Mineral
Potassium is the major mineral in
most root crops while sodium tends to be low. This makes some root crops
particularly valuable in the diet of patients with high blood pressure, who
have to restrict their sodium intake. In such cases the high potassium to
sodium ratio may be an additional benefit (Meneely and Battarblee, 1976).
However, high potassium foods are usually omitted in the diet of people with
renal failure (McCay et al., 1975). As root crops are low in physic acid
relative to cereals, those minerals liable to inactivation by dietary physic
acid are more available than in cereals.
This is especially important for iron,
which has been found to be 100 percent available in banana (Marriott and
Lancaster, 1983). In addition the high vitamin C concentration in some root
crops may help to render soluble the iron and make it more available than in
cereals and other vegetable foods. In the United Kingdom the iron supply from
potato ranks third of all individual food sources, accounting for up to 7
percent of the total household dietary iron intake. True e, al. (1978) found
that 150 g of potato will supply 2.3 to 19.3 percent of the dietary requirement
for iron recommended by the Food and Nutrition Board of the National Research
Council of America. there is some doubt about the availability of calcium and
phosphorus in cocoyam owing to the oxalate content.
An important, often unrecognized,
mineral contribution that potato can make is in the appreciable amount of
iodine it contains. This could be significant in goitrous areas of Africa and
Asia where iodine intake is low or marginal. Since over 96 percent of the zinc
in potato is available, again due to low levels of phytate, potato can also
significantly contribute this mineral. Yam can supply a substantial portion of
the manganese and phosphorus requirement of adults and to a lesser extent the
copper and magnesium. As indicated in Table 4.12, a hectare of sweet potato
will provide the calcium requirement for 60 times as many people and 12 times
the requirement of iron as the same area of land planted with rice.
Root crop leaves
Apart from the yellow variety of
sweet potato, which contains a high amount of beta-carotenes (up to 30 mg
retinol equivalent percent) most of the other root crops contain only
negligible amounts. However, their leaves contain a substantial amount of
beta-carotenes that could contribute significantly to the daily requirement of
vitamin A, especially for children, thereby helping to eradicate the ocular
diseases affecting about six to eight million children from Asia, Africa and
Latin America. Dietary retinol obtained from the consumption of animal foods is
relatively expensive and contributes about 14 and 20 percent to the vitamin A
intake of people in Asia and Africa respectively. Beta-carotenes from leaves
such as sweet potato or cassava, which contain about 800 mg/100 g and which is
about the same as beef liver, contribute as much as 86 percent in Asia and 80
percent in Africa.
The quantity of root crop leaves
required to meet the average daily requirement of retinol differs considerably,
with Cassava requiring only 50 g, dark green vegetable leaves 73 g, sweet potato
leaves 78 g and taro leaves 133 g.
Cassava leaves have a crude protein
content of 20-35 percent on a dry weight basis. The quality of the leaf protein
is generally good though it is deficient in methionine. Cassava leaves are low
in crude fibre and relatively high in calcium and phosphorus. Cassava varieties
in which the tuber contains cyanogenic glycosides usually show a similar
content in their leaves.
Methods of cooking and processing
Like many other foods, roots and
tubers are rarely eaten raw. They normally undergo some form of processing and
cooking before consumption. The methods of processing and cooking range from
simple boiling to elaborate fermentation, drying and grinding to make flour,
depending on the varieties of roots and tubers. The basic purpose of these
methods is to make roots and tubers and their products more palatable and
digestible and to make them safe for human consumption. Processing also extends
the storage life of roots and tubers, which are often highly perishable in their
fresh condition. Processing also provides a variety of products which are more
convenient to cook, prepare and consume than the original raw materials. Women
play a very active role in all the stages involved in the production and
processing of root crops. Assessment from five states in Nigeria indicated that
in cassava production women on average complete 34 percent of the field
preparation and 77 percent of the planting of cassava, 86 percent of the
weeding and 77 percent of the harvesting. The post-harvest activities of
processing, storage and marketing, are undertaken mainly by women, though
recent studies indicate that men are beginning to take an interest in the
processing of root crops through the purchasing and management of electrically
operated grinding machines.
