Original papers
Effect of Extrusion, Steam Explosion and Enzymatic Hydrolysis on Functional Properties of Wheat Bran
2018 Volume 24 Issue 4 Pages 591-598
Details
2018 Volume 24 Issue 4 Pages 591-598
This work evaluated the extrusion, steam explosion and enzymatic hydrolysis on the physical and chemical properties of wheat bran. At the same particle size, the three treatments effectively improve the water holding capacity and swelling capacity of wheat bran. Among them, steam exploded wheat bran had the highest water holding capacity and swelling capacity, followed by extruded wheat bran. All the three treatment have a weakened effect on sodium cholate adsorption capacity, cation exchange capacity and phytate content of wheat bran. Compared with enzymatic hydrolysis, steam explosion and extrusion have a stronger impact on these indexes. Moreover, water holding capacity, swelling capacity, L* value, sorption capacity of sodium cholate, cation exchange capacity and phytate content of decreased with the decrease of particle size of bran. In the range of 450–150 µm, the particle size had a significant effect on the physical and chemical properties of bran. Therefore, extrusion and steam explosion are highly potential for use as new treatment methods on wheat bran.
The wheat bran is a by-product of milling and has food (Curti et al., 2013) and nonfood application (Apprich et al., 2014). Wheat bran is a cheap and abundant source of dietary fiber which has linked to improved bowel heath and possible prevention of some disease such as colon cancer. It also contains minerals, vitamins and compounds such as phenolic acids, arabinoxylans and phytosterol which are known to possess health-promoting properties. Wheat bran is mainly used as livestock feed, only minor amounts are sold as commercial bran food purposes (Prückler et al., 2014). Nowadays, wheat bran consumption for human has increased gradually over the years (Prückler et al., 2014), production of wheat bran for human consumption is estimated to be about 90 million tonnes per year (Onipe et al., 2015). However, due to the nature of wheat bran, the processing of wheat bran directly into the food will have a negative effect on the quality of the product. It is important to choose an appropriate treatment method to improve the value of wheat bran.
As a treatment way of food raw materials, the extruding technique can integrate homogenization, crushing, sterilization, melting, ripening and other complicated operations, which has the characteristics of less pollution, low energy consumption and so on (Robin et al., 2012). In recent years, with the further research of extrusion technology, it has been widely applied in food processing. Besides being used to produce whole grain breakfast and leisure extruded food and other extruded foods (Anton and Luciano, 2007), it is also used for modification of food raw materials. The content of soluble dietary fiber in wheat bran could be greatly improved by this method (Long et al., 2014). Steam explosion is a kind of widely used physical and chemical treatment method (Wanderley et al., 2013), and it has the characteristics of low price, no pollution and high efficiency. Nowadays, this technology is widely applied not only in feed processing, sugar making, starter culture and treatment of lignocellulosic materials, but also in the field of food raw material processing (Conde-Mejía et al., 2012). Steam explosion can increase the content of pentosan and is beneficial to the dissolution of nutrients in the wheat bran (Aktas-Akyildiz et al., 2017). Enzymatic treatment refers to the technology of material conversion with the catalysis of enzymes under certain reaction conditions. The advantages of high efficiency, mild and safe enzymatic treatment provide a safer and healthier way for food processing. Enzyme hydrolysis technology can improve food processing technology (Pasha et al., 2013), improve food quality and safety (Gallo and Sayre 2009). At present, enzyme technology has been widely used in the dairy, meat products, baking, beverage, juice industry and other food fields. Therefore, extrusion, steam explosion and enzymatic hydrolysis are playing an increasingly important role in the process of wheat bran processing.
In present study, wheat bran was treated by different treatment methods, and then the difference of chemical and physical properties was compared. The purpose of this study is to provide a reference for the development of wheat bran treatment.
Materials Commercial wheat bran (WB) (FaDa Flour Co., Ltd, China). Phytic acid solution and Sodium cholate were purchased from Sigma (USA). All the chemical substance used in the experiment is analytical grade and distilled water was used to prepare all solution throughout the experiment procedures.
