Effects of steam explosion on yield and properties of soluble dietary fiber from wheat bran

Abstract

Wheat bran is abundant in dietary fiber, and an important indicator for evaluating the dietary fiber is the soluble dietary fiber (SDF) content. In this study, we analyzed the effect of steam explosion (SE) treatment on the SDF content of wheat bran. The parameters, including steam pressure, residence time, and mesh size were optimized, and it was found that the content of total SDF in wheat bran after SE treatment could be increased from 18.88% to 40.32%. The SDF characteristics from raw wheat bran and SE-treated wheat bran were investigated. The results show that the molecular weight of SDF decreased after SE treatment, and the SDF surface became disintegrated. In addition, the thermodynamic characteristic of SDF was improved after SE treatment, and similar functional groups were found to those SDF from raw wheat bran. These effects could potentially improve the physicochemical properties of SDF and increase the application value of wheat bran.

Introduction

As one of the pioneers cultivated crops, bread wheat is the main food source of approximately 35–40% of the population. Annually, the cultivated area for wheat is over 200 million hm² with an output of more than 650 million tons (Chaves et al., 2013). The majority of wheat grain is ground into flour, which is used to prepare various food products (e.g., bread, steamed buns, and biscuits) after wheat bran removal. As the main byproduct of wheat grain processing, the weight fraction of wheat bran reaches about 25% of the milled wheat (Prückler et al., 2014), resulting an annual production of wheat bran biomass of about 162.5 million tons. Thus, deep processing and comprehensive utilization of wheat bran could lead to immense economic benefits.

Wheat bran is mainly composed of an epidermis, peel, a seed coat, a bead layer, and an aleurone layer (Antoine et al., 2004), while dietary fiber is a key component of wheat bran accounting for about 50% (Rose and Inglett, 2010; Hell et al., 2014). According to the American Association of Cereal Chemists, dietary fiber is “the edible parts of plants or analogous carbohydrates that are resistant to digestion and absorption in the human small intestine with complete or partial fermentation in the large intestine.” To date, various studies have demonstrated the benefits of dietary fiber, such as its ability to prevent constipation, maintain intestinal health, and reduce blood cholesterol levels to maintain the health of the cardiovascular system. In addition, dietary fiber intake appears to be inversely proportional to the risk of developing type-2 diabetes and could also prevent obesity (Verma and Banerjee, 2010). The total dietary fiber is the sum of water-insoluble dietary fiber (IDF) and two fractions of water-soluble dietary fiber (SDF), which are high-molecular weight dietary fiber (SDFP; dietary fiber soluble in water but precipitated in 78% aqueous ethanol) and low-molecular weight dietary fiber (SDFS; dietary fiber soluble in water and aqueous ethanol) respectively (McCleary et al., 2013). The suitability of DF mainly depends on the ratio of IDF and SDF (Tejada-Ortigoza et al., 2018). Owing to the wider range of applications, SDF is preferred over the IDF (Mudgil and Barak, 2013). Hence, developing a suitable means to increase the SDF content of wheat bran would be of particular interest.

In this study, we report the use of SE treatment to increase the SDF content of wheat bran and enhance its resulting characteristics. After optimizing three important parameters of the SE technology, we compared raw wheat bran and SE-treated wheat bran to determine whether the value of wheat bran is enhanced by such treatment.

Materials and Methods

Materials and steam explosion treatment    The wheat bran was purchased from a commercial flourmill in China. Prior to use, the wheat bran was dried in a drying oven at 50 °C for 24 h, and the resulting dried sample was ground into powder using a grinder at a moderate speed for 1 min. The powder was sieved using different mesh sizes (Nos. 20, 40, 60, 80, and 100), and the sieved wheat bran was collected and stored at −20 °C in polyethylene bags prior to use. All reagents and chemicals employed in this study were of analytical grade.

