LEGUMES

Legume Family - Fabaceae

All types of beans and peas Soybean, peanut, alfalfa, clover Also includes various trees such as black

locust, redbud One of the largest dicot families - 13,000

species Ranks right behind grasses in human

impact

Family characteristics

Five-petalled irregular flower with bilateral symmetry

Fruit is a legume (dry dehiscent fruit - two lines of dehiscence) with one row of seeds

Seeds contain two large cotyledons

Legume flower

Irregular flower with bilateral symmetry

Often butterfly-shaped

Legume seeds

Important food staple worldwide

Rich in both oil and protein» Higher in protein than

any other food plants » Close to animal meat

in protein quality» Often called "poor

man's meat"

Legumes and nitrogen-fixing bacteria

High protein correlated with root nodules which contain nitrogen-fixing bacteria» convert atmospheric nitrogen to useful form

Because of this legumes enrich the soil» Farmers often rotate legumes with crops that

deplete soil nitrogen (soybean & corn)» "Green manure" crops plowed sometimes» Reduces need for fertilizers - legumes can

be cultivated worldwide - even in poor soils

Nitrogen cycle

Nitrogen » essential elements for all living organisms» major component of amino acids, proteins,

nucleic acids

Nitrogen gas (N2) about 79% of the air

» most living organisms cannot use this form of nitrogen

Nitrogen-fixing bacteria

Certain bacteria and cyanobacteria have ability to reduce nitrogen (N2) gas to ammonium NH4

+

» cells can convert NH4+ to compounds

» called nitrogen-fixation» organisms are called nitrogen-fixing

Nitrogen-fixing organisms

Some bacteria and some cyanobacteria Some live freely in the soil Most are found in symbiotic associations

in the root nodules of legumes Azolla is known to have a symbiotic

association with a nitrogen-fixing cyanobacterium

Non-legume plants

Must rely on the nitrogen compounds present in the soil

During decomposition microorganisms break down proteins and other nitrogen-containing molecules into ammonium NH4

+

Nitrogen compounds in soil

Some plants take up ammonium directly Bacteria in the soil quickly convert

ammonium to nitrite (NO2) and then nitrate - (NO3)

Nitrate is the form of nitrogen usually absorbed by plants

Fertilizer contain a mixture of both ammonium and nitrate

Nitrogen Cycle

NH4

NO2

NO3

bacteria

bacteria bacteria

Non-legumeplants

Other sources of nitrogen

Burning fossil fuels, volcanic activity, and lightning combine nitrogen and oxygen into NO2 and NO3

These are washed into the soil by rain and contribute to the nitrogen cycle

Denitrifying bacteria actually break down ammonium and nitrates returning nitrogen gas to the atmosphere

Legume food crops

Cultivated for thousands of years in both the Old World and New World» seeds easily harvested » seeds low water content and easily stored

for long periods of time These features plus their high protein

content and ease in growing make them ideal crops

Beans and peas -- Pulses

Some of the oldest and most common food crops

Good source of protein average about 25% for beans and 21% for peas

Traditionally cultivated for dry seeds Some varieties today have edible pods Beans warm season annuals Peas grown during the cooler seasons

Common Edible Beans & Peas

Black-eyed peas Butter beans Chick peas Fava (broad) beans Green beans Green peas Kidney bean Lentils

Lima beans Mung beans Navy bean Pinto beans Snow peas Split peas Wax bean

Peanuts

Also called goobers and groundnuts Native to South America Time of domestication is unknown

» gold and silver peanut-shaped jewelry dicovered in Peru in the tomb of a Moche warrior priest

» peanut played a prominent role in the ancient Moche civilization

» Carbon dating of tomb - 290 A.D.

