2. Post-harvest handling
and Value-adding
Techniques for Root
Crops
The root and tuber crops consist of the plant with
swollen roots and underground stems in which
large quantities of starch are stored. Root and
tuber are main sources of calories for a substantial
part of the rural population in many sub-Saharan
countries and also an important part of the urban
diet in a number of the countries. Root and tubers
are high-moisture vegetables but (from 60-90%) but
also considered as semi-perishable crops with
relatively poor post-harvest storage qualities.
3. Another objective of processing is to eliminate
undesirable constituents, such as cyanide in
cassava, the removal of which can be only
effected through series of operations. The most
important operation in processing roots and
tubers is drying.
The major traditional products from roots and
tubers are dried chips, non-gelatinized fermented
fours, fermented gelatinized grits and pre-
gelatinized flour. The root and tuber crops under
consideration include: Cassava, sweet potato and
yam
4. COMMON ROOT CROPS
CASSAVA
Cassava is the most widely cultivated root crop in the
tropics and because of long growth season (8–24
months), its production is limited to the tropical and
subtropical regions in the world. Cassava is a
perennial shrub belonging to the family
Euphorbiaceae. Cassava originated in South America
and subsequently was distributed to tropical and
subtropical regions of Africa and Asia. Cassava plays
an important role as staple for more than 500 million
people in the world due to its high carbohydrate
content.
5. A number of bioactive compounds, namely, Cyanogenic
Glucosides such as linamarin and lotaustralin, Non-
Cyanogenic Glucosides, hydroxycoumarins such as
scopoletin, terpenoids, and flavonoids, are reported in
cassava roots.
Yams
Yam is a member of the monocotyledonous family
Dioscoreaceae and is a staple food in West Africa, Southeast
Asia, and the Caribbean regions. Yam is consumed as raw
yam, cooked soup, and powder or flour in food
preparations. Yam tubers have various bioactive
components, namely, mucin, dioscin, dioscorin, allantoin,
choline, polyphenols, diosgenin, and vitamins such as
carotenoids and tocopherols. Mucilage of yam tuber
contains soluble glycoprotein and dietary fibre. Several
studies have shown hypoglycemic, antimicrobial, and
antioxidant activities of yam extracts.
6. Sweet potato
The origin of sweet potato is Central America, but at present it
is widely grown in many tropical and subtropical countries in
different ecological regions. It is the seventh largest food crop,
grown in tropical, subtropical, and warm temperate regions in
the world. Sweet potato can be grown all around the year under
suitable climatic conditions and complete crop loss under
adverse climatic conditions is rare; thus it is considered as an
“insurance crop.” The crop is particularly important in
Southeast Asia, Oceania, and Latin America regions and China
claims about 90% of total world production. Sweet potatoes are
considered as a typical food security crop for disadvantaged
populations as the crop can be harvested little by little over a
long period of time. In addition, sweet potatoes are rich in
dietary fibre, minerals, vitamins, and bioactive compounds
such as phenolic acids and anthocyanins, which also contribute
to the color of the flesh.
7. Gabi
Colocasia esculenta is a tropical plant grown primarily for its
edible corms, a root vegetable most commonly known as taro,
or kalo. It is the most widely cultivated species of several
plants in the family Araceae that are used as vegetables for
their corms, leaves, and petioles
Potato Potato
, (Solanum tuberosum), annual plant in the nightshade family
(Solanaceae), grown for its starchy edible tubers. The potato is
native to the Peruvian-Bolivian Andes and is one of the
world’s main food crops. Potatoes are frequently served whole
or mashed as a cooked vegetable and are also ground into
potato flour, used in baking and as a thickener for sauces. The
tubers are highly digestible and supply vitamin C, protein,
thiamin, and niacin.
8. STORAGE CONSIDERATION OF
ROOTS AND TUBERS
Cassava
Fresh roots will deteriorate if stored for more than 48 hours,
even in a cool place.
Primary deterioration, or physiological deterioration, begins
shortly after harvest (within 48 hours) and consists of blue-
black streaking followed by browning; It is usually associated
with damage at harvest and the degree of susceptibility varies
among varieties. Under subsistence conditions, the storage
difficulty is therefore overcome by leaving the roots in the
ground until needed. This system has many disadvantages.
Large areas of land cannot be released for planting other crops;
susceptibility to loss is increased,
the quality of cassava diminishes, making it unsuitable for some
preparations; and extra time is needed for intermittent
harvesting of cassava, especially when farms are situated at long
distances from villages.
9. Other rural cassava storage techniques include keeping
uprooted in holes covered with plant material and soil, piling it
in heaps and watering it daily; and putting small quantities into
water. All these practices are based on the principle of
preventing the loss of moisture from the cassava. However,
they can only extend the storage life of cassava from a few days
to a few weeks.
