Saponins

GP Savage, Lincoln University, Canterbury, New Zealand

This article is reproduced from the Encyclopedia of Food Sciences and Nutrition, vol. 8, pp. 5095–5097, ã 2003, Elsevier Science Ltd., with an
updated Bibliography section supplied by the editor.

Background Biological Effects of Saponins

Saponins are a heterogeneous group of glycosides that are Ingested saponins can influence animal performance and
widely distributed in plants of agricultural importance, partic- metabolism in a number of ways.
ularly legumes. Many of these legumes are staple items of the
human diet. Foods particularly rich in saponins are soya beans
Sensory Properties of Saponins
(Glycine max), chickpeas (Cicer arietinum), and beans derived
from Phaseolus vulgaris. Recent studies have shown that a bitter or astringent taste is related
When saponins are agitated in water, they form a soapy to amounts of soya saponin I isolated from pea and soya flour. It is
lather. Other properties generally ascribed to this wide group possible that saponins are a contributing factor to the undesirable
of compounds are hemolytic effects on red blood cells, organoleptic properties that humans associate with some legumes
cholesterol-binding properties, and a bitter taste. These prop- and legume products. The bitter taste of saponins may be respon-
erties characterize particular types of saponins and are not sible for the low palatability of lucerne to ruminants and may
necessarily shared by all members of the group. From a bio- explain the reduced feed intake observed in many experiments
logical point of view, some of these properties are beneficial, when using this material as forage. Many stocks will discriminate
whereas others are considered to be adverse. against feeds containing high levels of lucerne meal.
Of particular interest is the observation that dietary sapo-
nins reduce plasma cholesterol levels in primates, thus having
Erythrocyte Hemolysis
the potential to lower the risk of coronary heart disease in
humans. Saponins have pronounced hemolytic properties when given
intravenously, the degree of effect on the red blood cells vary-
ing among different mammalian species. The release of hemo-
globin from red blood cells is the direct result of the interaction
Chemical and Physical Properties of Saponins of saponins with membrane-bound sterols, which causes an
increase in the permeability of the plasma membrane, bringing
Saponins consist of an aglycone unit linked to one or more about the destruction of the cell.
carbohydrate chains (Figure 1). The aglycone or sapogenin The hemolytic activity of saponins has been widely used as
unit consists of either a sterol or the more common triterpene a means of detecting and assaying saponins in plant materials.
unit. In both the steroid and triterpenoid saponins, the carbo- The potentially toxic effects of intravenous injection of saponin
hydrate side chain is usually attached to the 3-carbon of the extracts have resulted in this class of compounds being
sapogenin. regarded as antinutritive factors in foods. Their low oral toxic-
Saponins possess surface-active or detergent properties ity and the potentially useful nutritive value in foods have only
because the carbohydrate portion of the molecule is water- recently been appreciated.
soluble, whereas the sapogenin is fat-soluble. The stability
and strength of forage saponin foams are affected by pH, and
Effects on Blood and Tissue Cholesterol Levels
this may have an effect on the development of bloat in rumi-
nants. Saponins are remarkably stable to heat processing, and Since many legume saponins form insoluble addition com-
their biological activity is not reduced by normal cooking. plexes with cholesterol, the effects of dietary saponin on cho-
Isolation of saponins from plant material involves extrac- lesterol might be expected. Saponin in the diet of chicks has
tion with a polar solvent after removal of lipids, with petro- been reported to reduce plasma cholesterol in cholesterol-fed
leum ether or chloroform, followed by various purification animals. Saponin extracted from Quillaia saponaria has been
techniques. A number of chromatographic procedures have shown to reduce liver (but not plasma) cholesterol levels
been used to separate individual saponins. in chicks. An exhaustive series of experiments, with a variety
The analysis of saponins is complex and potentially subject of saponins, have consistently demonstrated cholesterol-
to considerable errors during their isolation, separation, and lowering effects. These include the feeding of lucerne saponins
quantification stages. Thus, many early reports of the saponin to rats, rabbits, and monkeys. Some workers have suggested
content of food plants and processed food should be treated that dietary saponins do not have any effect on plasma choles-
with caution. The data presented in Table 1 were obtained terol concentrations. This is perhaps to be expected in experi-
using rigorous methodology and are the most reliable data ments with rats that received no dietary cholesterol.
available at present. More recent studies have shown that Experiments on humans have produced variable results.
many legume seeds contain several saponins, for example, Different saponin levels in a dietary supplement based on soy
five different saponins have been separated from soya beans. flour had no effect on plasma cholesterol levels in

