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9. Taro: Technological Interventions
9.1. Taro Flour, Achu and Starch
Harish K. Sharma, Pragati Kaushal, and Bahadur Singh
Department of Food Engineering and Technology, Sant Longowal Institute of Engineering and Technology, Sangrur, India
9.1.1 Taro
Taro (Colocasia esculenta), which is from the family Araceae, is a widely-produced tuber in tropical and semi-tropical areas for its underground corms. The different varieties of taro such as dasheen, eddo and kalo are popular in many parts of the world including Asia, West Africa, South America, Central America, and the Caribbean and Polynesian islands (www.wikipedia.com). The species, Colocasia esculenta (L.) Schott, in the family Araceae, contributes to important food crops. Taro corms contain nutritionally beneficial components such as resistant starch and mucilage.
World-wide, taro ranks fourteenth among staple vegetable crops, with about 12 million tonnes produced globally from about 2 million hectares with an average yield of 6.5 t/ha (FAO, 2010). It is primarily grown for its edible tubers and 81 % of its cormels contribute to the edible portion. It is consumed world-wide for its nutritional value (Oscarsson and Savage, 2007). Taro corms (Figure 9.1.1) contain a considerable amount of starch (70–80 g/100 g dw). However, the variations in starch content may be due to storage and temperature. During storage of tubers, the sucrose and starch content declines in wild-type tubers, whereas glucose and fructose levels remain unchanged (Hajirezaei et al., 2003). In transgenic tubers, starch degradation is accelerated and fructose levels increase slightly. Furthermore, a change in carbohydrate metabolism is accompanied by an elevated level of phosphorylated intermediates, and a stimulated rate of respiration (Hajirezaei et al., 2003).
Figure 9.1.1 Taro corm.
At low temperatures, stored tubers contain significantly lower concentrations of starch than those stored at higher temperatures (Knutsson, 2012). This may be due to the impact of high temperatures on starch transformation, increased respiration losses and the fact that sugar had been used for germination by tubers stored at high temperatures. An increased storage temperature results in decreased accumulation of sugar, but it also shortens the life of the tubers, since high storage temperatures activate the physiological processes within the tubers and increase their ability to start germinating (Fogelfors, 2001).
Taro contains 77.5 % moisture per 100 g edible corm portion (Lambert, 1982), while upland cultivated taro corms contain moisture content in the range of 63.6-72.4 % (Huang et al., 2007). Taro is an excellent energy source, supplying energy in the range 97.1-118.3 kcal/100 g fresh taro (Huang et al., 2007). Taro corms are moderately good sources of water-soluble vitamins compared to other tropical roots (Amon et al., 2011). Taro contains minerals such as sodium, calcium, potassium and magnesium, whose salts regulate the acid-base balance of the body (Lewu et al., 2010) and also contains phosphorus, zinc and iron (Lambert, 1982). Taro leaves are also frequently consumed as a vegetable in different parts of the world. Taro leaves contain a good amount of protein and are an excellent source of carotene, minerals (phosphorous, calcium, potassium, iron), vitamins (vitamin A, thiamine, riboflavin, niacin, vitamin C) and dietary fiber (Opara, 2001). Taro leaves contain greater amounts of the vitamin B-complex than whole milk (Lee, 1999) and are higher in protein than that of tannia (new cocoyam; Xanthosoma sagittifolium) and all other nutrients except oil (Deo et al., 2009). The fresh taro leaf lamina and petiole contain 80 and 94 % moisture, respectively (Deo et al., 2009). The compositional pattern of taro is given in Table 9.1.1.
Table 9.1.1 Composition of taro
- | Taro corms | Taro leaves | Taro petioles
Calories | 102.0 | 34.0 | 24.0 | 29.0
Moisture (%) | —. | 89.9 | — | 93.0
Protein (g) | 1.8 | 2.5 | 0.5 | 0.9
Fat (g) | 0.1 | 1.0 | 0.2 | 0.2
Carbohydrate (g) | 23.0 | 5.3 | 6.0 | 3.8
Fiber (g) | 1.0 | 2.1 | 0.9 | 1.0
Ash (g) | — | 1.3 |… | 1.3
Ca (mg) | 51.0 | 95.0 | 49.0 | 25.0
P (mg) | 88.0 | 338.0 | 25.0 | 12.0
Fe (mg) | 1.2 | 2.0 | 0.9 | 0.5
B-carotene equiv (mg) | Trace | 3300.0 | 180 (μg) | 180
Ascorbic Acid (mg) | 8.0 | 37.0 | 13.0 | 13.0
Thiamine (mg) | 0.1 | 0.1 | 0.02 | Trace
Riboflavin (mg) | 0.03 | 0.3 | 0.04 | Trace
Niacin (mg) | 0.8 | 1.5 | 0.4 | 0.4
References | FAO (1972) | O’Hair et al. (1982) | FAO (1972) | O’Hair et al. (1982)
9.1.2 Versatility of Taro
The digestibility of taro makes this tuber unique because of its small starch grains and hypoallergenic qualities. The starch extracted from taro corms appears as fine granules in the 0.5–5.0 micron range, and thus offers smooth-textured starch gel (Tattiyakul et al., 2005). Because of the small sizes of its starch granules, taro is highly digestible (98.5 %), and as such has been reported for use in the preparation of infant foods in Hawaii and other Pacific islands (Fetoh and Salwa, 2010). Taro corms, having yellow flesh, contain higher levels of β-carotene as compared to the corms with white flesh. Foods containing high levels of carotenoids have been shown to protect against chronic diseases, including certain cancers, cardiovascular disease and diabetes (Englberger et al., 2003). Taro has a low glycemic index and as such is an excellent food for diabetes, who require glucose to be released slowly into their bloodstream. The corms of Colocasia antiquorum are reported to have antioxidative and anti-inflammatory properties, which may be due to the presence of anthocyanins such as cyanidin-3-glucoside, pelargonidin-3-glucoside and cyanidin-3-chemnoside (Amon et al., 2011). The extracted anthocyanins from taro with 50 % methanol are identified as pelargonidin 3-glucoside, cyanindin 3-rhamnoside and cyanidin 3-glucoside (Harvey et al., 2006). Levels of anthocyanins are found highest in the skin of the corm, 16.0 mg%, with equal amounts, 4.29 mg%, in both corm and petiole (Harvey et al., 2006). Traditionally, Colocasia antiquorum is also used to alleviate stomach swelling and pain, and acts as an antipyretic. A South African study of traditional foods showed that a boiled extract of taro, or “indumbe” as it is colloquially known, possesses very high antioxidative activities (Lindsey et al., 2002).