ReviewHighland barley: Chemical composition, bioactive compounds, health effects, and applications
Graphical abstract
Introduction
Highland barley (Hordeum vulgare, Poaceae), one of the variations of the Gramineae wheat family according to plant taxonomy, is also classified as hulled and hull-less barley or highland barley (HB). It is also known as “Qingke” in Chinese and “Ne” in Tibetan. Green HB can be divided into two-row naked barley, four-row naked barley, and six-row naked barley. Four- and six-row naked barleys are primarily used in China. Six-row naked barley is primarily cultivated in Tibet, and four-row naked barley is primarily cultivated in Qinghai. According to its color, it can be divided into white, black, and purple barley (F. Zhang, Yang, Zhao, & Kan, 2003). HB is distributed in the Tibet Autonomous region, covering the Qinghai, Sichuan, Gansu, and Yunnan provinces of China (about 0.27 million hectares of planting area). Tibet and Qinghai are the major HB-producing areas with up to more than 80% of crop-planting area (Feng, Wang, & Wang, 2018). According to records from the Tibet and Qinghai Prefectures, these places accounted for approximately 80% of the whole HB output in 2018, with 777 200 and 95 200 tons, respectively (T. Guo, Horvath, Chen, Chen, & Zheng, 2020). HB is a very important plateau cereal crop. It has the characteristics of early maturity, cold tolerance, stable yield, and wide adaptability. China owns 77% of the total HB genetic resources in the world (Lu, Ding, Lu, Shao, & Huang, 1995). Molecular data indicate that Tibetan HB could be domesticated under unique natural-selection criteria compared with planted barley and they have equipped to harsh plateau environments (X. Zeng et al., 2015). HB varieties have greater nutritional content than hulled barley varieties because they contain high proteins, lipids, and soluble dietary fibers (SDFs) (G. Zhang, Junmei, & Jinxin, 2002). HB is characterized by nutritional functions superior to those of regular cereals and is becoming one of humanity's promising crops; thus, HB has attracted increased attention in recent years (Bhatty, 1986). HB has a unique chemical composition, such as high β-glucan content, high dietary fiber content, and high feeding value compared with many cereal crops (C.P. Wang et al., 2011). Moreover, HB is extremely rich in nutritional functional ingredients, including β-glucan, arabinoxylan, and polyphenols (Šimić et al., 2019), which are primarily accountable for its antioxidant, anticancer, and antibacterial properties (J. Song, Chen, Wei, & Liu, 2020; Fengmei Zhu, Du, & Xu, 2015). HB is used for food in many Eastern countries, including Pakistan, Afghanistan, Japan, Nepal, and China. Breeders in Western countries are breeding functional HB for the food industry. Furthermore, HB starch has a low glycemic index (GI) (39.4–47.5) and less than 55, so it can be perceived as an appropriate staple food for diabetics (Moza & Gujral, 2017). Regular daily intake of whole HB (WHB) flour is associated with low risks of chronic diseases, such as diabetes, colonic cancer, hyperlipidemia, high blood pressure, and gallstones (Idehen, Tang, & Sang, 2017). In contrast to the abundant previous critical reviews on the structure, properties, and modifications of common barley starch (Punia, 2019, Punia, 2020; Fan Zhu, 2017), information about the chemical composition and health-promoting values of HB is scarce. Accordingly, this review summarizes the current knowledge on the chemical composition of HB and health impacts based on in vitro and in vivo findings.
Section snippets
Proximate composition
There is a great diversity in the chemical composition (fat, protein, ash, starch and crude fiber) of HB grain (Table 1). Systematic analysis of HB varieties showed that HB flour had a lower level of protein and β-glucan and higher levels of lipid, crude fiber, and ash than waxy or high-amylose HB. A previous study showed that HB varieties have better nutritional value as they include further proteins, lipids, crude fiber and β-glucan (Kinner et al., 2011). Compared with other cereals, HB and
β-glucans
β-glucan is a glucopyranose-containing polysaccharide located in the endosperm cell walls and aleurone layer of barley grain (Lopez-Sanchez et al., 2016, Razzaq et al., 2016). The aleurone layer of barley contains 26% β-glucan and 67% arabinoxylan, whereas endosperm cell wall contains about 75% β-glucan and 20% arabinoxylan. Cereal β-glucans are linear homopolysaccharides comprising β-Dglucopyranosyl units primarily with (1 → 4) linkages and occasionally with single (1 → 3) linkages. β-glucan
In vitro models
Diverse in vitro tests have been used to assess the bioactivities of HB. The experimental designs and key findings of these studies are summarized in Table 2.
Food uses of HB
HB is an irreplaceable staple food for farmers and herdsmen in Tibetan areas. It is also an important raw material for the feed-processing and brewing industries in Tibetan areas. Traditional HB food primarily includes Zanba and sweet fermented grains with simple processing technology. HB is rich in nutrients, such as protein, amino acids, minerals, vitamins, and dietary fiber (K. Zhang et al., 2019). It is a food crop with dietary functions. It is also the main raw material for the beer
Conclusions and future research directions
HB has a unique composition of various phytochemicals, such as β-glucan, polyphenols (phenolic acids, flavonoids, and anthocyanins), polysaccharide (arabinoxylan), phytosterols (β-sitosterol and campesterol), and tocols (β-tocotrienol, α-tocotrienol, β-tocopherol, and α-tocopherol). HB is also a source of some minerals (Cu, Zn, Fe, Se, and Mg), vitamins (E and B), and dietary fiber. Hence, HB can supplement certain main cereals including wheat and rice for well-balanced nutrition. As a result
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
The research is funded by National Natural Science Foundation of China (Grant No. 31771900), the Key Projects of National Science &Technology Pillar Program (Grant No. 2018YFD0401004), and the Provincial Key R&D Program of Qinghai (Grant No. 2021-QY-214).
References (284)
- et al.
Issues surrounding health claims for barley
The Journal of Nutrition
(2008) - et al.
Hydrothermal and β-glucanase effects on the nutritional and physical properties of starch in normal and waxy hull-less barley
Animal Feed Science and Technology
(1999) - et al.
Effects of high β-glucan barley on visceral fat obesity in Japanese individuals: A randomized, double-blind study
Nutrition
(2017) - et al.
Effect of microwave roasting on antioxidant and anticancerous activities of barley flour
Journal of the Saudi Society of Agricultural Sciences
(2016) - et al.
Whole-grain diets reduce blood pressure in mildly hypercholesterolemic men and women
Journal of the American Dietetic Association
(2006) - et al.
Modulation of vascular function and anti-aggregation effect induced by (1→ 3)(1→ 6)-β-d-glucan of Saccharomyces cerevisiae and its carboxymethylated derivative in rats
Pharmacological Reports
(2017) - et al.
Risk factors for overweight and obesity: Results from the 2001 National Health Survey
Public Health
(2007) - et al.
Obese-type gut microbiota induce neurobehavioral changes in the absence of obesity
Biological Psychiatry
(2015) - et al.
Modeling of cooked starch digestion process using recombinant human pancreatic α-amylase and maltase-glucoamylase for in vitro evaluation of α-glucosidase inhibitors
Carbohydrate Research
(2015) - et al.
Tocols in hull-less and hulled barley genotypes grown in contrasting environments
Journal of Cereal Science
(2004)