714 Encyclopedia of Food and Health http://dx.doi.org/10.1016/B978-0-12-384947-2.00610-3

H3C CH3 complex that prevents the cholesterol being absorbed. Others
appear to affect cholesterol metabolism indirectly by interact-
OH ing with bile acids. An increased fecal excretion of bile acids is
observed in response to feeding additional saponins in the
diet. Bile acids thus diverted from the enterohepatic cycle
would be replaced by hepatic synthesis from cholesterol.
In the digestive tract, saponins form mixed micelles with
O cholesterol and bile salts; their hydrophobic triterpene or ste-
COOH roid groups stack together like small piles of coins. These
O CH2OH micelles are then too large to pass through the intestinal wall.
OH Bile salts normally pass through the wall of the small intes-
tine by both passive diffusion and active transport. Passive
HO
H diffusion takes place along the entire length of the ileum and
CH2OH
HO O jejunum; active transport is confined to the terminal ileum.
O
Saponins can interact with cell membranes, as shown by their
OH
hemolytic activity. It is possible that they may also have an
H effect on the cell membranes of the intestinal mucosa. How-
HO ever, the effects of saponins on both passive absorption and
O
O active transport can be explained simply as being due to the
CH3 reduction in the concentration of free bile acid, because bile
acids assist lipid absorption. Low concentrations of free bile
H
acids would also impair the efficiency of lipid absorption and
OH OH
presumably affect the absorption of fat-soluble vitamins. Thus,
Figure 1 Structure of a typical saponin (from soya beans). there may also be a significant metabolic effect within the
Reproduced from Saponins. In: Macrae, R., Robinson, R. K., and animal as well as in the digestive tract.
Sadler, M. J. (eds.) Encyclopaedia of Food Science, Food Technology
and Nutrition, Academic Press, 1993.
Effects on Growth
Table 1 Saponin content of some legume seeds When lucerne saponin was added at high levels to the diets of
monogastric animals, reduced feed efficiency and growth rates
1
Saponin content (g kg of dry were observed. It is clear that species differ considerably in
Legume matter)
their responses to dietary saponin, for example, poultry are
Chickpeas (Cicer arietinum L.) 2.3 more sensitive than rats. In contrast, soya bean saponins had
Green pea (Pisum sativum) 1.8 little effect on the growth rate of experimental animals. Some
Haricot bean (Phaseolus vulgaris) 4.1 saponins increase the permeability of the small intestinal
Kidney beans (Phaseolus 3.5 mucosal cells, thereby inhibiting the active transport of some
vulgaris) nutrients, but at the same time, they facilitate the uptake of
Lentils (Lens culinaris Medik.) 1.1 materials to which the gut would normally be impermeable.
Mung bean (Vigna radiata L.) 0.5 The biochemical mechanism that accounts for the growth-
Runner bean (Phaseolus 3.4 depressing effects has not been fully identified. In at least one
coccineus L.)
experiment, the addition of 1% cholesterol to the diets of
Soya beans (Glycine max L. 6.5
chicks completely overcame growth depression produced by
Merrill)
Yellow split pea (Pisum sativum) 1.1 0.3% saponin.
It is possible that, in addition to their effects on lipid
absorption, saponins also affect chymotrypsin and trypsin
hypercholesterolemic men. As the experiment was conducted activity, which would affect the absorption of protein.
on free-living subjects, it cannot be guaranteed that the subjects In addition to observing reduced intestinal uptake of cho-
actually consumed the experimental diets. lesterol in rat intestinal perfusates on the addition of soy sapo-
In a more closely supervised trial, with subjects having nor- nin extracts, some workers have also observed a significant
mal blood cholesterol levels, it was found that a dietary supple- reduction in cholate and glucose uptakes. It was observed that
ment containing saponins did not have a significant effect on the saponins could be washed out of the intestinal lumen,
plasma cholesterol level. Increased fecal excretion of bile acids suggesting that inhibition, at least in the short term, was not
and neutral sterols was observed. Foods containing saponins, or caused by modification of, or damage to, the intestinal mucosa.
diets supplemented with saponins, have been shown to reduce
blood cholesterol levels in humans under conditions that would
be expected to induce high levels of blood cholesterol. Metabolism of Saponins
Toxicity studies indicate that only very low levels of saponin
absorption occur. Saponins are between 10 and 1000 times
Mode of Action
more toxic when administered intravenously than when given
Saponins remain within the gastrointestinal tract. Some inter- orally. Destruction of saponins in the digestive tract of both
act directly with dietary cholesterol, producing an insoluble ruminants and monogastric animals has been observed.
716 Saponins

