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Legumes
Legumes are dicotyledonous plants in the family Fabaceae.
They have in common a number of structural and functional
characteristics:
• Their fruits are ‘pods’ – simple, dry fruits with (generally)
multiple embryos (seeds) attached to an elongated carpel
that dehisces (opens) along seams on two sides. Not all
legumes dehisce – alfalfa (Medicago sativa) does not.
• They are involved in a mutualistic association with nitrogenfixing bacteria (Rhizobium spp.) present in root nodules that
result in legumes having high levels of protein, as well as
adding available nitrogen to the soil
• Their flowers are not radially symmetric, but bilaterally
symmetric.
Legumes are frequently divided into two groups:
forage species like alfalfa, clover and vetch that are
eaten by grazing herbivores
‘grain’ species, cultivated for their seeds, like various
beans, peas, peanuts and lentils. This group are also
known as “pulse” crops.
All have high protein content. All add nitrogen to the soil (90
million metric tons/yr).
Let’s first consider beans…
There are many types of beans, and taxonomic distinctions
between them:
• broad bean (Vicia faba) is an Old World species that
originated in the Mediterranean area (or possibly Africa). It
was cultivated 6000 YBP. Since I’m not a fan, here are some
of the health problems they can cause:
favism – caused by the presence of vicine and convicine
in them. Individuals who are deficient in the titre of the
enzyme glucose 6 phosphate dehydrogenase (G6PDH)
suffer from a hemolytic anemia
these beans have high tyramine, and should be avoided
when taking MAO (monoamine oxidase) inhibitors
a health benefit – they are rich in L-dopa, which is used
to treat Parkinson’s disease
Broad beans
Broad bean flowers
The fruit (the pod) is 15 – 25 cm long in modern food
cultivars. Pods contain 3 – 8 seeds, each ~20 x 15 x 7.5 mm.
Broad beans are eaten before complete maturity, while young
and tender.
• Other dry beans (kidney, pinto, black, haricot) and some we
consume with the enclosing carpel (green, string) are all
varieties (cultivars) of a single species, Phaseolus vulgaris L.
These beans are originally from the Americas and were first
cultivated in MesoAmerica. They are a staple food.
Nutritional content per 100g:
carbohydrates
60 g
dietary fiber
25 g
lipids
1g
protein
24 g
B5 (pantothenic acid)
0.8 mg (19% RDI)
B9 (folic acid)
394 mg (99% RDI)
Fe
8 mg (64%)
Mg
140 mg (38%)
There is one health concern (that normally doesn’t apply): dry
beans should be soaked, then boiled for at least 10 minutes.
They (particularly red kidney beans) contain a lectin
phytohaemagglutinin, which can cause severe gastric upset.
What about flatulence? Caused by complex sugars that are
removed by soaking.
Compared to the dry beans, green and string beans provide
less starch and protein, but more vitamins A and C.
Some uses:
pinto beans – refried beans in Mexican foods
white (haricot, navy) beans – Boston baked beans
kidney beans – chili, Louisiana creole dishes, southern
U.S. red beans and rice
black (turtle) beans – burritos, feijoada (a national dish
of Brazil)
• Lentils (Lens culinaris)
Originate in the Near East, and one of the first crops
domesticated there. They are second only to soybeans in
protein content – 26%. As a result they are very important in
vegetarian diets.
The optical lens draws its name from the lentil, because the
seed has a ‘lens’ shape.
The largest producer is India, but Canada is both a significant
producer and a large exporter. Of a world total production of
3.2 million metric tons, Canada (mostly Saskatchewan)
produces about 520,000 tons, and exports around 400,000
tons.
This is a map of lentil growing areas (area of origin in red):
In India lentils are boiled to a thick stew-like consistency and
mixed with oil and spices to make dal.
In Ethiopia they are roasted then boiled to a very thick, stewlike consistency and mixed with berber sauce (long-cooked
cayenne pepper, onions and water).
In Europe and North America they are added to soups.
