- Email: [email protected]
Removal of chromophore in enzymatic hydrolysis by acid precipitation to improve the quality of xylo-oligosaccharides from corn stalk
Accepted Manuscript Removal of chromophore in enzymatic hydrolysis by acid precipitation to improve the quality of xylo-oligosaccharides from corn stalk Yue-Hai Wang, Jie Zhang, Yong-Shui Qu, Hong-Qiang Li PII: DOI: Reference:
S0960-8524(17)31373-1 http://dx.doi.org/10.1016/j.biortech.2017.08.068 BITE 18677
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
21 July 2017 10 August 2017 11 August 2017
Please cite this article as: Wang, Y-H., Zhang, J., Qu, Y-S., Li, H-Q., Removal of chromophore in enzymatic hydrolysis by acid precipitation to improve the quality of xylo-oligosaccharides from corn stalk, Bioresource Technology (2017), doi: http://dx.doi.org/10.1016/j.biortech.2017.08.068
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Removal of chromophore in enzymatic hydrolysis by acid precipitation to improve the quality of xylo-oligosaccharides from corn stalk Yue-Hai Wang1,2, Jie Zhang2, Yong-Shui Qu1, Hong-Qiang Li1* (1. State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China; 2. Beijing University of Chemical Technology, Beijing 100029, China) *Corresponding author. Tel./fax: +86 10 82544852. E-mail: [email protected]; [email protected] (Hong-Qiang Li)
Abstract: As the most representative functional sugar, the application areas and market demands of xylo-oligosaccharides (XOS) have been expanding year by year. Owing to the complex structure of corn stalk (CS), XOS obtained from CS are accompanied by problems such as low purity and high color value, which degrade the product. To improve the quality of XOS from CS, the enzymatic hydrolysis was precipitated by acid; then, the ethanol elution concentration was systematically investigated after optimizing the adsorption conditions. The results showed that the purity of XOS was increased to 87.28% from 67.31%, and the color value was decreased to 1050 from 4682 when the acid precipitation pH was 2. On the basis of acid precipitation, if the corresponding optimal conditions of XOS adsorption and elution were used, the highest purity of XOS was 97.87% obtained, with the lowest color value, 780, which reached the standard of the commercial XOS. Keywords: Corn stalk; Xylo-oligosaccharides (XOS); Acid precipitation; Activated carbon; Ethanol elution concentration
1.
Introduction As the most representative functional sugar, xylo-oligosaccharides (XOS) is a
short-chain polymer consists of 2-7 xylose units linked with β-1,4-glycosidic bonds. Except for the general properties of functional oligosaccharides(De Figueiredo et al., 2017; Vázquez et al., 2005; Zhang et al., 2017), XOS also has other characteristics, such
as, less effective dosage, excellent acid and heat stability(Courtin et al., 2009; Moure et al., 2006). The market demands of XOS have been rapidly expanding in the food,
health care products, animal husbandry, medicine and other areas(Moniz et al., 2016; Vázquez et al., 2000). XOS is mainly produced from xylan rich lignocellulosic material
either by enzymatic hydrolysis, autohydrolysis, chemical method or a combination of
these methods(Parajó et al., 2004; Xiao et al., 2013). As the main production method of XOS, enzymatic hydrolysis has the advantages of mild reaction conditions, high yield and fewer by-products(Tan et al., 2008). At present, XOS is mainly obtained by extracting and hydrolyzing the xylan from the corncob. This is based on corncob contains approximately 40% xylan(Yang et al., 2005), but the corncob is relatively limited in quantity and cost, which also
virtually increases the production cost of XOS. However, as the most representative of the lignocellulosic materials in China, the annual output of corn stalk (CS) is up to 350 million tons, accounting for about 60% of the total straw output(Zeng et al., 2007). CS is cheap and easy to get. In general, CS is directly discarded or burned in the harvested fields(Chapla et al., 2012), which wastes resources and causes pollution to the environment. Unfortunately, there are few studies on the producing of XOS from CS. Therefore, it has potential value to develop the technology of the production of XOS and other derivative products from CS. The XOS obtained by directly enzymatic hydrolysis of xylan extracted from CS often contain impurities such as monosaccharides, inorganic salts, ferulic acid, protein, lignin and its derivatives, and accompanied by high color values, low purity and other quality problems(Bian et al., 2013; Moure et al., 2006). In order to obtain high-quality XOS, subsequent refining steps are essential(Azelee et al., 2016). Lignin and its derivatives are not only the main components of XOS impurities(Montané et al., 2006), but also a key factor affecting the color value of sugar. How to effectively remove the lignin without losing sugar is an important part in the purification process of XOS. Sun et al.(Lourençon et al., 2015; Wang and Chen, 2013) explored the extraction of lignin from the black liquor by acid precipitation, and got remarkable results. Inspired by this, acid precipitation is used for the treatment of lignocellulose-containing XOS. In
this study, first of all, based the acid stability of XOS, efficiently removal of lignin from enzymatic hydrolyzate by acid precipitation, and the effect of acid precipitation pH on the quality of XOS was studied. Then, the ethanol elution concentration was systematically explored after optimizing the adsorption conditions of AC, in order to produce high-quality (high purity, low color value) XOS from CS.
2.
Materials and methods The process of production of XOS from CS was shown in Figure 1: first of all,
removed the non-structural components of the crushed CS; then, xylan was obtained by alkaline extraction and enzymatic hydrolysis to produce XOS; the enzymatic hydrolysate was adsorbed by AC after acid precipitation; followed by elution with ethanol, the eluate was concentrated and freeze-dried to obtain XOS. Figure 1
2.1
Materials Corn stalk was collected in Daxing, Beijing suburb. They were air dried, and
milled to ≤ 2 mm, stored in a sealed plastic bag.
2.2
Methods The specific preparation method of enzymatic hydrolysate can be seen in the
preliminary work of this group(Liu et al., 2016; Shen et al., 2016). 2.2.1
Acid precipitation The pH of the enzymatic hydrolyzate was adjusted to the set value, followed by
precipitation reaction at 50℃ for 1 h. After the reaction, the residue was removed by centrifugation.
2.2.2
Pretreatment of AC and optimization of adsorption conditions Pretreatment steps: AC was washed with 1% hydrochloric acid and then washed
with hot deionized water, dried at 105℃ for 8 h, finally cooled to room temperature. After pretreatment of AC, the initial pH, AC dosage, adsorption temperature and time were optimized by a single variable method. 2.2.3
Separation and purification of XOS The enzymatic hydrolysate was adsorbed with AC according to the optimized
adsorption conditions. After the reaction, 2% (w/v) of diatomaceous earth was added into the adsorption solution, the solid residue was separated by filtration. The AC filter cake was eluted with a set concentration of ethanol solution, and the ethanol eluate was concentrated and freeze-dried to obtain XOS.
2.3 2.3.1
Analytical method Determination of monosaccharides and oligosaccharides XOS samples (0.1 g) were dissolved in deionized water (25 mL) or directly filled
with XOS solution, filtered through a 0.45 µm polyether sulfone membrane, the contents of oligosaccharides and monosaccharides were determined with high performance liquid chromatograph (Li et al., 2013; Shen et al., 2016). 2.3.2
Salt content In this study, conductivity was used to determine the salt content of the solution.
