Starchy Staples

1
Starchy Staples For better or worse, we get a
significant number of our carbohydrate calories
from the plants and plant parts well consider
today. The plants well consider store starch in
specialized organs that are modified stems or
roots. The modified storage organs of stems
include
2

• stolons these are aboveground horizontal stems
  from which buds and roots may emerge at nodes.
  The best example is strawberries, in which we
  call the stolons runners. Another place you
  see stolons in this area is on beach grasses.

3

• rhizome rhizomes are underground stems (and
  may even have small leaves along them) with
  adventitious roots developing along the
  underside, and new shoots arising from nodes.
  The rhizome may itself be swollen into a storage
  organ, as in gingerroot. Alternatively, the tips
  of rhizomes can be expanded into storage organs,
  tubers, like the potato.

4
Since tubers (or expanded rhizomes) are stems,
the buds are sites for potential formation of new
above ground stems and plantlets. Thats what
the eyes of potatoes are. The roots themselves
can be expanded into tubers, as well. The most
familiar example of a fleshy, tuberous root is
the sweet potato. There are no nodes on tuberous
roots.
5
The taproot (main root) can also become a storage
organ. The best examples here are carrots and
turnips. Carrots havent always been (nor are
they all) orange.
6

• Carrots were first domesticated in Afghanistan
  from a wild Daucus carota that usually has a
  white root. However, many root colours occur,
  including red, purple and black, all due to
  anthocyanin pigments. The orange carrots we eat
  today were selected in Holland during the 17th
  century.
• There are two other forms of storage organs
  formed from modified stems bulbs and corms.
• bulbs are modified underground, upright stems
  with a basal plate, growing point, enclosed by
  thick, fleshy scales.
• Examples onion, garlic,
• tulip, lily

7

• corms corms are also short, thick, underground
  stems of plants that act as storage organs.
  Corms mostly are found in monocots, and consist
  of one (or occasionally more) internode(s) that
  is (are) used for storage. Inside a protective
  skin, it is mostly parenchyma cells. The obvious
  difference from bulbs is the internal structure
  solid in corms and layered in bulbs. Examples of
  corms crocuses, taro, Chinese water chestnut

8
Lets look, at least briefly, at the major
starchy staples Potato The potato originates in
the Andean highlands, at an elevation of around
4000 m. Many types of potatoes still grow in that
area. Among them are various types with brightly
coloured flesh blue and red most
common. The colours are anthocyanins, and
may have valuable antioxidant properties.
9
The white potato was being grown in northern
South America and Central America in the 16th
century when Pizarro and the conquistadors
invaded. It was a staple for Inca
civilization. The Spanish took the white potato
(Solanum tuberosum) back to Europe. It was used
mostly for animal food before the 18th century.
Why didnt Europe take to the potato rapidly? It
is from the family Solanaceae, with tomatoes,
bell peppers, eggplant, tobacco, deadly
nightshade and jimsonweed. All except tobacco
have poisonous leaves due to toxic alkaloids (and
you may consider tobacco leaves poisonous, too!).
10
Glycoalkaloids (particularly solanine) are also
present in the tuber when you see green
patches. Solanine causes weakness, confusion and
sometimes hallucinations in sub lethal toxic
doses. It somehow affects mitochondria. The
symptoms (but not mechanism) are also effects of
jimsonweed consumption.
In jimsonweed the alkaloids are atropine,
scopolamine and hyoscyamine. Atropine and
scopolamine are acetylcholine antagonists (block
neuromuscular synapses).
11
Back to potatoes - There are 200 tuber-bearing
species of Solanum. Only 8 have been cultivated.
There are, however, almost 6000 cultivars of S.
tuberosum. 85 of North American potatoes come
from 12 cultivars. Nutritional values of potatoes
(with skins) per 100g Carbohydrates 19g
Dietary fiber 2g Protein
2g Fat 0.1g Water 75g Iron, Vitamins C and
B6 gt10RDI Vitamins B1,B2,B3 lt10RDI Ca,Mg,P,K,N
a lt10RDI Much of this nutrient value is in the
cell layer just beneath the skin.
12

• Sir Walter Raleigh introduced potatoes to
  Ireland. It grew well there, and provided a ready
  source of calories for poor Irish Catholics,
  subjugated by the English.
• With this new food, the population of Ireland
  grew from 1.5 million in 1760 to 8.5 million in
  1840. Europes population doubled from 140 to 266
  million between 1700 and 1800. It wasnt the
  potato alone.
• the industrial revolution occurred simultaneously
• animal breeding became much more sophisticated
• farmers learned about crop rotation
• farmers also learned to use manure to fertilize
  fields
• But dependence on a single crop is dangerous.

