Elsevier

Carbohydrate Polymers

Volume 249, 1 December 2020, 116813
Carbohydrate Polymers

Structural characteristics and rheological properties of alkali-extracted arabinoxylan from dehulled barley kernel

https://doi.org/10.1016/j.carbpol.2020.116813Get rights and content

Abstract

Arabinoxylan (BIF-60) was isolated from barley water-insoluble fiber (BIF) by ethanol precipitation at 60 % (v/v). BIF-60 was composed of xylose (48.5 %) and arabinose (30.3 %). Its average molecular weight was 1360 kDa. Methylation and 1D/2D NMR analysis showed that BIF-60 possessed β-(l→4)-xylan as backbone, comprised of un-substituted (1,4-linked β-Xylp, 56.9 %), mono-substituted (1,2,4-linked and 1,3,4-linked β-Xylp, 22.1 %) and di-substituted (1,2,3,4-lin4ked β-Xylp, 18.4 %) xylose units, as well as other residues (T-Araf-(1→, T-Xylp-(1→, →5)-Araf-(1→, →2)-Araf-(1→, →3)-Araf-(1→ and →4)-Glcp-(1→). BIF-60 exhibited shear-thinning behaviour, low gel stability and weak gelling ability at high concentrations. This work provides a theoretical and experimental basis for molecular structure and properties of the alkali-extracted arabinoxylan from barley kernel, which could guide further functional research and application of barley-derived arabinoxylan.

Introduction

Barley (Hordeum vulgare L.) is widely cultivated throughout the world, ranking its total production of fourth after maize, rice and wheat in grain crops (Schulte et al., 2009). Besides being used in feeding, malting, brewing, and distilling industries, barley offers nutrition and many health benefits (Baik & Ullrich, 2008). Recently, non-starch polysaccharides in barley grain endosperm cell walls (Yangcheng, Gong, Zhang, & Jane, 2016; Zhang et al., 2018), such as β-glucan and arabinoxylan, have attracted a large amount of attention due to their high dietary fiber contents and health-promoting benefits (Ahmad, Anjum, Zahoor, Nawaz, & Ahmed, 2010). Barley enriched in β-glucan could satisfy the daily requirement of dietary fiber (Zhu, Du, & Xu, 2015). Although arabinoxylan is one of the major dietary fiber in barley kernel (accounting for 3–7 % of endosperm cell walls), it has received much less research attention than β-glucan due to its structural complexity and low solubility (Han, 2000; Izydorczyk & Dexter, 2008; Kim, Hong, & Shin, 2017; Köhnke, Pujolras, Roubroeks, & Gatenholm, 2008; Lazaridou, Chornick, Biliaderis, & Izydorczyk, 2008).

Arabinoxylan is a kind of water-soluble hemicellulose from cell wall of various cereals, including barley, sorghum, oat, wheat, millet, rye, maize and rice, etc. Barley-derived arabinoxylan has been used to promote bread properties in baking industry (Buksa & Krystyjan, 2019; Koegelenberg & Chimphango, 2017) and develop novel arabinoxylan films in packaging industry (Gröndahl, Gustafsson, & Gatenholm, 2006; Stepan et al., 2013; Stepan, Ansari, Berglund, & Gatenholm, 2014). In recent studies, barley-derived arabinoxylan has shown many biological activities, such as prebiotic effects (Tian et al., 2019), improving intestinal health (Kamiya et al., 2014), modulating immune responses (Badr El-Din, Ali, Alaa El-Dein, & Ghoneum, 2016; Song, Baik, Hong, & Sung, 2016), assisting in treating tumors and cancers (Ghoneum, Badr El-Din, Ali, & El-Dein, 2014; Golombick, Diamond, Manoharan, & Ramakrishna, 2016), regulating blood sugar (Hartvigsen et al., 2013; Neyrinck et al., 2018) and reducing plasma cholesterol (Gunness et al., 2016). It has been reported that structural features and solution properties of barley-derived arabinoxylan had great influence on its functional properties (Damen et al., 2011; Mendis, Leclerc, & Simsek, 2016; Sun, Cui, Gu, & Zhang, 2011). The chemical components and structural properties of arabinoxylans vary with different sources. Correia et al. (2011) found that the backbone of wheat bran-derived arabinoxylan consisted of 1,4-linked β-xylopyranosyl units with terminal l-arabinofuranosyl substituted at O-2 and/or O-3, sometimes decorated at O-2 with 4-O-methyl-d-glucuronic acid or ferulical esterified at the Araf side chain or extensively acetylated. The gelation ability of arabinoxylan plays an important role in physiological effects of consuming soluble fiber (Sletmoen & Stokke, 2013). Keogh et al. (2003) found that the quantity of arabinoxylan was not the main contributor to its hypocholesterolemic effects, while the molecular weight and viscosity of arabinoxylan were the critical factors in the glycemic index (GI) tract. Nevertheless, a systematic research on chemical components, structural features and rheological properties of arabinoxylan from barley kernel, which is considered a novel renewable resource, remains scarce.