The sieved wheat bran was loaded into the reaction chamber of a steam explosion test rig (QBS-80; ZhengdaoCo., Ltd., Hebi, China), and the cylinder was fixed using a piston. The temperature set to 300 °C, and six levels of steam pressure (i.e., 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 MPa) and five residence times (i.e., 60, 120, 180, 240, and 300 s) were employed for each sample. After treatment at the desired pressure for the desired time, the piston device was triggered for SE, which was completed within 0.0875 s. Then, the treated wheat bran samples were collected and analyzed.

Determination of SDF content    The content of SDFP and SDFS was evaluated in accordance with the AOAC integrated methodology (2011.25) with slight modifications (Garcia-Amezquita et al. 2019). Briefly, the wheat bran was dispersed in phosphate buffer (pH 7.0), and 0.147% α-amylase produced by Bacillus (w/w, 4 000 U g⁻¹; Sangon, Shanghai, China) was added. After hydrolysis at 60 °C for 30 min, the reaction was terminated at 95 °C for 10 min, and 0.043% neutral protease (w/w, 2 000 U g⁻¹; Sangon, Shanghai, China) and 0.552% glucoamylase (w/w, 100 000 U g⁻¹; Sangon, Shanghai, China) were added. After subsequent reaction at 40 °C for 30 min, the reaction was terminated at 95 °C for 30 min, and 1 mL sorbitol (0.1 g mL⁻¹) was added to the sample as an internal standard for SDFS analysis. The resulting hydrolysate was subjected to centrifugation at 8 000 g for 15 min prior to collection of the supernatant and the IDF was separated from SDF. Subsequently, ethanol (95%; Sangon, Shanghai, China) was added to the supernatant, and the resulting mixture was allowed to stand at 4 °C for 12 h. Finally, the mixture was subjected to centrifugation at 8 000 g for 15 min. The precipitated flocculate was collected after freeze-drying to determine the SDFP content, and the supernatant was used for SDFS content analysis using high-performance liquid chromatography.

To determine the SDFS content, 0.1 mL of amyloglucosidase (3 300 U mL⁻¹) was added to the supernatant (McCleary 2014). After hydrolysis for 1 h at 60 °C, the sample was deionized and vacuum dried at 60 °C. And the solid material was suspended in 2 mL of water and filtered using a 0.2 µm PTFE membrane (Garcia-Amezquita et al. 2019). The sample was injected into the liquid chromatograph, and SDFS was separated through a chromatographic column (300 × 7.8 mm) at 90 °C at a run rate of 0.5 mL min⁻¹ of Na₂ Ca-EDTA (50mg L⁻¹) for 30 min and then analyzed. The standard curves of D-sorbitol and D-glucose were obtained to determine the response factor (R_f, Eq. 1) to normalize SDFS refractive index (McCleary 2007), and the SDFS content was determined using Eq. 2.

  

where PAS is the peak area of D-sorbitol, W_GLC is the weight of D-glucose, PA_GLC is the peak area of D-glucose, and WS is the weight of D-sorbitol.

  

where SDFS is expressed as g·100 g⁻¹ of dry solids; WS is the weight of D-sorbitol (0.1 g), PAS is the peak area of D-sorbitol, PA_SDFS is the peak area of SDFS, and W_M is the weight of the sample.

Characterization of the SDF The SDF sample was mixed with KBr in a ratio of 1:200 (w/w) and ground thoroughly prior to the preparation of a pellet for analysis via Fourier transform infrared spectroscopy (Tracer-100) between 400 and 4 000 cm⁻¹. Thermal analysis was performed on 10 mg SDF samples using differential scanning calorimetry (DSC 3 500 Sirius) between 30 and 300 °C. Here, a heating rate of 5 °C min⁻¹ was employed along with a liquid nitrogen flow rate of 50 mL min⁻¹. A laser particle analyzer (BT-9300H) was used to determine the particle diameter and for the specific surface analysis.

