Tibetan Qingke barley is a cereal crop belonging to Hordeum of the family of Gramineae. It is also called hulless barley or naked barley because of its separation of glumes and bare grains. Its name in Chinese is Qingke, in Titetan is Ne, in English is Tibetan hulless barley and in Latin is Hordeum vulgare Linn. var. nudum (Ma and Xu, 1988; Dai et al., 2012; Dai et al., 2014).

Tibetan Qingke barley is the staple food of Tibetans and the principle raw material of zān ba (an Tibetan food, roasted qingke barley flour). Tibetan Qingke barley has been planted for about 3 500 years in Qinghai-Tibet Plateau, and it is mainly distributed in Tibet, Qinghai, northwest Sichuan, southwest Gansu and northwest Yunan of China (Fu et al., 2000).

1 Tibetan Qingke Barley, the Staple Food and Drink of Tibetans

1.1 Zanba (zān ba)

Zanba is a traditional staple food of Tibetan herdsmen. Zanba, a transliteration of fried noodles in standard Tibetan, is a powder of cooked Tibetan Qingke barley ground by hand mill. It is a daily staple food for Tibetans and they have it for three meals a day. When as a guest of Tibetan compatriots, the host will surely bring fragrant milk tea and highland barley fried noodles, golden yak butter and milky yellow Qula (casein) to you with both hands. The production method of Zanba is to dry the Tibetan Qingke barley (white or purple black) in the sun, fry and grind it without screening. The fried noodles made in this way is edible Zanba, and the Tibetans also mix Tibetan Qingke barley with peas to make Zanba.

Zanba is a bit similar to the fried noodles in northern China. However, the fried noodles in northern China are ground first and then fried, while the Tibetan zanba is first fried and then ground with hull. When eating Zanba, people usually put some yak butter (butter extracted from milk) in a bowl and pour tea, then add some zanba flour, and mix them with hands constantly.

The study shows that the nutritional value of Tibetan staple food zanba is not lower than that of other cereals, and some are higher than others (Figure 1). Zanba made of Tibetan Qingke barley is not only the traditional food of Tibetans, but also an important sacrificial food for Tibetans in religious festivals. People throw zanba in the sacrificial ceremony to show blessing.

Figure 1 Zanba (zān ba), the staple food of Tibetans

1.2 Qingke beer

Qingke beer, called “qiang” in Tibetan language, is made from Tibetan Qingke barley (Figure 2). In Tibetan areas, almost every household can brew Qingke beer. The brewing process is as follows: first of all, we should choose the first-class Tibetan Qingke barley that is full of grains and rich in lustre, wash it and drain the water away. Then put it in a large pan and boil it in water for two hours. Later, the cooked Tibetan Qingke barley is fished out. After air drying, the fermented distiller’s yeast is ground into powder and evenly sprinkled on it and stirred. Finally, put it in the pot and store it in a sealed way. The Qingke beer can be drunk usually after one week or even two to three days if the temperature is high. It is usually best to drink after taking out and adding water for an hour.

Figure 2 Qingke beer, the daily drink for Tibetans

Qingke beer is yellowish in color and sweet in acid. It is called "Tibetan beer", which is an indispensable drink in Tibetan life. It is also the best for celebrating festivals and entertaining guests.

With the development of Tibetan Qingke barley processing industry, Tibetan Qingke barley has become an important raw material of Tibetan Qingke barley biscuits, Tibetan Qingke barley shortbread, Tibetan Qingke barley patches, Tibetan Qingke barley red starter wine, Tibetan Qingke barley vinegar, Tibetan Qingke barley liquor, etc.

The planting area of Tibetan Qingke barley accounts for more than 70% of grain sown area in Tibet. Especially at high altitudes, Tibetan Qingke barley occupies a larger proportion of planting area. Large amounts of rice and wheat can be transported from the inland, but Tibetan Qingke barley is irreplaceable as a food crop in Tibet. Thus, it plays an important strategic role in ensuring the food security in Tibet.

2 Morphological Characteristics of Tibetan Qingke Barley

2.1 Flower spikes

The inflorescences of Tibetan Qingke barley are spikes. The spike-stalk is Z-shaped, generally composed of 15-20 nodal plates, and three spikelets are paratactically inserted on the bulge at the bend of each nodal plate(Figure 3). There are 2 glumes outside the base of each spikelet, which is an important taxonomic trait. The glumes of Tibetan Qingke barley are slender, and the width, tomentum and serrate of the glumes are different in different varieties.