Cassava
Although raw sweet cassava is
occasionally eaten in the Congo region, Tanzania and West Africa, cassava is
not generally consumed raw. A large variety of processing techniques have been
developed in different parts of the world resulting in a wide variety of
products. Those techniques serve not only to render the root palatable, and in
many cases storable, but they also have the effect of eliminating or reducing
cyanide (HCN) content to acceptable levels. Many processes such as soaking and
fermenting have been designed specifically to detoxify the root. Others, such
as boiling and roasting are designed to make cassava products more palatable.
The degree of reduction of cyanide in the final product varies greatly with the
type of processing techniques used. Many of the complex techniques used around
the world today originated in South America and were introduced to the other
regions with the cassava plant, or in some cases at a later date. Other
processes have been developed independently in the producing countries.
Roasting, boiling, frying
In Latin America roasting is the
simplest technique, but it is not commonly practiced. It is used only when no
cooking utensil is available. The whole roots are buried in hot ashes or placed
in front of the fire until cooked through. Sweet cassava roots are more often
prepared by boiling and are eaten either hot or cold or sometimes mashed. These
are general methods all over the world. In Latin America, a soup or stew called
cancocho or cocido is prepared by boiling cassava roots with vegetables. The
technique of deep frying cassava in fat is thought to have been introduced by
Europeans. In Uganda, the roots are peeled, washed, wrapped in banana leaves
and steamed in a pan (Goode, 1974). Roasting sweet cassava in ashes is widely
practiced in Africa. In South Africa, bitter varieties are also roasted but are
first peeled and rubbed with tobacco. In Zambia roots are often soaked before
roasting. Fried cassava is prepared after peeling, by washing, slicing and then
frying in oil.
Grating, pounding, baking, or
boiling
In Latin America, cassava roots arc
grated on spiny palm trunks or pounded into a pulp. The pulp is then squeezed
by hand and cooked in a variety of ways. Several groups shape the pulp into pies
or cakes which are then baked in hot ashes, sometimes being wrapped in a
protective covering of leaves before baking. Some groups, such as the
Nambicuara, sun dry the pulp balls, wrap them in leaves and place them in a
basket or bury them in the ground, to be used at times of food shortage. After
several months, they retrieve the fermented balls and cook them by baking in
hot ashes. The cassava pulp is boiled either by dropping the pie or balls into
the boiling water or by stirring the pulp into water to form a sort of
porridge. Porridge is sometimes made as a preliminary ste in the preparation of
flour. The pulp is boiled and skimmed off with a plated spoon, strained through
a mat of thin sticks and finally roasted in a pan to make flour.
Steaming
and fermenting peujeum. A
traditional product prepared in Java is peujeum (Stanton and Wallbridge, 1969).
The peeled cassava roots are steamed until tender, allowed to cool and then
dusted with finely powdered ragi, a rice flour starter culture flavoured with spices.
The cassava mash mixed with ragi is wrapped in banana leaves in an earthenware
pot and left for one or two days to ferment. The peujeum has a refreshing
acidic and slightly alcoholic flavour and is either eaten immediately or baked.
Sun drying and pounding or grinding
Into flour
Cassava roots, which may be soaked
in water first, are sun dried and pounded into a noun This seems to be a
general method everywhere. In the preparation of fuku in Zaire the dried roots
are pounded with partially fermented corn, the quantity depending on the
season. The resulting flour is roasted on a Rat tray to stop further
fermentation of the mixture, which was initiated by the fermenting maize. The
flour is eaten as a gruel prepared in boiling water. Cassava flour is the basis
of several other foods. In the preparation of nsua the flour is mixed with
water and filtered through a jute bag. After removal of the water the paste is
wrapped in a leaf and eaten raw. Ntinga is prepared in a similar way except
that a portion of the paste is boiled in water and mixed with the remaining
uncooked paste. The mixture is wrapped up in a leaf and cooked again.
Grating, pressing and roasting or
baking to make flour or bread
These methods are widely used to
prepare cassava flour or cassava bread in tropical America. Details vary from
one group to another but the methods fall into two main groups depending on
whether or not the roots are given a preliminary soaking:
Unsoaked
roots. The process is very laborious and
takes two or more days. The freshly dug roots are first washed to remove excess
soil and then peeled. The tubers are then reduced to a pulp, normally by
grating, but sometimes by crushing in a mortar or between stones. The pulp is
squeezed with a variety of devices to expel the liquid. The moist pulp is left
overnight in containers. Next day it is rubbed through a sieve to remove any
coarse fibres. The pulp is then cooked in one of two ways depending on whether
bread or flour is needed.
