Analysis of the main nutritional components will give a greater understanding of this food.
Main composition of quinoa seeds
The main nutritional components of quinoa are protein, carbohydrates and fat. These are compared with main stream cereals and legumes.
Proteins
The protein content of quinoa is higher than in cereals and ranges from 14-18% of the seed, as compared to maize (10%), rice (8%) and wheat (14%) (Table 1).
The metabolically active proteins, such as albumins and globulins, are found primarily in the embryo/germ of the seed. The germ accounts for 25-30% of the weight of a quinoa seed, 10% of a grain of maize and 2-3% of the grains of rice and wheat. Consequently, higher concentrations of albumins and globulins (44-77% of total protein) are found in quinoa seeds.
Gluten is a protein complex formed by interactions between prolamins and glutelins in cereals other than wheat. There is very little prolamin (0.5-7.0%) in quinoa to enter into the reaction that forms gluten. Therefore, it may be considered gluten free.
NB: At present, foods labelled gluten free in Australia and New Zealand must not contain any detectable gluten under the Food Standards administered by Food Standards Australia New Zealand (FSANZ). Claims to the effect that a food has a low gluten content should not be made unless the food contains no more than 20mg gluten per 100g of the food (equivalent to 200ppm). Coeliac Australia believes the gluten free standard in Australia should be the same as the widely accepted international standard of less than 20ppm. The gluten free standard in the United Kingdom, Europe and Canada is less than 20ppm and the United States has recently adopted this standard after a lengthy and rigorous scientific assessment. A study by Zevallos et al. (2012) quantified the amount of toxic gluten epitopes in 15 cultivars and found that all cultivars had levels that were below the maximum amount of gluten (20ppm) suggested for foods that may be labelled gluten free in the US. Furthermore, Zevallos et al. (2014) also found that addition of quinoa to the gluten free diet of celiac patients at 50 g of quinoa daily for six weeks was well tolerated and did not exacerbate the condition.
| Fat (g/100g) | Protein (g/100g) | Ash (mineral constituents) (g/100g) | Fibre (g/100g) | Carbohydrates (g/100g) | Energy (Kcal/100g) | |
|---|---|---|---|---|---|---|
| Quinoa | 6.3 | 16.5 | 3.8 | 3.8 | 69.0 | 399 |
| Rice | 2.2 | 7.6 | 3.4 | 6.4 | 80.4 | 372 |
| Barley | 1.9 | 10.8 | 2.2 | 4.4 | 8.7 | 383 |
| Maize | 4.7 | 10.2 | 1.7 | 2.3 | 81.1 | 408 |
| Wheat | 2.3 | 14.3 | 2.2 | 2.8 | 78.4 | 392 |
| Lupin | 7.0 | 39.1 | 4.0 | 14.6 | 35.3 | 361 |
| Beans | 1.1 | 28.0 | 4.7 | 5.0 | 61.2 | 367 |
| Soybean | 18.9 | 36.1 | 5.3 | 5.6 | 34.1 | 451 |
Carbohydrates
Quinoa seed carbohydrates contain between 58-68% starch and 5% sugar. Amylose content of this starch is low at 11-12%, compared to rice (17%), maize, or wheat (28%).
The diameter of starch granules in quinoa (0.5-8.0µm) is smaller than for maize (1-23µm) and wheat (2-40µm). Size of starch granules, and amylose and gluten contents are some properties that influence the quality of the dough used for baking and the manufacture of pastas.For an acceptable quality, the limits of incorporation of quinoa flour seem to be 10-13% in bread making, 30-40% in pastas and up to 60% in biscuits.
Fat
Quinoa shows fat concentrations in the range of 2-10%. Quinoa is a valuable dietary source of the essential fatty acids. Linoleic and linolenic acids account for 55-63% of the lipid fraction.
Essential amino acids in quinoa
Quinoa possesses a well-balanced protein fraction. All essential amino acids are present in the proteins of quinoa seeds (Table 2).
Amino acids are the building blocks of proteins in our body. Essential amino acids can never be made by our body and must be consumed through diet. It can be difficult to get the full variety of essential amino acids without a meal plan that includes regular intake of foods from a variety of food groups. According to Elango et al. (2012), when one amino acid is deficient for protein synthesis, then all other amino acids are in excess and are therefore oxidized. This is primarily because excess amino acids cannot be stored. Based on this, they have set dietary reference intake (DRI) levels for essential amino acid intake based on a person's age and body weight. Their results suggest that mean protein intake recommendations for adults is 0.93g/kg body weight/day and for children 1.3g/kg body weight per day. Since quinoa has higher protein level than rice, maize or wheat (Table 1), it can boost the supply of essential amino acids in diets supplemented with quinoa.
