Saponins are a diverse group of chemicals compounds present abundantly in plant foods. The name ‘saponin’ is derived from the Latin word ‘sapo’ meaning ‘soap’, because saponin molecules form soap-like foams when shaken with water.
Saponins are plant-derived secondary compounds, which are found in more than 100 families of wild and cultivated plants. They are naturally produced as foam-producing compounds by many plants, including groundnut and other oil seeds. They are usually found in legumes such as soybean, peanuts, chickpeas, broad beans, and lentils, quinoa, sunflower seeds, spinach leaves, tea leaves, quinoa seeds, sugar beet, oats, yucca, tomato seeds, fenugreek seeds, asparagus, brinjal, yam, and allium family (onion, garlic, leek, etc).
Due to the bitterness, throat-irritating and inhibitory activity of saponins, they are considered to be ‘antinutrients’.
Recent studies have shown that a bitter or astringent taste is related to amounts of saponin isolated from pea and soya flour and plant saponins are a contributing factor to the undesirable organoleptic properties that humans associate with some legumes and legume products.
In the digestive tract, this antinutrient compound stack together like small piles of coins, which are too large to pass through the intestinal wall. The working of digestive enzymes such as amylase, glucosidase, trypsin, chymotrypsin and lipase is hampered in the presence of saponins, thereby affecting carbohydrate and protein absorption and the overall growth rate of an individual. In addition, they form insoluble saponin–mineral complexes with iron, zinc, and calcium and decrease the nutrient bioavailability.
These insoluble complexes again interact with bile acid and cholesterol and increase excretion of bile acids. Low concentrations of free bile acids can, however, impair the efficiency of lipid absorption and presumably affect the absorption of fat-soluble vitamins.
It should be, thus, noted that the low levels of saponins in foods may not be injurious to health but could become toxic when consumed at higher concentrations in the diet.
On the contrary, saponins are also attracting considerable interest as a result of their hypocholesterolemic, immunostimulatory, and anticarcinogenic properties.
Ways to reduce the saponin content
Saponin content from the different sources can be reduced firstly by soaking the foods. A lot of saponins are lost when the soaking water is discarded. Loss of saponin increases with increased duration of soaking. Greater losses occur during soaking in salt water than in plain
water. Secondly, cooking of saponin-rich foods reduces the amount by 40%. However, loss of saponin is greater during pressure cooking than during ordinary cooking. Greatest amounts of saponin are lost during soaking in salt water followed by pressure cooking.
However, to ensure further reduction, alcohol extraction technique works best. But it is not a reliable household process.
As the amounts are reduced and not completely removed, foods containing saponins should not be consumed in large amounts. Also if you are suffering from digestive issues, we would recommend you to watch your diet for the antinutrients.