Antifungal properties of quinoa (Chenopodium quinoa Willd) alkali treated saponins against Botrytis cinerea. http://dx.doi.org/10.1016/j.indcrop.2007.11.003

Abstract

Quinoa (ChenopodiumquinoaWilld) is a Latin American food staple readily available in large quantities in Peru, Bolivia and Ecuador. The outer husk of the grain is removed prior to consumption to reduce its bitter taste. At present, quinoa husks are considered as a by-product with no commercial value, despite its high content of triterpenoid saponins (20–30%). Due to this, the present work was undertaken to test if quinoasaponins have antifungalpropertiesagainstBotrytiscinerea and if this activity is enhanced after alkaline treatment, since recent reports indicate that alkaline treatment of quinoasaponins increase their biological activity. Six products were tested againstB. cinerea: (1) non-purified quinoa extract, (2) purified quinoa extract, (3) alkalitreated non-purified quinoa extract, (4) alkalitreated purified quinoa extract, (5) non-purified quinoa extract treated with alkali but without thermal incubation and (6) purified quinoa extract treated with alkali but without thermal incubation.
Untreated quinoa extracts showed minimum activity against mycelial growth of B. cinerea. Also, no effects were observed against conidial germination, even at 7 mg saponins/ml. However, when the saponin extracts were treated with alkali, mycelial growth and conidial germination were significantly inhibited. At doses of 5 mg saponins/ml, 100% of conidial germination inhibition was observed, even after 96 h of incubation. Fungal membrane integrity experiments based on the uptake of the fluorogenic dye SYTOX green showed that alkalitreatedsaponins generate membrane disruption, while non-treatedsaponins had no effects.
The higher antifungal activity of alkaline treatedsaponins is probably due to the formation of more hydrophobic saponin derivatives that may have a higher affinity with the sterols present in cell membranes.