Saponins

The term saponin comes from the Latin word sapo, meaning "soap", reflecting a readiness to form stable soap-like foams in aqueous solutions. The biological role of saponins is not completely understood, but they are generally considered to be part of a plant's defence system against pathogens and herbivores, particularly because of their bitter flavour. Saponins comprise aglycones and sugar, each representing about 50% of the total weight of the molecule. In quinoa, saponins are a complex mixture of triterpene glycosides 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-oic acid and 3?,23?,30?-trihydroxy-olean-12-en-28-oic acid, while the most common sugars are arabinose, glucose and galactose. Saponins are traditionally considered very antinutritional because of their haemolytic activity, and there is therefore a longstanding controversy about their functions in food. It is believed that saponins can form complexes with membrane sterols of the erythrocyte, causing an increase in permeability and a subsequent loss of haemoglobin. However, recent extensive studies of the biological activity of saponins in vitro and in vivo have identified associations with several health benefits, including anti-inflammatory, anticarcinogenic, antibacterial, antifungal and antiviral effects. Saponins are also of interest as valuable adjuvants and the first saponin-based vaccines have been introduced commercially. Traditionally, quinoa seeds are either abraded mechanically to remove the bran - which is where the saponins are predominantly located - or washed with water to remove bitterness prior to use. During washing, valuable nutrients are lost and the chemical composition and amino acid profiles of quinoa seeds can be altered. Following treatment, the level of saponin content in to-be-consumed quinoa seeds remains a major concern in terms of bitterness and possible negative biological effects. A mathematical model based on Fick's second law has been created to optimize the leaching process of saponins from quinoa seeds during washing with water. Many studies have focused on the effects of agronomic variables (e.g. irrigation and salinity) on the saponin profiles of quinoa. It has been observed that saponins decrease in samples that have been exposed to drought and saline regimes - suggesting that irrigation and salinity may regulate the saponin content in quinoa and affect its nutritional and industrial values. Studies are underway to evaluate and compare the saponin content in seven varieties of quinoa grown in Italy and six varieties grown in Chile under rainfed or low irrigation conditions. Seeds from the more arid or stressing Chilean localities have a higher saponin content.