Molecular weight determination The molecular weight of the SDF was determined using liquid gel permeation chromatography (GPC). Here, a sample of SDF (50 mg) was dissolved in a solution of NaNO₃ (25 mL, 0.1 mol L⁻¹; Sangon, Shanghai, China) prior to filtration using a microporous membrane (0.45 µm). Then, the filtered solution was utilized to determine the molecular weight using a 20 µL aliquot of solution at a run rate of 0.8 mL min⁻¹. A Ultrahydrogel™ linear column (7.8 mm × 300 mm) was selected at a temperature of 30 °C. A calibration curve was obtained using Dextran T-300 (MW 300 600), Dextran T-150 (MW 133 850), Dextran T-40 (MW 36 800), Dextran T-10 (MW 9 750), and Dextran T-5 (MW 2 700), and this curve was employed for molecular weight calculations.

Scanning electron microscopy    The SDF microstructure was observed using scanning electron microscopy (SEM; HITACHI TM3030). The SDF sample was fixed using a double-sided scotch tape and then sputter-coated with gold for 60 s. Subsequently, the SDF sample was placed into the scanning electron microscope at an accelerating voltage of 15.0 kV.

Physicochemical properties of the SDF obtained from wheat bran    The water-holding capacity (WHC), oil-holding capacity (OHC), and swelling capacity (SWC) of the obtained SDF were determined using the method of previous studies with slight modifications (Abdul-Hamid and Luan, 2000; Kosmala et al., 2013). Specifically, distilled water (10 mL) and SDF (0.5 g) were mixed, and the mixture was incubated at 25 °C for 12 h. Thereafter, the mixture was subjected to centrifugation at 8 000 g for 15 min, and the precipitate was collected for WHC determination (Eq. 3). In addition, a sample of the SDF (0.5 g) was mixed with olive oil (10 mL). The resulting mixture was incubated at 25 °C for 2 h prior to centrifugation at 8 000 g for 15 min. The obtained precipitate was collected for OHC determination (Eq. 4). Furthermore, a sample of the SDF (0.5 g) was mixed with distilled water (10 mL), and the mixture was left to hydrate for 12 h at 25 °C. The resulting volume was recorded after this time for SWC determination (Eq. 5).

  

where W₁ is the weight of the sediment (g), and W₂ is the original weight of SDF (g).

  

where W₁ is the weight of the sediment (g), and W₂ is the original weight of SDF (g).

  

where V₁ is the volume of the hydrated SDF, V is the volume of SDF prior to hydration, and W is the weight of SDF before hydration.

The glucose adsorption capacity of the SDF was determined based on the method of Chau et al. (2007). Specifically, a glucose solution (100 mL, 100 mmol L⁻¹; Sangon, Shanghai, China) was added to SDF (0.5 g), and the resulting mixture was placed in an incubator (400 rpm, 37 °C) for 6 h prior to centrifugation at 8000 g for 15 min. The glucose concentration of the supernatant was measured to determine glucose adsorption capacity. The pancreatic lipase inhibition capacity and α-amylase inhibitory effect were measured using the method of Chen et al. with some modifications (Benitez et al., 2019). In this case, SDF (0.5 g), olive oil (10 mL), phosphate buffer (50 mL, pH 7.2; Sangon, Shanghai, China), and pancreatic lipase (30 000 U g⁻¹) solution (7.1 mg pancreatic lipase dissolved in 10 mL phosphate buffer; Sangon, Shanghai, China) were mixed, and the mixture was incubated at 37 °C for 1 h. Then, the reaction was terminated at 90 °C for 10 min, and the amount of free fatty acid was determined via titration using NaOH (0.05 mol L⁻¹) to assess the pancreatic lipase inhibition capacity. In addition, SDF (0.5 g; Sangon, Shanghai, China), α-amylase produced by Bacillus (4 000 U g⁻¹, 4 mg; Sangon, Shanghai, China), and potato starch solution (100 mL, 4%, w/v; Sangon, Shanghai, China) were mixed and incubated at 37 °C for 1 h. Thereafter, the reaction was terminated by adding NaOH (80 mL, 0.1 mol L⁻¹; Sangon, Shanghai, China). After centrifugation at 6 000 rpm for 15 min, the released glucose content in the supernatant was measured to determine the α-amylase inhibitory effect. The cation-exchange capacity was then determined using the method of Huang and Ma with some modifications (Huang and Ma, 2016). More specifically, SDF (0.5 g) and HCl (15 mL, 0.1 mol L⁻¹) were mixed, and the mixture was incubated at 4 °C for 24 h. Thereafter, the mixture was filtered, and the residue was washed thoroughly to remove any traces of HCl, as confirmed by AgNO₃ titrations. Finally, the residue was soaked in a 15% NaCl (Sangon, Shanghai, China) solution for ion substitution, and the substituted H⁺ was titrated using NaOH with phenolphthalein as an indicator.