To prepare bread, the cassava pulp is placed on a hot clay or stone griddle,
pressed down into a thin layer and toasted on each side. The large, flat
circular cakes are known as cassava bread, cassava casabe, beigu or couac
depending on the locality. When fresh, the bread is soft inside and some people
prefer to prepare it daily. More commonly, cassava bread is sun cried for
several days during which time it hardens through. It can be stored in this
form for several months. Cassava bread is normally eaten dipped into gruel or
stew, which serves to soften it (Jones, 1959). Other types of bread can be made
by adding additional ingredients to the cassava, for example in Brazil a
special bread is prepared by adding pounded or grated Brazil nut to the cassava
pulp.
To prepare flour, the cassava pulp is stirred continuously while cooking on
the griddle in order to prevent lumps forming. The resulting flour also stores
well and is variously known as farinha de mandioca, farinha seca, farinha
surruhy, kwak or koeak. It may be eaten dry, mixed with hot or cold water to
make a paste or gruel or mixed with other foods. Various modifications and
other methods, both simple and complex, are also used.
A traditional Philippine dish based
on the cassava root is known as cassava rice or landang. Freshly dug roots are
peeled and grated, the grated mass is put into jute sacks and pressed between
two wooden blocks to squeeze out the juice. It is then put into a winnowing
basket and whirled until pellets are formed. At intervals the pellets are
sieved and those not passing through are put back and whirled again. The
pellets are dried on a mat and then steamed in a coconut shell on a screen mesh
placed over a vat of boiling water. The cooked pellets are placed in the
winnowing basket and separated by hand. In an alternative process the peeled
roots are submerged in fresh, clean water in an earthenware jar or wooden
vessel for five to seven days until soft. They are then macerated, the fibres are
removed and the remainder is dried and made into pellets as described. The
pellets from both methods are dried thoroughly in the sun for three to five
days and stored until needed. Cassava rice can be eaten without further
cooking.
Soaked
roots. In Latin America the cassava
tubers, either peeled or unpeeled, are soaked in water usually for three to
eight days but sometimes even longer IO allow some fermentation to occur. After
removal from the water the peels are removed where necessary and the softened
roots are either crushed by hand or grated to m eke a pulp and processed as for
farinha seca. This method is also used to prepare cassava bread but more often
the end product is cassava flour. Many variations of this basic process exist.
In West Africa, after fermentation
the cassava is pounded or ground to produce a paste which is consumed or stored
depending on the country. In parts of Nigeria, the paste is boiled for 20
minutes and then removed for more pounding. In Cameroon, the wet paste is
divided into two portions and wrapped in leaves before cooking. In Mozambique
cassava paste is mixed with flavouring ingredients including onion and salt,
before being wrapped in leaves and boiled.
The preparation of pastes by
pounding cassava is a peculiarly African process not practiced in South
America. The pastes are consumed in a variety of forms, the best known being
fufu. The term fufu and its variants are widely used in West Africa to refer to
a sticky dough or porridge prepared from any pounded starchy root including
yam, cocoyam and cassava.
In the preparation of fufu the roots
are peeled, washed, grated and left to ferment for two to three days. To
ferment the cassava the grated mass is either simply left to stand (Doku, 1969)
or put into sacks and weighed with stones to squeeze out the juice. The
resulting dough is used at once for cooking or it is stored in basins covered
with cold water which is changed daily. The resulting product is consumed in
different ways in different countries accompanied by stew or soup.
Gari the most popular cassava
product consumed in Africa. To prepare gari cassava roots are washed, peeled
and grated. The pulp is then placed in cloth bags or sacks made from jute and
left to ferment, the fermentation time varying from three to six days. It is
the fermentation process that gives gari its characteristic sour flavour, which
distinguishes it from Brazilian farinha. During this stage pressure is applied
to squeeze out the cassava juice. The cassava pulp, at about 50 percent water
content, is taken out of the sacks and sieved to remove any fibrous material.
It is then heated or "garified" in shallow pans and stirred
continuously until it becomes light and crisp.