• A different genus of beans, Vigna, includes black-eyed peas
(V. unguiculata), mung beans (V. radiata) and black gram (V.
mungo). Growing areas and uses differ:
Black-eyed peas are originally native to Africa, but are now
grown in southern Asia, Africa, the West Indies, and the
southern U.S. Along with peanuts, George Washington Carver
promoted cultivation of this bean.
In the south the traditional dish is called “hoppin John”, and
consists of black-eyed peas and pork (jowls, fatback or
hocks). It is also traditionally served with greens (mustard or
collard) and cornbread.
In the West Indies, the traditional dish is rice and beans.
mung beans are native to India, even the name comes from a
word in Hindi.
In Chinese cuisine they may be eaten whole or as bean
sprouts. They are also ground up to produce bean thread (or
cellophane) noodles.
Black gram (or black turtle bean) is originally from India,
where it is still used to make urad dal. It is also ground to
make various dishes. Though it is late in the story of beans,
it’s worth mentioning that beans are valuable in a diabetic
diet.
Two more bean genera: first the chick pea or garbanzo bean
(Cicer arietinum): chick peas are tropical and need a lot of
rain (400 mm). There are two types:
Desi-type is a smaller seed with a rougher coat, and closely
resembles archaeological evidence of origin. It is now grown
in India, Ethiopia and Mexico, but originated in the fertile
crescent (southeast Turkey). This type has a notably low
glycemic index (particularly good for diabetics). In India it is
ground as a coating flour and roasted as a snack.
Kabuli-type is grown around the Mediterranean and
Afganistan. This is the type used in the mid-East to make
falafal and hummus.
Chickpeas are a good source of zinc and protein. They are also
very high in dietary fiber. They are low in fat, and most of the
fat content is monounsaturated.
There are other legumes than beans. Peas (Pisum sativum),
due to their rapid growth (they, like the beans, are annual
plants) and ability to control parentage, were the plants used
by Gregor Mendel to develop the basic laws of genetics.
There are many types: green peas, split peas, and snow peas
(with edible pods) among them. Unlike many beans, that are
tolerant of heat and drought, peas are ‘cool season’ plants. The
cultivars you see grown around here are among the many that
grow best at a temperature of about 13°C.
Comparing dry split peas and fresh peas, there are clear
differences in nutritional value (per 100 g):
Green peas
split peas
Carbohydrates
14.5 g
60 g
Fiber
5.1 g
26.1 g
Protein
5.4 g
25 g
Vitamin C
40 mg (67%)
----Vitamin B1
----0.7 mg (54%)
Pantothenic acid (B5)
----1.7 mg (34%)
Folic acid (B9)
----274 g (69%)
In Asia, dry peas are roasted, salted and eaten as a snack.
In England, dry peas are rehydrated and mashed as “mushy
peas”
Soybeans (Glycine max) are native to and were first cultivated
in China about 5,000 years ago. They were brought to Europe
in the 17th century. They were then brought to North America
only about a century later, but not widely grown until the
1920s.
Soybeans are very nutritious. In dry soybeans, protein is about
40% of seed weight and highly unsaturated (‘good’) oil about
20%. The protein contains all essential amino acids.
Soybean oil (along with canola oil) are the only vegetable
sources for omega-3 fatty acids.
Soybeans contain isoflavones (phytoestrogens) that may either
aid in cancer prevention or cause cancers (an active debate).
These same isoflavones have been suggested to reduce
cholesterol. The FDA and American Heart Association think
this is only meaningful for individuals with very high
cholesterol.
Unlike many kinds of protein, that in soybeans is heat stable,
so that soy products can be cooked at high temperatures
without destroying protein value.
Soybeans also contain useful amounts of many vitamins and
minerals.
Soybeans are used in many different ways and products.
