Today is World Pulses Day , which is proposed as an opportunity to raise awareness about the nutritional benefits they have. Chickpeas, lentils, peas, broad beans… great representatives of the Mediterranean diet. Among the foods of plant origin, legumes take the prize for their high content of carbohydrates, proteins and fiber, and their high quality . So much so that meat consumption could even be reduced if more legumes were consumed. Today I am going to tell you three curiosities that you probably did not know about this magnificent food.
Where do the gases in legumes come from?
As we have said, legumes have a significant amount of carbohydrates, especially those called oligosaccharides , that is, long chains whose links are represented by sugars. Among them, some with strange names stand out, such as verbascose , stachyose or raffinose , which are characterized by inserting glucose, fructose and galactose molecules in their chain. If they only had fructose and glucose there would be no problem; but in the galactose is the problem . In order to break these oligosaccharides, and therefore digest them, it is necessary to separate this galactose, something that is achieved with an enzyme called alpha-galactosidase . But we human beings do not produce this enzyme in our body , so these chains pass unbroken through our digestive system, until they reach the large intestine .
There, the bacteria of our misnamed “intestinal flora” , whose correct name is microbiota, degrade the oligosaccharides that have remained intact, and take advantage of the sugars that are released as a result, in a fermentation process . And the residues of that fermentation are, effectively, those gases that are so uncomfortable later, that seek to leave our body through the shortest path, causing those well-known winds .
In addition, fiber also contributes to the production of these gases, by protecting nutrients during the digestion process. For this reason, adding vegetables such as chard, cabbage or spinach to the recipe, despite being an excellent choice at a nutritional level , can increase these undesirable effects.
Some tricks to reduce flatulence caused by legumes are to soak them well , which facilitates the hydrolysis of these oligosaccharides. Cooking them over low heat and chewing the food very well before swallowing also causes some of these chains to break in the process.
The peanut, the underground legume
Among the legumes, the strangest is the peanut. So much so, that it is generally considered a dried fruit . Normal legumes, such as beans or chickpeas, have a fairly common life cycle. The plant grows, and when the time comes, it produces beautiful symmetrical flowers with a shape reminiscent of butterflies , it is pollinated by insects, and the ovary then grows in the form of a long pod inside which the seeds are formed. If no one eats those seeds, and they end up falling to the ground, a new plant will come out that will close the cycle. Easy.
But the peanut is different . The beginning of the story does not change. The plant grows and blooms, with beautiful, butterfly-like yellow or orange flowers. The difference lies in the maturation. And it is that when it is fertilized, the petals dry and the flower’s petiole begins to grow downwards, until it touches the ground. Then, once the ovary of the flower is touching the substrate, the peanut begins to grow, burying itself as it develops, maturing underground . In this curious aspect lies the difficulty of its collection. If it is removed too early, it will not have matured. But if it is removed too late, it may have germinated.
This feature is so characteristic that it is what gives the peanut its scientific name: Arachis hypogaea ; from the Greek ὑπόγαιον , hypógaion , meaning “underground”.
Why do legumes have so much protein?
One of the reasons they are so high in protein is that we have been breeding legumes for millennia. Whether it’s lentils in Egypt, peas in Mesopotamia, or soybeans in India , legumes have been on our plates for around 5,000 years . Genetic improvement is not just inserting genes in a laboratory. Actually, human beings have been genetically improving plants since they began to grow them for food; it is an effect of coupling biological evolution with artificial selection.
But why legumes? Why not cereals, or citrus? Although to a lesser extent, wild legumes also have relatively high protein content. Why are legumes so special?
On their roots, legumes usually have nodules in which a bacterium called Rhizobium leguminosarum lives in symbiosis. These bacteria are capable of obtaining nitrogen from the air and retaining it, something that is of great value in ecosystems . As is known, 78% of the composition of our atmosphere is nitrogen, so these bacteria make this nutrient no longer limiting for the plant. Normally, plants need to obtain nitrogen from the soil , in the form of salts.
The nitrogen fixed by bacteria is used by plants, and these, through their metabolism, transform it into amino acids. Amino acids are the chemical base of proteins , and this is how plants store them, especially in fruits and seeds, which is what we ultimately eat.
REFERENCES
Broughton, W.J. and Perret, X. (1999) ‘Genealogy of legume-Rhizobium symbioses’, Current Opinion in Plant Biology, 2(4), pp. 305–311. doi:10.1016/S1369-5266(99)80054-5.
Burris, R.H. et al. (1943) ‘Studies of Biological Nitrogen Fixation with Isotopic Nitrogen’, Soil Science Society of America Journal, 7(C), pp. 258–262. doi:10.2136/sssaj1943.036159950007000C0039x.
Demolon, A. and Dunez, A. (1945) ‘Observations on the ecology of Rhizobium leguminosarum (Bact. Radicicola)’, Weekly Reports of the Sessions of the Academy of Sciences, 221(10–13), pp. 309–311.
Smith, B.W. (1950) ‘Arachis Hypogaea. Aerial Flower and Subterranean Fruit’, American Journal of Botany, 37(10), pp. 802–815. doi:10.1002/j.1537-2197.1950.tb11073.x.
