A dietary staple for 5,000 years, the Inca called it the “Mother of Grains.” Comparing its nutritional value to that of dried, whole milk, the FAO of the United Nations recently designated it a “Super Crop.” Little wonder, it contains all nine essential amino acids and is a good source of manganese, magnesium, iron and phosphorous. This wonder cereal is Chenopodium quinoa, or “Quinoa” (pronounced KEEN-wah). Native to the Andes Mountains of Bolivia, Chile, and Peru, Quinoa produces abundant seeds at elevations between 7,000 and 10,000 ft. To make the seed palatable, the seed coats (or pericarp) must be removed, because they contain high levels of bitter-tasting compounds, called “saponins.”
Saponins are glycosides found in many plants in the Families Acreraceae (maple), Caryophyllaceae (carnation), Sapindaceae (soapberry), and Hippocastanacea (horse chestnut). Imparting that bitter taste, not only do they reduce palatability to grazers but also protect plants by repelling microbes, fungi, and insects. They get their name from the soapwort plant (Saponaria spp.), used historically to make soap (Latin: “sapo”). Saponins are mild detergents that are used commercially as foaming agents and surfactants. Certain saponins can also be lethal to aquatic organisms.
In groundbreaking laboratory experiments beginning over a quarter century ago, Kurt Hostettmann et al. determined that saponins can kill aquatic snails by increasing the permeability of the gills, thus leading to losses of essential electrolytes. Today, saponins from the seed cake of tea (Camellia sinensis) are used extensively to kill the Golden Apple Snail (Pomacea canaliculata) in rice paddies in China. The problem is that tea saponins, like most molluscicides, are more lethal to fish than snails, killing 100% of fish but only 66% of the snails at 1.5 ppm/ 24hrs.
Dr. Ricardo San Martin, Professor of Chemical and Bioprocess Engineering at the Catholic University of Chile in Santiago, Chile, had an innovative idea. He wondered if the abundant saponins (25-30%) in the readily available seed husks of Quinoa could be used to kill Pomacea canaliculata. At first, he was disappointed, finding that there was no molluscicidal activity up to 35 ppm saponins. Then, he tried treating the husks with alkali to convert the bidesmosidic saponins to more active monodesmosidic saponins. Surprisingly, 100% of the snails were killed at 10 ppm saponins in 24 hrs, and no fish were harmed at the highest rate tested (16 ppm saponins).
In 2005, the EPA approved the use of Quinoa saponins as biopesticides for a variety of plant diseases (bacteria, fungi, and viruses). Now, Professor San Martin has a patent pending on a “selective molluscicide that is able to kill mollusks in an aqueous environment while not harming non-mollusk species” based on partially hydrolyzed Quinoa saponins. Let us hope that Professor San Martin’s creative thinking pays off. Will the Mother of Grains also be the mother of a selective, aquatic molluscicide? Time will tell! Posted by Jess Van Dyke
US Patent application #20070196517 for a Modified Saponin Molluscicide:
Source of Quinoa (Sergio Nunez):