In our previous work, barley kernel was pretreated and extracted with hot water. After removing the aqueous extract, barley water-insoluble fiber (BIF) was obtained and has been shown to improve the intestinal health (Li et al., 2019). This work aims to elucidate the chemical compositions, structure characteristics and rheological properties of the alkali-extracted arabinoxylan in barley kernel.

Section snippets

Materials and reagents

Dehulled barley kernel was purchased from Dongtai, Jiangsu Province, China. Thermostable α-amylase and porcine pancreatin were purchased from Aladdin (Shanghai, China). T-series dextran standards with various molecular weight (1.0 × 104, 2.0 × 104, 5.0 × 104, 7.0 × 104, 5.0 × 105 and 2.0 × 106 Da) and glucose (180 Da) were offered by Pharmacia Corp. (Uppsala, Sweden). Monosaccharide and derivatives standards (L-fucose, L-rhamnose, D-arabinose, D-galactose, D-mannose, D-ribose, D-fructose,

Physicochemical properties of BIF-60

Table 1 summarizes the yields, chemical components and monosaccharide composition of BIF-60. Main component of BIF-60 was neutral sugar and no starch was detected, which is consistent with the report of Pitkänen, Tuomainen, Virkki, Aseyev, and Tenkanen (2008). Small amounts of protein (2.5 %) and ash (2.0 %) were observed. HPAEC-PAD analysis indicated that BIF-60 mainly consisted of xylose (48.5 ± 2.2 %), arabinose (30.3 ± 0.9 %) and trace amount of glucose (2.7 ± 0.3 %). Molar ratio of

Discussion

Arabinoxylan, as a common source of dietary fiber, can not only enhance probiotic values, but also improve Type 2 diabetes, gastrointestinal cancer and cardiovascular disease in human bodies (Holman, Young, & Gadsby, 2015). The health benefits of arabinoxylan are related to its structural features and high viscosity (Schulze et al., 2007; Wang et al., 2020). Nie et al. (2017) reported that highly branched arabinoxylan composed of xylose (60 %) and arabinose (32 %) might improve the symptoms of

Conclusions

In this work, an alkali-extracted arabinoxylan (BIF-60) was obtained from dehulled barley kernel, and its structural features suggested that a highly-branched β-(l→4)-xylan existed in BIF-60, including un-substituted (1,4-linked β-Xylp, 56.9 %), mono-substituted (1,2/3,4-linked β-Xylp, 22.1 %) and di-substituted (1,2,3,4-linked β-Xylp, 18.4 %) xylose units via (1→4) linkages. Barley-derived arabinoxylan solution transferred from near-Newtonian fluid to non-Newtonian fluid when concentration

CRediT authorship contribution statement

Lin-Yan Li: Investigation, Writing - review & editing. Yu-Xiao Wang: Investigation, Visualization. Ting Zhang: Investigation. Jian-Fang Zhang: Investigation. Meng Pan: Investigation. Xiao-Jun Huang: Supervision. Jun-Yi Yin: Supervision, Funding acquisition, Writing - review & editing. Shao-Ping Nie: Resources, Supervision, Funding acquisition.

Declaration of Competing Interest

The authors declare no competing financial interests.

Acknowledgements

The financial supports from National Natural Science Foundation of China (31871755), National Science Fund for Distinguished Young Scholars of China (31825020), Scientific and Technological Innovation Foundation for Distinguished Young Scholars of Jiangxi Province of China (20192BCB23005), and Research Project of State Key Laboratory of Food Science and Technology, Nanchang University (SKLF-ZZB-201921) were gratefully acknowledged.

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