The conductivity of the salt solution was measured using a conductivity meter (Rex, DDS-307, Shanghai Instrument Electric Scientific Instrument Co., Ltd.). The
concentration of NaCl in the solution was calculated by plotting the conductivity and NaCl concentration standard curve. 2.3.3
Color value XOS samples (0.2 g) were dissolved in deionized water (100 mL) and filtered
through a 0.45 µm membrane. The absorbance at 420 nm was measured by a UV spectrophotometer (UV765, Shanghai Precision & Scientific Instrument Co., Ltd.). And then calculated the color value of XOS (Angelus, 1994). 2.3.4
UV spectrum XOS samples (0.1 g) were dissolved in deionized water (25 mL) or directly filled
with XOS solution, the supernatant was used to analysis after centrifugation. The UV spectrum was measured at 250-600 nm using a UV spectrophotometer (UV765, Shanghai Precision & Scientific Instrument Co., Ltd.). The scanning interval was 1 nm and the blank sample was deionized water. 3.
Results and discussion
3.1
Selection of AC and optimization of adsorption conditions
3.1.1
Selection of AC Six types of AC and their adsorption ratios of XOS in the experiment were
shown in Table 1:
Table 1 The adsorption performance of six different types of AC was investigated through the preparation of 1% (w/v) XOS (Shandong Longli Biotechnology Co., Ltd.)
solution, the adsorption reaction was carried at 70℃ for 40 min with the oscillation frequency was 200 rpm, the initial pH was 7, and the AC dosage was 0.1% (w/v), the adsorption results were shown in Table 1. It could be clearly seen from Table 1, different types of AC had different adsorption properties. From the perspective of particle size, the adsorption effect of powdered AC was better than that of granular. At the same time, the adsorption performance of the dry wood powder (AC-6) was better than that of the other five kinds of AC. Therefore, AC-6 was used in the follow-up experiment. 3.1.2
Optimization of adsorption conditions The optimization results of the adsorption conditions were shown in Figure 2. In
the figure, a, b, c and d represented the optimization results of the initial pH, adsorption time, adsorption temperature and AC dosage, respectively. As shown in Figure 2a, with the increased of the initial pH, the decoloration ratio of AC decreased gradually, and the sugar loss ratio increased gradually, This was due to the nature of the AC, acid conditions were more conducive to adsorption. From the point of view of adsorption time and temperature, the decoloration ratio remained constant at 40 min, indicated that the adsorption of AC was saturated and prolonged the adsorption time, which only resulted in higher sugar loss. When the adsorption temperature was about 50℃, with the increased of temperature, the decoloration ratio increases faintly, but the sugar loss ratio increased more rapidly. With the increased of temperature, exacerbated the molecular thermal motion, the adsorbed pigment molecules underwent a desorption reaction. Simultaneously, increased temperature caused more energy input, not worth the candle. As shown in figure 2d, with the increased of the AC dosage, the decoloration ratio increased rapidly. When the dosage reached 0.04
g/mL, the decoloration ratio increased slowly, because the adsorption of AC on the pigment belongs to the physical adsorption, so there was bound to saturation, continued to add the dosage would only increase the cost of production(Bansal and Goyal, 2005). In summary, the optimum conditions for the adsorption reaction after
acid precipitation were as follows: the initial pH of the solution was 2, the AC dosage was 0.04 g / mL and the adsorption was carried out at 50 ℃ for 40 min. Figure 2 3.2
Effect of acid precipitation pH on the quality of XOS Acid precipitation is the common method of decoloration of sugar solution, the
main principles are as follows: during the alkali treatment, the ether bond in the natural lignin is destroyed, so that the degradation of lignin macromolecules into alkali lignin, which in the form of lignin sodium salt and is completely dissolved in a colloidal state. Occurrence of electrophilic substitution reaction when the solution is neutralized with acid, that is, acid ions in the acid to replace the sodium ions in alkali lignin, the reaction causes the alkali lignin colloid to be destroyed to produce the insoluble or water-insoluble lignin, so as to achieve the purpose of removing lignin. In the acid precipitation process, pH is the decisive factor affecting its effect(Wang and Chen, 2013). For this reason, the experiment was carried out by designing the crude
enzymatic hydrolysate at different pH conditions, followed by the production of XOS by AC-ethanol method. After adsorption with AC, eluted with 50% ethanol solution to investigate the effect of acid precipitation pH on XOS quality. 3.2.1
UV spectrum of the hydrolysate after acid precipitation
The UV spectrum of the hydrolysate after different acid precipitation pH were investigated. The results showed that there was a significant difference in UV absorption about the same concentration of the hydrolysate after different acid precipitation pH treatment. The absorption peaks of the hydrolysate were at 280 nm and 324 nm. According to the literature, 280 nm was the characteristic absorption peak of lignin(Johnson et al., 1961; Morrison, 1974), the absorption peak was generated by the electron transition of conjugated structures such as aromatic rings in lignin molecules. The absorption peak at 324 nm was mainly derived from the combined hydroxycinnamic acid, which was obtained by the absorption shift at the original 330 nm, it was found that the XOS samples contained a small amount of ferulic acid and p-coumaric acid from the area of the absorption peak(Scalbert et al., 1985). At the same time, acid precipitation treatment could be largely removed lignin of the hydrolysate. With the gradually decreased of acid precipitation pH, the lignin absorption peak gradually weakened. When the pH was below 3, the absorption at 280 nm became extremely weak, indicated that the lignin in the hydrolysate was substantially removed, which also proved the necessity of acid precipitation. 3.2.2
Effect of acid precipitation on the purity, yield and color value of XOS The purity, yield and color value of the XOS obtained from different acid
precipitation pH were shown in Figure 3. It can be seen from the figure, different pH value had a significant impact on the purity, yield and color value of XOS. When the acid precipitation pH was higher than 5, the purity and color value of the XOS products were not affected at all. With the gradually decreased of pH, the purity of the obtained XOS was significantly increased, while the color value decreased significantly. In contrast to the XOS without acid precipitation treatment, the purity of XOS was increased by 19.97%, 87.28%, and the color value was decreased by 77.57%
to 1050 when the acid precipitation pH value was 2. This was due to the gradual reduction of alkali lignin in the solution with the decreased in pH. Since the excellent acid stability of XOS, the yields of XOS remained basically constant with the gradually decreased of acid precipitation pH. It can be clearly seen that the acid precipitation of the hydrolysate could significantly improve the quality of the obtained XOS. When the pH was 2, the precipitation effect was the best, subsequent experiments were carried out with pH 2 for acid precipitation treatment. Figure 3 3.3
Effect of acid precipitation coupled ethanol elution concentration on the quality of XOS In this study, the hydrolysate was purified by AC-ethanol method to produce