Sweet potato
After harvesting sweet potato are cured by subjecting them to
a temperature of 27oC – 34oC at 85-90% humidity for 4-7 days.
Curing promotes the development of suberized (cork-like)
layers and reduces the incidence of infection by fungal disease
- producing organisms.
10. Sweet Potato
Sound, healthy tubers, can be kept for 2-3 months when
stored in a cool, dark place. Also, it can be stored for short
periods on the floor of well-ventilated rooms, or in trenches
40-50crn deep, with sides, lined with layer of grass. Sweet
potato can be stored in lined pit and covered with a layer of
grass, after which the pit is covered with at least 15cm of soil
(Pfeiffer, 1982).
selecting for storage only the fully mature and undamaged
roots. curing the roots at 30° to 32°C and at 85% to 90%
relative humidity for four to seven days
handling the roots carefully and limiting their handling to a
strict minimum
keeping the storage temperature at the lowest level possible
(an optimum of 13°C)
keeping the relative humidity as close as possible to 85%-
11. Yams
In practice most yams, unlike cassava, are normally stored
fresh. A small proportion is however processed and stored dry
as sun-dried chips or flour. The simplest storage technique is
leaving the tubers in the ground until needed.
A number of structures are traditionally used for yam storage,
the commonest being the yam barn. In this traditional
structure, lack of proper control of physical conditions,
physiological processes, pests and micro-organisms lead to
considerable losses (10-15% by weight in the first 3 months
and 50% after 6 months)
12. Potato
Temperature and tuber damage are the two most important
factors in successful potato storage. Very careful handling is
the key to preventing damage. Harvesting is best done when
the soil is slightly moist to prevent abrasion and the tubers
lifted carefully to avoid damage. Ideally they should be left to
dry for few hours in the field, collected in field containers and
placed in a cool, shady place. Potatoes for food (ware potatoes)
must not be exposed to light for more than a few hours
otherwise they turn green, develop an unpleasant taste and
may become toxic.
13. It is important to make the distinction between ware potato
storage and seed potato storage. The objective of ware potato
storage main is to obtain the maximum quantity of tubers, of
acceptable quality to the consumers, at a rate to meet consumer
demand. This requires the lowest possible quantitative and
qualitative losses, with no or little sprouting, kept in the dark
to prevent greening and firm tubers, all at an economical cost.
In seed potatoes storage the objective is to have optimum
development of sprouts prior to planting. In both cases the
farmer requires the maximum return from his investment in
time, materials, equipment and buildings.
Temperature influences the rate of respiration of the tubers,
sprout growth and the development of microorganisms
causing rotting
Ware potatoes can be stored up to six months in tropical
highlands without significant losses provided that:
14. the variety of potato is one with a long dormancy or the
tubers are treated with a sprout inhibitor if storage duration
is required to continue beyond the period of dormancy;
the potatoes are free from diseases, damage or insect
infestation;
storage temperatures are kept to levels that do not induce
high rates of respiration;
the relative humidity within the store is kept at sufficiently
high levels to reduce water loss from the tubers;
the potatoes are not wet as a result of rain or condensation.
Ware potatoes can be stored up to six months in tropical
highlands without significant losses provided that:
15. VALUE- ADDING OF ROOT CROPS
Products of root and tuber crops are manufactures through a
wide range of processes. Some products, such as beverages
made from sweet potatoes, may acquire additional processing.
For each process there are generally various options that differ
in technological sophistication. Starch, for example, can be
extracted either manually with rustics equipment or by means
of high technology in a fully automated factory. The type and
complexity of the technology you use depends on several
factors:
16. Scale of operation
Capital investment
Operator’s level of education
Value of product
Conversion of extraction rate
Product quality or purity
Raw material characteristics
Availability of services (water,
fuel and electricity)
Cost of labor.
17. ROOTS AND TUBER
PR0DUCTS
PRIMARY
PROCESSED
1.Fresh root and
tubers
At harvest
Clean and graded
With improved shelf life
Prepared
Non-commercial quality (for
animal feed)
Boiled (tubers) to remove anti
nutritional
Ensiled (roots) for storage as
animal feed.
18. 2. Fresh leaves and vines
3. Sun-dried pieces, chips and slices or roots
and tuber
4. Flakes and granules
5. Flour
6. Fermented starch
7. Modified starches
SECONDARY PROCESSED
1. Starch and Flour
a.Bakery good, soups and sauces bases, processed meats, pastas,
noodles, beverages bases and snack foods
b.Textiles, paper, glue, plywood, oil and pharmaceuticals
c.Animal feed rations
d.Alcohol
e.Glucose
f.Monosodium glutamate
19. 2. Fresh roots and tubers
a. Frozen, canned and vacuum-packed
b. Protein enriched via fermentation
c. Use in beverages, jam and sauce production
d. Snack foods (chips, crisp, etc)
e. Delicacies
3. By-product
a. Animal feed
b. Products of industrial processing