Results and Discussion

Effect of steam explosion on extraction yield of SDFP and SDFS    To evaluate the effect of SE treatment on the extraction yield of SDF from wheat bran, a three-factor experiment was designed at six levels of steam pressure (i.e., 0.2, 0.4, 0.6, 0.8, 1.0, and 1.2 MPa) using five residence times (i.e., 60, 120, 180, 240, and 300 s), and 5 different mesh sizes (Nos. 20, 40, 60, 80, and 100). The three-factor analysis of variance showed that each factor in this experiment had a significant effect on the extraction yield of SDF, and the three factors had significant interaction effects (p < 0.05, Table 1). As shown in Figure 1, the yield of SDF was influenced by the three conditions significantly. Figure 1A shows that with the steam pressure increasing to 0.8 MPa, the yield of SDF increased from 9.87% to 17.51% (p < 0.01) and then reached a plateau with the constant increase in steam pressure. As shown in Figure 1B, with the residence times increasing to 180 s, the yield of SDF increased from 12.59% to 15.69% (p < 0.01) and reached a plateau with increasing residence times. Figure 1C shows that yield of SDF increased from 12.31% to 16.32% (p < 0.01) when the sieving mesh size was increased to 60 and decreased gradually (p < 0.05) with the Nos. of sieving mesh size keep increasing. Based on these results, the optimal SE treatment parameters were set to 0.8 MPa, 180 s and Nos. 60. Combined with the optimized conditions, the yield of SDFP from the treated wheat bran increased significantly from 9.59 ± 0.15% (SDFP from raw wheat barn) to 22.24 ± 0.15% (SDFP from SE treated wheat bran), denoting an improvement of 132%. The content ratio of SDFP:SDFS showed a slight change from 1.02 to 1.23 indicating that the SDFS content increased 1.92-fold after SE treatment. Based on these results, the content of total SDF in wheat bran could increase from 18.88% to 40.32% after SE treatment.

Fig. 1.

Average SDF yield under different steam pressures (A, n = 75), residence times (B, n = 90), and mesh sizes (C, n = 90). The values are means ± SEs. Variance analysis was performed and the method of least significant difference was used for multiple comparisons. The lowercase letters indicate the significant differences at 0.05 level.

Table 1. Variance Analysis of three factors for SDF yield from wheat bran subjected to steam explosion

Source	Sum of squares	Degree of freedom	Mean square	F value	p-value
Steam pressure	43.36	5	8.67	1139.13**	< 0.0001
Residence time	5.98	4	1.49	196.36**	< 0.0001
Mesh size	8.23	4	2.06	270.29**	< 0.0001
Steam pressure * Residence time	2.16	20	0.11	14.20**	< 0.0001
Residence time * Mesh size	0.30	16	0.02	2.48**	0.0015
Steam pressure * Mesh size	1.49	16	0.09	12.25**	< 0.0001
Steam pressure * Residence time * Mesh size	0.85	84	0.01	1.34*	0.0415
error	2.28	300	0.01
Treatment	62.37	149	0.42
Total	64.66	449	0.14

Notice: ** indicate the significant differences at 0.01 level and * indicate the significant differences at 0.05 level.