XOS. AC method was in accordance with the force difference of the adsorption site of sugar and non-sugar impurities, to achieve the purpose of purification. It is worth noting that, there was a significant difference in the adsorption capacity of AC to carbohydrate and other chromophore, while different concentrations of ethanol could elute different polymeric oligosaccharides. Therefore, the ethanol elution concentration played an important role in the quality (purity, color, etc.) of the XOS products(Akpinar and Penner, 2015). The acid precipitation coupled ethanol elution concentration were systematically investigated on the basis of different acid precipitation pH, in order to obtain high-quality XOS with high purity and low color. Since different concentrations of ethanol elution of different polymerization degree of oligosaccharides, there might be many problems with single concentration elution, such as incomplete elution, unsatisfactory separation effect of each oligosaccharides. In this study, ethanol elution concentration was systematically
investigated on the basis of single concentration. Ethanol elution was systematically investigated using four experimental regimens: 50% single concentration; 20%, 50% two concentration gradient; 10%, 30%, 50% three concentration gradient; 15% , 30%, 50%, 70% four concentration gradient. The experimental results were shown in Figures 4, 5 and 6. Figure 4 was the purity, yield and color value of XOS obtained by different ethanol elution concentration; Figure 5 showed the content of individual oligosaccharides in the XOS; Figure 6 was the component of the XOS. Comparison of yields of XOS obtained from different pretreatment methods was shown in Table 2. As it can be seen from Figure 4a, 5a and 6a, regardless of the purity or color value, the XOS obtained by single concentration elution were not the best results, unsatisfactory separation effect of each oligosaccharides, and simultaneously, XOS products contained some monosaccharide, ash and other impurities. Single concentration elution did not take into account the difference in the adsorption capacity of AC to oligosaccharides with different degrees of polymerization, and different ethanol concentrations eluted different polymerization degree of oligosaccharides. In addition, XOS could be used in feed, food and other industries according to their purity(Moure et al., 2006). Based on the above analysis, subsequent refining process using ethanol gradient elution, simultaneous production of different varieties of XOS. Figure 4 Table 2 As a control, the XOS standard was purchased from Shandong Longli. The purity of Longli XOS was 98.31% and the color value was 747 obtained by experimental determination. It could be obviously seen from Figure 4, The best XOS
was found in four concentration gradient, the highest purity of XOS was 97.87% obtained from 30% ethanol eluate, with the lowest color value, 780. In addition, the main components of the XOS were xylotetraose and xylopentaose, which contain a small amount of monosaccharide and ash, reached the standard of commercial XOS. In this concentration gradient, the purity of the XOS obtained from the 50% ethanol elution was also up to 93.36% and the yield of XOS was increased to 81.51% from 71.20%, which can be seen the necessity of gradient elution. As shown in Figure 5 and 6, different ethanol concentrations eluted different polymerization degree of oligosaccharides. AC was less adsorbable to inorganic salts and monosaccharides, used low concentration of ethanol to elute them; followed by less than 20% of the ethanol concentration mainly eluted xylobiose, xylotriose and other low degree of polymerization of XOS; 20% to 50% of the ethanol concentration mainly eluted xylotriose to xylopentaose and other medium degree of polymerization of XOS; more than 50% of the ethanol concentration mainly eluted xylopentaose to xyloheptaose and other high degree of polymerization of XOS. In addition, according to the structural characteristics of AC(Adinaveen et al., 2013), it had strong adsorption to aromatic substances such as lignin and its derivatives. As it was shown in Figure 6, more than 50% of the ethanol concentration began to elute such substances, which was the leading cause of the low purity and higher impurity content of the XOS obtained from 70% ethanol elution. Figure 5 Figure 6 For further proof that the acid precipitation coupled elution concentration could effectively remove the chromophore in the enzymatic hydrolysate to improve the
quality of XOS from CS. In this study, the hydrolysate without acid precipitation treatment was eluted with 15%, 30%, 50% and 70% four concentration gradient, the experimental results were shown in Table 3. It can be seen from Table 3 that the acid precipitation coupled elution concentration could significantly improve the quality of the XOS. In contrast to the XOS without acid precipitation treatment, the purity of XOS was increased by 10% and the color value was decreased by 50% when the acid precipitation pH value was 2. This was due to the chromophore was effectively removed by the acid precipitation coupled elution concentration, which could also be seen the necessity of this study. Table 3 4
Conclusions The purity of XOS was increased to 87.28% from 67.31%, and the color value
was decreased to 1050 from 4682 when the acid precipitation pH value was 2. The optimum adsorption conditions of the hydrolyzate after acid precipitation were as follows: the initial pH of the solution was 2, the activated carbon dosage was 0.04 g/mL and the adsorption was carried out at 50℃ for 40 min. Under the optimum conditions, the highest purity of XOS was 97.87% obtained from 30% ethanol eluate, with the lowest color value, 780, which reached the standard of the commercial XOS. Acknowledgement This work was supported by the following foundations: National Natural Science Foundation of China (No. 21206008). References
[1]
Adinaveen, T., Kennedy, L.J., Vijaya, J.J., Sekaran, G. 2013. Studies on structural, morphological, electrical and electrochemical properties of activated carbon prepared from sugarcane bagasse. J. Ind. Eng. Chem., 19(5), 1470-1476.
[2]
Akpinar, O., Penner, M.H. 2015. Preparation of cellooligosaccharides : comparative study. J. Food. Agric. Environ., 6(1), 55-61.
[3]
Angelus, J. 1994. International Commission for Uniform Methods of Sugar Analysis. Colney England Gs(11), 1208-1215.
[4]
Azelee, N.I.W., Jahim, J.M., Ismail, A.F., Fuzi, S.F.Z.M., Rahman, R.A., Illias, R.M. 2016. High xylooligosaccharides (XOS) production from pretreated kenaf stem by enzyme mixture hydrolysis. Ind. Crop. Prod., 81, 11-19.
[5]
Bansal, R.C., Goyal, M. 2005. Activated Carbon Adsorption. Environ.sci.technol(3).
[6]
Bian, J., Peng, F., Peng, X.P., Peng, P., Xu, F., Sun, R.C. 2013. Structural features and antioxidant activity of xylooligosaccharides enzymatically produced from sugarcane bagasse. Bioresour. Technol., 127(1), 236-241.
[7]
Chapla, D., Pandit, P., Shah, A. 2012. Production of xylooligosaccharides from corncob xylan by fungal xylanase and their utilization by probiotics. Bioresour. Technol., 115(5), 215-221.
[8]
Courtin, C.M., Swennen, K., Verjans, P., Delcour, J.A. 2009. Heat and pH stability of prebiotic arabinoxylooligosaccharides, xylooligosaccharides and fructooligosaccharides. Food chem., 112(4), 831-837.
[9]
De Figueiredo, F.C., Carvalho, A.F., Brienzo, M., Campioni, T.S., De, O.-N.P. 2017. Chemical input reduction in the arabinoxylan and lignocellulose alkaline extraction and xylooligosaccharides production. Bioresour. Technol., 228, 164-170.
[10]
Johnson, D., Moore, W., Zank, L. 1961. The spectrophotometric determination of lignin in small wood samples. Tappi, 44(11), 793-798.
