 ± 1a 50 ± 0.5b 100 ± 4d 140 ± 5e
Cellulose 17 20 18 21 18 26 23 24 11 16
± ± ± ± ± ± ± ± ± ±
b
1 0.4b 0.2b 1b 0.4b 1c 1c 1c 1a 0.3b
Hemicellulose 36 22 48 32 38 42 46 40 54 49
± ± ± ± ± ± ± ± ± ±
0.2c 1a 0.3f 1b 1d 1e 0.4f 1e 0.4g 0.1f
LEDF1-9: see Table 1. UDF represent untreated dietary fiber. Letters (a–g) indicate significant differences (p≤0.05).
Chiewchan, and Devahastin (2012) with slight modifications. Briefly, LEDF (500 mg) was mixed with 25 mL of 50 mmol/L glucose solution and dialyzed with tubing have a nominal molecular weight cut-off (MWCO) of 12 kDa (Solarbio, 8,000–14,000 MWCO). The dialysis bag was dialyzed against 100 mL distilled water at 37 °C. Glucose solution without DF was used as a control. The glucose that diffused out of the dialysis bag was determined at 30, 60 and 120 min using the glucose kit. The GRI was calculated as:
2.6. Water holding capacity (WHC) and oil holding capacity (OHC) of LEDF WHC of LEDF was determined using the method of Zhang etal (2017) with slight modifications. Briefly, LEDF (50 mg) was mixed with 5.0 mL distilled water. After suspending for 30 s, it was kept at room temperature for 24 h. Then the mixture was centrifuged at 7000×g for 20 min at 25 °C. The supernatant was removed and the residue was weighed. The WHC was the amount of water held/100 g of sample ignoring any extraction of material into the supernatant. It was calculated as: WHC = (Wi - Wo) / Wo
GRI = 100 - (CS × 100 / CC)
where CS is the total glucose diffused from the LEDF (mmol/L), and Cc is the total glucose diffused from a control sample (mmol/L).
(4)
where Wi is the weight of residue (mg), and Wo is the weight of LEDF (mg). OHC of LEDF was measured using the method of Zhang et al (2017) with slight modifications. Briefly, LEDF (30 mg) was mixed with 5.0 mL soybean oil. After suspending for 30 s, it was kept at room temperature for 6 h. Then the mixture was centrifuged at 7000×g for 20 min at 25 °C. The supernatant was removed and residue was weighed. The OHC was the amount of oil held/100 g of sample and calculated as: OHC = (W2 - W1) / W1
2.9. Bile acid retardation index (BRI) of LEDF BRI of LEDF was determined using the method of Adiotomre, Eastwood, Edwards, and Brydon (1990) with slight modifications. Briefly, LEDF (0.2 g) was mixed with 25 mL sodium taurocholate solution (source: ox bile) and dialyzed in 100 mL of 0.2 mol/L sodium phosphate buffer with sodium azide (1 g/L, pH 7.0) at 37 °C. Sodium taurocholate solution without DF was used as a control. After 60 min, two mL of the diffused material were taken for analysis. The concentration of diffused taurocholic acid was measured using high-performance liquid chromatography (L600, Pgeneral, Beijing, China). The chromatographic column was an ODS C18 column (10 × 250 mm, 5 μm, YMC Co. Ltd., Kyoto, Japan), column temperature was 25 °C, flow rate was 1.0 mL/min, and injection volume was 10 μL. Reagent A (acetonitrile) was adjusted from 22 to 42% for 30 min. Reagent B was 0.15% disodium hydrogen phosphate (pH 3.0). BRI was calculated as:
(5)
where W2 is the weight of residue (mg), and W1 is the weight of LEDF (mg). 2.7. Glucose adsorption capacity (GAC) of LEDF GAC of LEDF was determined using the method of Ma and Mu, 2016a with some modifications. Briefly, LEDF (500 mg) was mixed with 100 mL of 50 mmol/L glucose solution and kept at 37 °C for 6 h. The mixture was centrifuged at 7000×g for 20 min at 25 °C. The glucose content in the supernatant was determined using the phenol-sulfuric acid method (Masuko et al., 2005). Briefly, the supernatant (20 μL) was diluted 10 times, and mixed with 200 μL phenol solution (5%) and 1000 μL sulfuric acid. The absorbance of the mixed solution was measured at 490 nm after 20 min. Standard glucose with different concentrations (0–0.25 mg/mL) were used to obtained the calibration curve. The GAC was calculated as: GAC = (CO - CS) / WS × VG
(7)
BRI = 100- (CS × 100 / CC)
(8)
where CS is the total taurocholic acid diffused from LEDF (mmol/L), and Cc is the total taurocholic acid diffused from the control sample (mmol/L). 2.10. Principal components analysis (PCA) PCA was used to obtain the correlation between the variation in chemical composition and functional properties of samples as well as to determine the optimal extrusion condition used to get the DF from L. edodes. PCA and the subsequent statistical analysis were done using the Statistical Package for the Social Science (SPSS for Windows version 20.0, SPSS Inc., Chicago, IL, USA). Principal components with observed eigenvalues greater than 1.0 in the PCA were further evaluated (Navarro Silvera et al., 2011). Dimensionality reduction was done using extracting factors. The scores of each extracted factor were calculated by measuring the factor score coefficient matrix. The function is shown in the following equation.
