The right way to cook Beans/ Legumes/ Pulses

 

Science behind cooking beans, pulses and legumes

Dal or lentils is the staple food in every Indian home. Both the rich and the common person who lives on the street enjoy it. It is what chicken soup is to the west – it is India’s comfort food. A large percentage of Indians are vegetarian and lentils have long been part of the indigenous diet as a common source of protein. Dals or lentils, peas and beans are cooked practically daily in almost every Indian home, vegetarian or not. Each region has its own favorites and cooking methods.
Beans and legumes are so popular, for their protein and micronutrient content. But what else is there to know about them, which yes, are technically and scientifically has proven how their cooking methods can make a huge difference to improve the bioavailability more? Let’s start by knowing the anti-nutrients present in beans and low- moderate- high anti-nutrient content in them and the ways to reduce it.
Fresh and dried, whole and split, husked and dehusked- beans and legumes, owing to their nutrient-dense attributes need to be consumed in a right way as well to obtain the maximum benefit. The reason for this is linked to 2 antinutritional factors found in legumes and beans:
1) presence of flatulence causing oligosaccharides, namely raffinose and stachyose to a lesser extent,
2) presence of toxic lectins that have been associated with food poisoning.

Raffinose: The raffinose family of oligosaccharides are almost ubiquitous in the plant kingdom, being found in a large variety of seeds and kegumes. Our body does not possess the enzyme to break down raffinose and it passes undigested through the stomach and upper intestine. In the lower intestine, they are fermented by gas-producing bacteria which do possess the α-GAL enzyme and make carbon dioxide, methane, and/or hydrogen—leading to the flatulence- commonly associated with eating beans and other vegetables.

Lectins: Lectins are a type of protein, specifically classified under antinutrients. Studies suggest that certain lectins can reduce the body’s ability to absorb nutrients. Lectins are thought to have evolved as a natural defence in plants, essentially as a toxin that deters animals from eating them. About 30% of the foods we eat contain significant amounts, where beans, legumes and pulses top the contribution apart from few fruits and veggies. Agglutinins, which are found in legumes like beans, are an example of a group of lectins. Same here these lectins remain undigested and so they travel through our gut unchanged and thus play important roles in several bodily processes, including immune function and cell growth. However, eating large amounts of certain types of lectins can damage the gut wall. This causes irritation that can result in symptoms like gastritis problems and even nausea and vomiting.

Luckily, there are several ways to reduce the lectin and raffinose content of these healthy foods to make them safe to eat. Research shows that by cooking, sprouting, or fermenting foods that are high in lectins, we can easily reduce their anti- nutrient contents to negligible amounts.
It's OK to eat beans and other legumes in moderation provided that you tolerate them well and that they are prepared in a way that makes their nutrients more bioavailable.
The best way to inactivate lectins in beans & legumes:
So, how long should you soak and cook beans and other legumes, and at what temperature, if you want to minimize their antinutrients content? And are there any differences between cooking methods (e.g. pressure-cooking vs boiling)? Let's take a look at some facts according to the research papers,

• Neither dry nor moist heating/ steaming for several hours has any significant effect on the lectin activity of common legumes—a much higher temperature is needed to inactivate legume lectins and raffinose.
• Soaking beans and legumes in water and then cooking them in fresh water close to more than 90°C (i.e. boiling) appears to be highly effective at inactivating lectins and eliminating the raffinose.   
• Pressure cooking seems to be particularly effective at inactivating lectins.
• Well sprouted and fermented beans, legumes have also proven to have low lectin content. 

Lectin and raffinose content in beans/ legumes: High vs Low Lectin Varieties

To give you a rough idea of the lectin content of different beans, I’ve charted some common legumes into different categories depending on their lectin content. Each bean/legume included in the chart is put into one of three categories—high, high/moderate, or moderate/low lectin content—based on how researchers and articles have described the lectin content of the respective variety.

Low/ Moderate	Moderate/ High	Very High
Cowpeas/ black eyes beans	White kidney beans	Red kidney beans
Fresh peas	Chick peas	Soybeans
Lentils	Groundnut	Double beans
Black gram	Dried Broad beans	Green peas
Adzuki		White peas
Brown peas		Lima beans
Green gram		Horse gram
Moth beans		Fresh Broad beans

All the mentioned varities are commonly used in Indian cooking, found in almost every Indian kitchen. But to give you an idea of how popular and Pulses and lentils are in Indian Cuisine- Over 50 different varieties of pulses, legumes and beans are known in India (That will take some more researching and going through the research articles and literatures to know the lectin and raffinose contents wrt to it's cooking method and growing regions).
According to a research article, raw red kidney beans contain from 20,000 to 70,000 hemagglutinating units (hau) of phytohemagglutinin (when fully cooked, their lectin content drops to 200 to 400 hau). White kidney beans, by contrast, contain only about one-third the amount of phytohemagglutinin the red variety contains, and moong/ green gram contain even less, about 5% to 10% the amount that white kidney beans contain.
Another example: A study published in the Indian Journal of Agricultural Biochemistry found the lectin content of chickpeas to be in the range of 1160 to 1375 hau/g grain, which was almost twice as high as the lectin content of lentils (513 to 617 hau/g).
A hemagglutinating unit (hau) is a measure of lectin content. In their raw form, red kidney beans contain 20,000–70,000 hau. Once they’re thoroughly cooked, they contain only 200–400 hau, which is considered a safe level and to have the bioavailability of the micronutrients viable. When properly cooked, red kidney beans are a valuable and nutritious food that shouldn’t be avoided.