[11]
Li, H.Q., Jiang, W., Jia, J.X., Xu, J. 2013. pH pre-corrected liquid hot water pretreatment on corn stover with high hemicellulose recovery and low inhibitors formation. Bioresour. Technol., 153C(2), 292-299.
[12]
Liu, K.X., Li, H.Q., Zhang, J., Zhang, Z.G., Xu, J. 2016. The effect of non-structural components and lignin on hemicellulose extraction. Bioresour. Technol., 214, 755-760.
[13]
Lourençon, T.V., Hansel, F.A., Silva, T.A.D., Ramos, L.P., Muniz, G.I.B.D., Magalhães, W.L.E. 2015. Hardwood and softwood kraft lignins fractionation by simple sequential acid precipitation. Sep. Purif. Technol., 154, 82-88.
[14]
Moniz, P., Ailing, H., Duarte, L.C., Kolida, S., Rastall, R.A., Pereira, H., Carvalheiro, F. 2016. Assessment of the bifidogenic effect of substituted xylo-oligosaccharides obtained from corn straw. Carbohyd. Polym., 136, 466-473.
[15]
Montané, D., Nabarlatz, D., Martorell, A., Vanessa Tornéfernández, A., Fierro, V. 2006. Removal of Lignin and Associated Impurities from Xylo-oligosaccharides by Activated Carbon Adsorption. Ind. Eng. Chem. Res., 45(7), 2294-2302.
[16]
Morrison, I.M. 1974. Lignin-carbohydrate complexes from Lolium perenne. Phytochemistry, 13(7), 1161-1165.
[17]
Moure, A., Gullón, P., Domínguez, H., Parajó, J.C. 2006. Advances in the manufacture, purification and applications of xylo-oligosaccharides as food additives and nutraceuticals. Process Biochem., 41(9), 1913-1923.
[18]
Nabarlatz, D., Torras, C., Garcia-Valls, R., Montané, D. 2007. Purification of xylo-oligosaccharides from almond shells by ultrafiltration. Sep. Purif. Technol., 53(3), 235-243.
[19]
Parajó, J.C., Garrote, G., Cruz, J.M., Dominguez, H. 2004. Production of xylooligosaccharides by autohydrolysis of lignocellulosic materials. Trends Food Sci. Tech., 15(3–4), 115-120.
[20]
Scalbert, A., Monties, B., Lallemand, J.Y., Guittet, E., Rolando, C. 1985. Ether linkage between phenolic acids and lignin fractions from wheat straw. Phytochemistry, 24(6), 1359-1362.
[21]
Shen, R., Li, H.Q., Zhang, J., Xu, J. 2016. Effects of Impurities in Alkali-Extracted Xylan on Its Enzymatic Hydrolysis to Produce Xylo-Oligosaccharides. App. Biochem. Biotechnol., 179(5), 740-752.
[22]
Tan, S.S., Li, D.Y., Jiang, Z.Q., Zhu, Y.P., Shi, B., Li, L.T. 2008. Production of xylobiose from the autohydrolysis explosion liquor of corncob using Thermotoga maritima xylanase B (XynB) immobilized on nickel-chelated Eupergit C. Bioresour. Technol., 99(1), 200-204.
[23]
Vázquez, M.J., Alonso, J.L., Domínguez, H., Parajó, J.C. 2000. Xylooligosaccharides: manufacture and applications. Trends Food Sci. Tech., 11(11), 387-393.
[24]
Vázquez, M.J., Garrote, G., Alonso, J.L., Domínguez, H., Parajó, J.C. 2005. Refining of autohydrolysis liquors for manufacturing xylooligosaccharides: evaluation of operational strategies. Bioresour. Technol., 96(8), 889-896.
[25]
Wang, G., Chen, H. 2013. Fractionation of alkali-extracted lignin from steam-exploded stalk by gradient acid precipitation. Sep. Purif. Technol., 105(5), 98-105.
[26]
Xiao, X., Bian, J., Peng, X.P., Xu, H., Xiao, B., Sun, R.C. 2013. Autohydrolysis of bamboo (Dendrocalamus giganteus Munro) culm for the production of xylo-oligosaccharides. Bioresour. Technol., 138(6), 63-70.
[27]
Yang, R., Xu, S., Wang, Z., Yang, W. 2005. Aqueous extraction of corncob xylan and production of xylooligosaccharides. LWT-Food Sci. Technol., 38(6), 677-682.
[28]
Yuan, Q.P., Zhang, H., Qian, Z.M., Yang, X.J. 2010. Pilot‐plant production of xylo‐oligosaccharides from corncob by steaming, enzymatic hydrolysis and nanofiltration. J. Chem. Technol. Biot., 79(10), 1073-1079.
[29]
Zeng, X., Ma, Y., Ma, L. 2007. Utilization of straw in biomass energy in China. Renew. Sust. Energ. Rev., 11(5), 976-987.
[30]
Zhang, H., Yong, X., Yu, S. 2017. Co-production of functional xylooligosaccharides and fermentable sugars from corncob with effective acetic acid prehydrolysis. Bioresour. Technol., 234, 343-349.