(6)
where CO is the concentration of the original glucose solution (mg/mL), CS is the concentration of the supernatant glucose once the adsorption reached equilibrium (mg/mL), WS is the weight of LEDF (mg), and VG is the volume of glucose solution (mL). 2.8. Glucose retardation index (GRI) of LEDF The GRI of LEDF was determined using the method of Peerajit, 3
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Fig. 1. Functional properties of LEDF. (A) Water holding capacity; (B) Oil holding capacity; (C) Glucose adsorption capacity; (D) Glucose retardation index; (E) Bile acid retardation index. UDF, untreated dietary fiber. LEDF1-9, treated using different extrusion conditions. Letters (a–j) indicate significant differences (p≤0.05).
Fi = FAC ×
σ
n
(9)
TP =
∑ βi Fi i=1
where Fi is the factor score, FAC is the factor score coefficient, and σ is the variance of the corresponding factor. The final evaluation was obtained by calculating the total points scored. Based on the total score, a comprehensive ranking of the different extrusion conditions could be obtained. The mathematical model used was:
(10)
where TP is the total points scored, i is the number of extracted factor, β is the explanatory variance of each extraction factor, and F is the factor score.
4
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2.11. Statistical analyses All experimental runs were carried out in triplicate. Experimental data were analyzed using SPSS. Results were expressed as mean ± standard deviation (SD). The differences in means were evaluated using the Duncan's multiple-range tests for means with 95% confidence limit (p≤0.05). 3. Results and discussion 3.1. Proximate composition analysis of DF from L. edodes Crude protein, ash, IDF, SDF, TDF and chemical constituents of DF with untreated and treated L. edodes (LEDF1-LEDF9) is shown in Table 2. With various extrusion conditions, the contents of TDF varied but did not change significantly (p > 0.05). The experimental results were similar to those reported by Andersson, Andersson, Jonsäll, Andersson, and Fredriksson (2017) and Honců et al. (2016). The parameters of the extrusion process would affect the fiber content (Tiwari & Cummins, 2009) and might result in the conversion of some IDF into SDF (Honců et al., 2016). However, the TDF content was less affected by the extrusion and the results were similar to those reported by Andersson et al. (2017) and Huang and Ma (2016). It might be due to the degradation of the IDF and a redistribution of IDF to SDF in the extrusion process (Huang & Ma, 2016). The content of hemicellulose and cellulose were significantly (p≤0.05) increased. The results suggested that the extrusion might destroy the fiber structures, which leads to the increased interaction between enzymes and DF (Min, Dong, Wang, Zhou, & Mao, 2010). It also improved the effect of cellulase treatment and increased the hydrolysis of cell wall substances (Cheng et al., 2017). 3.2. Functional properties of DF from L. edodes 3.2.1. WHC and OHC of LEDF The WHC and OHC represent the ability of DF to retain free water or oil in the gastrointestinal tract ( Toru et al., 2009). These physicochemical properties are important for food research and development, where low-fat products produce and remove fat from chyme or intestinal (Zhang et al., 2017). Fig. 1A shows that WHC of LEDF was not significantly (p≤0.05) changed in comparison to the extrusion treated and untreated DF. Compared to the original fibers, the OHC of LEDF4 and LEDF8 were significantly (p≤0.05) increased (Fig. 1B). This might be due to the influence of extrusion, which affects the pore size and channels of DF (Zhang et al., 2017). 3.2.2. GAC of LEDF GAC is used to evaluate the ability of DF to delay glucose absorption in the gastrointestinal tract (Chen et al., 2015). Ma and Mu, 2016a had reported that GAC values might be related to the viscosity, porosity, and specific surface area of DF. As shown in Fig. 1C, GAC resulted in significant changes (p≤0.05) with different extrusion conditions. LEDF2 and LEDF5 were significantly (p≤0.05) increased. GAC of LEDF1 and LEDF8 were decreased (p≤0.05). The result suggested that the extrusion might alter the porosity and specific surface area of the DF, thereby enhancing or weakening the trapping of glucose molecules in the fiber network, affecting the interaction between glucose and fibers (Ma and Mu, 2016b). 3.2.3. GRI of LEDF The GRI is used to evaluate the blocking of glucose diffusion in DF in the gastrointestinal tract. The GRI values seems to be consistent with the content of SDF, internal structure and surface properties of DF (Liu et al., 2016). Fig. 1D shows that the GRI of DF was higher in 30 min. As the times increases, the values of GRI decreased gradually. Similar trends were reported by Chen et al. (2015) and Peerajit et al. (2012).
Fig. 2. Principal component analysis of DF before and after extrusion treatment. (A) Component plot of PCA; (B) Scree plot of PCA; (C) The total score and comprehensive ranking. UDF represents untreated dietary fiber. LEDF1-9 represents DF treated by different extrusion conditions. 5
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Table 3 Functional properties of LEDF5. Water holding capacity (g/100g)
Oil holding capacity (g/100g)
Glucose adsorption capacity (mg/mg)
Glucose retardation index (%)
Bile acid retardation index (%)
550 ± 10
680 ± 10
0.67 ± 0.003
30 min 60 min 120 min
38 ± 1
38 ± 1 11 ± 1 15 ± 1
3.4. Physicochemical and functional properties of DF obtained using the optimal conditions (LEDF5)
The GRI of LEDF8 was significantly (p≤0.05) higher than other extrusion groups for all three time points. The GRI values of LEDF8 at 30 min were higher than rice bran (21–6.4%) reported by Qi et al. (2016) and lower than soy hulls (78-65%) reported by Liu et al. (2016). The results suggested that extruded LEDF could be used to reduce postprandial blood sugar values effectively.