 
Soaking time for beans, legumes and pulses

Soaking dried beans for several hours in water reduces the time required to cook beans, but pre-soaking also has another advantage: it helps break down some of the indigestible sugars that can cause flatulence (intestinal gas), heartburn, reflux, bloating and other digestive problems.  The ideal pre-soaking time for each dried legume depends on a number of factors, including its size, maturity at harvest, moisture level, age/freshness (older beans must be soaked for longer), and digestibility of the carbohydrates it contains.
General soaking time is discussed below:
Pulses (lentils)- 2 to 4 hrs
Fresh beans/ legumes- 3 to 5 hrs
Dried small beans/ legumes- overnight (preferably 8-10 hrs)
Dried bigbeans/ legumes- overnight (preferably 12-15 hrs)
Or in hot water for 1-5hrs depending on the beans and legumes.
Rinse the beans/ legumes thoroughly and discard the rinsed water. Do not add salt as this can prevent the absorption of water! Let the beans absorb water for several hours –to reduce the ability of the cooked beans to cause gas and bloating, change the water a couple of times during the soaking process. After soaking, drain the beans and rinse them thoroughly with clean water. Cook the beans until they are tender but not mushy.
In fact, according to a study published in the Journal of Agricultural and Food Chemistry, common edible beans that have been prepared and cooked properly are unlikely to cause lectin or raffinose related adverse effects in healthy people.
Researchers say it's OK to eat beans and other legumes in moderation provided that you tolerate them well and that they don't replace more nutrient-dense foods, and that they are prepared in a way that makes their nutrients more bioavailable.
 
Note: Avoid cooking dried beans in a slow cooker, as the low heat isn’t enough to kill the toxins. Canned beans, however, are already cooked, so no worries there.
You really can’t go wrong with any type of beans. Try incorporating these little gems into your routine and you will reap all the potential health benefits if cooked in the right way. Set a goal; aim to eat beans 4 times a week!

Why You Should Use the Chart Only as a Rough Guide:
Since the information above has been compiled from many different sources and those sources may differ in how they define high, moderate, and low lectin beans/legumes, you should use the chart only as a rough guide. What's more, research suggests that the same bean or legume may contain varying amounts of lectins depending on when and where the plant was grown and how it was processed after harvesting. According to a study, published in The Journal of Clinical Nutrition, it is also possible that the lectin-related activities of a food may vary from one day to another. Not only for lectins, this applies for nutritional values as well. So, the suggested anti-nutrient content and soaking time for Indian grown beans, lentils and pulses are mentioned keeping the maximum nutrient bioavailability w.r.t. cooking temperatures and methods.

References:
1. Freed, D. (1999). Do dietary lectins cause disease? The evidence is suggestive—and raises interesting possibilities for treatment. BMJ, 318(7190): 1023-1024.
2. Lajolo F. and and Genevese M. (2002). Nutritional Significance of Lectins and Enzyme Inhibitors from Legumes, Journal of Agricultural and Food Chemistry, 50(22):6592-8.
3. Pusztai, A (1991). Plant lectins. Cambridge University Press, Cambridge, UK.
4. Grant, G and van Driessche, E. (1993). Legume Lectins. Physiochemical and nutritional properties, Recent Advances in Anti-Nutritional Factors in Legume Seeds. Wageningen Pers.
5. Pusztai, A. and Grant, G. (1998). Assessment of lectin inactivation by heat and digestion. Methods Mol Med., 9:505-14.
6. Bad Bug Book, 2nd edition. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. Food and Drug Administration.
8. Grant, G et al (1982). The effect of heating on the hemagglutinating activity and nutritional properties of bean Phaseolus vulgaris seeds. Journal of the Science of Food and Agriculture, 33, 1324-1326.
9. Liener, I. (1994). Implications of antinutritional components in soybean foods. Crit. ReV. Food Sci. Nutr., 34, 31-67.
10. Bressani, R. (1993). Grain quality of common beans. Food ReV. Int. 9, 237-297.
11. Deshpande, S. (1992). Food legumes in human nutrition: a persona perspective. Crit. ReV. Food Sci. Nutr., 32, 333-363.
12. G. Grant et al (1991). A survey of the nutritional and haemagglutination properties of several tropical seeds, Livestock Research for Rural Development, Volume 3, Number 3.
13. Bad Bug Book, 2nd edition. Foodborne Pathogenic Microorganisms and Natural Toxins Handbook. Food and Drug Administration.
14. G. Grant et al (1995). Consumption of diets containing raw soya beans (Glycine max), kidney beans (Phaseolus vulgaris), cowpeas (Vigna unguiculata) or lupin seeds (Lupinus angustifolius) by rats for up to 700 days: effects on body composition and organ weights. British Journal of Nutrition, 73(1):17-29.
15. A. Pusztai et al (1979). Nutritional evaluation of kidney beans (pxshaseolus vulgaris): Chemical composition, lectin content and nutritional value of selected cultivars. Journal of the Science of Food and Agriculture, Volume 30, Issue 9, pages 843-848.