Characterization of the SDF The thermodynamic properties of the SDF samples were determined using DSC. Previous studies reported that the peak temperature of treated SDF, obtained from broken treatment, was higher than that obtained from raw SDF (Zhang, Bai, and Zhang 2011; Zhang, Huang, and Ou 2011). Based on the DSC analysis, the peak temperature from treated wheat bran (199.6 °C) was higher than that from raw wheat bran (193.3 °C, Fig. 2A). The significant peak temperature difference indicated that a greater amount of energy is required to decompose the crystal structure of the SDF obtained from SE treated wheat bran. Owing to the close relationship between short-chain and the presence of strong hydrogen bonds (Matin et al., 2005), the content of short-chain SDF should increase after treatment. In addition, the endothermic and exothermic processes remained unchanged upon increasing the temperature to 330 °C; this indicates that the SDF samples obtained from SE-treated and raw wheat bran both exhibited high thermal stabilities.

Fig. 2.

Thermodynamic characteristics (A) and functional group analysis (B) of SDF obtained from raw wheat bran and SE-treated wheat bran. To separate the two spectra in Fig. 2B, the peak values of SDF from SE treatment were reduced.

The functional groups were also analyzed to determine whether the main structure of SDF was altered after SE treatment. We found the absorption peaks near 3 440 cm⁻¹, which could be attributed to the O-H vibration, indicating the existence of many hydrogen bonds in the associative state; near 2 930 cm⁻¹, typically denoting absorption C-H vibrations of the methyl or methylene group of sugars; near 1 620 cm⁻¹ owing to C=O vibrations; near 1 510 cm⁻¹ typically caused by C-H vibrations in CH₃, CH₂ and CH groups of sugars; near 1 100 cm⁻¹ owing to C-O vibrations because of the pyranoside ring, indicating a C-O-C and C-O-H sugar ring structure; and near 760 cm⁻¹ suggesting β-D-pyranose (Fig. 2B). The positions of the peak, which represent different functional groups, exhibited few changes (Fig. 2B). This indicates that the structure of the raw SDF was similar to that of the SDF obtained from the SE-treated wheat bran; thus, the main health effects obtained from consuming such products should be maintained after SE treatment.

Molecular weight distribution and particle diameter analysis    As previously reported, the composition of wheat bran is particularly complex, and the molecular weights of the various components show a large distribution (Cui et al., 2000). In addition, the molecular weight can be reduced by SE treatment (Wang et al., 2015). Thus, the molecular weights of the treated and untreated SDF samples were measured by liquid GPC. The results are listed in Table 2. Owing to the complex composition of SDF, SE treatment was found to significantly affect the SDF molecular weight distribution. Specifically, the weight-average molecular weight (Mw) of SDF after SE treatment was 67 kDa, which is significantly smaller than that of raw SDF (101 kDa). In addition, both the number-average molecular weight (Mn) and the polydispersity (Mw/Mn) of the SDF decreased significantly after SE treatment. These results demonstrate that the polydispersity of SDF obtained from SE-treated wheat bran became narrower, while the particle size decreased, resulting in enhanced physicochemical properties (Chau and Huang, 2003).

Table 2. Effect of SE treatment on the molecular weight and particle size of SDF

Samples	Mw (kDa)	Mn (kDa)	Mw/Mn	Median diameter (µm)	Volume mean diameters (µm)	Specific surfaceareas (m2/kg)
SDF from raw wheat bran	101	23	4.4	24.93	39.00	126.50
SDF from SE-treated wheat bran	67	17	3.9	23.17	36.72	236.70

To further confirm the reduction in the SDF particle size after SE treatment, the particle diameters were measured. The results showed that the particle size of the SDF obtained from treated wheat bran significantly decreased compared to the SDF from raw wheat bran. The volume mean diameters of the SDF obtained from the raw and SE-treated wheat bran samples were 39.00 and 36.72 µm, respectively, while the median diameter were 24.93 and 23.17 µm, respectively. In addition, the specific surface areas were calculated to be 126.5 and 236.7 m²/kg, respectively (Table 2). These results indicate that SE treatment significantly reduced the SDF particle size, which consequently enhanced the corresponding physicochemical properties (Chau and Huang, 2003).