Extruded wheat bran (EWB) The bran was extruded using a twin-screw extruder (Jinan Saixin Machinery Co., Jinan, China) at moisture content of 40 %, the final barrel temperature at 160 °C and screw speed at 120 rpm. At first, 1 kg material was used and the extruded material was collected 5 min after the beginning of run, that is after the stabilization of process condition. Finally, extruded wheat bran was packed in polyethylene bags after drying in a drum wind dryer (DH-101-2BS, Tianjin, China). The detailed parameters of the twin-screw extruder are shown in Table 1.
| Item | Parameter |
|---|---|
| Feeding section | 36/36T, 2-112/112, 88/88 |
| Plasticizing section | 88/44, 5-56/56, 4-36/36, 2-45°/5/45 |
| Empty Exhaust | 36/36 left, 2-88/88, 88/44 |
| mixing section | 4-56/56, 45°/5/30, 90°/5/30, 88/88, 4-56/ 56, 90°/5/45 |
| Vacuum exhaust section | 45°/5/45 left, 2-112/112 |
| Extrusion section | 88/44, 4-56/56 |
Note: 2-45°/5/45, 2 kneading originals, kneading discs arranged at 45° misalignment, kneading discs 5, length 45 mm; 2-88/88, the number of threading elements is 2 and the threading length is 88 mm; 36/36 left, 36 mm left spiral element;36/36T, starting spiral element; The 88/44 is 1/2 of the length of the 88/88 transport screw.
Steam exploded wheat bran (SEWB) Wheat bran was soaked in water for about 1 h, the final moisture content was 70 %. Approximately 500 g samples were treated with high-pressure steam in the steam explosion reactor (ZhengDao Bio Energy Co., Ltd., Hebi, China). The final pressure in the reactor was 0.8 MPa and the residence time was 5 min. Finally, steam exploded wheat bran was packed in polyethylene bags after drying in a drum wind dryer (DH-101-2BS, Tianjin, China).
Enzymatic hydrolyzed wheat bran (EHWB) The wheat bran was mixed with 100 mL of distilled water (DW) in a 150 mL conical flask. An amount of enzyme (cellulase : xylanase, 1:3, Novozymes, China) corresponding to 0.3 % (w/ w) of wheat bran was added to the suspension. Then adjusting the suspension pH to 4.5 with citric acid (Sinopharm chemical reagent Co., Ltd, China) while vortexing for 5 h when the temperature was 50 °C. And removing the buffer and enzymolysis solution from the hydrolyzed sample. Finally, enzymatic hydrolyzed wheat bran was packed in polyethylene bags after drying in a drum wind dryer (DH-101-2BS, Tianjin, China).
Particle size distribution The four kinds of wheat bran were dry milled at 16800 rpm for 20 seconds using hammer-type cyclone mill (3100, Perten Instrument Co., Ltd. Sweden). Then, the milling material was passed through a mesh size of 420 µm. The fraction that passed though the mesh size of 420 µm was further sieved though the mesh size of 250 µm, the mesh size of 178 µm and the size of 150 µm. The bran with particle size bigger than 420 µm or smaller than 150 µm was omitted. The bran samples were then divided into three portions. The sizes of bran were 420-250 µm, 250-178 µm and 178-150 µm, respectively. The yield of each particle size of bran is shown in Table 2.
| Particle size (µm) | WB | EHWB | EWB | SEWB |
|---|---|---|---|---|
| 420-250 | 58.62±2.03 | 57.62±1.92 | 57.50±1.89 | 45.23±2.01 |
| 250-178 | 4.75±0.21 | 5.02±0.17 | 5.58±0.19 | 15.28±0.20 |
| 178-150 | 9.29±0.35 | 10.05±0.31 | 11.15±0.38 | 17.45±0.36 |
*Data are expressed as mean ± standard deviation. Different letters indicate significant differences at p < 0.05 in the same line. WB: wheat bran, EHWB: enzymatic hydrolyzed wheat bran, EWB: extruded wheat bran, SEWB: steam exploded wheat bran.
