SAPO = SOAP
With the modern concern of agriculture in term of sustainability and free AGP farming, phytogenics are developing. Among them, saponin is one of the most common popular compound used by nutritionists mostly to reduce the production of ammoniac in Swine and Poultry farming. But recent researches show that Saponins have actually wider spectrum of action with significant benefits on animal growth performance.
Saponin derives its name from “Sapo” which means 'soap' in Latin. They are indeed high molecular weight glycosides that can form stable soap-like foam in aqueous solution. They are made of polar and non-polar structural elements that explains their soap-like behavior in aqueous solutions (amphiphilic behavior).
Figure 1: Example of saponin structure
An easy and simple method to underline the presence of saponin in a compound is the foam test. When mixing the ingredient with water, we can notice the presence of foam (cf Fig 2). This semi-quantitative test can help to compare different ingredients to assess their level of saponin. The high foam volume indicates high saponin content.
Figure 2: Foam produced by an aqueous solution of saponin
Saponin is actually a family of several compounds extracted from plants. The most common source of saponin has been the Yucca but we can now find more economical solution. Fenugreek is now a popular solution as it helps to reduce the cost per unit of saponin versus Yucca. As the saponin family is diverse, all the sources are not all equivalent. Fenugreek for example has an interesting benefit of attractant that Yucca does not provide. The use of Fenugreek in the diet helps to increase feed intake in Swine in addition to the other properties of the saponins.
Figure 3: Fenugreek seeds on the top and Yucca roots on the bottom
The benefits of Saponin in the reduction of ammonia excretion are nowadays well known and widely used by nutritionists. This features seems common to all saponins. They limit the production in large intestine/caeca by bacteria through the inhibition of urease enzyme activity (enzyme which transform urea into ammonia). Saponins have 2 other suppressive effects on ammonia. They are binding it by adsorption reducing their volatility and they are limiting as well the proliferation of the proteolytic bacterial flora in the gut responsible for transforming undigested protein into ammonia. One of the other effects of saponins that has been studied by the scientific community is their effect on protozoa and especially protozoa belonged to Eimeriagenus (coccidia). Literature reports reduction on coccidiosis incidence reduction of oocyst per gram of faeces and haemorrhagic problem in colon when saponins is fed to broiler. The oocyst’s wall of Eimeriais very strong and resistant. It was assumed that saponin did not destroy the oocyst’s wall but entered the wall through a mycropyle cap which is present at the polar end of oocyst. A gap exists between this cap and oocyst’s wall and by entering, saponin disturbed sporoocyst. Beside this mode of action, saponin can lysed the protozoa by directly binding the outer membrane of protozoa. Thanks to their structure, saponins are binding with the steroids in the membrane causing the cell content to leak. This mode of action is used in ruminant to control ruminal protozoan population. Since rumen protozoa are key in the turnover of bacterial protein in the rumen their elimination could increase microbial protein supply to the host. Furthermore, it reduces methane emission and associated energy losses. Another characteristic of saponin, commonly used in human medicine and nutrition, is their anti-cholesterol effect. Saponin has been reported to reduce cholesterol in blood, meat and eggs. Not only total cholesterol but the most harmful LDL-cholesterol was reduced. Diverse mechanisms have been proposed to explain the hypocholesterolemic effect of saponins. The oldest proposed mechanism is the formation of insoluble complexes of saponins with cholesterol, avoiding their solubilisation in mixed micelles and later absorption. Another mechanism suggested for the interaction of saponins with the absorption of cholesterol has been related to the interaction with bile salts, by inhibition of their physiological reabsorption due to the formation of aggregates with saponins. As a consequence, the synthesis of new bile salts from cholesterol by the liver is forced, leading to a cholesterol decrease. Latest researches show that the mechanism could be also due to inhibition at the gene level of two key enzymes of cholesterol biosynthesis. In the same time, catabolism of cholesterol seems to be increased and some lipoprotein receptor activities are enhanced leading to a higher uptake of LDL-cholesterol. General effect can be due to a combination of this different mode of action. Such hypocholesterolemic effect can be interesting for egg producers interested in launch “Low cholesterol” egg and meat for the premium market. Some studies have underlined as well for some saponins some antimicrobial activity and mould inhibition. But more studies are needed to define clearly the mechanisms. Several other effects are still under study. Recent researches demonstrated for some saponin some anti-oxidant activities, some positive effects on animal immune system, benefits on fertility and semen quality, improvement of egg hatchability and reduction of embryonic mortality. Saponins category is a huge but promising world. Understanding the effect of each saponin remains a challenge for scientific communities but it will certainly be subject to many more publications in a near future to benefit their application into the sphere of Animal nutrition
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