Figure 1. The process of production of XOS from corn stalk Figure 2. Optimization of adsorption conditions Figure 3. Effect of acid precipitation on the purity, yield and color value of XOS Figure 4. The purity, yield and color value of XOS obtained by different ethanol elution concentration Figure 5. Content of individual oligosaccharides in the XOS Figure 6. Components of the XOS obtained by different ethanol elution concentration
Table 1
Six types of activated carbon and their adsorption ratios of XOS Adsorption rate of
Name
Type
Factory XOS (%)
24.37±1.12 AC-1
Particle (AR)
Tianjin Yongda Chemical Reagent Co., Ltd 34.06±0.51
AC-2
Powder (AR)
AC-3
Wood powder
31.07±0.98 Beijing Modern Oriental Fine
28.35±1.32 AC-4
Coconut shell
Chemicals Co., Ltd
particle
38.74±1.01 AC-5
Wet wood powder
AC-6
Dry wood powder
47.65±1.95
Table 2 Comparison of yields of XOS obtained from different pretreatment methods
XOS purity Material
CS
XOS yield
Method
AC-ethanol
Reference (%)
(%)
97.87
81.51
This study
80.00
(Chapla et al., 2012)
93.00
------
(Bian et al., 2013)
AC column Corncob
-----chromatography
Sugarcane
Ethanol
bagasse
precipitation
Almond shells
Ultrafiltration
93.00
58.30
(Nabarlatz et al., 2007)
Corncob
Nanofiltration
74.53
16.93
(Yuan et al., 2010)
Table 3
Comparison of the purity and color value of the obtained XOS
XOS Content（%）
Color value
pH=2
Untreated
pH=2
Untreated
15%
84.66±1.08
67.84±0.92
1562±78
4861±113
30%
97.87±0.66
80.99±1.52
780±59
2132±68
50%
93.36±1.05
79.66±1.34
892±41
2015±56
70%
71.26±1.09
50.06±0.53
4269±106
8965±135
Concentration
Highlights:
The chromophore in enzymatic hydrolyzate seriously degrades the XOS product Lignin in enzymatic hydrolyzate can be efficient removed by acid precipitation High purity, low color value of XOS was obtained from ethanol gradient elution
S0960-8524(17)31373-1 http://dx.doi.org/10.1016/j.biortech.2017.08.068 BITE 18677
To appear in:
Bioresource Technology
Received Date: Revised Date: Accepted Date:
21 July 2017 10 August 2017 11 August 2017
Please cite this article as: Wang, Y-H., Zhang, J., Qu, Y-S., Li, H-Q., Removal of chromophore in enzymatic hydrolysis by acid precipitation to improve the quality of xylo-oligosaccharides from corn stalk, Bioresource Technology (2017), doi: http://dx.doi.org/10.1016/j.biortech.2017.08.068
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Removal of chromophore in enzymatic hydrolysis by acid precipitation to improve the quality of xylo-oligosaccharides from corn stalk Yue-Hai Wang1,2, Jie Zhang2, Yong-Shui Qu1, Hong-Qiang Li1* (1. State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, China; 2. Beijing University of Chemical Technology, Beijing 100029, China) *Corresponding author. Tel./fax: +86 10 82544852. E-mail: [email protected]; [email protected] (Hong-Qiang Li)
Abstract: As the most representative functional sugar, the application areas and market demands of xylo-oligosaccharides (XOS) have been expanding year by year. Owing to the complex structure of corn stalk (CS), XOS obtained from CS are accompanied by problems such as low purity and high color value, which degrade the product. To improve the quality of XOS from CS, the enzymatic hydrolysis was precipitated by acid; then, the ethanol elution concentration was systematically investigated after optimizing the adsorption conditions. The results showed that the purity of XOS was increased to 87.28% from 67.31%, and the color value was decreased to 1050 from 4682 when the acid precipitation pH was 2. On the basis of acid precipitation, if the corresponding optimal conditions of XOS adsorption and elution were used, the highest purity of XOS was 97.87% obtained, with the lowest color value, 780, which reached the standard of the commercial XOS. Keywords: Corn stalk; Xylo-oligosaccharides (XOS); Acid precipitation; Activated carbon; Ethanol elution concentration
1.
Introduction As the most representative functional sugar, xylo-oligosaccharides (XOS) is a
short-chain polymer consists of 2-7 xylose units linked with β-1,4-glycosidic bonds. Except for the general properties of functional oligosaccharides(De Figueiredo et al., 2017; Vázquez et al., 2005; Zhang et al., 2017), XOS also has other characteristics, such
as, less effective dosage, excellent acid and heat stability(Courtin et al., 2009; Moure et al., 2006). The market demands of XOS have been rapidly expanding in the food,
health care products, animal husbandry, medicine and other areas(Moniz et al., 2016; Vázquez et al., 2000). XOS is mainly produced from xylan rich lignocellulosic material
either by enzymatic hydrolysis, autohydrolysis, chemical method or a combination of
these methods(Parajó et al., 2004; Xiao et al., 2013). As the main production method of XOS, enzymatic hydrolysis has the advantages of mild reaction conditions, high yield and fewer by-products(Tan et al., 2008). At present, XOS is mainly obtained by extracting and hydrolyzing the xylan from the corncob. This is based on corncob contains approximately 40% xylan(Yang et al., 2005), but the corncob is relatively limited in quantity and cost, which also
virtually increases the production cost of XOS. However, as the most representative of the lignocellulosic materials in China, the annual output of corn stalk (CS) is up to 350 million tons, accounting for about 60% of the total straw output(Zeng et al., 2007). CS is cheap and easy to get. In general, CS is directly discarded or burned in the harvested fields(Chapla et al., 2012), which wastes resources and causes pollution to the environment. Unfortunately, there are few studies on the producing of XOS from CS. Therefore, it has potential value to develop the technology of the production of XOS and other derivative products from CS. The XOS obtained by directly enzymatic hydrolysis of xylan extracted from CS often contain impurities such as monosaccharides, inorganic salts, ferulic acid, protein, lignin and its derivatives, and accompanied by high color values, low purity and other quality problems(Bian et al., 2013; Moure et al., 2006). In order to obtain high-quality XOS, subsequent refining steps are essential(Azelee et al., 2016). Lignin and its derivatives are not only the main components of XOS impurities(Montané et al., 2006), but also a key factor affecting the color value of sugar. How to effectively remove the lignin without losing sugar is an important part in the purification process of XOS. Sun et al.(Lourençon et al., 2015; Wang and Chen, 2013) explored the extraction of lignin from the black liquor by acid precipitation, and got remarkable results. Inspired by this, acid precipitation is used for the treatment of lignocellulose-containing XOS. In
this study, first of all, based the acid stability of XOS, efficiently removal of lignin from enzymatic hydrolyzate by acid precipitation, and the effect of acid precipitation pH on the quality of XOS was studied. Then, the ethanol elution concentration was systematically explored after optimizing the adsorption conditions of AC, in order to produce high-quality (high purity, low color value) XOS from CS.
2.
Materials and methods The process of production of XOS from CS was shown in Figure 1: first of all,
removed the non-structural components of the crushed CS; then, xylan was obtained by alkaline extraction and enzymatic hydrolysis to produce XOS; the enzymatic hydrolysate was adsorbed by AC after acid precipitation; followed by elution with ethanol, the eluate was concentrated and freeze-dried to obtain XOS. Figure 1
2.1
Materials Corn stalk was collected in Daxing, Beijing suburb. They were air dried, and
milled to ≤ 2 mm, stored in a sealed plastic bag.
2.2
Methods The specific preparation method of enzymatic hydrolysate can be seen in the
preliminary work of this group(Liu et al., 2016; Shen et al., 2016). 2.2.1
Acid precipitation The pH of the enzymatic hydrolyzate was adjusted to the set value, followed by
precipitation reaction at 50℃ for 1 h. After the reaction, the residue was removed by centrifugation.
2.2.2
Pretreatment of AC and optimization of adsorption conditions Pretreatment steps: AC was washed with 1% hydrochloric acid and then washed
with hot deionized water, dried at 105℃ for 8 h, finally cooled to room temperature. After pretreatment of AC, the initial pH, AC dosage, adsorption temperature and time were optimized by a single variable method. 2.2.3
Separation and purification of XOS The enzymatic hydrolysate was adsorbed with AC according to the optimized
adsorption conditions. After the reaction, 2% (w/v) of diatomaceous earth was added into the adsorption solution, the solid residue was separated by filtration. The AC filter cake was eluted with a set concentration of ethanol solution, and the ethanol eluate was concentrated and freeze-dried to obtain XOS.
2.3 2.3.1
Analytical method Determination of monosaccharides and oligosaccharides XOS samples (0.1 g) were dissolved in deionized water (25 mL) or directly filled
with XOS solution, filtered through a 0.45 µm polyether sulfone membrane, the contents of oligosaccharides and monosaccharides were determined with high performance liquid chromatograph (Li et al., 2013; Shen et al., 2016). 2.3.2
Salt content In this study, conductivity was used to determine the salt content of the solution.