Water holding capacity (WHC) The evaluation of water holding capacity (WHC) was performed as previously described by Esposito (Esposito et al., 2005) with some modifications. 2.5 g of each sample was accurately weighted and taken in the graduated test tubes. 50 mL of distilled water and stirred for 30 min at room temperature. After that the supernatants were removed by allowing the wet samples to drain on a fine-meshed wire screen. The hydrated samples were carefully removed and weighted. Analyses were performed in triplicate.
Swelling capacity (SWC) Swelling capacity (SWC) of bran was determined based on the method described by Kuniak (Kuniak and Marchessault 2010). Sample (0.5 g) was soaked in 5.0 mL of distilled water in a 10 mL graduated cylinder. The bran was left to soak in the graduated cylinder for 24 h during which the bran absorbed water and swelled. Afterwards, the volume occupied by the swollen bran was read. Analyses were performed in triplicate.
Color analysis Color parameters (L*, a* and b*) of samples were carried out in triplicate, using a WSC-S color difference meter (Shanghai Precision Instrument Co., Ltd., China). A glass cell containing flour placed above the light source, and L*, a* and b* values were recorded. The L* values indicates the lightness, 0–100 representing dark to light. The a* value gives the degree of the red-green color, with a higher positive a* value indicating more red. The b* value indicates the degree of the yellow-blue color, with a higher positive b* value indicating more yellow.
Sodium cholate absorption capacity Sodium cholate was purchased from the Sigma Company. The in vitro binding procedure of bran to bile salts was a modification of that by Kahlon (Kahlon et al., 2000). Fifty milligrams of the bran sample was added to bile salt solution (50 mL) and sodium cholate (0.1 g) in 150 mL conical flask, and the individual substrate solution without samples was used as blank. Then flasks were incubated for 2 h in a 37 °C shaking water bath, and then centrifuged (4000 rpm) for 20 min. After that 1 mL supernatant was taken to determine the content of sodium salt at 620 nm using spectrophotometer. Analyses were performed in triplicate.
Cation-exchange capacity Using the method of Ralet (Ralet et al., 1993) with some modifications. The samples were immersed in 0.1 mol/L HCl solution. After 48 h, excess acids was remove with distilled water, and 10 % silver nitrate (AgNO3) solution until the chlorine ions was not identified and then freeze-drying. 0.5 g of freeze dried treated sample was accurately weighted, dispersed in 100 mL of 5 % (w/v) NaCl solution and magnetic stirred and slowly titrated with 0.1 mol/L NaOH and pH values were recorded. Analyses were performed in triplicate.
Phytic acid The phytate was determined by the method described by Buddrick (Buddrick et al., 2014) with some modifications. For the analysis of the bran, 1.0 g of sample was extracted with 100 mL of 0.2 mol/L HCl for 3 h followed by 4 min at 5000 rpm. The extract (0.5 mL) was pipetted into a 15 mL centrifuge tube. Then 1 mL of ammonium iron sulphate solution was added. The tubes were incubated in a boiling water bath for 30 min then cooled in ice water to adjust to room temperature. Once the tubes had reached room temperature, 1.5 mL of 2,2′-bipyridine solution was added. The absorbance was immediately measured at 519 nm against distilled water. Analyses were performed in triplicate.
Statistical analysis The data reported are average of triplicate observations and expressed as mean ± standard deviation (SD). The significance of treatment effects was analyzed using Duncan's multiple range tests after SPSS one-way ANOVA (SPSS PASW Statistic 19.0, SPSS Inc. Chicago, IL, USA). p < 0.05 was considered significant.
