13.3.1 Nutritional Factors
EFY is a highly nutritious crop. The proximate compositions of EFY tubers are given in Table 13.1. It is also rich in minerals, vitamin A, thiamine, niacin and riboflavin (Sankaran et al., 2008a.b). The mineral contents (mg/100 g tuber, dry weight basis) are as follows: Na (26.22–26.77), K (26.12–26.55), Ca (2.20-2.28) and Mg (1.2–1.42) (Lenka and Nedunchezhiyan, 2014).
Table 13.1 Proximate biochemical composition of EFY (on dry weight basis)
Nutrients/species | Percent composition
Moisture | 65.06–71.79
Crude protein | 1.12-1.63
Crude fat | 0.105-0.141
Total ash | 4.78-3.98
Crude fibre | 2.66-2.81
Starch | 23.37–18.58
Total sugar | 1.93-1.57
Updated from: Singh et al. (1999);Sreerag et al. (2014)
13.3.2 Anti-nutritional Factors (Acridity)
The edible part of EFY is the tuber (corm). Historical reports of these EFY suggest that tubers are acrid, causing irritation and inflammation, which causes swelling of mouth and throat. The EFY may result in gastrointestinal disturbances and is also responsible for several health complications when large amounts are ingested into the human body (Bhandari and Kawabat., 2004; Saadi and Mondal, 2011). Moreover, this health complication is related to the presence of needle-like raphides composed of toxic anti-nutrients and calcium oxalate crystals. The intensity of irritation has been found to differ widely among different species. Among edible species, acrid cultivars show calcium oxalate levels in the range of 660–850 mg/100 g, while non-acrid cultivars have acridity in the range of 120–140 mg/100g (Srivastava et al., 2014; Sundaresan and Nambian, 2008). In addition, phytate is widespread in roots and tubers. Oxalates and phytate are well-known anti-nutrients of plant food, and are associated with a decrease in the bioavailability of nutritionally significant mineral elements. These organic substances can bind essential minerals to form insoluble or indigestible complexes in the lumen of intestinal tracts, thereby preventing their absorption (Jayachandran et al., 2010; Kumar et al., 2014).
Processing to Remove Anti-Nutrient Factors from EFY Acridity of the tubers can be reduced/eliminated by suitable processing methods, such as boiling, baking, frying and drying by different modes. The traditional processing systems like pre-soaking and the addition of ingredients like tamarind, curd, etc., in the cooking medium can reduce acridity. Among the various methods, boiling is found to be the most effective method in reducing the calcium oxalate content by 50 % (Sundaresan and Nambisan, 2008). Studies on drum drying of EFY have indicated a reduction of about 25 % in calcium oxalate content in the dried product (Sundaresan and Nambisan, 2008). Indigenous people in Southern Yunnan and Hunan, Central China, cook konjac tubers with plant ash or plaster in hot water to eliminate acridity. The Jinuo people of China use young konjac leaves (A. yunnanensis, A. yuloensis, A. krausei) as vegetables. They cook them in boiling water and fry in oil to eliminate bitterness and acidity (Chattopadhyay et al., 2009; Kumar et al, 2014; Long, 1998).
13.4 Traditional Processing and Value Addition of EFY
As mentioned earlier, five species of Amorphophallus have been used as a food source (Chua et al., 2010). Flour extracted from the corm of this species is used to make noodles, tofu and snacks. The gel prepared from flour of the corm has been used by the Chinese for detoxification, tumour-suppression, blood stasis alleviation and phlegm liquefaction. In Japan, Amorphophallus is a household name and is used in the preparation of konyakku. The edible aroid like Amorphophallus is a tuberous vegetable with good taste and nutritive value. It forms an important food source throughout the world due to the indisputable palatability, cooking quality, medical utility and therapeutic value of its tubers (Suja et al., 2014).
13.4.1 EFY as Food
The corms and cormels of EFY are usually boiled or baked and eaten as vegetable. The sprouts and petioles which resemble asparagus sprouts are used as vegetables in some parts of Asia (Misra et al., 2007). In Tripura, the tribal people consume the leaf lamina, petiole (pseudostem), corm and cormels of wild species of EFY (Sankaran et al., 2008a, b). In China, the bulbils of A. yuloensis are eaten by indigenous people in the southern and south-western Yunnan Provinces (Long, 1998).
Traditional Indian Foods The EFY-based traditional food products like deep fried chips and roasted cubes are common in the Tamil Nadu State of India. The roasted yam cubes are prepared by cutting EFY into cubes and cooking with fresh spices (ginger and garlic paste) followed by slow cooking in a pan until crispiness is obtained. Also, it is a common ingredient of sambar, a savory vegetable stew of drumsticks, okra (ladies finger), potatoes, egg plant, onion and tomatoes prepared with ground spices and seasoned with tamarind juice, very common in South India (Ray, 2015). In the Tamil Nadu and Kerala states of India, the traditional curry dishes like Kaalan, Mezukku Puratti, Poriyal and Aviyal are also prepared using EFY as an ingredient. In Goa, the EFY-based soup khatkhatem is prepared by cutting tubers into cubes, which are deep fried before being added to a simmering pot of vegetarian stew. Also, the EFY chutney (mixed paste) is also prepared, which has an important place in Goan dishes. In the Car Nicobar Islands of India, the tribes consume wild EFY tubers collected from the forest. They are boiled in hot water with salt and chilli powder and consumed along with wild pork (Damodaran et al., 2008).
Traditional Japanese Foods in Japan A. kojac is used in many traditional foods. Konnyaku, a traditional Japanese recipe, is a gel-like food having a light taste and an elastic texture. It is made by adding slaked lime to the colloidal solution of the flour obtained from the dried tubers of A. konjac (Nagayama et al., 1975). The Ito konnyaku is a type of Japanese food consisting of konjac cut into noodle-like strips. It is usually sold in plastic bags with accompanying water. The konnyaku made in noodle form is called shirataki and used in other Japanese foods like sukiyaki and gyudon (Akesowan, 2002, 2008). Konjac can also be made into a popular Asian fruit jelly snack, known as konjac candy, served in plastic cups. The indigenous people make noodles and sauce from EFY tubers. The konjac snack is a very popular food item in the Western Hunan province of China (Long, 1998).
Traditional Chinese and Korean foods Encouraged by Japanese needs and an opening up of the Western food industry, it has been reported that China and Korea have been planting thousands of hectares of konjac as a cash crop in poor rural areas. Official policies in China and Korea have existed since the mid-1990s, encouraging rural regions, including minority-held provinces, to grow konjac for food and health products (Parry, 2010). Kojac curd can be braised with duck and chicken meat, because it has a high amount of absorbing flavour, for example., “konjac braised with duck” has become a traditional Chinese dish, which can also be processed as canned food (Liu et al., 1998). In addition, konjac curd can be properly dehydrated and puffed, adjusted in flavour and colour and made into various foods such as astringent and hot dried beef (Liu et al., 1998). Chinese steamed bread (CSB), a kind of wheat-based traditional fermented Chinese food, has been consumed for almost two millennia in China. It is gaining popularity and widely consumed by people living in Southeast Asia. The basic ingredients for making CSB are wheat flour, water, yeast and salt; sugar and shortening are optional. In general, KGM addition was found to produce dough with a weak network. Moreover, the bread became softer and more resistant to staling on storage (Liu et al., 2014; Sim et al., 2011; Zhu, 2014).