Scanning electron microscopy observations    Surface morphologies of the SDF samples were observed. The surface of SDF obtained from raw wheat bran was intact and smooth (Fig. 3A). Conversely, the surface of the SDF obtained from the SE-treated wheat bran was partially disintegrated (Fig. 3B), with honeycomb-like holes clearly observed on the surface and a loose texture. These observations indicate that SE treatment alters the spatial structure of SDF, which imparts superior physicochemical properties (Esposito et al., 2005). In these SEM results, a decrease in the SDF particle size was also observed, which was consistent with the particle diameter analysis. These results therefore indicated that the quantity of short-chain dietary fiber should increase after SE treatment, which could further improve the WHC, OHC, and other characteristics of the SDF (Zhang et al., 2011).

Fig. 3.

Scanning electron microcopy images of SDF obtained from raw wheat bran (A) and SE-treated wheat bran (B).

Effect of SE treatment on physicochemical properties of SDF extracted from wheat bran    The physicochemical properties of SDF mainly include physical properties (such as the WHC, OHC, and SWC) and chemical properties (such as the glucose adsorption capacity, pancreatic lipase inhibition capacity, α-amylase inhibitory effect, and cation-exchange capacity). It was previously reported that the WHC, OHC, and SWC are closely related to the food properties of the final SDF product (Esposito et al. 2005). Thus, these three characteristics were quantified for the raw and treated wheat bran samples, and significant improvements were found in all cases (Table 3). The results showed that WHC increased from 2.18 ± 0.18 to 3.53 ± 0.13 g/g, the OHC increased from 2.18 ± 0.18 to 3.53 ± 0.13 g/g, and the SWC increased from 2.18 ± 0.18 to 3.53 ± 0.13 g/g. The increase in WHC, OHC and SWC might be attributed to a rise in the number short-chains and the surface area of SDF induced by SE treatment (Wang et al., 2015).

Table 3. Effect of SE treatment on the WHC, OHC, and SWC of SDF

	WHC (g/g)	OHC (g/g)	SWC (mL/mL)
SDF from raw wheat bran	2.18 ± 0.18	1.49 ± 0.07	2.07 ± 0.12
SDF from SE-treated wheat bran	3.53 ± 0.13**	2.58 ± 0.06**	3.15 ± 0.15**

Notice: The t-test was performed and ** indicate the significant differences at 0.01 level.

The glucose adsorption capacity, pancreatic lipase inhibition capacity and α-amylase inhibitory effect are important parameters when attempting to evaluate the health effects of SDF. In this context, we found that after SE treatment, the glucose adsorption capacity increased from 2.09 ± 0.10 to 4.24 ± 0.14 mmol/g, the pancreatic lipase inhibition capacity increased from 0.20 ± 0.01 to 0.35 ± 0.01%, and the α-amylase inhibitory effect increased from 28.45 ± 1.98 to 55.17 ± 0.75% (Table 2). This indicates that the SDF obtained from the treated wheat bran is more beneficial to human health than that obtained from the untreated wheat bran. In addition, the cation-exchange capacity was found to be 1.41 ± 0.07 (mmol/g) in the SDF obtained from the SE-treated wheat bran, which is 2.76 times larger than that of the SDF obtained from the raw wheat bran, indicating that the capacity to bind ions improved significantly after SE treatment (Table 4).

Table 4. Effect of SE treatment on the glucose adsorption capacity, pancreatic lipase inhibition capacity, α-amylase inhibitory effect, and cation-exchange capacity of SDF

Samples	Glucose adsorption capacity (mmol/g)	Pancreatic lipase inhibition capacity (%)	α-amylase inhibitory effect (%)	Cation-exchange capacity (mmol/g)
SDF from raw wheat bran	2.09 ± 0.10	0.20 ± 0.01	28.45 ± 1.98	0.51 ± 0.03
SDF from SE-treated wheat bran	4.24 ± 0.14**	0.35 ± 0.01**	55.17 ± 0.75**	1.41 ± 0.07**

Notice: The t-test was performed and ** indicate the significant differences at 0.01 level.