Figure 3 Panicle and spikelet of Tibetan Qingke barley

Floret has internal glume and external glume in 1 piece respectively. The external glume is broad and round, which encircles caryopsis from the side, with awn at the terminal. The internal glume is thin, blunt and keel-shaped. There are 3 stamens and 1 pistil inserted in the floret, and the pistil is a dichotomous penniform stigma connected with an ovary. There are 2 pieces of lodicules at the base between ovary and external glume. The flowering of Tibetan Qingke barley is achieved by water absorption and expansion of lodicule cells to burst through the external glume.

2.2 Grain

In botany, the grain of Tibetan Qingke barley is bare grain and completely separated from glume. The grain length of Tibetan Qingke barley is 6~9 mm, width is 2~3 mm, and the shape includes spindle and ellipse, etc. The surface of Tibetan Qingke barley grain is smoother than that of hulled barley. It has a variety of colors, such as yellow, greyish green, green, blue, red, white, brown, purple, black and so on. The Tibetan Qingke barley grain is developed from the whole ovary after fertilization, and in production, the fruit of Tibetan Qingke barley is the seed (grain), also called caryopsis. Seeds consist of three parts: embryo, endosperm and cortex. There is no epiblast in the embryo, and there are 4 pieces of differentiated leaf primordia in the embryo. The endosperm contains more starch and less gluten, and the grain contains 45%~70% of starch and 8%~14% of protein.

2.3 Root

The root system of Tibetan Qingke barley belongs to fibrous root system, which is composed of primary root and secondary root. The primary roots grow from the embryo of the seed, and the number of primary roots is usually 5~6 but can be as high as 7~8(Figure 4). Under good soil conditions, the primary root depth of Tibetan Qingke barley sowed in autumn can reach 60~70 cm when overwintering. At the late stage of growth, the primary root depth of some varieties can reach about 200 cm. The number of primary roots is closely related to the seed size and seed vigor. The seeds are large and well-stacked with strong vitality and a great number of primary roots, and the seedlings are also strong. Conversely, seeds are thin and not full with small thousand seed weight, which produce less primary roots and the seedlings are weak and thin. Primary root plays an important role in absorbing and supplying seedling nutrition during seedling stage from seed germination to root formation.

Figure 4 Seed of Tibetan Qingke barley

2.4 Stem

The stems of Tibetan Qingke barley are erect and hollow, consisting of several nodes and internodes, which can be divided into aboveground stem nodes and underground stem nodes. The underground stem nodes usually have 7~10 densely packed non-growing internodes, forming tillers. The aboveground stem nodes usually have 4~8 obviously elongated internodes, forming stems. The height of the plants is generally 80 cm~120 cm, and the plant height of short stem varieties is 60 cm~90 cm. The diameter of the stems is 2.5 mm~4 mm.

The stem of Tibetan Qingke barley in the early stage of maturity is an upright cylinder with a smooth and green surface. In the late stage of maturity, the color turns yellow, and there are a few varieties with purple stems. The vascular bundles of stem nodes are dense and interlaced with each other, forming solid diaphragm. The lower and upper internodes of the stems are mostly surrounded by sheaths.

There are five internodes in the aboveground stems of common varieties of Tibetan Qingke barley and three internodes in short stem varieties. The internodes of basal part of stems are short and gradually lengthen from bottom to top. Whether the first and the second internodes of basal part of stems are short or not is closely related to their lodging resistance. In cultivation, the length of the base internode should be shortened as much as possible to promote the robust development of internodes, and the lower panicle internodes should be appropriately elongated. The thickness of stem wall also has a certain relationship with lodging resistance. If the stem wall is thick, then the elasticity is good, and the stem focus will move down, which may improve the lodging resistance. 

2.5 Leaf

The leaves of Tibetan Qingke barley are thick and wide. They are borne on stem nodes. The top leaf is called flag leaf. The leaves of Tibetan Qingke barley can be divided into three types according to their morphology and function: complete leaf, incomplete leaf and metamorphosis leaf. The leaves of Tibetan Qingke barley are the main organs for photosynthesis. Each complete stem usually has 4 to 8 leaves, and the number of leaves in the main stem varies with the type of cultivar. Winter and semi-winter varieties have more leaves, but spring varieties are less. The number of leaves in the main stem is also closely related to the environmental conditions of its growth and development. When there is sufficient fertilizer and water, the number of leaves in the main stem increases.