Gari is eaten in a variety of forms.
It is sometimes eaten dry or made into a paste. More commonly it is steeped in
cold water, thus causing the particles to swell and soften but retaining their
granular form. Alternatively, gari is mixed with cold water to make a thin
gruel which is drunk with milk. A popular way of preparing gari in Nigeria is
to soak it in boiling water to form a thick paste, eba, sometimes known as
fufu.
Products essentially similar to gari
are known by various names and are made throughout West Africa with minor
variations to the processing. Recently gari processing has been mechanized in
Nigeria.
A regional standard for Africa for
gari was adopted by the Codex Alimentarius Commission (1986) which classified
gari into five categories according to grain size and specified their essential
composition and quality factors. These include raw material cassava and
characteristic colour, taste and odour of gari and specification on acidity
(not less than 0.6 percent nor more than 1 percent m/m determined as lactic
acid). Total hydrocyanic acid (not exceeding 2 mg/kg determined as free HCN),
moisture (not exceeding 12 percent m/m), crude fibre (not exceeding 2 percent
m/m), ash content (not exceeding 2.75 percent m/m) and should be practically
free from extraneous matter. Optionally edible fats or oils and salt may be added
and gari may be enriched with added vitamins, proteins and other nutrients but
addition of food additives was not allowed.
The methods used to process cassava
in the South Pacific vary from island to island although boiling or baking the
tubers are fairly widespread techniques. In the Solomon Islands the roots are
often grated and mixed with coconut or banana as a pudding. In the New
Hebrides, cassava is grated, wrapped in banana leaves and baked in an oven.
One method peculiar to the islanders
in the South Pacific is the fermentation of tuber roots in pits, a process
which prolongs the shelf-life of the product indefinitely. On the island of
Mango in Tonga an abandoned pit estimated to be about 100 years old was found
to contain food in an edible condition. Traditionally the pit is dug to a depth
depending on the size of the family and lined with leaves of coconut, giant
swamp taro or banana. The prepared food, which could be cassava, banana, taro
or a mixture of all three, is placed in the pit to fill it and covered with
more leaves, with rocks or logs placed on top to keep it in place. Fermentation
proceeds for four to six weeks, after which the whole or part of the product is
removed. Sometimes the fermentation is carried out with the addition of fresh water
and sea water. In a modification of this process in Fiji, the unpeeled cassava
root is fermented in a basked lowered into a lagoon. When it is required, it is
removed, drained and pounded to a dough. The dough is kneaded with previously
grated coconut, formed into balls, wrapped in breadfruit leaves and eaten
either steamed or boiled. This product keeps for several months. If fresh water
is used for the fermentation, the pulp is mixed with sugar or fruit, wrapped in
leaves and steamed or boiled. This is known as bila and is a favourite food in
Fiji. It keeps for several days.
Extraction of starch to prepare
sipipa, tapioca and pot bammie
The juice obtained from grated
cassava contains a certain amount of starch which settles out on standing for a
few hours. In the Americas the liquid is decanted off, the starch residue is
rinsed and then processed. It may be sun dried and eaten raw, or baked into
crisp cakes called sipipa, which are highly prized as a delicacy by some
groups. If it is still wet the starch is heated on a griddle when the starch
grains burst and form granules known as tapioca flakes or globules. In Jamaica,
starch is obtained by mixing grated cassava roots with water and straining the
pulp through a towel. The starch is allowed to settle out for a few hours. The
water is decanted off and the starch is either dried briefly, then salted and
baked into pot bammie, or dried for several days, pounded in a mortar, mixed
with flour and cooked into dumplings.
In Asia the traditional methods of
extracting starch are similar to those used in tropical America and Africa. The
starch in the extracted cassava juice is washed and sun dried on a mat. Moist
wet starch is used commercially to produce tapioca. To prepare tapioca the wet
starch is gelatinized into globules and sun dried.
In the South Pacific starch is
extracted from cassava roots by grating, washing and draining and is then dried
in an oven to produce a granular, tapioca-like product.
In Padaids Island the pulp, from
which the starch has been extracted, is also used. It is formed into balls of
five to six cm in diameter and dried over a fire for about a week. When
required for eating the dried cassava is grated again and mixed with coconut
milk and water (Massal and Barrau, 1956).