All of the above experimental results offered a comparative study of the chemical composition and functional properties of DF from L. edodes residues. LEDF5 was selected as the optimal extrusion conditions through PCA analysis and this extrusion process significantly (p≤0.05) increased the SDF fractions. The WHC, OHC, GAC, GRI, and BRI of LEDF5 are shown in Table 3. The WHC and OHC of LEDF5 were higher than other fiber-rich products, such as foxtail millet (Setaria italic), bran (Zhu et al., 2018), wheat bran (Long, Ye, & Zhao, 2014) and extruded orange pomace (Huang and ma., 2016). At the same time, LEDF5 showed good binding ability or blocking index with glucose and bile acid compared with carrot pomace fiber treated using high hydrostatic pressure (Yu, Bei, Zhao, Li, & Cheng, 2018) and rice bran (Qi et al., 2016). Thus, LEDF5 had the potential to be used in functional foods to alter the viscosity and texture of the product and promote human health.
3.2.4. BRI of LEDF BRI predicts the ability of DF to delay bile acid absorption in the gastrointestinal tract. Bile acids are harmful to gastric epithelial cells (Ma et al., 2015). Increasing the absorption of bile acids helps to promote the conversion of cholesterol to bile acids, lowers the levels of total cholesterol and LDL levels, and reduces the risk of cardiovascular diseases (Feng, Dou, Alaxi, Niu, & Yu, 2017; Niu, Xie, Zhang, Sheng, & Yu, 2013). Fig. 1E shows that different pretreatment methods have a significant (p≤0.05) influence on the values of BRI. LEDF6 showed the highest BRI and LEDF5 was second high. These two groups had much higher binding capacity than the original samples. The differences in BRI might be related to the particle size distribution (López-Vargas, Fernández-López, Pérez-Álvarez, & Viuda-Martos, 2013), SDF content (Ma and Mu, 2016a) and the relationship between the internal structure and surface properties of fibers and bile acid diffusion (Liu et al., 2016). These values were higher than lime residues (28%) (Peerajit et al., 2012), as well as similar to pure pectin (43%) (Adiotomre et al., 1990).
4. Conclusions Different extrusion conditions have impact on the physicochemical and functional properties, such as WHC, OHC, GAC, GRI, and BRI of DF. The optimal extrusion conditions for the pretreatment of DF from L. edodes (LEDF) were obtained through PCA analysis. According to the comprehensive ranking results, the optimal extrusion conditions were extrusion temperature of 130 °C, moisture content of 40% and screw speed of 125 r/min. With this condition, the LEDF showed higher glucose adsorption capacity (0.67 mg/mg), bile acid retardation index (38%) and the cellulose hydrolysis resulted 3.6% soluble and 88% insoluble dietary fiber. The major components were cellulose (26%) and hemicellulose (42%). The LEDF might be suggested for use in functional foods.
3.3. PCA analysis LEDF samples and variables in Tables 2 and Fig. 1 were all included in the analysis. Regression analysis was done and Pearson's correlation coefficients were calculated to determine the correlations between the variations in functional properties of the samples in detail. There was a significant (p≤0.05) positive correlations between WHC and cellulose (r = 0.64) and between GRI-120 min and hemicellulose (r = 0.76). Furthermore, it was observed that GRI-30, GRI-60 and GRI-120 min had significant (p≤0.05) positive correlations with each other and their correlation coefficients were ranging from 0.76 to 0.88 (GRI-30 and GRI-60 min: r = 0.82; GRI-30 and GRI-120 min: r = 0.88; GRI-60 and GRI-120 min: r = 0.76). At the same time, GRI-120 min and BRI also had significant (p≤0.05) positive correlations (r = 0.63). Three major factors were extracted using PCA and the results are shown in Fig. 2. These three principal components (PC1, PC2 and PC3) explained 39, 27, and 14% of the variation, respectively. The total variance of the original variables indicated the minimal loss of information from the original variables. The screen plot suggested that PC1 contained most of the information, followed by PC2 and PC3. The higher the absolute value of the loading for a particular variable the greater contribution of that variable to its PC. The important variables in PC1 were GRI and the content of hemicellulose, WHC, GAC and the content of cellulose in PC2 and finally PC3 was influenced by OHC. Using the variance contribution rate of each factor as the weighing factor, the final result was obtained by calculating the total score of the weighing factors. Based on the score, the comprehensive ranking of the different extrusion conditions was obtained (Fig. 2C). The optimal extrusion conditions (LEDF5) were extrusion temperature of 130 °C, moisture content of 40% and screw speed of 125 r/min.