Among them:
•
fermented to make soy sauce
•
extracted to make soy milk (for the lactose intolerant)
•
made into a ‘cheese’ we call tofu
which is then used in many products, e.g. tofutti
•
boiled green as edamame (Japanese additive to dishes)
•
made into a paste with rice and fermented (miso) used
in Japanese soups
•
sprouted for use as an alternative to mung beans
•
made into textured vegetable protein (TVP) added as a
high protein extender to many meat products
•
extracted for soy oil used in many products (and the
‘waste’ dry protein is then used in animal feed)
•
lecithin is an additive in chocolate and many baked
goods. It’s a lipid extracted from soybeans.
It should be obvious that soybeans are widely used, and I
haven’t even mentioned industrial uses for soy oil.
One possible concern: most (89%) of the soybeans now
grown in the U.S. are GMO. In 1995 Monsanto introduced a
“Roundup Ready” soybean that, unlike previous genotypes,
was not killed by glyophosphate, the active ingredient in the
herbicide. The gene that made the soybean resistant came
from a bacterium, Agrobacterium sp. The gene, EPSP (5enolpyruvyl shikimic acid-3-phosphate synthase) is also in
soybeans, but in an alternative allele that leaves ‘natural’
soybeans sensitive and vulnerable. Like it or not, we’re all
consuming GMO foods through this transgenic plant.
Lastly, peanuts (Arachis hypogaea) are native to South
America (probably Argentina or Bolivia). It gets its species
name from the strange way its fruit matures. After pollination,
the fruit develops into a legume pod 3 to 7 cm (1 to 2 inches)
long containing 1 to 3 (rarely 4) seeds, which forces its way
underground to mature.
You know, because you have to crack the pod open, that this
fruit, unlike most other legumes, is indehiscent (doesn’t open).
Raw peanuts are very nutritious. Contents (per 100 g) are:
Carbohydrate
20.91 g
dietary fiber
8.7 g
protein
25.09 g
fat (oil)
47.58 g
20% or more of RDIs of thiamin, riboflavin, niacin,
pantothenic acid, folic acid, B6, Mg, P, Zinc, and
less of many others
How many ways do we use them? Give George Washington
Carver credit for a large number of the literally 100s (~300)
of ways. A short list would include peanut butter, roasted
snacks, as ‘beer nuts’, in candies, boiled…
Peanut oil is widely used in cooking because it has the highest
smoke and flash point of all vegetable oils.
Peanut oil is used in the manufacture of paint, varnish,
lubricating oil, leather dressings, furniture polish, insecticides,
and nitroglycerin. Soap is made from saponified peanut oil,
and many cosmetics contain peanut oil and its derivatives.
Peanut shells are put to use in the manufacture of plastic,
wallboard, abrasives, and fuel. They are also used to make
cellulose (used in rayon and paper) and mucilage (glue).
Problems with peanuts:
•
peanuts are considered an incomplete protein, with
relatively low amounts of the essential amino acids
lysine, cystine and methionine
•
peanuts are also an unbalanced source of fat because
they are devoid of required omega-3 fatty acids
•
peanuts may be contaminated with the mold Aspergillus
flavus which produces aflatoxin, a carcinogen
•
some people have severe allergic reactions to peanuts.
Exposure can cause fatal anaphylactic shock. It is now
believed that the underlying mechanism is a result of
the tendency in North America to roast peanuts.
Roasting makes the allergin, Ara h2, inhibit the
digestive enzyme trypsin more strongly, so that it
doesn’t get digested. That also protects one of the
other strong allergins, Ara h1, from digestion. as well.
In Asia, where peanuts are not roasted, the occurrence
of peanut allergies is very rare.
Major producers are the India, China (both almost entirely for
the oil), U.S., Argentina, Sudan, Senegal, and Brazil. We are
major importers.
Apparent Group topics:
Cacao/chocolate
Teas (green/black/white/herbal)
Fruit crops (dates/pomegranates/figs/durian)
Coffee (arabica/robusta/fair trade)
Ginger/ginger root
Plants as drugs (marijuana/cocaine/painkillers/cancer cures)
Peanuts and peanut allergies
GMO
Cinnamon
Plants as herbal medicines (ginseng/aloe vera)