The conductivity of the salt solution was measured using a conductivity meter (Rex, DDS-307, Shanghai Instrument Electric Scientific Instrument Co., Ltd.). The
concentration of NaCl in the solution was calculated by plotting the conductivity and NaCl concentration standard curve. 2.3.3
Color value XOS samples (0.2 g) were dissolved in deionized water (100 mL) and filtered
through a 0.45 µm membrane. The absorbance at 420 nm was measured by a UV spectrophotometer (UV765, Shanghai Precision & Scientific Instrument Co., Ltd.). And then calculated the color value of XOS (Angelus, 1994). 2.3.4
UV spectrum XOS samples (0.1 g) were dissolved in deionized water (25 mL) or directly filled
with XOS solution, the supernatant was used to analysis after centrifugation. The UV spectrum was measured at 250-600 nm using a UV spectrophotometer (UV765, Shanghai Precision & Scientific Instrument Co., Ltd.). The scanning interval was 1 nm and the blank sample was deionized water. 3.
Results and discussion
3.1
Selection of AC and optimization of adsorption conditions
3.1.1
Selection of AC Six types of AC and their adsorption ratios of XOS in the experiment were
shown in Table 1:
Table 1 The adsorption performance of six different types of AC was investigated through the preparation of 1% (w/v) XOS (Shandong Longli Biotechnology Co., Ltd.)
solution, the adsorption reaction was carried at 70℃ for 40 min with the oscillation frequency was 200 rpm, the initial pH was 7, and the AC dosage was 0.1% (w/v), the adsorption results were shown in Table 1. It could be clearly seen from Table 1, different types of AC had different adsorption properties. From the perspective of particle size, the adsorption effect of powdered AC was better than that of granular. At the same time, the adsorption performance of the dry wood powder (AC-6) was better than that of the other five kinds of AC. Therefore, AC-6 was used in the follow-up experiment. 3.1.2
Optimization of adsorption conditions The optimization results of the adsorption conditions were shown in Figure 2. In
the figure, a, b, c and d represented the optimization results of the initial pH, adsorption time, adsorption temperature and AC dosage, respectively. As shown in Figure 2a, with the increased of the initial pH, the decoloration ratio of AC decreased gradually, and the sugar loss ratio increased gradually, This was due to the nature of the AC, acid conditions were more conducive to adsorption. From the point of view of adsorption time and temperature, the decoloration ratio remained constant at 40 min, indicated that the adsorption of AC was saturated and prolonged the adsorption time, which only resulted in higher sugar loss. When the adsorption temperature was about 50℃, with the increased of temperature, the decoloration ratio increases faintly, but the sugar loss ratio increased more rapidly. With the increased of temperature, exacerbated the molecular thermal motion, the adsorbed pigment molecules underwent a desorption reaction. Simultaneously, increased temperature caused more energy input, not worth the candle. As shown in figure 2d, with the increased of the AC dosage, the decoloration ratio increased rapidly. When the dosage reached 0.04
g/mL, the decoloration ratio increased slowly, because the adsorption of AC on the pigment belongs to the physical adsorption, so there was bound to saturation, continued to add the dosage would only increase the cost of production(Bansal and Goyal, 2005). In summary, the optimum conditions for the adsorption reaction after
acid precipitation were as follows: the initial pH of the solution was 2, the AC dosage was 0.04 g / mL and the adsorption was carried out at 50 ℃ for 40 min. Figure 2 3.2
Effect of acid precipitation pH on the quality of XOS Acid precipitation is the common method of decoloration of sugar solution, the
main principles are as follows: during the alkali treatment, the ether bond in the natural lignin is destroyed, so that the degradation of lignin macromolecules into alkali lignin, which in the form of lignin sodium salt and is completely dissolved in a colloidal state. Occurrence of electrophilic substitution reaction when the solution is neutralized with acid, that is, acid ions in the acid to replace the sodium ions in alkali lignin, the reaction causes the alkali lignin colloid to be destroyed to produce the insoluble or water-insoluble lignin, so as to achieve the purpose of removing lignin. In the acid precipitation process, pH is the decisive factor affecting its effect(Wang and Chen, 2013). For this reason, the experiment was carried out by designing the crude
enzymatic hydrolysate at different pH conditions, followed by the production of XOS by AC-ethanol method. After adsorption with AC, eluted with 50% ethanol solution to investigate the effect of acid precipitation pH on XOS quality. 3.2.1
UV spectrum of the hydrolysate after acid precipitation
The UV spectrum of the hydrolysate after different acid precipitation pH were investigated. The results showed that there was a significant difference in UV absorption about the same concentration of the hydrolysate after different acid precipitation pH treatment. The absorption peaks of the hydrolysate were at 280 nm and 324 nm. According to the literature, 280 nm was the characteristic absorption peak of lignin(Johnson et al., 1961; Morrison, 1974), the absorption peak was generated by the electron transition of conjugated structures such as aromatic rings in lignin molecules. The absorption peak at 324 nm was mainly derived from the combined hydroxycinnamic acid, which was obtained by the absorption shift at the original 330 nm, it was found that the XOS samples contained a small amount of ferulic acid and p-coumaric acid from the area of the absorption peak(Scalbert et al., 1985). At the same time, acid precipitation treatment could be largely removed lignin of the hydrolysate. With the gradually decreased of acid precipitation pH, the lignin absorption peak gradually weakened. When the pH was below 3, the absorption at 280 nm became extremely weak, indicated that the lignin in the hydrolysate was substantially removed, which also proved the necessity of acid precipitation. 3.2.2
Effect of acid precipitation on the purity, yield and color value of XOS The purity, yield and color value of the XOS obtained from different acid
precipitation pH were shown in Figure 3. It can be seen from the figure, different pH value had a significant impact on the purity, yield and color value of XOS. When the acid precipitation pH was higher than 5, the purity and color value of the XOS products were not affected at all. With the gradually decreased of pH, the purity of the obtained XOS was significantly increased, while the color value decreased significantly. In contrast to the XOS without acid precipitation treatment, the purity of XOS was increased by 19.97%, 87.28%, and the color value was decreased by 77.57%
to 1050 when the acid precipitation pH value was 2. This was due to the gradual reduction of alkali lignin in the solution with the decreased in pH. Since the excellent acid stability of XOS, the yields of XOS remained basically constant with the gradually decreased of acid precipitation pH. It can be clearly seen that the acid precipitation of the hydrolysate could significantly improve the quality of the obtained XOS. When the pH was 2, the precipitation effect was the best, subsequent experiments were carried out with pH 2 for acid precipitation treatment. Figure 3 3.3
Effect of acid precipitation coupled ethanol elution concentration on the quality of XOS In this study, the hydrolysate was purified by AC-ethanol method to produce