Conflicts of interest The authors confirm that they have no conflicts of interest with respect to the study described in this manuscript. Acknowledgements This study was supported by a grant from the Tianjin Municipal Science and Technology Foundation (Grant No. 18PTZWHZ00190) and the National Natural Science Foundation of China (NSFC 31371879). References Adiotomre, J., Eastwood, M. A., Edwards, C. A., & Brydon, W. G. (1990). Dietary fiber: In vitro methods that anticipate nutrition and metabolic activity in humans. American Journal of Clinical Nutrition, 52, 128–134. Akram, K., Shahbaz, H. M., Kim, G. R., Farooq, U., & Kwon, J. H. (2017). Improved extraction and quality characterization of water-soluble polysaccharide from gammairradiated Lentinus edodes. Journal of Food Science, 82, 296. Andersson, A. A., Andersson, R., Jonsäll, A., Andersson, J., & Fredriksson, H. (2017). Effect of different extrusion parameters on dietary fiber in wheat bran and rye bran. Journal of Food Science, 82, 1344–1350. Bach, F., Helm, C. V., Bellettini, M. B., Maciel, G. M., & Haminiuk, C. W. I. (2017). Edible mushrooms: A potential source of essential amino acids, glucans and minerals. International Journal of Food Science and Technology, 52, 11. Cheng, L., Zhang, X., Hong, Y., Li, Z., Li, C., & Gu, Z. (2017). Characterisation of
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Physicochemical and functional properties of extruded dietary fiber from mushroom Lentinula edodes residues
T
Zihan Xue, Qiqi Ma, Qingwen Guo, Ramesh Kumar Santhanam, Xudong Gao, Zhongqin Chen, Cong Wang, Haixia Chen∗ Tianjin Key Laboratory for Modern Drug Delivery & High-Efficiency, School of Pharmaceutical Science and Technology, Tianjin University, Tianjin, 300072, PR China
A R T I C LE I N FO
A B S T R A C T
Keywords: Dietary fiber Lentinula edodes Mushroom
Dietary fiber from Lentinula edodes (LEDF) residues were obtained using various extrusion conditions and their physicochemical and functional properties, such as glucose adsorption capacity (GAC), water holding capacity, oil holding capacity, glucose retardation (GRI) and bile acid retardation index (BRI) were measured. Based on principal component analysis, the optimal extrusion conditions were determined, i.e., extrusion temperature 130 °C, moisture content 40% and screw speed 125 r/min. The dietary fiber contained 3.6% soluble and 88% insoluble dietary fiber and the major components were cellulose (26%) and hemicellulose (42%). Compared with untreated fibers, GAC and BRI of LEDF with optimal extrusion conditions increased 0.46 mg/mg and 28%, respectively. Regression analysis suggested that GRI and hemicellulose showed a significant positive correlation (p≤0.05). Overall, it could be suggested that the LEDF obtained with the optimized extrusion condition might be used as a potential ingredient in functional foods.
1. Introduction Dietary fiber (DF) is an indigestible food material obtained from plant sources. These fibers are classified into two types based on their solubility in water, i.e., soluble dietary fiber (SDF) and insoluble dietary fiber (IDF). DF passes through the digestive system, absorbs water, ease bowel movements and gets fermented by the bacteria in the colon that produce short-chain fatty acids ( Khor, Ng, Chan, & Dong, 2017). It has several health benefits such as helping with weight control, preventing hyperglycemia and hyperlipidemia, and reducing the risk of cardiovascular diseases and cancer (Fuller, Beck, Salman, & Tapsell, 2016; Sawicki et al., 2017). The biological activities of DF are determined by their physical and chemical properties (Requena et al., 2016). To improve the microstructure and composition of DF, many studies implemented various pretreatment techniques such as high-speed homogenization, high-pressure homogenization (Hua et al., 2017), hot air drying (Talens, Arboleya, Castro-Giraldez, & Fito, 2017) and shear emulsifying assisted enzymatic hydrolysis (Ma et al., 2015). Extrusion is one of the commonly used physical pretreatment techniques in the food processing industry due to its high efficiency and convenience. It has the ability to reduce the size of solid particles and change the physicochemical characteristics through high shear rate, efficient heat transfer and rapid mixing of materials (Duque,
∗
Manzanares, & Ballesteros, 2017). Several studies reported that the extrusion had a role in the modification and quality improvement of starch, lipids and proteins (Guo et al., 2018; Philipp, Oey, Silcock, Beck, & Buckow, 2017; Zhang et al., 2013). Extrusion can be done using single-screw extrusion or twin-screw extrusion. The factors affecting extrusion include screw speed, extruder temperature, solid-liquid ratio in the extruder, etc. (Duque et al., 2017). Due to the influence of these multiple factors, the microstructure and macrostructure of the products will be altered. Duque et al. (2017) reported that the viscosity and retention time of the material in the extruder will be reduced by increasing the temperature of the barrel which also avoids the excessive degradation of cellulose and lignin. Different water contents contribute to the softening of cellulose and influence the shear force on the microstructure of fibers (Karunanithy & Muthukumarappan, 2010). Screw speed affects the structure of the DF by changing the residence time and influencing mechanical energy on the materials (Karunanithy & Muthukumarappan, 2013). Lentinula edodes (Berk.) Pegler is an edible and medicinal mushroom, that has a role in nutrition and health. It has been used in Japan, Korea, eastern Russia and China as a medicinal fungus (Lull, Wichers, & Savelkoul, 2005). Several studies reported the medicinal value of L. edodes. Most of the studies focused on culture media extracts, L. edodes mycelium, polysaccharides and isolated compounds such as eritadenine
Corresponding author. E-mail address: [email protected] (H. Chen).
https://doi.org/10.1016/j.fbio.2019.100452 Received 25 September 2018; Received in revised form 29 August 2019; Accepted 4 September 2019 Available online 06 September 2019 2212-4292/ © 2019 Elsevier Ltd. All rights reserved.
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(Matsuhisa et al., 2015; Morales et al., 2018; Ren, Xu, Lu, & Yin, 2018). Akram, Shahbaz, Kim, Farooq, and Kwon (2017) reported that the exposure of this mushroom to gamma rays could increase the yield of soluble polysaccharides. Lu, Guo, Yao, and Jian (2016) characterized the moisture transformation and distribution of L. edodes with hot-air drying. Bach, Helm, Bellettini, Maciel, and Haminiuk (2017) showed that after extraction of the bioactive constituents from L. edodes, the remaining residues were rich in DF. However, little information was available on the biological activities and functional properties of DF from L. edodes (LEDF) obtained from the residue using different extrusion conditions. The purpose of this study was to determine the physicochemical and functional properties of DF from L. edodes residues using various extrusion conditions. Principal component analysis (PCA) was used to determine the relationship of the conditions, and physicochemical and functional properties.