Saponins are degraded by rumen bacteria and by microflora Calvert GD, Bligh L, Illman RJ, Topping DL, and Potter JD (1981) A trial of the effects of
found in the cecum of rats, mice, and chicks. Since saponin in soya bean flour and soya-bean saponins on plasma lipids, faecal bile acids and
neutral sterols in hypercholesterolaemic men. British Journal of Nutrition
the cecum is past the major sites of absorption, the release of
45: 277–281.
sapogenins and sugars is considered to be insignificant. Cheeke PR (1971) Nutritional and physiological implications of saponins: a review.
Canadian Journal of Animal Science 51: 621–632.
Dinda B, Debnath S, Mohanta BC, and Harigaya Y (2010) Naturally occurring
triterpenoid saponins. Chemistry & Biodiversity 7(10): 2327–2580.
Conclusion Fenwick DE and Oakenfull D (1983) Saponin content of food plants and some prepared
foods. Journal of the Science of Food and Agriculture 34: 186–191.
The substantial evidence that saponins from a number of plant Gestetner B, Birk Y, and Tencer Y (1968) Soybean saponins. Fate of ingested soybean
species can reduce plasma cholesterol levels in man is likely to saponins and the physiological aspects of their hemolytic activity. Journal of
Agricultural and Food Chemistry 16: 1031–1035.
encourage further interest in these plant foods. It is generally Güçlü-Üstündağa Ö and Mazza G (2007) Saponins: properties, applications and
recognized that the overall nutritional value of many Western- processing. Critical Reviews in Food Science and Nutrition 47(3): 231–258.
type diets would be considered improved if more legumes or Heaton KW (1972) Bile salts in health and disease. Edinburgh: Churchill Livingstone.
legume-based products were consumed regularly. The accep- Johnson IT, Gee JM, Price K, Curl C, and Fenwick GR (1986) Influence of saponins on
gut permeability and active nutrient transport in vitro. Journal of Nutrition
tance of more legumes in Western-type diets is limited by
116: 2270–2277.
undesirable taste characteristics, some of which may be due Malinow MR, McLaughlin P, Kohler GO, and Livingston AL (1977) Prevention of
to the higher levels of saponin found in many legume seeds. elevated cholesterolemia in monkeys by alfalfa saponins. Steroids 29: 105–110.
There is little doubt that saponins can be incorporated into Malinow MR, Connor WE, McLaughlin P, et al. (1981) Cholesterol and bile acid balance
human diets at levels that can give a beneficial effect and would in Macaca fascicularis. Effects of alfalfa saponins. Journal of Clinical Investigation
67: 156–162.
not entail a risk of acute toxicity. The fact that saponins can Man S, Gao W, Zhang Y, Huang L, and Liu C (2010) Chemical study and medical
increase the permeability of intestinal mucosa raises the possi- application of saponins as anti-cancer agents. Fitoterapia 81(7): 703–714.
bility of interesting nutritional and pharmacological uses. Oleszek WA (2002) Chromatographic determination of plant saponins. Journal of
Chromatography A 967(1): 147–162.
Pathirana C, Gibney MJ, and Taylor TG (1980) Effects of soy protein and saponins on
serum, and liver cholesterol in rats. Atherosclerosis 36: 595–599.
See also: Cereals: Dietary Importance; Cholesterol: Factors Pistelli L, Bertoli A, Lepori E, Morelli I, and Panizzi L (2002) Antimicrobial and
Determining Blood Cholesterol Levels; Fats: Classification and antifungal activity of crude extracts and isolated saponins from Astragalus
Analysis; Legumes in the Diet; Protein: Digestion, Absorption and verrucosus. Fitoterapia 73(4): 336.
Metabolism; Pulsed Electric Fields; Soy Beans: Properties and Potter JD, Illman RJ, Calvert GD, Oakenfull DG, and Tapping DL (1980) Soya saponins,
plasma lipids, lipoprotein and fecal bile acids. Nutrition Reports International
Analysis.
22: 521–528.
Price KR, Curl CL, and Fenwick GR (1986) The saponin content and sapogenol
composition of the seed of 13 varieties of legume. Journal of the Science of Food
and Agriculture 37: 1185–1191.
Further Reading Sidhu GS and Oakenfull DG (1986) A mechanism for hypocholesterolaemic activity of
saponins. British Journal of Nutrition 55: 643–649.
Anderson JO (1957) Effect of alfalfa saponin on the performance of chicks and laying Sirtori CR, Agradi E, Conti F, Mantero O, and Gatti E (1977) Soybean protein diet in the
hens. Poultry Science 36: 873–876. treatment of type II hypercholesterolaemia. Lancet I: 275–277.
Birk Y (1969) Saponins. In: Liener IE (ed.) Toxic constituents of plant food stuffs, Sparg SG, Light ME, and van Staden J (2004) Biological activities and distribution of
pp. 169–210. New York: Academic Press. plant saponins. Journal of Ethnopharmacology 94(2–3): 219–243.
Birk Y, Bondi A, Gestetner B, and Ishaaya I (1963) A thermostable haemolytic factor in Yayla Y, Alankus-Caliskan O, Anil H, Bates R, Stessman C, and Kane V (2002) Saponins
soybeans. Nature 197: 1089–1090. from Styrax officinalis. Fitoterapia 73(4): 320.