Water holding capacity and swelling capacity Table 3 shows the water holding capacity of WB, EWB, SEWB and EHWB. According to the values of Table 3, the water holding capacity of four kinds of bran decreases with the particle size of bran. At the same particle size, water holding capacity of EWB and SEWB were significantly different (p < 0.05) from that of WB and EHWB. There was no significant difference (p > 0.05) between water holding capacity of WB and EHWB in the same case. The highest value was 4.36 g/g (EWB, 420–250 µm) while the lowest was 3.70 g/g (WB, 178-150 µm). In the same particle size, EWB had the highest water holding capacity.
| Particle size (µm) | WB | EHWB | EWB | SEWB |
|---|---|---|---|---|
| 420-250 | 4.07±0.07c | 4.16±0.12c | 4.42±0.13a | 4.36±0.03b |
| 250-178 | 3.97±0.07c | 3.99±0.09c | 4.29±0.04a | 4.25±0.05b |
| 178-150 | 3.70±0.03c | 3.73±0.09c | 4.22±0.08a | 4.18±0.08b |
*Data are expressed as mean ± standard deviation. Different letters indicate significant differences at p < 0.05 in the same line. WB: wheat bran, EHWB: enzymatic hydrolyzed wheat bran, EWB: extruded wheat bran, SEWB: steam exploded wheat bran.
The swelling capacity of different fractions during sieving of different bran types varied significantly are shown in Table 4. The swelling capacity decreased with decrease in the fineness of the particle. At the same particle size, swelling capacity of EWB and SEWB were significantly different (p < 0.05) from that of WB and EHWB. However, in the medium size (250–178 µm), there was no significant difference (p > 0.05) between swelling capacity of WB and EHWB. The highest value was 4.56 mL/g (EWB, 420-250 µm) while the lowest was 2.28 mL/g (WB, 178-150 µm). In the same particle size, EWB had the highest swelling capacity.
| Particle size (µm) | WB | EHWB | EWB | SEWB |
|---|---|---|---|---|
| 420-250 | 2.71±0.04c | 2.84±0.03b | 4.56±0.08a | 4.47±0.03a |
| 250-178 | 2.65±0.01c | 2.73±0.06c | 3.59±0.03a | 3.09±0.11b |
| 178-150 | 2.28±0.07c | 2.50±0.03d | 3.30±0.09a | 2.94±0.08b |
*Data are expressed as mean ± standard deviation. Different letters indicate significant differences at p < 0.05 in the same line. WB: wheat bran, EHWB: enzymatic hydrolyzed wheat bran, EWB: extruded wheat bran, SEWB: steam exploded wheat bran.
WHC and SWC were determined by the content in water soluble fiber components of foods (G. López et al., 1996) and their values should have a similar evolution. Besides, some components of bran, such as hemicelluloses and lignin, had water affinity (Holloway and Greig, 2010). Extrusion (Long et al., 2014), and steam explosion (Aktas-Akyildiz et al., 2017) were benefit to the formation of soluble dietary fiber and pentosan in bran. The chemical structure of soluble dietary fiber and pentosan contains a large number of hydrophilic group, which can increase the water holding capacity of bran (Buksa et al., 2014). Therefore, the EWB and SEWB have a stronger WHC and SWC than WB and EHWB.
In addition to the chemical composition of fibre, some physical properties (structure and particle size ) are important to understand the behaviour of the dietary fiber during hydration (Auffret et al., 1994) . The reduction of wheat bran WHC and SWC with the size of the bran may be due to the small size of the bran, which has accumulated too Large, spatial geometric gap is too small, dense tissue, water penetration resistance, a small amount of water adsorption, resulting in a decline in swelling force and water holding capacity. The structures are severely damaged, stacked on top of each other, and the ability to form a three-dimensional mesh-like interwoven structure is reduced or even eliminated.