In the Solomon Islands of Anuta and
Tikopia, cassava is used to produce a fermented product called ma manioka on
Anuta and masi manioka on Tikopia (Yen, 1978). On Tikopia, the cassava roots
are soaked in water for five or more days until soft. They are then peeled, broken
up, squeezed and ensiled in pits lined with leaves. On Anuta, where there is no
suitable surface water, the roots are packed loosely in pits and left for a few
weeks. They are then recovered, peeled and resumed to the same pits for a
funkier period. Ma is used as an emergency food baked alone or in combination
with freshly pounded starchy roots and fruits.
Processing cassava juice - cassava
reep, beer
The cassava juice or yard, obtained
by pressing the grated cassava, is commonly used to prepare sauces and
beverages in South America and the West Indies. The yard is boiled down to a
thick syrupy consistency. The soup is known as cassava reep in the West Indies.
Groups inhabiting the area around the headwaters of the Amazon tributaries
produce a refreshing sweet-tasting drink by boiling yard for several hours. An
alcoholic drink may also be prepared by fermenting the cassava juice.
Preparation of beverages from
cassava root
In addition to cassava juice, the
whole root, the sliced, grated or pounded roots and cassava bread or flour are
all used as starting materials for the preparation of beverages. Both
non-alcoholic and alcoholic drinks are made.
Non-alcoholic
drinks. The roots are peeled, grated,
squeezed by hand and cooked. When cold they are masticated for a few minutes
and allowed to stand for a short period but not long enough to produce an
alcoholic drink. Similar drinks are made from cassava flour or bread.
Alcoholic
drinks . The preparation of cassava beers
is widespread in tropical America. These are known as either kashiri or chicha.
A number of different methods are used. The most common methods are the
following:
Processing without mastication. The drink is usually prepared by fermenting whole cassava
roots. The tubers are left for up to a week in a stream for fermentation to
occur. They are then removed and m ashed. Water is added to the mash which is
left to stand for three days before drinking. Other methods of preparation are
also used.
Many groups use cassava bread to
prepare beverages. In Guyana freshly made cassava bread is dipped into water,
placed in a shallow heap in a dark corner of the house and left, covered with
leaves, for three to five days while moulds develop. The broken bread is then
placed in large earthenware pots and left for a further two to five days.
Finally water is added and fermentation takes place to produce a mildly
intoxicating beverage. Other methods are used in Brazil and in Suriname to
prepare alcoholic drinks from cassava bread.
Processing with mastication. The custom of mastication in the preparation of alcoholic
drinks is common in tropical America. The majority of the traditional alcoholic
drinks are prepared in this way. Mastication speeds up fermentation because the
salivary enzymes initiate the conversion of starch to sugar.
A variety of beverages is prepared
from masticated cassava. In the Brazilian tropical forest, thinly sliced and
boiled pieces of cassava are squeezed, chewed and left to ferment for one to
three days. In the West Indies, a drink known as paiwari is prepared by this
method. Other fruits, vegetables, maize and sweet potato may also be added as
ingredients to the beer.
Beverage making from cassava is not
generally practiced in Africa. Goode (1974) describes a method of preparation
of beer in Uganda. The flour is mixed with water and left to ferment for a
week. It is then roasted over a fire and put into a container to which water
and yeast are added. After about a week the liquid is drained, sugar is added
and the beer is left to ferment for four days. Cassava flour is also used to
make beer in South Africa, Southwest Zambia and Angola.
Cooking and processing of yam
By far the greater part of the
world's yam crop is consumed fresh. Traditionally processed yam products are
made in most yam-growing areas, usually as a way of utilizing tubers that are
not fit for storage.
Usually fresh yam is peeled, boiled
and pounded until a sticky elastic dough is produced. This is called pounded
yam or yam fulu.
The only processed yam product
traditionally made at village level is yam flour. Except by the Yoruba people
in Nigeria, yam flour is regarded as an inferior substitute for freshly pounded
yam because it is often made from damaged tubers. Yam flour is favoured in the
Yoruba area where the reconstituted food is known as amala. To a limited
extent, yam flour is also manufactured in Ghana where it is known as kokonte.
The nutritional value of yam flour is the same as that of pounded yam.
