Saponins

The term saponin comes from the Latin word sapo,meaning "soap", reflecting a readiness to form stablesoap-like foams in aqueous solutions. The biologicalrole of saponins is not completely understood, butthey are generally considered to be part of a plant'sdefence system against pathogens and herbivores,particularly because of their bitter flavour. Saponinscomprise aglycones and sugar, each representingabout 50% of the total weight of the molecule. Inquinoa, saponins are a complex mixture of triterpeneglycosides that derive from seven aglycones:oleanolic acid, hederagenin, phytolaccagenic acid,serjanic acid, 3?-hydroxy-23-oxo-olean-12-en-28-oic acid, 3?-hydroxy-27-oxo-olean-12-en-28-oicacid and 3?,23?,30?-trihydroxy-olean-12-en-28-oicacid, while the most common sugars are arabinose,glucose and galactose. Saponins are traditionallyconsidered very antinutritional because of theirhaemolytic activity, and there is therefore a longstandingcontroversy about their functions in food.It is believed that saponins can form complexeswith membrane sterols of the erythrocyte, causingan increase in permeability and a subsequent lossof haemoglobin. However, recent extensive studiesof the biological activity of saponins in vitro and invivo have identified associations with several healthbenefits, including anti-inflammatory, anticarcinogenic,antibacterial, antifungal and antiviral effects.Saponins are also of interest as valuable adjuvantsand the first saponin-based vaccines have been introducedcommercially. Traditionally, quinoa seedsare either abraded mechanically to remove thebran - which is where the saponins are predominantlylocated - or washed with water to removebitterness prior to use. During washing, valuablenutrients are lost and the chemical composition andamino acid profiles of quinoa seeds can be altered.Following treatment, the level of saponin contentin to-be-consumed quinoa seeds remains a majorconcern in terms of bitterness and possible negativebiological effects. A mathematical model basedon Fick's second law has been created to optimizethe leaching process of saponins from quinoa seedsduring washing with water.Many studies have focused on the effects of agronomicvariables (e.g. irrigation and salinity) on thesaponin profiles of quinoa. It has been observedthat saponins decrease in samples that have beenexposed to drought and saline regimes - suggestingthat irrigation and salinity may regulate the saponincontent in quinoa and affect its nutritional and industrialvalues.Studies are underway to evaluate and comparethe saponin content in seven varieties of quinoagrown in Italy and six varieties grown in Chile underrainfed or low irrigation conditions. Seeds fromthe more arid or stressing Chilean localities have ahigher saponin content.