Barley genotypes are classified as hulled and hull-less. The hull-less variety has better nutritional value compared to the hulled one [120, 128]. Hull-less barley generally has higher amino acid, total protein, and digestible energy contents compared to hulled barley [129–131]. Barley can be described as a perfect source for obtaining β-glucans and complex carbohydrates, two critical constituents of dietary fiber [132]. Barley grain contains 60%–80% carbohydrates, 9%–13% protein contents, 1%–2% fat, and 10%–15% water [132, 133]. The most limiting essential amino acid of cereal species, namely lysine, is found in higher levels in some cultivars [129–131]. Starch is the carbohydrate to be found most plentifully in barley grain, its levels varying between 62% and 77% in terms of the dry grain weight [132, 134]. The dietary fiber content of barley is 14%–25%. Arabinoxylan content is 4%–11%, while the β-glucans, cellulose, and lignin contents are 3%–7% [135–138]. Barley is rich in vitamins, particularly B vitamins, and it also has valuable mineral contents, especially trace minerals [139, 140]. Apart from β-glucans, the compounds in barley such as tocotrienol, phytoestrogens, lignans, polyphenols and phytic acid have been associated with health benefits [140, 141].
Epidemiological studies show that regular barley consumption has the possible ability of lowering the risks of various chronic diseases including colon cancer [111, 142, 143], chronic heart disease [111, 118, 144, 145], gallstones [111, 146, 147], and high blood pressure [111, 148]. There are reports of the role of barley in the maintenance of colon health [111, 149], the induction of stimulation of the immune system [111, 150], and immuno-enhancement [111]. In addition, barley consumption provides a protective effect against toxins, diabetes mellitus, and neurological problems such as Alzheimer disease [111, 151, 152].
3.2.5 Flaxseed
Flaxseed comes from Linum usitatissimum L., which is commonly called the flax plant and belongs to the family Linaceae [153–155]. It is also called linseed [156, 157], and it is native to Western Asia and Mediterranean areas [153–155]. Today, however, it is grown in over 50 countries, mainly in areas of the northern hemisphere. Canada produces and exports the largest quantity of flaxseed in the world [153, 158], and India, the United States, China, and Ethiopia are the other major countries that grow flax plant for its seeds [158–161]. In the world, India ranks first in terms of flaxseed cultivation area and third in terms of flaxseed production [158, 160, 161]. The first known evidence of flax cultivation is the use of the flax plant in the manufacture of linen fabric in eastern Turkey in 6000 BC [162, 163]. Flaxseed is used from past to present to obtain linseed oil for industrial purposes such as linoleum, paint, varnish, cosmetics, and ink production [157, 164, 165]. While flax fiber is valuable in producing high-quality linen clothing, milled or ground flaxseed is commonly used as a component of fertilizers and in foodstuffs for animals [162, 163]. Flaxseed is also of value in functional foods because it has several beneficial pharmaceutical and nutritional properties [157, 166].
The seeds of flax plants are oval-shaped and flat; their tips are pointed. They range in color from dark shades to yellow [160, 162]. Seeds are about 3.0–6.4 mm long, 1.8–3.4 mm wide, and 0.5–1.6 mm thick [155, 162]. Embryos account for 55% of hand-cut flaxseed’s overall weight, while the seed coat and endosperm represent 36% of overall weight. Finally, the embryo axis accounts for 4% [160, 162]. Oily flaxseeds are generally larger than fibrous flaxseeds [155, 167]. Flaxseeds possess a chewy, crisp texture and they have a pleasing nutty flavor [155, 168].