13
Potatoes are low in vitamins A and D. A
potato-dependent diet can lead to rickets. Potato
blight (Phytophthora infestans) appeared in
Europe in 1844, and in Ireland in 1845. 75 of
that crop was lost. In 1847 80 was lost. This
was the Irish potato famine.
Infected tubers develop grey or dark patches that
are reddish brown beneath the skin, and quickly
decay to a foul-smelling mush caused by the
infestation of secondary soft bacterial rots.
Seemingly healthy tubers may rot later when in
storage.
14
Prior to the potato blight, half of Irish farms
were less than 5 acres, but sufficient to feed a
family. The blight meant families could not pay
their land tax. The Penal Laws meant that the
Irish lost their land and became tenant farmers
on the land. Crop failure meant they could not
pay the land rent, either. As a result of the
potato famine, 3 million people died and 4
million emigrated. Today, Europe and Russia
produce over 70 of the world crop. In terms of
individual countries Russia ranks 1st, China 2nd,
Poland 3rd, and the U.S. 4th. Potato blight is
again important strains resistant to the
dominant fungicide have appeared, and unlike the
original one, they reproduce sexually, producing
variety.
15
Resistance to one or more strains of blight has
been found in native Andean potatoes,
particularly in S. bulbocastanum. The gene
responsible for resistance has been identified,
cloned and inserted into a susceptible
domesticated cultivar. Is this use of molecular
genetic tools (and the production of a GM potato)
something we should oppose or support? Discussion
16
The other potatoes sweet potatoes and
yams Sweet potato (Ipomoea batatas), in the same
family (Convulvulaceae) as morning glory, has a
tuberous storage root. The plant is a perennial
vine. Sweet potato was domesticated in tropical
America at least 5,000 YBP. It spread from the
site of origin into the Caribbean and also onto
Polynesian Islands and New Zealand. In North
America, we tend to call sweet potatoes yams,
which is incorrect.
17
Sweet potatoes require a long, warm growing
season. The root matures in 2 9 months. They
are well adapted to tropical growing conditions,
but susceptible to chilling injury. That explains
the importance of this crop throughout the
tropics. China is the largest producer (of a
world total of 127 million metric tons, China
produces 105 million), but it has become
important in the diet of many African countries
(e.g. Burundi, where per capita consumption is
130 kg annually). There are different flesh
colours grown and preferred in different areas.
In North America, we want the yellow-orange colour
18
There are white-fleshed types used in Spanish
cooking, and called batatas the Japanese
kotobuki is yellow the Okinawan cultivar is
purple fleshed in New Zealand they grow an old
isolate, the kumara, that is red-purple. Sweet
potatoes are rich in dietary fiber and vitamins
A, C, and B6. Preliminary evidence suggests that
it is a good source of carbohydrates for
diabetics that evidence suggests it stabilizes
blood sugar levels and reduces insulin
resistance, even though a portion of the
carbohydrate is present as sugar (thats the
reason it tastes sweet).
19
True yams are not species of Ipomoea, but species
in the genus Dioscorea. They are large tubers
that can be 2.5 m long and weigh 70 kg. They are
a staple food in tropical West Africa, China,
Southeast Asia, Central America, the Caribbean,
and Pacific Islands. There are many species in
the genus, but only 10 are major food sources.
Cultivation in Africa and Asia may date back to
8000 BC.
20
Nigeria is the leading producer, growing more
than 2/3 of the worlds total crop. The African
yam contains toxins, and preparation involves
days of pounding, leaching and boiling to remove
them before cooking. Yams are treated in
relatively similar ways in Asia. Not all the
chemicals have negative impact. Yams are the
original source of diosgenin, used in research to
make the first birth control pills. Diosgenin
inhibits ovulation. Other saponins (sapogenic
glycosides) were used to make cortisone. Again
there are different flesh colours White (D.
rotunda) and yellow (D. cayenensis) are
native to Africa. Purple yam (D. alata) is from
southeast Asia A different white yam (D.
opposita) is Chinese
21
Yams vary in toxicity. Some, e.g.. Japanese
mountain yam, can be pickled to remove toxic
components, then grated and eaten raw. Elsewhere
yams may be boiled, roasted, fried or cooked in
soups and stews. The places where yam remains an
important food source are mostly West Africa and
the Pacific Islands.
22
The air potato (D. bulbifera) is native to
Africa and Asia, but has become invasive in
Florida. What is eaten (where its eaten) is a
bulbil, a tuber-like growth at the base of the
leaves. The time to grow a crop of yams
is 8 12 months. Harvest is difficult because
the tubers go so deep into the soil. As a food
source, yams have been replaced in recent years
by cassava.
the bulbil
23
Cassava (or manioc) we know cassava essentially
only as the source for tapioca. However, Manihot
esculenta is an important food source for many
tropical populations. Its origin is in tropical
America, probably Brazil where wild plants can
still be found. The species is in the spurge
family, Euphorbiaceae, that also includes
cactus-like desert species of southern Africa,
poinsettia, castor bean and rubber trees. It was
cultivated before recorded history in tropical