Table 1 Design of extrusion process parameters for L. edodes. Group
Barrel temperature (°C)
Moisture content (%)
Screw speed (r/min)
1 2 3 4 5 6 7 8 9
100 100 100 130 130 130 160 160 160
20 40 60 20 40 60 20 40 60
100 125 150 100 125 150 100 125 150
2.3. Extraction and preparation of DF from L. edodes residues The DF extraction procedure was done using the method of Ma et al. (2015) with some modifications. Briefly, extruded L. edodes powders were soaked in water (1:20, w/v) and hydrolyzed with cellulase (0.9%, w/w, pH 5.0) in a water bath at 60 °C. After 4 h, the enzymatic hydrolysis was terminated by heating to 95 °C for 10 min. The resulting solutions were allowed to cool to room temperature (22 to 25 °C) and centrifuged (Heal Force Neofuge 15 R, Shanghai Lishen Scientific Equipment Co. Ltd., Shanghai, China) at 7000×g for 20 min. The resulting precipitate was air dried to constant weight. Finally, LEDF was obtained. The extraction efficiency of LEDF was calculated using the following equation.
2. Materials and methods 2.1. Materials Dried L. edodes were purchased at Qingguang Vegetable Base (Tianjin, China) and identified by Prof. Haixia Chen and a voucher specimen (No. TJC201001) was deposited in the herbarium of the School of Pharmaceutical Science and Technology, Tianjin University (Tianjin, China) for further reference. They were sliced into pieces of approximately uniform size (about 1 cm in length) with a knife and then treated with 75% ethanol (1:20, w/v) at 85 °C for 2 h to remove most of the pigments and fats (Ma et al., 2018). After repeating three times and drying in air for about 3 d, the raw materials were obtained. Glucose assay kits (glucose oxidase-peroxidase method) were obtained from Shanghai Rongsheng Biotech Co. Ltd. (Shanghai, China) and the glucose content was determined using a UV spectrometer (UV-9200, Shimadzu, Kyoto-fu, Japan) with a glucose calibration curve (0 to 10 mg/mL). α-Amylase (source: Aspergillus oryzae; enzyme activity: 30 U/mg) and protease (source: Bacillus licheniformis; enzyme activity: 200 U/mg) were purchased from Solebo Biotech Ltd. (Beijing, China). Cellulase (source: Trichoderma; enzyme activity: 10 U/mg) was purchased from Tianjin Nuoao Enzyme Preparation Technology Co. (Tianjin, China). All chemicals and reagents used were of analytical grade and purchased from Jiangtian Chemical Technology Co. Ltd. (Tianjin, China).
Y = W1 × 100% / W0
(1)
where Y (%) is the extraction efficiency of LEDF, W0 is the weight (g) of samples, and W1 is the DF weight (g) of the precipitate. Total dietary fiber (TDF), IDF and SDF were measured using AOAC official method 991.43 (2000). LEDF was digested with α-amylase and protease to remove starch and protein. The residue was washed with warm distilled water to obtained IDF. SDF was obtained from the supernatant by precipitation with 4 vol of 95% ethanol. The TDF content was the sum of the IDF and SDF (Huang & Ma, 2016).
2.4. Proximate composition of LEDF The content of crude protein was determined using the Kjedahl method with a nitrogen-to-protein conversion factor of 6.25 (AOAC 955.04, AOAC, 2000). The content of ash was determined using incineration in a muffle furnace at 550 °C (AOAC Method 940.26, AOAC, 2000).
2.2. Extrusion treatment on L. edodes residues L. edodes residues were extruded using a DS56-X twin-screw co-rotating, self-wiping extruder with length/diameter ratio of 25 (SYSLG32II, Jinan Saixin Machinery Co., Jinan, Shandong province, China). The die has a 3 mm diameter hole and feed rate was maintained at 300 g/ min. The parameters used were based on previous studies (Duque et al., 2017; Haghighi-Manesh & Azizi, 2018; Yan, Ye, & Chen, 2015). The barrel temperature was adjusted to 100, 130 and 160 °C. The moisture content of raw materials was kept at 20, 40 and 60%. The screw speed was maintained at 100, 125 and 150 r/min. An orthogonal test method was used to optimize the conditions (Yan et al., 2015) and the experimental design is shown in Table 1. Nine groups of samples with different extrusion conditions were collected, air dried for about 3 d and ground into fine powder using a universal high-speed smashing machines (Tianjin City Taisite Instrument Co. Ltd., Tianjin, China). Then it was passed through a 50-mesh sieve and stored in a sealing bag (22 × 34 cm, Haimen Lihua Laboratory Equipment Sales Department, Haimen, Jiangsu province, China) at −20 °C for a maximum of two wk prior to analysis. The group without extrusion was taken as the control group.