Quinoa contains more histidine, isoleucine, lysine, and methionine + cysteine than rice, maize and wheat.
Methionine + cysteine and phenylalanine + tyrosine are listed in sets of twos, because our bodies can convert methionine into cysteine and phenylalanine into tyrosine.
| Essential amino acid | Quinoa | Rice | Maize | Wheat |
|---|---|---|---|---|
| Histidine | 3.2 | 2.1 | 2.6 | 2.0 |
| Isoleucine | 4.4 | 4.1 | 4.0 | 4.2 |
| Leucine | 6.6 | 8.2 | 12.5 | 6.8 |
| Lysine | 6.1 | 3.8 | 2.9 | 2.6 |
| Methionine + cysteine | 4.8 | 3.6 | 4.0 | 3.7 |
| Phenylalanine + tyrosine | 7.3 | 10.5 | 8.6 | 8.2 |
| Threonine | 3.8 | 3.8 | 3.8 | 2.8 |
| Tryptophan | 1.1 | 1.1 | 0.7 | 1.2 |
| Valine | 4.5 | 6.1 | 5.0 | 4.4 |
Vitamins in quinoa
Quinoa satisfy the requirement of most vitamins. Quinoa seeds contain more riboflavin (B2), α-tocopherol (E), ascorbic acid (C), and β-carotene (A) than rice, barley or wheat (Table 3).
There is little difference in the vitamin content between sweet and bitter quinoa.
The removal of saponins from bitter quinoa either by polishing or by washing is expected to enhance the vitamin concentrations slightly by altering the grain weight.
| Vitamin | Quinoa | Rice | Barley | Wheat |
|---|---|---|---|---|
| β-carotene (A) | 0.39 | NR | 0.01 | 0.02 |
| Thiamin (B1) | 0.38 | 0.47 | 0.49 | 0.55 |
| Riboflavin (B2) | 0.39 | 0.1 | 0.2 | 0.16 |
| Niacin (B3) | 1.06 | 5.98 | 5.44 | 5.88 |
| Folic acid (B9) | 0.08 | |||
| Acorbic acid (C) | 16.4 | 0 | 0 | 1.50 |
| Tocopherols (E) | 8.71 | 0.18 | 0.35 | 1.15 |
Minerals in quinoa
Quinoa contains more Calcium (Ca), Iron (Fe), Potassium (K), Magnesium (Mg), Copper (Cu), Manganese (Mn) and Chlorine (Cl) than the other cereals (Table 4).
Mineral losses resulting from polishing the grain are estimated at 12-15% for Ca, P, Fe, K, Na, and Zn, 3% for Mg and 27% for Cu. While, losses of minerals upon washing are estimated at 29% for Ca, 20% for Mg, 48% for Na, 49% for K, 38% for Cu, 52% for Fe and 27% for Mn.
Quinoa contains saponins in the pericarp which give a bitter taste. The amount of saponin in the pericarp can vary in different cultivars. There are two ways of removing the saponin – washing with water or peeling by friction. Mechanical abrasion systems usually fail to remove all saponin, mainly due to the disc-like shape of the seeds. On the other hand, the efficiency of washing with water to remove saponin depends on factors such as seed:water ratio, duration of washing, and temperature of the water.
Saponins and phytic acid (see Antinutrients) can also reduce the availability of some minerals in the quinoa seeds.
| Mineral | Quinoa | Rice | Barley | Wheat | Maize |
|---|---|---|---|---|---|
| Ca | 1487 | 69 | 430 | 503 | 171 |
| P | 3837 | 1378 | 3873 | 4677 | 2926 |
| Fe | 132 | 7 | 32 | 38 | 21 |
| K | 9267 | 1183 | 5028 | 5783 | 3771 |
| Mg | 2496 | 735 | 1291 | 1694 | 1371 |
| Na | 122 | 69 | 203 | 89 | 69 |
| Cu | 51 | 2 | 3 | 7 | - |
| Mn | 100 | 23 | 19 | 39 | 5 |
| Zn | 44 | 6 | 35 | 47 | 29 |
| Cl | 1533 | - | 260 | 633 | 137 |
| S | 1933 | - | - | - | - |
| SiO2 | 1315 | - | 5 | 197 | - |
| Al | 110 | - | - | - | - |
| B | 10 | .3 | 5 | - | 2 |
| Co | 0.05 | 0.01 | 0.08 | 0.02 | - |
| Mo | 0.01 | 0.9 | 0.5 | - | 0.6 |
Antinutrients in quinoa
Saponins and phytic acid are the two main antinutrients present in quinoa seeds. Saponins and phytic acid are present not only in the outer layers of quinoa seeds but also evenly distributed in the quinoa endosperm.