Conclusion

In this study, we analyzed the effect of SE treatment on the SDF content of wheat bran. Three treatment parameters (i.e., steam pressure, residence time, and mesh size) were optimized, and the results show that SDF yield from wheat bran increased significantly after SE treatment using the optimized conditions. In addition, the SDF molecular weight decreased and the corresponding physicochemical properties improved, thereby enhancing the application value of this material compared with SDF obtained from raw wheat bran. As a significantly large quantity of wheat bran is produced annually, optimizing such processes to improve the properties of SDF would lead to immense economic benefits to the food industry.

Compliance with Ethical Standards

Conflict of Interest    The authors declare that there is no conflict of interest.

Ethical Approval    This article does not contain any studies with human or animal subjects.

Informed Consent    Not application.

Acknowledgement    This work was financially supported by the National Key Technology Support Program of China (2018YFD0300703-2, 2017YFD0301101 and 2013BAD07B14).

References

•  Abdul-Hamid,  A. and  Luan,  Y.S. (2000). Functional properties of dietary fibre prepared from defatted rice bran. Food Chem., 68, 15-19.
•  Antoine,  C.,  Peyron,  S.,  Lullien-Pellerin,  V.,  Abecassis,  J., and  Rouau,  X. (2004). Wheat bran tissue fractionation using biochemical markers. J. Cereal Sci., 39, 387-393.
•  Benitez,  V.,  Rebollo-Hernanz,  M.,  Hernanz,  S.,  Chantres-  S.,  Aguilera,  Y., and  Martin-Cabrejas,  M. A. (2019). Coffee parchment as a new dietary fiber ingredient: Functional and physiological characterization. Food Res. Int., 122, 105-113.
•  Chau,  C.F. and  Huang,  Y.L. (2003). Comparison of the chemical composition and physicochemical properties of different fibers prepared from the peel of Citrus sinensis L. Cv. Liucheng. J. Agric. Food Chem., 51, 2615-2618.
•  Chau,  C.F.,  Wang,  Y.T., and  Wen,  Y.L. (2007). Different micronization methods significantly improve the functionality of carrot insoluble fibre. Food Chem., 100, 1402-1408.
•  Chaves,  M.S.,  Martinelli,  J.A.,  Wesp-Guterres,  C.,  Graichen,  F.A.S.,  Brammer,  S.P.,  Scagliusi,  S.M.,  Silva,  Rd.,  Wiethölter,  P.,  Torres,  G.A.M.,  Lau,  E.Y.,  Consoli,  L., and  Chaves,  A.L.S. (2013). The importance for food security of maintaining rust resistance in wheat. Food secur., 5, 157-176.
•  Cui,  W.,  Wood,  P.J.,  Blackwell,  B., and  Nikiforuk,  J. (2000). Physicochemical properties and structural characterization by two-dimensional NMR spectroscopy of wheat β-D-glucan—comparison with other cereal β-D-glucans. Carbohyd. Polym., 41, 249-258.
•  Esposito,  F.,  Arlotti,  G.,  Bonifati,  A.M.,  Napolitano,  A.,  Vitale,  D., and  Fogliano,  V. (2005). Antioxidant activity and dietary fibre in durum wheat bran by–products. Food Res. Int., 38, 1167-1173.
•  Garcia-Amezquita  L.E.,  Tejada-Ortigoza,  V.,  Pérez-Carrillo,  E.,  Serna-Saldivar,  S.O.,  Campanella,  O.H.,  Welti-Chanes,  J. (2019). Functional and compositional changes of orange peel fiber thermally–treated in a twin extruder. LWT-Food Sci. Technol., 111, 673-681.
•  Huang,  Y.L. and  Ma,  Y.S. (2016). The effect of extrusion processing on the physiochemical properties of extruded orange pomace. Food Chem., 192, 363-369.