XOS. AC method was in accordance with the force difference of the adsorption site of sugar and non-sugar impurities, to achieve the purpose of purification. It is worth noting that, there was a significant difference in the adsorption capacity of AC to carbohydrate and other chromophore, while different concentrations of ethanol could elute different polymeric oligosaccharides. Therefore, the ethanol elution concentration played an important role in the quality (purity, color, etc.) of the XOS products(Akpinar and Penner, 2015). The acid precipitation coupled ethanol elution concentration were systematically investigated on the basis of different acid precipitation pH, in order to obtain high-quality XOS with high purity and low color. Since different concentrations of ethanol elution of different polymerization degree of oligosaccharides, there might be many problems with single concentration elution, such as incomplete elution, unsatisfactory separation effect of each oligosaccharides. In this study, ethanol elution concentration was systematically
investigated on the basis of single concentration. Ethanol elution was systematically investigated using four experimental regimens: 50% single concentration; 20%, 50% two concentration gradient; 10%, 30%, 50% three concentration gradient; 15% , 30%, 50%, 70% four concentration gradient. The experimental results were shown in Figures 4, 5 and 6. Figure 4 was the purity, yield and color value of XOS obtained by different ethanol elution concentration; Figure 5 showed the content of individual oligosaccharides in the XOS; Figure 6 was the component of the XOS. Comparison of yields of XOS obtained from different pretreatment methods was shown in Table 2. As it can be seen from Figure 4a, 5a and 6a, regardless of the purity or color value, the XOS obtained by single concentration elution were not the best results, unsatisfactory separation effect of each oligosaccharides, and simultaneously, XOS products contained some monosaccharide, ash and other impurities. Single concentration elution did not take into account the difference in the adsorption capacity of AC to oligosaccharides with different degrees of polymerization, and different ethanol concentrations eluted different polymerization degree of oligosaccharides. In addition, XOS could be used in feed, food and other industries according to their purity(Moure et al., 2006). Based on the above analysis, subsequent refining process using ethanol gradient elution, simultaneous production of different varieties of XOS. Figure 4 Table 2 As a control, the XOS standard was purchased from Shandong Longli. The purity of Longli XOS was 98.31% and the color value was 747 obtained by experimental determination. It could be obviously seen from Figure 4, The best XOS
was found in four concentration gradient, the highest purity of XOS was 97.87% obtained from 30% ethanol eluate, with the lowest color value, 780. In addition, the main components of the XOS were xylotetraose and xylopentaose, which contain a small amount of monosaccharide and ash, reached the standard of commercial XOS. In this concentration gradient, the purity of the XOS obtained from the 50% ethanol elution was also up to 93.36% and the yield of XOS was increased to 81.51% from 71.20%, which can be seen the necessity of gradient elution. As shown in Figure 5 and 6, different ethanol concentrations eluted different polymerization degree of oligosaccharides. AC was less adsorbable to inorganic salts and monosaccharides, used low concentration of ethanol to elute them; followed by less than 20% of the ethanol concentration mainly eluted xylobiose, xylotriose and other low degree of polymerization of XOS; 20% to 50% of the ethanol concentration mainly eluted xylotriose to xylopentaose and other medium degree of polymerization of XOS; more than 50% of the ethanol concentration mainly eluted xylopentaose to xyloheptaose and other high degree of polymerization of XOS. In addition, according to the structural characteristics of AC(Adinaveen et al., 2013), it had strong adsorption to aromatic substances such as lignin and its derivatives. As it was shown in Figure 6, more than 50% of the ethanol concentration began to elute such substances, which was the leading cause of the low purity and higher impurity content of the XOS obtained from 70% ethanol elution. Figure 5 Figure 6 For further proof that the acid precipitation coupled elution concentration could effectively remove the chromophore in the enzymatic hydrolysate to improve the
quality of XOS from CS. In this study, the hydrolysate without acid precipitation treatment was eluted with 15%, 30%, 50% and 70% four concentration gradient, the experimental results were shown in Table 3. It can be seen from Table 3 that the acid precipitation coupled elution concentration could significantly improve the quality of the XOS. In contrast to the XOS without acid precipitation treatment, the purity of XOS was increased by 10% and the color value was decreased by 50% when the acid precipitation pH value was 2. This was due to the chromophore was effectively removed by the acid precipitation coupled elution concentration, which could also be seen the necessity of this study. Table 3 4
Conclusions The purity of XOS was increased to 87.28% from 67.31%, and the color value
was decreased to 1050 from 4682 when the acid precipitation pH value was 2. The optimum adsorption conditions of the hydrolyzate after acid precipitation were as follows: the initial pH of the solution was 2, the activated carbon dosage was 0.04 g/mL and the adsorption was carried out at 50℃ for 40 min. Under the optimum conditions, the highest purity of XOS was 97.87% obtained from 30% ethanol eluate, with the lowest color value, 780, which reached the standard of the commercial XOS. Acknowledgement This work was supported by the following foundations: National Natural Science Foundation of China (No. 21206008). References
[1]
Adinaveen, T., Kennedy, L.J., Vijaya, J.J., Sekaran, G. 2013. Studies on structural, morphological, electrical and electrochemical properties of activated carbon prepared from sugarcane bagasse. J. Ind. Eng. Chem., 19(5), 1470-1476.
[2]
Akpinar, O., Penner, M.H. 2015. Preparation of cellooligosaccharides : comparative study. J. Food. Agric. Environ., 6(1), 55-61.
[3]
Angelus, J. 1994. International Commission for Uniform Methods of Sugar Analysis. Colney England Gs(11), 1208-1215.
[4]
Azelee, N.I.W., Jahim, J.M., Ismail, A.F., Fuzi, S.F.Z.M., Rahman, R.A., Illias, R.M. 2016. High xylooligosaccharides (XOS) production from pretreated kenaf stem by enzyme mixture hydrolysis. Ind. Crop. Prod., 81, 11-19.
[5]
Bansal, R.C., Goyal, M. 2005. Activated Carbon Adsorption. Environ.sci.technol(3).
[6]
Bian, J., Peng, F., Peng, X.P., Peng, P., Xu, F., Sun, R.C. 2013. Structural features and antioxidant activity of xylooligosaccharides enzymatically produced from sugarcane bagasse. Bioresour. Technol., 127(1), 236-241.
[7]
Chapla, D., Pandit, P., Shah, A. 2012. Production of xylooligosaccharides from corncob xylan by fungal xylanase and their utilization by probiotics. Bioresour. Technol., 115(5), 215-221.
[8]
Courtin, C.M., Swennen, K., Verjans, P., Delcour, J.A. 2009. Heat and pH stability of prebiotic arabinoxylooligosaccharides, xylooligosaccharides and fructooligosaccharides. Food chem., 112(4), 831-837.
[9]
De Figueiredo, F.C., Carvalho, A.F., Brienzo, M., Campioni, T.S., De, O.-N.P. 2017. Chemical input reduction in the arabinoxylan and lignocellulose alkaline extraction and xylooligosaccharides production. Bioresour. Technol., 228, 164-170.
[10]
Johnson, D., Moore, W., Zank, L. 1961. The spectrophotometric determination of lignin in small wood samples. Tappi, 44(11), 793-798.
[11]
Li, H.Q., Jiang, W., Jia, J.X., Xu, J. 2013. pH pre-corrected liquid hot water pretreatment on corn stover with high hemicellulose recovery and low inhibitors formation. Bioresour. Technol., 153C(2), 292-299.
