Grain
Quinoa grain contains antinutritional factors, notably saponins, tannins, protease inhibitors and phytic acid (Arendt et al., 2013). The varieties that have been developed to respond to the increasing demand of quinoa are mainly of the bitter type and contain high levels of saponins (Quiroga et al., 2015).
Saponins
Saponins are glyclosides that give bitter taste and astringence and are generally considered as antinutritional substances, though they can also have beneficial effects (Hill, 2003). Quinoa contains variable amounts of saponins in the seed coat, depending on genotype and conditions of cultivation: levels ranging from 0.02 to 2.3% have been reported (Arendt et al., 2013; Hill, 2003). Quinoa varieties containing more than 0.11% free saponin are called "bitter varieties", while others are called "sweet" (Arendt et al., 2013). The presence of saponins is known to depress growth in monogastric animals when they are fed non-processed quinoa grain. As modern quinoa cultivars are mainly of the bitter type, it is necessary to remove saponin from the seeds (see Processes) to alleviate bitterness and antinutritional effects.
Saponins can also have beneficial effects as their detergent activity increases the permeability of the intestinal mucosa and improves the uptake of substances that are not usually absorbed in the intestine like drugs; they have antifungal activity; they lower cholesterol in blood. In ruminants, the use of saponin may decrease the risk of bloat (Hill, 2003). Saponins have been found to have molluscicide effect: saponins extracted from quinoa bran has been -used to control the invasive aquatic snail Pomacea maculata in the Ebro Delta, in Spain. Quinoa saponins used at 7-8 ppm killed about 90% of snails in rice fieldswithout affecting fish, crustaceans or algae (Castillo-Ruiz et al., 2018).
Phytic acid
Quinoa grain has been reported to contains phytic acid in the 1.05-1.35 % range, though these amounts are similar to those found in "true" cereals (Koziol, 1992; Arendt et al., 2013).
Foliage
Oxalates and saponins
Quinoa leaves contain very high levels of oxalates. In India, oxalates content ranging from 9 to 14% DM have been reported (Prakash et al., 1993). Oxalates are known to have toxic effects, by damaging kidney tubules and causing hypocalcaemia (Duncan et al., 1997), but no such effects have been reported with quinoa foliage.
Quinoa leaves contain saponins (0.13–0.17 g/kg dry matter) that are produced rather late during plant development (Mastebroek et al., 2000), but in a much lower amounts than in the seeds. Saponin was reported to act as a deterrent in the use of quinoa leaves for fodder and vegetable purposes (Bhargava et al., 2008).