America (Central and South America) and long
before European exploration. Export to Europe
and Africa resulted from Spanish and
Portuguese exploration. It has become a
staple crop in Africa since it grows well
under harsh conditions (flooding,
drought).
24
Cassava has a high percentage of starch (30 of
fresh weight), and also vitamin C (25 mg/100 g),
calcium (50 mg/100g), and phosphorus (40
mg/100g), but little protein (1). There isnt
much protein in the root, but the leaves have
about 30 protein. For these leaves to be a major
protein source, they need to be supplemented with
a source of methionine. Cassava is a carbohydrate
staple for 1 billion people. Cassava produces
starch energy so efficiently that the U.S. D.O.E.
is sequencing the genome in the belief it could
become a source of renewable energy.
25
The cassava root must be processed to be
consumed. The epidermal layer accumulates
cyanogenic glycosides. Initial digestion of them
releases highly toxic hydrocyanic acid. There are
two varieties (not biologically, but
practically) a sweet form that can be eaten by
peeling the root, then cooking it by boiling,
steaming or frying. It has fairly low levels of
the cyanogenic glycosides. The other form is
called bitter it has high levels of the
glycosides. To prepare it for safe consumption it
is peeled, dried, soaked, boiled, grated,
drained, and fermented. In South America it is
peeled, presoaked, grated, then squeezed to
express liquid that contains most of the
glycosides. Then it is roasted to dryness, to be
reconstituted when needed.
26
A problem is that the amount of cyanogenic
glycosides increases when the plant is under
drought stress. In sub-Saharan Africa, where the
protection offered by sufficient sulfur (from
protein) in the diet against small to moderate
glycoside intake is frequently absent, a disease
called konso occurs. The motor parts of the
cortex are affected, causing an irreversible
paralysis the disease name means tied
legs. The Rockefeller Foundation is supporting
genetic research to reduce cyanogenic glycoside
production and the problem where cassava is so
important as a source of calories. Australian
research is trying to reduce the remnant HCN in
processed cassava.
27
Jerusalem artichoke is a misnomer for the tuber
of a North American sunflower, Helianthus
tuberosus. It was harvested by native
Americans, and carried back to Europe by Samuel
Champlain in the early 17th century. The common
name may result from it being called sunflower in
Italian (girasole).
28
The tubers store the carbohydrate inulin instead
of starch. From commercial crops the inulin is
used as a source for fructose production. Theyve
been promoted, but not yet produced, as a
potential source of biofuels. The tubers break
down when cooked (e.g. in a stew) into a tender,
tasty root vegetable particularly healthy for
diabetics. The plants are easy to grow, and will
return from even small bits of tuber left after
digging up a crop. That also makes them weedy for
many gardeners. The quality of the tubers
apparently also declines when they are left,
rather than replanted in fertile soil. They are
also notorious as a cause of flatulence.
29
Taro - is a corm harvested from Colocasia
esculenta. We know it from Hawaiian tradition,
where it is sweetened and called poi, and from
Chinese cooking, where a kind of dim sum called
wu kwok is a deep fried, egg-shaped ball of
taro with a little pork and spice inside (or,
from a fancier dish I call duck with yam that
has a layer of duck meat and skin atop a layer of
mashed taro, the whole lightly breaded and deep
fried). Leaves and flowers are also eaten in some
places. The plant is actually inedible if
ingested raw because of needle-shaped raphides in
the plant cells. Raphides are a type of
elongated crystalline form of calcium oxalate
aggregated in bundles within a plant cell.
Because of the needle-like form, large numbers in
the tissue of, say, a leaf can render the leaf
unpalatable to herbivores.
30
Taro leaves are a good source of thiamin,
riboflavin, iron, P, K, Cu, Mn, and zinc, and a
very good source of vitamins B6, C, and niacin.
Taro corms are very high in starch, and are a
good source of dietary fiber.
31
Finally, a couple of oddities Oca otherwise
called New Zealand yam, biologically it is Oxalis
tuberosa. Its origin is probably Peru, from where
it was exported to Europe. In Europe it was a
failure, due to specific environmental needs. In
New Zealand it was and remains successful. What
is used is a starchy tuber that is said to
resemble a small, shrivelled carrot. They come in
a variety of colors, including red, white, purple
and yellow. Like potatoes, the consumable part is
mostly carbohydrate, but here is very high in
sugar content (thus quite sweet). Preparation
includes use raw, pickled, boiled, fried, and in
soups or stews.
32
Jicama is a tropical vine grown for its
tuberous root. Jicama, too, comes from tropical
Mexico and Central America. Spanish explorers
carried it to Asia and the Pacific Islands, as
well as using it on their ships. It stores well,
retaining crispness and moistness (like a fresh
carrot). Both on the ships and currently it is
eaten raw, for example in salads. It can also be
cooked, for example in a mixed vegetable stir
fry. After spreading widely, jicama was
re-introduced to South America in what was then
French Guiana in the mid-1800s and is still
grown in the South American tropics.