[12]
Liu, K.X., Li, H.Q., Zhang, J., Zhang, Z.G., Xu, J. 2016. The effect of non-structural components and lignin on hemicellulose extraction. Bioresour. Technol., 214, 755-760.
[13]
Lourençon, T.V., Hansel, F.A., Silva, T.A.D., Ramos, L.P., Muniz, G.I.B.D., Magalhães, W.L.E. 2015. Hardwood and softwood kraft lignins fractionation by simple sequential acid precipitation. Sep. Purif. Technol., 154, 82-88.
[14]
Moniz, P., Ailing, H., Duarte, L.C., Kolida, S., Rastall, R.A., Pereira, H., Carvalheiro, F. 2016. Assessment of the bifidogenic effect of substituted xylo-oligosaccharides obtained from corn straw. Carbohyd. Polym., 136, 466-473.
[15]
Montané, D., Nabarlatz, D., Martorell, A., Vanessa Tornéfernández, A., Fierro, V. 2006. Removal of Lignin and Associated Impurities from Xylo-oligosaccharides by Activated Carbon Adsorption. Ind. Eng. Chem. Res., 45(7), 2294-2302.
[16]
Morrison, I.M. 1974. Lignin-carbohydrate complexes from Lolium perenne. Phytochemistry, 13(7), 1161-1165.
[17]
Moure, A., Gullón, P., Domínguez, H., Parajó, J.C. 2006. Advances in the manufacture, purification and applications of xylo-oligosaccharides as food additives and nutraceuticals. Process Biochem., 41(9), 1913-1923.
[18]
Nabarlatz, D., Torras, C., Garcia-Valls, R., Montané, D. 2007. Purification of xylo-oligosaccharides from almond shells by ultrafiltration. Sep. Purif. Technol., 53(3), 235-243.
[19]
Parajó, J.C., Garrote, G., Cruz, J.M., Dominguez, H. 2004. Production of xylooligosaccharides by autohydrolysis of lignocellulosic materials. Trends Food Sci. Tech., 15(3–4), 115-120.
[20]
Scalbert, A., Monties, B., Lallemand, J.Y., Guittet, E., Rolando, C. 1985. Ether linkage between phenolic acids and lignin fractions from wheat straw. Phytochemistry, 24(6), 1359-1362.
[21]
Shen, R., Li, H.Q., Zhang, J., Xu, J. 2016. Effects of Impurities in Alkali-Extracted Xylan on Its Enzymatic Hydrolysis to Produce Xylo-Oligosaccharides. App. Biochem. Biotechnol., 179(5), 740-752.
[22]
Tan, S.S., Li, D.Y., Jiang, Z.Q., Zhu, Y.P., Shi, B., Li, L.T. 2008. Production of xylobiose from the autohydrolysis explosion liquor of corncob using Thermotoga maritima xylanase B (XynB) immobilized on nickel-chelated Eupergit C. Bioresour. Technol., 99(1), 200-204.
[23]
Vázquez, M.J., Alonso, J.L., Domínguez, H., Parajó, J.C. 2000. Xylooligosaccharides: manufacture and applications. Trends Food Sci. Tech., 11(11), 387-393.
[24]
Vázquez, M.J., Garrote, G., Alonso, J.L., Domínguez, H., Parajó, J.C. 2005. Refining of autohydrolysis liquors for manufacturing xylooligosaccharides: evaluation of operational strategies. Bioresour. Technol., 96(8), 889-896.
[25]
Wang, G., Chen, H. 2013. Fractionation of alkali-extracted lignin from steam-exploded stalk by gradient acid precipitation. Sep. Purif. Technol., 105(5), 98-105.
[26]
Xiao, X., Bian, J., Peng, X.P., Xu, H., Xiao, B., Sun, R.C. 2013. Autohydrolysis of bamboo (Dendrocalamus giganteus Munro) culm for the production of xylo-oligosaccharides. Bioresour. Technol., 138(6), 63-70.
[27]
Yang, R., Xu, S., Wang, Z., Yang, W. 2005. Aqueous extraction of corncob xylan and production of xylooligosaccharides. LWT-Food Sci. Technol., 38(6), 677-682.
[28]
Yuan, Q.P., Zhang, H., Qian, Z.M., Yang, X.J. 2010. Pilot‐plant production of xylo‐oligosaccharides from corncob by steaming, enzymatic hydrolysis and nanofiltration. J. Chem. Technol. Biot., 79(10), 1073-1079.
[29]
Zeng, X., Ma, Y., Ma, L. 2007. Utilization of straw in biomass energy in China. Renew. Sust. Energ. Rev., 11(5), 976-987.
[30]
Zhang, H., Yong, X., Yu, S. 2017. Co-production of functional xylooligosaccharides and fermentable sugars from corncob with effective acetic acid prehydrolysis. Bioresour. Technol., 234, 343-349.
Figure 1. The process of production of XOS from corn stalk Figure 2. Optimization of adsorption conditions Figure 3. Effect of acid precipitation on the purity, yield and color value of XOS Figure 4. The purity, yield and color value of XOS obtained by different ethanol elution concentration Figure 5. Content of individual oligosaccharides in the XOS Figure 6. Components of the XOS obtained by different ethanol elution concentration
Table 1
Six types of activated carbon and their adsorption ratios of XOS Adsorption rate of
Name
Type
Factory XOS (%)
24.37±1.12 AC-1
Particle (AR)
Tianjin Yongda Chemical Reagent Co., Ltd 34.06±0.51
AC-2
Powder (AR)
AC-3
Wood powder
31.07±0.98 Beijing Modern Oriental Fine
28.35±1.32 AC-4
Coconut shell
Chemicals Co., Ltd
particle
38.74±1.01 AC-5
Wet wood powder
AC-6
Dry wood powder
47.65±1.95
Table 2 Comparison of yields of XOS obtained from different pretreatment methods
XOS purity Material
CS
XOS yield
Method
AC-ethanol
Reference (%)
(%)
97.87
81.51
This study
80.00
(Chapla et al., 2012)
93.00
------
(Bian et al., 2013)
AC column Corncob
-----chromatography
Sugarcane
Ethanol
bagasse
precipitation
Almond shells
Ultrafiltration
93.00
58.30
(Nabarlatz et al., 2007)
Corncob
Nanofiltration
74.53
16.93
(Yuan et al., 2010)
Table 3
Comparison of the purity and color value of the obtained XOS
XOS Content（%）
Color value
pH=2
Untreated
pH=2
Untreated
15%
84.66±1.08
67.84±0.92
1562±78
4861±113
30%
97.87±0.66
80.99±1.52
780±59
2132±68
50%
93.36±1.05
79.66±1.34
892±41
2015±56
70%
71.26±1.09
50.06±0.53
4269±106
8965±135
Concentration
Highlights:
The chromophore in enzymatic hydrolyzate seriously degrades the XOS product Lignin in enzymatic hydrolyzate can be efficient removed by acid precipitation High purity, low color value of XOS was obtained from ethanol gradient elution