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5. COMPOSITION AND UTILIZATION


5.1 Composition of the Taro Corm and Leaf
5.2 Acridity in Taro
5.3 Utilization of Taro

5.1 Composition of the Taro Corm and Leaf

The main economic parts of the taro plant are the corms and cormels, as well as the leaves. The fresh weight composition of the taro corm is shown in Table 3. The fresh corm has about two-thirds water and 13-29% carbohydrate. The composition of the carbohydrate fraction is shown in Table 4, indicating that the predominant carbohydrate is starch. The starch itself is about four fifths amylopectin and one-fifth amylose. The amylopectin has 22 glucose units per molecule, while the amylose has 490 glucose units per molecule. The starch grains are small and therefore easily digestible. This factor makes taro suitable as a specialty food for allergic infants and persons with alimentary disorders. However, the smallness of the starch grains makes taro less suitable as a source of industrial starch. The starch in the corm is more concentrated at the corm base than at the corm apex.

Taro contains about 7% protein on a dry weight basis. This is more than yam, cassava or sweet potato. The protein fraction is low in histidine, lysine, isoleucine, tryptophan, and methionine, but otherwise rich in all the other essential amino acids. The protein content of the corm is higher towards the corm’s periphery than towards its centre. This implies that care should be taken when peeling the corm; otherwise a disproportionate amount of the protein is lost in the peel.

The taro leaf, like most higher plant leaves, is rich in protein. It contains about 23% protein on a dry weight basis. It is also a rich source of calcium, phosphorus, iron, Vitamin C, thiamine, riboflavin and niacin, which are important constituents of human diet. The fresh taro lamina has about 20% dry matter, while the fresh petiole has only about 6% dry matter.

Table 3. Proximate Composition of the Taro Corm on a Fresh Weight Basis

Component

Content

Moisture

63-85%

Carbohydrate (mostly starch)

13-29%

Protein

1.4-3.0%

Fat

0.16-0.36%

Crude Fibre

0.60-1.18%

Ash

0.60-1.3%

Vitamin C

7-9 mg/100 g

Thiamine

0.18 mg/100 g

Riboflavin

0.04 mg/100 g

Niacin

0.9 mg/100 g

Source: Onwueme, 1994.

5.2 Acridity in Taro

Contact of the raw taro corm with the mouth or skin results in considerable itchiness, acridity and discomfort. Even raw leaves and petioles can cause acridity. The intensity of the acridity varies considerably among taro cultivars, with preference among growers and consumers going to cultivars with low acridity. Also for the same cultivar, environmental stress (such as drought or nutrient stress) during the growing season may result in higher levels of acridity.

Acridity has been attributed to the presence of bundles (called raphides) of calcium oxalate crystals in the taro tissues. Presumably, itchiness arises when the crystals are released and inflict minute punctures on the skin when in contact with it. More recent evidence (Bradbury & Holloway, 1988) suggests that the crystals have to interact with a certain chemical on the raphide surface before acridity is experienced. Fortunately for the consumer, acridity disappears when the taro corm or taro leaf is cooked by boiling, roasting, frying or other means.

Table 4. Percentage Composition of Taro Corm Carbohydrate.

Carbohydrate

%

Starch

77.9

Pentosans

2.6

Crude Fibre

1.4

Dextrin

0.5

Reducing sugars

0.5

Sucrose

0.1

Source: Onwueme, 1994

5.3 Utilization of Taro

By far the largest quantity of taro produced in the Asia/Pacific region is utilised starting from the fresh corm or cormel. They are boiled, baked, roasted or fried and consumed in conjunction with fish, coconut preparations, etc. A favourite and peculiarly Pacific way to prepare taro is to roast it in hot stones (mumu or umu) in dug-out earth ovens. This is quite common when taro is used in feasts and ceremonies.

Taro leaves are used for human food in most producing countries within the region. The leaves are usually boiled or prepared in various ways mixed with other condiments. The high protein content of the leaves favourably complements the high carbohydrate content of the corm which goes with it. Similarly, the stolons of stolon-producing cultivars of taro are often used for human consumption.

Processed, storable, forms of taro are not common in the Asia/Pacific region. Geographically the most widespread are taro chips for human consumption. They are usually made by peeling the corm, washing, slicing into thin pieces and blanching. The pieces are then fried in vegetable oil, allowed to cool and drain, and then packaged. While taro chips are made in most of the countries, their availability is sporadic and quantities produced are small.

Another processed, packaged form of taro is Poi, a sour paste made from boiled taro. Its production and utilisation is quite limited - mainly in the Hawaiian Islands. The details of Poi production are presented when taro cultivation in the Hawaiian Islands is discussed.

Taro flour is available in some places and is used as a thickener for soups and other preparations. To make the flour, the corm is peeled, sliced, and soaked overnight in water. It is then immersed in 0.25% sulphurous acid for 3 hours and blanched in boiling water for 4-5 minutes. The slices are dried at 57-60ºC and then milled into flour. In less elaborate village situations, the sliced corms are simply sun-dried and then milled to produced the flour.

Taro peels and wastes are fed to domestic livestock. Efforts have been made in Hawaii to produce silage from the large quantities of taro tops which are left after the corms are harvested.


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