2.5. Chemical composition analysis of LEDF The content of cellulose and hemicellulose were estimated using the method of Chylińska, Szymańskachargot, Kruk, and Zdunek (2016). Briefly, LEDF (100 mg) was placed into a glass crucible and boiled in 100 mL neutral detergent solution (3% sodium dodecyl sulphate) for 1 h. The neutral detergent fraction (NDF) was obtained by washing with boiling water and acetone, and drying at 105 °C. Similarly, the acidic detergent fraction (ADF) was obtained through boiling in acidic detergent solution (2% cetyltrimethyl ammonium bromide). The hemicellulose and cellulose yield were estimated as: Hemicelluloses (g/100 g) = (MNDF – MADF) / MLEDF × 100
(2)
Cellulose (g/100 g) = MADF / MLEDF × 100
(3)
where M is the mass of the respective compounds. 2
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Table 2 Protein, ash, insoluble, soluble and total dietary fiber and cellulose and hemicellulose in modified and unmodified LEDF. Chemical constituents (g/100g) SDF (g/100g) UDF LEDF1 LEDF2 LEDF3 LEDF4 LEDF5 LEDF6 LEDF7 LEDF8 LEDF9
2.3 1.8 2.2 2.0 2.5 3.6 2.4 2.3 2.2 2.0
± ± ± ± ± ± ± ± ± ±
a
0.2 0.1a 0.2a 0.3a 0.3a 0.1b 0.2a 0.4a 0.1a 0.2a
IDF (g/100g) 88 91 90 92 86 88 88 88 87 89
± ± ± ± ± ± ± ± ± ±
a
0.1 0.2b 1b 0.4c 0.4a 0.3a 0.4a 0.2a 0.3a 0.2a
TDF (g/100g) 91 94 92 94 89 91 90 91 89 91
± ± ± ± ± ± ± ± ± ±
Protein (g/100g)
a
f
1 2a 1a 1a 0.1a 0.4a 1a 0.2a 0.2a 0.4a
11 ± 0.03 11 ± 0.03f 12 ± 0.03c 11 ± 0.03d 11 ± 0.03d 9.5 ± 0.03a 11 ± 0.1d 10 ± 0.03b 11 ± 0.03f 11 ± 0.1e
Ash (mg/100g) g
300 ± 10 160 ± 10f 80 ± 3c 110 ± 3d 70 ± 2c 50 ± 1b 30 ± 1a 50 ± 0.5b 100 ± 4d 140 ± 5e
Cellulose 17 20 18 21 18 26 23 24 11 16
± ± ± ± ± ± ± ± ± ±
b
1 0.4b 0.2b 1b 0.4b 1c 1c 1c 1a 0.3b
Hemicellulose 36 22 48 32 38 42 46 40 54 49
± ± ± ± ± ± ± ± ± ±
0.2c 1a 0.3f 1b 1d 1e 0.4f 1e 0.4g 0.1f
LEDF1-9: see Table 1. UDF represent untreated dietary fiber. Letters (a–g) indicate significant differences (p≤0.05).
Chiewchan, and Devahastin (2012) with slight modifications. Briefly, LEDF (500 mg) was mixed with 25 mL of 50 mmol/L glucose solution and dialyzed with tubing have a nominal molecular weight cut-off (MWCO) of 12 kDa (Solarbio, 8,000–14,000 MWCO). The dialysis bag was dialyzed against 100 mL distilled water at 37 °C. Glucose solution without DF was used as a control. The glucose that diffused out of the dialysis bag was determined at 30, 60 and 120 min using the glucose kit. The GRI was calculated as:
2.6. Water holding capacity (WHC) and oil holding capacity (OHC) of LEDF WHC of LEDF was determined using the method of Zhang etal (2017) with slight modifications. Briefly, LEDF (50 mg) was mixed with 5.0 mL distilled water. After suspending for 30 s, it was kept at room temperature for 24 h. Then the mixture was centrifuged at 7000×g for 20 min at 25 °C. The supernatant was removed and the residue was weighed. The WHC was the amount of water held/100 g of sample ignoring any extraction of material into the supernatant. It was calculated as: WHC = (Wi - Wo) / Wo
GRI = 100 - (CS × 100 / CC)
where CS is the total glucose diffused from the LEDF (mmol/L), and Cc is the total glucose diffused from a control sample (mmol/L).
(4)
where Wi is the weight of residue (mg), and Wo is the weight of LEDF (mg). OHC of LEDF was measured using the method of Zhang et al (2017) with slight modifications. Briefly, LEDF (30 mg) was mixed with 5.0 mL soybean oil. After suspending for 30 s, it was kept at room temperature for 6 h. Then the mixture was centrifuged at 7000×g for 20 min at 25 °C. The supernatant was removed and residue was weighed. The OHC was the amount of oil held/100 g of sample and calculated as: OHC = (W2 - W1) / W1
2.9. Bile acid retardation index (BRI) of LEDF BRI of LEDF was determined using the method of Adiotomre, Eastwood, Edwards, and Brydon (1990) with slight modifications. Briefly, LEDF (0.2 g) was mixed with 25 mL sodium taurocholate solution (source: ox bile) and dialyzed in 100 mL of 0.2 mol/L sodium phosphate buffer with sodium azide (1 g/L, pH 7.0) at 37 °C. Sodium taurocholate solution without DF was used as a control. After 60 min, two mL of the diffused material were taken for analysis. The concentration of diffused taurocholic acid was measured using high-performance liquid chromatography (L600, Pgeneral, Beijing, China). The chromatographic column was an ODS C18 column (10 × 250 mm, 5 μm, YMC Co. Ltd., Kyoto, Japan), column temperature was 25 °C, flow rate was 1.0 mL/min, and injection volume was 10 μL. Reagent A (acetonitrile) was adjusted from 22 to 42% for 30 min. Reagent B was 0.15% disodium hydrogen phosphate (pH 3.0). BRI was calculated as:
(5)
where W2 is the weight of residue (mg), and W1 is the weight of LEDF (mg). 2.7. Glucose adsorption capacity (GAC) of LEDF GAC of LEDF was determined using the method of Ma and Mu, 2016a with some modifications. Briefly, LEDF (500 mg) was mixed with 100 mL of 50 mmol/L glucose solution and kept at 37 °C for 6 h. The mixture was centrifuged at 7000×g for 20 min at 25 °C. The glucose content in the supernatant was determined using the phenol-sulfuric acid method (Masuko et al., 2005). Briefly, the supernatant (20 μL) was diluted 10 times, and mixed with 200 μL phenol solution (5%) and 1000 μL sulfuric acid. The absorbance of the mixed solution was measured at 490 nm after 20 min. Standard glucose with different concentrations (0–0.25 mg/mL) were used to obtained the calibration curve. The GAC was calculated as: GAC = (CO - CS) / WS × VG
(7)
BRI = 100- (CS × 100 / CC)
(8)
where CS is the total taurocholic acid diffused from LEDF (mmol/L), and Cc is the total taurocholic acid diffused from the control sample (mmol/L). 2.10. Principal components analysis (PCA) PCA was used to obtain the correlation between the variation in chemical composition and functional properties of samples as well as to determine the optimal extrusion condition used to get the DF from L. edodes. PCA and the subsequent statistical analysis were done using the Statistical Package for the Social Science (SPSS for Windows version 20.0, SPSS Inc., Chicago, IL, USA). Principal components with observed eigenvalues greater than 1.0 in the PCA were further evaluated (Navarro Silvera et al., 2011). Dimensionality reduction was done using extracting factors. The scores of each extracted factor were calculated by measuring the factor score coefficient matrix. The function is shown in the following equation.