3 Nutritional Characteristics of Tibetan Qingke Barley

3.1 β-glucan

According to the information of the Academy of Agricultural and Animal Husbandry Sciences of Tibet Autonomous Region (Qiang, 2009, Tibet Science and Technology, (2): 22-23), Tibetan Qingke barley is the highest β-glucan triticeae crop in the world. The average content of β-glucan is 6.57%, and the average content of Tibetan Qingke barley 25 of excellent varieties can reach 8.6%, 50 times the average content of wheat. β-glucan prevents colon cancer by reducing the contact of intestinal mucosa with carcinogens and indirectly inhibiting the role of carcinogenic microorganisms; prevents cardiovascular disease by lowering blood lipid and cholesterol synthesis; and prevents diabetes by controlling blood sugar (Qiao et al., 2012, Jiangsu Agricultural Science, 40(1): 4-7). β-glucan can improve the body's defense ability and regulate physiological rhythm.

3.2 Dietary fiber

The total effective fiber content of Tibetan Qingke barley is 16%, of which the insoluble effective fiber is 9.68%, 8 times that of wheat, and the soluble effective fiber is 6.37%, 15 times that of wheat. Dietary fiber is considered as a scavenger of digestive system because of its good effect of clearing intestines and defecating toxins (Yu et al., 2008; Niu et al., 2011).

3.3 Amylopectin

Tibetan Qingke barley starch generally contains 74%~78% amylopectin, and the new variety of Tibetan Qingke barley with 25 amylopectin cultivated by the Academy of Agriculture and Animal Husbandry of Tibet Autonomous Region has reached or closed 100% (Zang et al., 2004). Amylopectin contains a large amount of gel mucus, which is weakly alkaline after heating. It has an inhibitory effect on excessive gastric acid and can alleviate and protect lesions.

3.4 Rare ingredients

Tibetan Qingke barley contains a variety of rare ingredients that are beneficial to human health. Tibetan Qingke barley flour contains thiamine (vitamin B1) 0.32 mg/100 g, riboflavin (vitamin B2) 0.21 mg/100 g, niacin 3.6 mg/100 g, and vitamin E 0.25 mg/100 g. These substances have positive effects on promoting human health and development. It also contains some mineral elements, such as calcium, phosphorus, iron, copper, zinc and trace elements, like selenium. Selenium is one of the essential trace elements identified by the World Health Organization (WHO), and the only anti-cancer and anti-cancer element identified by the WHO.

4 Where does Tibetan Qingke Barley Come From?

Tibetan Qingke barley is mainly planted in Tibet, Qinghai, Sichuan, Yunnan and other places. It has been planted as the main grain on the Qinghai Tibet Plateau for 3 500 years. Barley might be one of the earliest domesticated crops (Badr et al., 2000). Now most barley was used for animal feed, malt, health food, etc. (Newman and Newman, 2006). Is Tibetan Qingke barley the same as cultivated barley?

The origin and domestication history of Tibetan Qingke barley have been controversial at home and abroad. At present, there are two main views: one is that Tibetan Qingke barley is native wild barley in Tibet, was domesticated from six-row wild barley; the other is that Tibetan Qingke barley originated from barley in the Fertile Crescent area of Western Asia (von Bothmer et al., 1990; Konishi, 2001; Tanno and Takeda, 2004).

Where did Tibetan Qingke barley actually originate? And how did Tibetan Qingke barley get into Tibet? There has been no final conclusion in the academic circles.

Authors’ Contributions

LJH was responsible for collecting literature, revising and supplementing manuscripts; QTY was responsible for translating and revising manuscripts in English; FXJ was responsible for conceiving papers and writing, revising and finalizing manuscripts. All the authors read and agreed to the final text.

Acknowledgment

The study was granted by the Cuixi Innovation Fund for Research and Development Project funded by Cuixi Academy of Biotechnology. The authors would like to thank Zoey Wang, Gina Wang, Shirley Yu, Amber Xu, Irene Zhuo, Sophie Zhou, Yuki Dong for their participation in the English translation and proofreading of this manuscript.

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