Читать книгу Quinoa - Atul Bhargava - Страница 13

The nutritional excellence of quinoa has been known since ancient times in the Inca Empire. The importance that quinoa could play in nutrition has been emphasized not only in developing countries but also in the developed world. Quinoa seeds have a higher nutritive value than most cereal grains and contain high-quality protein and large amounts of carbohydrates, fat, vitamins and minerals. Perisperm, embryo and endosperm are the three areas where reserve food is stored in quinoa seed (Prego et al., 1998).

The mean protein content reported for quinoa grain is 12–23% (González et al., 1989; Koziol, 1992; Ruales and Nair, 1994a, 1994b; Ando et al., 2002; Karyotis et al., 2003; Abugoch, 2009), which is higher than that of barley, rice or maize, and is comparable to that of wheat (USDA, 2005; Abugoch, 2009). Moreover, the essential amino acid balance is excellent because of a wide range of amino acids, with higher lysine (5.1–6.4%) and methionine (0.4–1%) contents (Prakash and Pal, 1998; Bhargava et al., 2003, 2006a; Abugoch, 2009). Quinoa protein can supply around 180% of the histidine, 274% of the isoleucine, 338% of the lysine, 212% of the methionine + cysteine, 320% of the phenylalanine + tyrosine, 331% of the threonine, 228% of the tryptophan and 323% of the valine recommended by FAO/WHO/UNU in protein sources for adult nutrition (Vega-Gálvez et al., 2010). Starch is the most important carbohydrate in quinoa grains, making up approximately 58.1–64.2% of the dry matter (Repo-Carrasco et al., 2003). Quinoa starch consists of two polysaccharides: amylose and amylopectin. The amylase content of quinoa starch varies between 3% and 20%, while the amylose fraction of quinoa starch is quite low (Abugoch, 2009). The starch of quinoa is highly branched, with a minimum degree of polymerization of 4600 glucan units, a maximum of 161,000 and a weighted average of 70,000 (Praznik et al., 1999). Granules of quinoa starch have a polygonal form, with a diameter of 2 μm, being smaller than starch of the common grains (Vega-Gálvez et al., 2010). The total dietary fibre of quinoa is near that of cereals (7–9.7% by difference, db), and the soluble fibre content is reported between 1.3% and 6.1% (db) (Ranhotra et al., 1993; USDA, 2005).

The ash content of quinoa (3.4%) is higher than that of rice (0.5%), wheat (1.8%) and other traditional cereals (Cardozo and Tapia, 1979). Quinoa grains contain large amounts of minerals like Ca, Fe, Zn, Cu and Mn (Repo-Carrasco et al., 2003). Calcium (874 mg/kg) and iron (81 mg/kg) in the seeds are significantly higher than most commonly used cereals (Ruales and Nair, 1992). Minerals like P, K and Mg are located in the embryo, while Ca and P in the pericarp are associated with pectic compounds of the cell wall (Konishi et al., 2004). The abundant mineral content makes the grains valuable for children and adults who can benefit from calcium for bones and from iron for blood functions (Konishi et al., 2004).

The oil content in quinoa ranges from 1.8 to 9.5%, with an average of 5.0–7.2% (DeBruin, 1964; Koziol, 1990) that is higher than that of maize (3–4%). Quinoa oil is rich in essential fatty acids such as linoleate and linolenate (Koziol, 1990) and has a high concentration of natural antioxidants like α-tocopherol and γ-tocopherol (Repo-Carrasco et al., 2003). The antioxidant activity of quinoa could be of particular interest to medical researchers and needs more attention (Bhargava et al., 2006a).

Few reports are available on the vitamin content of quinoa grain. Ruales and Nair (1992) reported appreciable amounts of thiamin (0.4 mg/100 g), folic acid (78.1 mg/100 g) and vitamin C (16.4 mg/100 g). Koziol (1992) gave riboflavin and carotene content as 0.39 mg/100 g and 0.39 mg/100 g respectively, and concluded that quinoa contains substantially more riboflavin (B₂), α-tocopherol (vitamin E) and carotene than wheat, rice and barley. In a 100 g edible portion, quinoa supplies 0.20 mg vitamin B₆, 0.61 mg pantothenic acid, 23.5 μg folic acid and 7.1 μg biotin (Koziol, 1992). Recent reports have also confirmed that quinoa is rich in vitamins A, B₂ and E (Repo-Carrasco et al., 2003).

However, several antinutritional substances such as saponins, phytic acid, tannins and protease inhibitors have been found in quinoa seed, which can have a negative effect on the performance and survival of monogastric animals when it is used as the primary dietary energy source (Vega-Gálvez et al., 2010).

The leaves of quinoa contain ample amount of ash (3.3%), fibre (1.9%), vitamin E (2.9 mg α-TE/100 g) and Na (289 mg/100 g) (Koziol, 1992). Prakash et al. (1993) reported that leaves have about 82–190 mg/kg of carotenoids, 1.2–2.3 g/kg of vitamin C and 27–30 g/kg of proteins. A recent study on the leaf quality parameters in quinoa has shown that the leaves contain ample amount of carotenoids (230.23–669.57 mg/kg), which was higher than that reported for spinach, amaranth and C. album (Gupta and Wagle, 1988; Prakash and Pal, 1991; Shukla et al., 2003; Bhargava et al., 2006b, 2007).