(6)
where CO is the concentration of the original glucose solution (mg/mL), CS is the concentration of the supernatant glucose once the adsorption reached equilibrium (mg/mL), WS is the weight of LEDF (mg), and VG is the volume of glucose solution (mL). 2.8. Glucose retardation index (GRI) of LEDF The GRI of LEDF was determined using the method of Peerajit, 3
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Fig. 1. Functional properties of LEDF. (A) Water holding capacity; (B) Oil holding capacity; (C) Glucose adsorption capacity; (D) Glucose retardation index; (E) Bile acid retardation index. UDF, untreated dietary fiber. LEDF1-9, treated using different extrusion conditions. Letters (a–j) indicate significant differences (p≤0.05).
Fi = FAC ×
σ
n
(9)
TP =
∑ βi Fi i=1
where Fi is the factor score, FAC is the factor score coefficient, and σ is the variance of the corresponding factor. The final evaluation was obtained by calculating the total points scored. Based on the total score, a comprehensive ranking of the different extrusion conditions could be obtained. The mathematical model used was:
(10)
where TP is the total points scored, i is the number of extracted factor, β is the explanatory variance of each extraction factor, and F is the factor score.
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2.11. Statistical analyses All experimental runs were carried out in triplicate. Experimental data were analyzed using SPSS. Results were expressed as mean ± standard deviation (SD). The differences in means were evaluated using the Duncan's multiple-range tests for means with 95% confidence limit (p≤0.05). 3. Results and discussion 3.1. Proximate composition analysis of DF from L. edodes Crude protein, ash, IDF, SDF, TDF and chemical constituents of DF with untreated and treated L. edodes (LEDF1-LEDF9) is shown in Table 2. With various extrusion conditions, the contents of TDF varied but did not change significantly (p > 0.05). The experimental results were similar to those reported by Andersson, Andersson, Jonsäll, Andersson, and Fredriksson (2017) and Honců et al. (2016). The parameters of the extrusion process would affect the fiber content (Tiwari & Cummins, 2009) and might result in the conversion of some IDF into SDF (Honců et al., 2016). However, the TDF content was less affected by the extrusion and the results were similar to those reported by Andersson et al. (2017) and Huang and Ma (2016). It might be due to the degradation of the IDF and a redistribution of IDF to SDF in the extrusion process (Huang & Ma, 2016). The content of hemicellulose and cellulose were significantly (p≤0.05) increased. The results suggested that the extrusion might destroy the fiber structures, which leads to the increased interaction between enzymes and DF (Min, Dong, Wang, Zhou, & Mao, 2010). It also improved the effect of cellulase treatment and increased the hydrolysis of cell wall substances (Cheng et al., 2017). 3.2. Functional properties of DF from L. edodes 3.2.1. WHC and OHC of LEDF The WHC and OHC represent the ability of DF to retain free water or oil in the gastrointestinal tract ( Toru et al., 2009). These physicochemical properties are important for food research and development, where low-fat products produce and remove fat from chyme or intestinal (Zhang et al., 2017). Fig. 1A shows that WHC of LEDF was not significantly (p≤0.05) changed in comparison to the extrusion treated and untreated DF. Compared to the original fibers, the OHC of LEDF4 and LEDF8 were significantly (p≤0.05) increased (Fig. 1B). This might be due to the influence of extrusion, which affects the pore size and channels of DF (Zhang et al., 2017). 3.2.2. GAC of LEDF GAC is used to evaluate the ability of DF to delay glucose absorption in the gastrointestinal tract (Chen et al., 2015). Ma and Mu, 2016a had reported that GAC values might be related to the viscosity, porosity, and specific surface area of DF. As shown in Fig. 1C, GAC resulted in significant changes (p≤0.05) with different extrusion conditions. LEDF2 and LEDF5 were significantly (p≤0.05) increased. GAC of LEDF1 and LEDF8 were decreased (p≤0.05). The result suggested that the extrusion might alter the porosity and specific surface area of the DF, thereby enhancing or weakening the trapping of glucose molecules in the fiber network, affecting the interaction between glucose and fibers (Ma and Mu, 2016b). 3.2.3. GRI of LEDF The GRI is used to evaluate the blocking of glucose diffusion in DF in the gastrointestinal tract. The GRI values seems to be consistent with the content of SDF, internal structure and surface properties of DF (Liu et al., 2016). Fig. 1D shows that the GRI of DF was higher in 30 min. As the times increases, the values of GRI decreased gradually. Similar trends were reported by Chen et al. (2015) and Peerajit et al. (2012).
