STARCHY STAPLES • Potato, Sweet potato, Cassava• Most of staples popular in Pakistan• Starch food reserves in underground organs

(roots or modified stem)• Starch-polymer of glucose molecule• Tropical origin• High in carbohydrates, low in proteins

STARCH MOLECULE• Amylose poly-(1-4) glucose, a straight chain• Tends to coil up into a helix• Amylopectin is poly(1-4) glucose with branches• Open molecular structure than amylose• Because it has more ends broken more quickly than amylose by amylase enzymes

Modified Organs

• Rhizome underground horizontal stem • Food storage organ• Leaves reduced in form of scales on

surface of rhizome• Roots adventitious• Buds on nodes give rise to new plants

• Tubers enlarged storage tip of rhizome• White potato• Eyes are buds that form new plant• Bulbs modified storage organs mostly in

monocots• Underground stems with fleshy leaves• Onions, Tulips• New bulbs can develop in the leaves axils

White Potatoes

• Solanum tuberosum associated with Ireland• Established in 1965 • Dietry staple food for Irish people• Ideal climate and soil for potato • Small plots of land sufficient to feed a family• Historian link population explosion to

presence of reliable food

• Average adult consumption of potato 4 to 6kg each day

• Reliance on potatoes set the disaster: Irish potato famine of 1845-1849

• Pathogen Phytophthora infestans cause of late blight of potato

• Fungus attacks leaves, blacken them stopping tuber growth

• In cool wet weather, fungus kills plant within a week

• Disease appeared in 1845 in Ireland• Widespread destruction of potato crop• 1million people died from starvation• Resulted 20-30% decline of population in

Ireland in Ireland in less than a decade• Conflicts between English rulers and Irish

people another reason• In history, Ireland a colony of English people

and Irish were shamelessly exploited

Solanum tuberosum• Genus Solanum- cultivated potato • 2,000 species in Solanaceae• S. tuberosum 6,000 cultivars• Europe produce 70% of world crop• China second leading producer and next Brazil• Stem of two types• Ordinary foliage bearing stems• Underground rhizome that ends in tubers

• Anatomically, tuber modified version of dicot stem

• Enlarged pith, a ring of vascular bundle, and narrow cortex

• Vascular tissue appear black in potato chips with narrow cortex on outside and large pith

within ring• Cool season crop with maximum tuber

production ranging under 15to 18C

• Higher temperature inhibit tuber production (29C)• Potato cultivation through propagation by

seed potatoes, small tubers or cut pieces containing at least one eye

• Seed potatoes cultivation- asexual reproduction producing plants genetically identical to their parents and maintaining desired traits within a cultivar

• Seed potatoes checked for diseases• Fast method• Disadvantage- Share same susceptibility

to adverse environmental conditions• Susceptible to Phytophthora infestans

and Colorado potato beetle• Potato beetles became resistant to

chemical insecticides used for control

white

Red Russet

Potatoes Varieties

• Round white used for baking, chips, fires

• Russets elongate, cylindrical tubers, excellent for baking purposes, common in Pakistan

• Russets potatoes high in starch• Round red and long white relatively new

• Good for boiling steaming, roasting

• Potatoes rich in carbohydrates (25% of fresh weight)

• Parenchyma cells within pith filled with starch grains

• Vitamin, minerals and fibers in cortex and periderm

• Nutritional value enhanced when consumed with skin

Sweet Potatoes

• Ipomoea batatus• Storage root in family Convolvulaceae• Habitat vine• Columbus discovered sweet potatoes• Native to South America• China dominating country in production

• Drier, starchier variety in Northern States

• Sweeter, moist, deep orange (Yams) common in South

• Rich in carbohydrates, vitamins and minerals

• 50% more calories than white potatoes• Root source of carotene, vitamin A, C• Thanksgiving diet

Bananas• Important dietary staple in in tropical

countries• Popular dessert, source of starch and

potassium• Sweet banana• Tree habitat • Herbaceous with height of 6meters or

20 feet

• Bananas native to Southeast Asia• Cultivated 2500 years• Genus Musa in Musaceae• Require tropical climate with constant

moisture• Cultivated for food, fibre, foliage

(natural waxed paper)

Banana Tree

Plantains• Important food in poor countries• Planta-sole of foot• Genus Plantago• P. ovata P. afra (Grown in India)• Twice the size of banana• Sour or sweet in taste• Ripe black plantain more sweet than banana

Plantains

• Ten times more B-carotene than banana

• Source of vitamin A, C, B6, potassium, iron and magnesium

• Helpful in treating ulcers

• Green, unripe varieties have enzymes for healing

CASSAVA• Manihot esculenta• Family Euphorbiaceae• Known as Manioc, Yuca, Mandioca• Ranks fourth behind rice, sugar and corn as

source of calories in tropical countries• Tall shrub with palmately compound leaves• Can tolerate dry period upto 6 moths

CASSAVA

Cassava plant Roots

• Varieties may be sweet or bitter• Hydrocyanic acid (HCN)• If not removed, toxin may cause death by

cyanide poisoning• HCN liberate through enzymatic actions

cyanogenic glycosides• Sweet and bitter varieties differ only on

cyanide content• Environmental conditions influence cyanide

production

• Sweet variety can be bitter under different condition

• Traditional methods for treating bitter ones varies• May include drying, soaking, boiling, draining• Processed to make flour• In Indonesia, peeled roots sliced, dried in sun,

allows HCN to diffuse• Resulting chips called gaplek

• Stored for long period of time or ground into flour

• Breads, cakes, cookies, noodles• Starch rich (30% of fresh weight)• Protein content is being improved

through cassava breeding programmes• Roots also contain calcium, vitamin B and

C• Being used for Bioethanol

Recommended Links• http://www.all-about-potatoes.com/types-of-

potatoes.html• www.botany.org• http://www.geneconserve.pro.br/bio_rogers.

htm• http://www.mrothery.co.uk/biochm/biochmn

otes.htm