Sixteenth century

Spanish explorers discovered peanuts in South America and took to Europe

Trading introduced peanuts to Africa where it became widely cultivated

The slave trade brought the peanut to North America

Today a staple crop in the south grown in Georgia, North Carolina, Texas, Alabama, Oklahoma and Virginia

Peanut - Arachis hypogea

Unusual plant After pollination the

flower stalk grows downward pushing the developing fruit into the soil

Fruit matures underground - typically with two seeds (peanuts)

Nutrition

Highly nutritious with 45-50% oil and 25-30% protein

Over one billion pounds per year consumed in the US

Mainly as a snack food, in candy, and in peanut butter

Half the U.S. crop is used to make peanut butter

Peanut butter

First developed by a St. Louis physician in the 1890's as a nutritious and easily digested food for invalids who had difficulty chewing

Consume enough peanut butter each year to “fill the Grand Canyon”

Peanut oil

Found in margarine, shortening, salad dressing, and cooking oil

Soaps, cosmetics, and shaving cream Industrial products such as plastics and

paints Pressed cake that remains after the

extraction of oil is used as a high protein livestock feed

Versatility of the peanut

George Washington Carver (1864-1943) » Developed over 300 food and industrial

uses for the peanut » Encouraged its cultivation in the South» Revitalized Southern agriculture exhausted

by years of cotton cultivation » Also introduced other soil-enriching

legumes like soybean

Soybean - Glycine max

Relatively new to the West but used in the Orient for centuries

It was considered one of the sacred crops of the ancient Chinese

Domesticated in northern China at least 3000 years ago

History in North America

Introduced in late 18th or early 19th century

Little interest until the 1920's Today U.S. - world's leading producer Often called the "Cinderella crop" Reasons: versatility of the soybean and

its suitability for growing in the corn belt region

Nutritional value of soybeans

One of the richest foods with 13-25% oil and 30-50% protein

Higher protein content than beef Although originally used solely as animal

feed, the soy protein is used more and more in the human diet

Food use of soybean

Since ancient times in Asia, soybeans have been consumed in hundreds of different ways

Not edible raw Cooked they can be eaten whole Often made into a paste, curd, or "milk"

Soy Products

Soy sauce» Traditionally made by fermenting soybeans in

brine but today some synthetic Soy milk

» Beans soaked in water and pureed » Mixture is heated and the liquid poured off as

soy milk» Non-dairy substitute for milk and baby formula

(for lactose intolerant) individuals

Tofu

Made from the curds of soy milk Extremely versatile and used in main

dishes in Japanese and Chinese meals Made into cheeses, sour cream, and

other imitation dairy products Ice cream-like desert - Tofutti

Soy flour

After the extraction of oil, the meal that remains can be made into flour

Can be mixed with wheat flour in a variety of bread, pasta, baked goods, and breakfast foods

Replacing just a small fraction of the wheat flour with soy flour significantly improves the protein content

Other soybean foods

Miso - (from Japan) prepared from soybeans, salt, and rice; fermented by fungi for a several months and then ground into a paste and used as a spread, in soups, etc

Tempeh- (from Indonesia) fermented soybean cakes made by inoculating parboiled soybeans with a fungus and allowing it to grow for a few days. The fungal mycelium binds the soybeans together into a cake which can be sliced and cooked in various ways

More Soy Products

Textured vegetable protein » Produced by spinning the soy protein into long slender

fibers

» Picks up flavors from other substances

» Made into imitation meats and used as meat extenders

Lecithin - common food additive» Lipid extracted from soybeans

» Stabilizes and extends the shelf life

» Added to packaged foods - cake mixes, instant beverages, whipped toppings, and salad dressings

Soybean oil Food uses

» Cooking oil, salad oil, margarine, shortening, and prepared salad dressings

» Americans consume almost 6 gallons per year

Industrial uses» Paints, inks, soaps, cosmetics, biodiesel fuel

» Soybean-based "plastic" car body built by Henry Ford in 1940

– Ford's commitment to the soybean was so great that at one point he stated his goal was to "grow cars rather than mine them"

Other legumes of interest

Forage plants - alfalfa and clover Super tree - Leucaena leucocephala

» tropical tree that is one of the fastest growing species of woody plants for fire wood, wood pulp, and enriching the soil

Beans of the future:» Winged bean - all parts of plant are edible - pod,

seeds, leaves, flowers, root

» Tepary bean - adapted to arid tropical areas

Summary

Legumes are second only to the cereals in their importance in human nutrition and are an excellent source of high quality protein

Nitrogen fixation is important for generating nitrogen compounds that can be used by plants

Soybean has been transformed into a variety of food products and is increasing its role in the human diet