Every day I find myself talking about Quinoa with people who, moved by curiosity or interest, try to approach this world for different reasons and purposes and, regardless of the reasons that may be at the basis of their interest in this plant, the biggest concern, for the most part, is represented by saponins. But why are we so alarmed? Are they really that harmful and hard to get rid of or do they scare us just because we don’t know about them?
Let’s try to understand together what they are and what their effects can be, both negative and positive. The term saponin derives from the Latin sapo, which means soap, to demonstrate its predisposition to foam in contact with water. Among the most common plants, licorice, oats and basil contain saponins.
In addition to the unpleasant taste, saponins can also have a toxic effect on humans if taken in large quantities. However, it is important to underline that their toxicity, if taken by ingestion, is extremely low and the harmful effects translate into irritation of the pharyngeal and intestinal mucosa, vomiting and stomach pain. The effects can be much more serious if it is taken parenterally (i.e. by injection or infusion) as saponins cause haemolysis (destruction of red blood cells). In particular, I would like to underline that this does not happen with ingestion as the haemolytic activity of saponins takes place only if the molecule remains intact, which does not happen during digestion as it is split into its two components. In cold-blooded animals, and in particular in fish, saponins have a highly toxic effect even if ingested. For this reason, some plants have been used since ancient times in fishing.
In contrast to the harmful effects and unattractive taste, saponins, however, possess excellent beneficial qualities and are used in various sectors: mainly in the chemical (agricultural), cosmetic and pharmaceutical sectors. The main pharmacological actions of saponins are:
The quinoa seed is covered with a thin protective tissue, called episperm or seminal integument, which, in turn, is made up of four layers, each with different characteristics and functions. Saponins are found only in the first outer layer of the episperm.
Based on the saponin content, Quinoa is classified into 3 categories: sweet (low or no saponin content), semi-sweet (medium saponin content) and bitter (high saponin content). The maximum acceptable content for human consumption is 0.11% after cooking or boiling. If we want to understand the level of saponins contained in Quinoa without resorting to chemical analysis, there is a manual method that is however very reliable. Just take a test tube (16 cm high x 1.6 cm diameter), place 0.5 g of Quinoa in the tube with 5 ml of distilled water. At this point shake it for 30 seconds, then let it rest for another 10 seconds and proceed to measure the thickness of the foam produced. If the thickness is less than 0.7 cm it is a sweet quinoa; a thickness between 0.7 and 1.8 cm describes a semi-sweet quinoa; if the thickness of the foam exceeds 1.8 cm we are in the presence of a bitter quinoa.
Over the past 30 years, there has been a constant effort to obtain sweet quinoa varieties through genetic improvements and hybridisation. The results, from the point of view of the saponin content in the seed, were in some ways acceptable, but at the same time it was noted that the sweet varieties may have some limits. Above all, there is a lack of a defence tool (represented by saponins) against microorganisms, birds and insects. Furthermore, these varieties in many cases were observed to produce smaller seeds (this does not mean that the size of the seed is directly proportional to the saponin content, just think of the wild varieties with a small and very bitter seed). Although efforts in this direction continue, attention is also directed to the development of more efficient industrial techniques for the removal of saponins from bitter varieties. One of the most important and delicate phases of the quinoa transformation process is, in fact, the removal of saponins. This operation must be carried out in such a way as not to affect the nutritional qualities of the product. The saponin removal process can be done without water (dry), with water (wet) or with a mixed process. It is a work traditionally done manually by women even if today the process, as we will see later, is mainly carried out mechanically through industrial processes. In this processing phase, in addition to the critical aspects of the saponin removal process, it is important to consider the environmental impact due to the high consumption of water and energy. In this sense, considering that the wet technique also requires a drying action on the seeds (and more energy), the “dry” technique is more environmentally friendly. Furthermore, the dry process facilitates the use of saponins as a by-product in cosmetics or agriculture.