Color parameters Color parameters (L*, a* and b*) of different fractions showed significant variation (Table 5). As expected, all fractions from WB had higher L* (lightness) value than the corresponding fractions from other bran types. Different fractions from EWB showed higher a* (redness and greenness) and b* (yellowness and blueness) value than others. The a* and b* values decreased with increase in fineness of the particle size. L* value of different fraction ranged from 66.60 to 66.78, 53.57 to 53.79, 46.35 to 46.77 and 43.19 to 44.22, for WB, EWB, SEWB and EHWB, respectively. L* value represents the brightness of the flour. The greater the value of L*, the brighter is the fraction.
| Particle size (µm) | Types | L* | a* | b* |
|---|---|---|---|---|
| 450-250 | WB | 66.60±0.22a | 7.17±0.23d | 20.20±0.40c |
| EHWB | 53.79±0.08b | 9.96±0.20c | 24.33±0.33a | |
| EWB | 46.35±0.33c | 13.93±0.04a | 23.30±0.28b | |
| SEWB | 43.19±0.87d | 11.91±0.44b | 20.05±0.21c | |
| 250-178 | WB | 66.76±0.40a | 7.34±0.13d | 21.23±0.08b |
| EHWB | 53.57±0.12b | 10.53±0.34c | 24.31±0.14a | |
| EWB | 48.13±0.14c | 14.47±0.08a | 24.40±0.04a | |
| SEWB | 43.63±0.24d | 12.87±0.06b | 20.46±0.18c | |
| 178-150 | WB | 66.78±0.33a | 7.59±0.34d | 22.21±0.07c |
| EHWB | 53.75±0.26b | 11.41±0.44c | 24.85±0.12b | |
| EWB | 48.77±0.35c | 14.99±0.20a | 26.24±0.22a | |
| SEWB | 44.22±0.48d | 13.33±0.23b | 21.33±0.29d |
Color influences the overall acceptability of resultant product. Compared with WB, L* value of EWB and SEWB decreased significantly whereas a* value increased in the same particle size. Extrusion and steam explosion could lead to Maillard reaction and caramelization of bran, and both of them could produce black substances (Gong et al., 2012), so that the brightness value of bran will be decreased. The higher b* values has been reported to be an indication of the protein content (FF and RA 1998). Because of the Maillard reaction, the EWB has higher b* value. However, EHWB had higher b* value may be due to enzyme addition.
Besides, the increase of a* value may be related to a lot of lignin in wheat bran (Seguin et al., 2012). The coniferl aldehyde group can react with phloroglucinol to produce acid catalyzed condensation reaction, forming a red chromophore.
Sodium cholate absorption capacity According to the Fig. 1, after 2 h sodium cholate adsorption, for the large size bran (420–250 µm), the adsorption capacity of sodium cholate were 67.45 mg/g, 66.80 mg/g, 60.50 mg/g and 63.80 mg/g; the adsorption capacity of bran with diameter of 250-178 µm were 63.13 mg/g, 62.30 mg/g, 56.70 mg/g and 58.86 mg/g; the adsorption capacity of wheat bran with small particle size (178-150 µm) were 60.58 mg / g, 59.35 mg / g, 55.25 mg / g and 55.31 mg / g, respectively for WB, EHWB, EWB and SEWB.
Sodium cholate absorption capacity of different pretreatment wheat bran
*Different letters indicate significant differences at p < 0.05 in the figure. WB: wheat bran, EHWB: enzymatic hydrolyzed wheat bran, EWB: extruded wheat bran, SEWB: steam exploded wheat bran.
Compared with WB, the above three treatment methods all have a weakened effect on the adsorption capacity of sodium cholate. The effect of EWB and SEWB on the adsorption capacity of sodium cholate was obviously stronger than EHWB. The adsorption capacity of sodium cholate decreased with the decrease of particle size of wheat bran.
The adsorption capacity of sodium cholate increased with the insoluble dietary fiber content. Researcher suggested that extrusion (Long et al., 2014), steam explosion (Aktas-Akyildiz et al., 2017) and enzymolysis (Zhang et al., 2011) can effectively reduce the content of insoluble dietary fiber in the bran. This may be the reason that the treatment can reduce the sodium cholate absorption capacity of wheat bran.