Preparation of yam flour
The tubers are sliced to a thickness
of about 10 mm, more or less, depending on the dryness of the weather. The
slices are then parboiled and allowed to cool in the cooking water. The
parboiled slices are peeled and dried in the sun to reduce the moisture
content.
The dried slices are then ground to
flour in a wooden mortar and repeatedly sieved to produce a uniform texture.
Today small hand-operated or enginedriven corn mills or flour mills are
increasingly used.
Industrial processing
Yams have not been processed to any
significant extent commercially. Dehydrated yam flours and yam flakes have been
produced by sun drying. The manufacture of fried products from D. alata has
also been attempted recently. Both chips and French fries have been
manufactured. Preservation of yam in brine has been attempted, but with little
success. Since pounded yam has so much prestige and is the most popular way of
eating yam, two attempts have been made to commercialize the process. The first
was the production of dehydrated pounded yam by drum drying. This product could
then be reconstituted without further processing. This production was first
attempted in Côte d'Ivoire in the mid-1960s, under the trade name
"Foutoupret", by air drying precooked, grated or mashed yam (Coursey,
1967). Onayemi and Potter (1974) used drum drying to produce a flake which can
easily be reconstituted into pounded yarn by mixing with boiling water. This is
the basis of the commercial product called "Poundo" in Nigeria, which
was initially successful. To reduce wastage of raw material, peeling is done by
using a 10 percent lye at 104°C with varying immersion times depending on the
cultivar of yam (Steele and Sammy, 1976). Sulphite is added to prevent enzymic
browning. In the second commercial project a type of food processor resembling
a blender was developed. The yam is cooked, fumed and churned in a process
equivalent to pounding, to give enough pounded yam for two to four servings.
Both projects appeared at first to be very successful, but later people
reverted to the manual pounding of yam which gives a characteristic viscosity
and firmness that is difficult to simulate mechanically. Attempts to
manufacture fried yam chips, similar to French fried potatoes have been
reported from Puerto Rico.
Cocoyam
Cocoyam is used in essentially the
same way as yam. It can be eaten boiled, fried or pounded into fufu, although
it is not considered as prestigious as yam. It has also been made info porridge
or pottage, as well as chips and flour. Cocoyam flour has the added advantage
that it is highly digestible and so is used for invalids and as an ingredient
in baby foods.
Taro is the traditional staple in
the Pacific Islands, where it is made into a series of food products similar to
those described for cassava. Poi is a very popular Hawaiian and Polynesian dish
made by pressure cooking the raw tuber, which is then peeled and mashed to a
semi-fluid consistency. It is passed through a series of strainers, the final
one having openings of about 0.5 mm diameter. It is then bagged and sold, or
else stored at room temperature where it undergoes lactic acid fermentation.
Coconut products can be added to the fermented poi before consumption. In
Nigeria cocoyam is grated, mixed with condiments and wrapped in leaves. It is
steamed for about 30 minutes and served with sauce. Popularly known as ikokore,
it is very common in the western Nigeria. A modification is available in
Cameroon where cocoyam is made into balls and cooked with additional
ingredients. This is known as epankoko.
Banana and plantain
One advantage of banana is that the
dessert varieties can be eaten raw without any funkier processing. In many
parts of Africa cooking banana is prepared by boiling or steaming, mashing,
baking, drying or pounding to fufu. In Cameroon, green banana is boiled and
served in a sauce of palm oil with fish, cooked meat, green beans, haricot
beans and seasonings. In Uganda, where it is the staple, it is boiled with
other ingredients including beans. Ghee is added together with pepper, salt and
onions. This dish is called akatogo. Omuwumbo is prepared by wrapping the pulp
in banana leaves and steaming it for about an hour. It is then pressed in the
hands to a firm mass and eaten. The green form of banana is dried and stored.
Known as mutere, it may be used for cooking after grinding into flour (Goode,
1974), but it is mainly used as a famine reserve. The same procedure is used in
Gabon, in Cameroon, in South and Central America and in the West Indies
(Fawcet, 1921).
A soup called sancocho is made in
Colombia by boiling slices of green banana with cassava and other vegetables,
while in the West Indies boiled green banana is served with salted fish or
meat.