•  Hell,  J.,  Kneifel,  W.,  Rosenau,  T., and  Boehmdorfer,  S. (2014). Analytical techniques for the elucidation of wheat bran constituents and their structural features with emphasis on dietary fiber–A review. Trends Food Sci. Tech., 35, 102-113.
•  Kosmala,  M.,  Milala,  J.,  Kołodziejczyk,  K.,  Markowski,  J.,  Zbrzeźniak,  M., and  Renard,  CM. (2013). Dietary fiber and cell wall polysaccharides from plum (Prunus domestica L.) fruit, juice and pomace: Comparison of composition and functional properties for three plum varieties. Food Res. Int., 54, 1787-1794.
•  Matin  M.R.,  Wahab,  S.A.,  Katsumoto,  Y.,  Matsuura,  H., and  Ohno,  K. (2005). Thermal stability of the hydration structure of short-chain poly(oxyethylene) in carbon tetrachloride: an infrared spectroscopic observation of the breakdown of hydrogen bonds. Chem. Letters, 34, 502-503.
•  McClear,  B.V. (2007). An integrated procedure for the measurement of total dietary fibre (including resistant starch), non–digestible oligosaccharides and available car-bohydrates. Anal. Bionanl, Chem., 389, 291-308.
•  McCleary,  B.V. (2014). Modification to AOAC official methods 2009.01 and 2011.25 to allow for minor overestimation of low molecular weight soluble dietary fiber in samples containing starch. J. AOAC Int., 97, 896-901.
•  McCleary,  B.V.,  Sloane,  N.,  Draga,  A., and  Lazewska,  I., (2013). Measurement of total dietary fiber using AOAC method 2009.01 (AACC international approved method 32-45.01): evaluation and updates. Cereal Chem., 90, 396-414.
•  Mudgil,  D. and  Barak,  S. (2013). Composition, properties and health benefits of indigestible carbohydrate polymers as dietary fiber: a review. Int. J. Biol. Macromol., 61, 1-6.
•  Prückler,  M.,  Siebenhandl-Ehn,  S.,  Apprich,  S.,  Höltinger,  S.,  Haas,  C.,  Schmid,  E., and  Kneifel,  W. (2014). Wheat bran-based biorefinery 1: Composition of wheat bran and strategies of functionalization. LWT Food Sci. Technol., 56, 211-221.
•  Rose,  D.J. and  Inglett,  G.E. (2010). Two-stage hydrothermal processing of wheat (Triticum aestivum) bran for the production of feruloylated arabinoxylooligosaccharides. J. Agric. Food Chem., 58, 6427-6432.
•  Tejada-Ortigoza,  V.,  Garcia-Amezquita,  L. E.,  Serna-Saldívar,  S.O.,  Martin-Belloso,  O., and  Welti–Chanes,  J. (2018). High hydrostatic pressure and mild heat treatments for themodification of orange peel dietary fiber: Effects onhygroscopic properties and functionality. Food Bioprocess Tech., 2018, 11, 110-121.
•  Verma,  A.K. and  Banerjee,  R. (2010). Dietary fibre as functional ingredient in meat products: a novel approach for healthy living—a review. J. Food Sci. Technol., 47, 247-257.
•  Wang,  L.,  Xu,  H.,  Yuan,  F.,  Fan,  R., and  Gao,  Y. (2015). Preparation and physicochemical properties of soluble dietary fiber from orange peel assisted by steam explosion and dilute acid soaking. Food Chem., 185, 90-98.
•  Zhang,  M.,  Bai,  X., and  Zhang,  Z. (2011). Extrusion process improves the functionality of soluble dietary fiber in oat bran. J. Cereal Sci., 54, 98-103.
•  Zhang,  N.,  Huang,  C., and  Ou,  S. (2011). In vitro binding capacities of three dietary fibers and their mixture for four toxic elements, cholesterol, and bile acid. J. Hazard. Mater., 186, 236-239.