Fig. 2. Principal component analysis of DF before and after extrusion treatment. (A) Component plot of PCA; (B) Scree plot of PCA; (C) The total score and comprehensive ranking. UDF represents untreated dietary fiber. LEDF1-9 represents DF treated by different extrusion conditions. 5
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Table 3 Functional properties of LEDF5. Water holding capacity (g/100g)
Oil holding capacity (g/100g)
Glucose adsorption capacity (mg/mg)
Glucose retardation index (%)
Bile acid retardation index (%)
550 ± 10
680 ± 10
0.67 ± 0.003
30 min 60 min 120 min
38 ± 1
38 ± 1 11 ± 1 15 ± 1
3.4. Physicochemical and functional properties of DF obtained using the optimal conditions (LEDF5)
The GRI of LEDF8 was significantly (p≤0.05) higher than other extrusion groups for all three time points. The GRI values of LEDF8 at 30 min were higher than rice bran (21–6.4%) reported by Qi et al. (2016) and lower than soy hulls (78-65%) reported by Liu et al. (2016). The results suggested that extruded LEDF could be used to reduce postprandial blood sugar values effectively.
All of the above experimental results offered a comparative study of the chemical composition and functional properties of DF from L. edodes residues. LEDF5 was selected as the optimal extrusion conditions through PCA analysis and this extrusion process significantly (p≤0.05) increased the SDF fractions. The WHC, OHC, GAC, GRI, and BRI of LEDF5 are shown in Table 3. The WHC and OHC of LEDF5 were higher than other fiber-rich products, such as foxtail millet (Setaria italic), bran (Zhu et al., 2018), wheat bran (Long, Ye, & Zhao, 2014) and extruded orange pomace (Huang and ma., 2016). At the same time, LEDF5 showed good binding ability or blocking index with glucose and bile acid compared with carrot pomace fiber treated using high hydrostatic pressure (Yu, Bei, Zhao, Li, & Cheng, 2018) and rice bran (Qi et al., 2016). Thus, LEDF5 had the potential to be used in functional foods to alter the viscosity and texture of the product and promote human health.
3.2.4. BRI of LEDF BRI predicts the ability of DF to delay bile acid absorption in the gastrointestinal tract. Bile acids are harmful to gastric epithelial cells (Ma et al., 2015). Increasing the absorption of bile acids helps to promote the conversion of cholesterol to bile acids, lowers the levels of total cholesterol and LDL levels, and reduces the risk of cardiovascular diseases (Feng, Dou, Alaxi, Niu, & Yu, 2017; Niu, Xie, Zhang, Sheng, & Yu, 2013). Fig. 1E shows that different pretreatment methods have a significant (p≤0.05) influence on the values of BRI. LEDF6 showed the highest BRI and LEDF5 was second high. These two groups had much higher binding capacity than the original samples. The differences in BRI might be related to the particle size distribution (López-Vargas, Fernández-López, Pérez-Álvarez, & Viuda-Martos, 2013), SDF content (Ma and Mu, 2016a) and the relationship between the internal structure and surface properties of fibers and bile acid diffusion (Liu et al., 2016). These values were higher than lime residues (28%) (Peerajit et al., 2012), as well as similar to pure pectin (43%) (Adiotomre et al., 1990).
4. Conclusions Different extrusion conditions have impact on the physicochemical and functional properties, such as WHC, OHC, GAC, GRI, and BRI of DF. The optimal extrusion conditions for the pretreatment of DF from L. edodes (LEDF) were obtained through PCA analysis. According to the comprehensive ranking results, the optimal extrusion conditions were extrusion temperature of 130 °C, moisture content of 40% and screw speed of 125 r/min. With this condition, the LEDF showed higher glucose adsorption capacity (0.67 mg/mg), bile acid retardation index (38%) and the cellulose hydrolysis resulted 3.6% soluble and 88% insoluble dietary fiber. The major components were cellulose (26%) and hemicellulose (42%). The LEDF might be suggested for use in functional foods.
3.3. PCA analysis LEDF samples and variables in Tables 2 and Fig. 1 were all included in the analysis. Regression analysis was done and Pearson's correlation coefficients were calculated to determine the correlations between the variations in functional properties of the samples in detail. There was a significant (p≤0.05) positive correlations between WHC and cellulose (r = 0.64) and between GRI-120 min and hemicellulose (r = 0.76). Furthermore, it was observed that GRI-30, GRI-60 and GRI-120 min had significant (p≤0.05) positive correlations with each other and their correlation coefficients were ranging from 0.76 to 0.88 (GRI-30 and GRI-60 min: r = 0.82; GRI-30 and GRI-120 min: r = 0.88; GRI-60 and GRI-120 min: r = 0.76). At the same time, GRI-120 min and BRI also had significant (p≤0.05) positive correlations (r = 0.63). Three major factors were extracted using PCA and the results are shown in Fig. 2. These three principal components (PC1, PC2 and PC3) explained 39, 27, and 14% of the variation, respectively. The total variance of the original variables indicated the minimal loss of information from the original variables. The screen plot suggested that PC1 contained most of the information, followed by PC2 and PC3. The higher the absolute value of the loading for a particular variable the greater contribution of that variable to its PC. The important variables in PC1 were GRI and the content of hemicellulose, WHC, GAC and the content of cellulose in PC2 and finally PC3 was influenced by OHC. Using the variance contribution rate of each factor as the weighing factor, the final result was obtained by calculating the total score of the weighing factors. Based on the score, the comprehensive ranking of the different extrusion conditions was obtained (Fig. 2C). The optimal extrusion conditions (LEDF5) were extrusion temperature of 130 °C, moisture content of 40% and screw speed of 125 r/min.
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