Saponins
Saponin concentrations can vary from 0.01-4.65% of dry matter for different varieties of quinoa with a mean value of 0.65%. Quinoa containing 0.11% (on a fresh weight basis) saponins or less can be considered sweet.
Two major saponins, Saponin A at 0.7% and Saponin B at 0.2% dry basis, were identified in quinoa seeds. Scrubbing and washing reduced Saponin A by 56% and completely removed Saponin B.
Remaining saponin (0.3g/100g dry basis or 0.01g in a 100g edible portion) in polished and washed quinoa seeds is in fact less than that found in common foodstuffs (Table 5).
| Foodstuff | Saponin (g/100g edible portion) |
|---|---|
| Chickpeas | 3.47-5.00 |
| Red kidney beans | 1.40 |
| Peanuts | 0.58 |
| Spinach | 0.55 |
| Mung bean sprouts | 0.54 |
| Canned baked beans | 0.38 |
| Brown lentils | 0.37 |
| Canned broad (faba) beans | 0.31 |
| Green peas | 0.25 |
| Asparagus | 0.13 |
| Garlic | 0.11 |
| Leek | 0.10 |
| Green beans | 0.10 |
| Onion | 0.02 |
| Quinoa (polished and washed) | 0.01 |
Phytic acid
Phytic acid can form insoluble complexes with multivalent cations such as Ca2+, Fe2+, Fe3+, Mg2+, and Zn2+ thereby reducing their bioavailability.
The phytic acid concentration in quinoa (1.18g/100g of grain) is higher than that found in barley (1.07g), maize (0.94g), rice (0.89g) and wheat (0.99g).
Polishing and washing removes about 30% of the phytic acid.
The phytic acid concentration in processed quinoa seeds (0.8g/100g dry basis or 8mg/g) is comparable to whole grain rye flour (7.7mg/g), whole grain wheat flour (8.7mg/g), lentils (8.4mg/g) and faba bean (8.0mg/g).
The minimum amounts of phytic acid to avoid negative effects on iron and zinc absorption were found to be 10 and 50mg per meal, respectively.
Conclusions
The chemical composition of quinoa seeds can vary with variety/cultivar/ecotype and growing conditions, including environmental factors and management practices.
It is believed that the potential of quinoa is not as a replacement for any of the currently available foodstuffs but rather as an ideal dietary complement.
In addition to the quality of its protein, quinoa is a good source of magnesium, zinc, and copper and provides at least a tenth of the daily allowances of B6, pantothenic acid, folic acid, and biotin.
Quinoa could well find a niche in improving the nutritional quality of snacks, breads, pastas, breakfast cereals, and other prepared foods.
References
Elango R, Ball RO and Pencharz PB (2012) Recent advances in determining protein and amino acid requirements in humans. British Journal of Nutrition, Vol. 108, pages S22–S30.
Fake C (2013) Vegetable plant families and their characteristics. University of California Cooperative Extension, http://ucanr.edu/sites/placernevadasmallfarms/files/170644.pdf.
Koziol MJ (1992) Chemical composition and nutritional evaluation of quinoa (Chenopodium quinoa Willd.). Journal of Food Composition and Analysis, Vol. 5, pages 35-68.
Ruales J and Nair BM (1993) Content of fat, vitamins and minerals in quinoa (Chenopodium quinoa Willd.) seeds. Food Chemistry, Vol. 48, pages 131-136.
Ruales J and Nair BM (1993) Saponins, phytic acid, tannins and protease inhibitors in quinoa (Chenopodium quinoa Willd.) seeds. Food Chemistry, Vol. 48, pages 137-143.
Stikic R, et al. (2012) Agronomical and nutritional evaluation of quinoa seeds (Chenopodium quinoa Willd.) as an ingredient in bread formulations. Journal of Cereal Science, Vol. 55, pages 132-138.
Zevallos VF, Ellis HJ, Šuligoj T, Herencia LI and Ciclitira PJ (2012) Variable activation of immune response by quinoa (Chenopodium quinoa Willd.) prolamins in celiac disease. The American Journal of Clinical Nutrition, August 2012, Vol. 96, no. 2, pages 337-344.
Zevallos VF, Herencia LI, Chang F, Donnelly S, Ellis HJ and Ciclitira PJ (2014) Gastrointestinal effects of eating quinoa (Chenopodium quinoa Willd.) in celiac patients. The American Journal of Gastroenterology, February 2014, Vol. 109, pages 270-278.