Mention has already been made of the
fermentation of banana in pits in the Pacific. The fermented product is formed
into loaves and baked. Known as mast, it keeps for over a year while buried in
the pit, and baked masi stored in air-tight baskets in a deep hole may last for
generations (Cox, 1980). The starch pseudo-stem and corm of the false banana,
or ensete, is prepared by similar methods in Ethiopia. The fermented product,
called kocho is used to prepare a flat, baked bread. Ripe bananas are preserved
by sun drying. Known as banana figs, they are eaten as a sweetmeats. This
product keeps for months or even years.
In West Africa bananas are parboiled
before drying. Oven drying is practiced in Polynesia. The dried product is then
bound tightly in leaves and stored until it is needed (Massal and Barrau,
1956). A similar technique is practiced in India.
In Burundi where banana occupies
about 25 percent of the arable land, it is mainly used for the production of
beer. It has been estimated that local beer is consumed at a rate of
1.21/caput/day. Making beer from banana is common in East Africa. Green banana
is buried in pits covered with leaves to ripen for about a week, at which stage
it also starts to ferment. The peels are removed, the pulp is mixed with grass
in a trough and the juice is squeezed out. The residue is washed and added to
the bulk of the juice. Roasted sorghum flour or millet is added and the mass is
fermented for one to two days, covered with fresh banana leaves. In a
modification of the process, honey is added to the fermented banana pulp.
Sweet potato
Sweet potato can also be eaten
boiled, fried or roasted. When sliced, dried in the sun and ground, it gives a
flour that remains in good condition for a long time. In Indonesia sweet potato
is soaked in salt water for about an hour to inhibit microbial growth before
drying. The flour is used as a dough conditioner in bread manufacturing and as
a stabilizer in the ice-cream industry.
Sweet potato has been processed into
chips (crisps) in much the same way as potato and the product is now popular in
Asia. The sugar-coated chips are popular in China, the sailed variety is
popular in the United States of America, while those spiced with cayenne pepper
and citric acid have been tested in Bangladesh with favourable results (Kay,
1985). Starch is produced from sweet potato in much the same way as from the
other starchy roots except that the solution is kept alkaline (pH 8.6) by using
lime, which helps to flocculate impurities and dissolve the pigments. The
starch shows properties intermediate between potato starch and corn/ cassava
starch in terms of viscosity and other characteristics. In Japan about 90
percent of the starch produced from sweet potato is used in the manufacture of
starch syrup, glucose and isomerized glucose syrup, lactic acid beverages,
bread and other food manufacturing industries.
In Japan, sweet potato starch is
also used for the production of distilled spirits called shochu (Sakamoto and
Bouwkamp, 1985). The process is very similar to that of whisky production
except that the koji, equivalent to the malt starter in whisky production, is
obtained by inoculating steamed rice soaked in water overnight with Aspergillus
kawachii for two days at 35 to 37°C. The koji is mixed with starch water and
yeast to promote saccharification and fermentation. The filtrate is finally
distilled. The yield is about 8001 from I tonne of sweet potato.
Potato
The preparation of chuño negro is
very similar to that of chuño blanco except that during trampling the skin is
not removed, the soaking process is omitted, and the residue is simply sun
dried after trampling. The product is dark brown-black in colour, and hence the
name. It is usually soaked in water for one or two days before being cooked in
order to remove any residual bitter flavours.
A more prestigious potato
preparation that is popular in large cities and in Peru is papa seca. The
potato is boiled, peeled, sliced and sun dried and then ground into a fine
flour. The flour is normally used for a special dish called carapulca which is
prepared with meat, tomato, onions and garlic, but it may also be made into
soup.
These traditional techniques are
particularly important for processing the bitter varieties of potato with a
high alkaloid content, which would otherwise have been too toxic for food use.
Christiansen (1977) found that the level of glycoalkaloids could be reduced,
from 30 mg/100 g in the fresh potato, to about 4 mg in chuño blanco and 16 mg
in chuño negro. In the Andean highlands, where frost, storm or drought can lead
to destruction of crops, irregular yields and food shortages, it is essential
to cultivate some frost-resistant bitter varieties of potato that can be
processed into reserve food from year to year.
A good review of simple technologies
for root crop processing is provided by the United Nations Development Fund for
Women publication, Root crop processing, 1989.