Cation exchange capacity With the increase of NaOH volume, the pH value of the solution system gradually increases. The cation exchange capacity is inversely proportional to the pH value. The larger the pH value, the weaker the cation exchange capacity. With the reduction of wheat bran particle size, the cation exchange capacity also showed a downward trend which is shown in the Fig. 2. Three kinds of treatment methods have a significant decline in the cation exchange capacity of wheat bran.
Cation exchange capacity of different pretreatment wheat bran
WB: wheat bran, EHWB: enzymatic hydrolyzed wheat bran, EWB: extruded wheat bran, SEWB: steam exploded wheat bran.
Dietary fiber contains a number of carboxyl, hydroxyl side groups play a major role in the cation exchange. It is not through a simple combination to reduce the body's absorption of ions, but by changing the instantaneous concentration of ions in the digestive tract pH, osmotic zone and redox potential impact, play a buffer role, which will help digestion and absorption (Pulido et al., 2000). The decrease of particle size of wheat bran can damage the structure of dietary fiber, thus reducing the cation exchange capacity. And, the pH value of SEWB is low, may be due to steam explosion process acid; while EHWB at a lower pH may be due to the addition of a buffer solution during the enzymatic hydrolysis.
Phytic acid As can be seen from Fig. 3, the phytate contents of WB, EHWB, EWB and SEWB in the size of 420-250 µm were 62.39 mg/g, 59.06 mg/g, 48.15 mg/g and 45.42 mg/g, respectively; in the middle size (250-178 µm) were 56.64 mg/g, 55.24 mg/g, 44.21 mg/g and 36.03 mg/g; They were 50.27 mg/g, 49.79 mg/g, 38.76 mg/g and 34.82 mg/g in the range of 178-150 µm.
Phytate contents of different pretreatment wheat bran
*Different letters indicate significant differences at p < 0.05 in the figure. WB: wheat bran, EHWB: enzymatic hydrolyzed wheat bran, EWB: extruded wheat bran, SEWB: steam exploded wheat bran.
Compared with WB, EHWB showed no significant change in phytate content (p > 0.05). However, the content of phytate in bran after extrusion and steam explosion decreased significantly (p < 0.05). Among them, steam explosion treatment to reduce the capacity of phytate is the strongest. Phytate content decreased with decreasing bran particle size, particle size has a significant effect (p < 0.05) on phytate content.
According to Bullock (Bullock et al., 1993) and Schlemmeretal (Schlemmer et al., 1995), phytic acid is considered to have good thermal stability, phytate is quite stable under heat treatment up to 110 °C, like home cooking, roasting, pressure cooking, etc. Therefore, extrusion and steam explosion of these two high-temperature treatment could lead to reduced phytate content of bran, which was similar to the situation during extrusion (Nwabueze 2007). On the other hand, under the action of high temperature (110 °C), the hemicellulose and other substances in the wheat bran undergo high temperature self-hydrolysis, resulting in acetic acid-based acidic substances, also played a role in promoting phytate hydrolysis reaction (Guo et al., 2015).
In summary, extrusion, steam explosion and enzymatic hydrolysis of these three treatment on the water holding capacity, swelling capacity, color, sodium cholate adsorption capacity, cation exchange capacity and phytate content of bran have a great difference. The properties of EHWB and WB are closer. The three treatment significantly improve the water holding capacity and swelling power of coarse bran, but reduce the lightness, sodium cholate, cation exchange capacity and phytate content. Moreover, the particle size of bran also has a significant impact on its physical and chemical indicators. Therefore, extrusion and steam explosion could play an important role in wheat bran processing.
Acknowledgements The Project Supported by the Foundation of Engineering Research Center of Food Biotechnology, Ministry of Education, Key Project of Tianjin Education Commission Scientific Research Plan (2017ZD02) and Innovation of Modern Agricultural Project (F18RO2) are gratefully acknowledged.