The chemical composition of flaxseed depends upon the environmental conditions in which the flax is grown and differs significantly among varieties [169]. The Canadian Grain Commission reported that one variety of Canadian flaxseed had a composition including 41% fat, 20% protein, 28% total dietary fiber, 7.7% moisture, and 3.4% ash [170]. Minor components in flaxseed are vitamins (A, B, D, E) and minerals (cadmium, selenium, etc.), cyanogenic glycosides, trypsin inhibitor, phytic acid, lignans, lina-tine, polyphenols, and cyclolinopeptides (CLs) [162, 170, 171]. Flaxseed includes 8–10 g/kg total polyphenols, about 5 g/kg esterified polyphenols, and 3–5 g/kg etherified polyphenols [172]. It constitutes the richest available resource for obtaining n-3 fatty acid, also known as alpha-linolenic acid. This particular acid accounts for roughly 55% of the total fatty acids that are present in the seeds of this plant [157, 163]. Alpha-linolenic acid may be metabolized by certain types of enzymes in the human intestine to docosahexaenoic acid and eicosapentaenoic acid [157, 173]. It was established that increasing the intake of long-chain polyunsaturated fatty acids in one’s diet, and particularly one’s intake of docosahexaenoic and eicosapentaenoic acids, can reduce disease risks [157, 174].
Studies report that flaxseed has a unique potential in preventing diseases including cardiovascular diseases, rheumatoid arthritis, osteoporosis, constipation, and various cancers (colon, breast, prostate cancers) and that it has positive effects on the immune system. Although the seeds of flax plants contain cyanogenic glycosides, linatine, and phytic acid, which negatively affect nutritional absorption, researchers have shown that no apparent negative results are experienced from the daily intake of 50 g of flaxseed [160].
3.2.6 Psyllium
Psyllium is present in seeds of plants of the genus Plantago, a genus that contains about 200 species growing widely within the world’s moderate climatic regions [175, 176]. It is a crop that has historically been utilized by people for millennia. For example, it was reported to have been used by the Chinese in 250 BC for both the plant itself and for the psyllium of the seeds. Although Plantago plants are harvested around the world, only the species Plantago ovata Forsk and Plantago psyllium are being commercially produced as main seasonal crops in various American, European, and South Asian countries as a result of their seed mucilage, pharmaceutical, cosmetic, and food-grade qualities [177]. From past to present, psyllium has traditionally been harvested for use as a fiber supplement for dietary support, as well as a laxative agent [175, 178]. Currently, psyllium has been utilized in the landscape industry and in domestic and industrial wastewater treatment [176, 178–180]. Psyllium husk is used in the pharmaceutical industry as a medically bioactive polysaccharide; it is also utilized for treating various diseases, as will be described below in detail [180, 181]. Furthermore, it has valuable roles within the food industry, specifically in the creation of gels and for increasing consistency and stability [180, 182]. The species called Plantago ovata Forsk is widely grown in Iran and India [176, 180]. India leads the global market in both producing and exporting this product. Approximately 39,000 tons of psyllium seeds are produced each year in India, and 85% of psyllium seeds are supplied to the world market annually by India [176, 183, 184]. Blond psyllium, ispa-ghula, Indian plantago, and spagel are various common names for Plantago ovata Forsk [176, 180]. Psyllium plants grow to 15 cm in length. They are covered with fuzzy hairs, white in color, which grow at right angles to the leaves and stems. Seeds have small dimensions (1.5–2 cm) with brown or reddish brown coloring, and they possess large amounts of albuminous substances and mucilage. Seeds undergo drying and crushing, a process by which psyllium husk is obtained [177]. The latter constitutes the major product of psyllium seed. Remaining seed materials are often used in food products for animals [176, 183, 184].
The various possible applications of psyllium in pharmaceutical fields and in functional food production can be explained as being due to the unique chemical properties of psyllium husk. Psyllium husk has 6.83% moisture, 4.07% total ash, 2.62% soluble ash, 0.94% protein, and 84.98% total carbohydrate on a dry basis. As seen, the main components of psyllium husk are polysaccharides [178]. Psyllium husk can be considered as a neutral arabinoxylan containing 21.96% arabinose, 56.72% xylose on a molar basis, and some other sugar residues [178, 185, 186]. The monosaccharide composition of psyllium husk consists of rhamnose (1.5%), galactose (3.76%), glucose (0.64%), and mannose (0.40%) other than arabinose and xylose. Psyllium husk contains the lowest amount of phosphorus (140 μg/g) and magnesium (150 μg/g) while the major mineral substances of psyllium husk are potassium (8500 μg/g) and calcium (1500 μg/g) [178].
The psyllium polysaccharides mentioned above have been associated with the treatment of many diseases
