Figure 9.1.2 Schematic representation of taro flour production.
Cleaning, Peeling and Trimming The cleaning operation aims to remove soil and other foreign material from the taro corm surface, portion damaged by weevils or other pests, and any other unwanted portions of the corms. Taro corms are washed properly to ensure that all sand and dirt are removed. Washing them thoroughly with water is essential to remove adhering mucilage. Clean cloth and sacking can also be used to facilitate washing. Taro corms are peeled immediately with an abrasive peeler or other tools. Various peeling machines that have been developed are not universally accepted because of the cost concern for many small-scale producers and too much wastage.
Cutting Taro cutting separates corms into small pieces and increases their drying surface, as more surface area is exposed to the air and speeds up the drying process. Slicing root and tubers prior to cooking is also important, as it allows rapid and even cooking. Manually cutting of taro corms is carried out by stainless steel knives to avoid undesirable browning reactions. The cutting of taro corms is a tedious exercise and induces enzymatic browning reactions.
Blanching Taro corms suffer from enzymatic browning reactions. The enzyme, polyphenol oxidase catalyzes the oxidation of polyphenols, resulting in the complex formation leading to change in colour. Taro slices are exposed to mild heat treatment to prevent enzymatic browning and off-flavour prior to inactivation of enzymes to preserve colour, modify texture, and preserve nutritional value. Hot water and steam are the most commonly used heating media for blanching in the food industry. The peeled taro corms undergo a pre-cooking stage in boiling water to avoid browning and improve final yield. Corms are dipped in hot water for a few minutes before drying to stop the enzymatic action, which may not be stopped by the sun-drying process (FAO, 1990). Blanching of taro corms may be carried out at 90 °C using distilled water for 2 min to inactivate polyphenol oxidase enzyme (Kaushal et al., 2012). For taro (Colocasia esculenta), the pressure cooking of 7 min and blanching at temperature 65 °C for 1 h are preferred (Dash and Gurumoorthi, 2011). The effects of blanching of taro are given in Table 9.1.4.
Table 9.1.4 Effects of blanching of taro (Colocasia esculenta)
S. no | Sample | Treatment | Observations | References
1 | Taro flour | Blanching in hot Water (100 °C/2 min), 2 % w/v NaCl, 2 % w/v Sodium Hypochlorite and 50 % v/v Ethanol | Greatest reducing sugar content in blanched samples whereas samples treated with 2 % sodium chloride solution had the least | Baidoo et al. (2014)
2 | Taro | Blanching (98 °C for 10 s) leaves | Inactivation of peroxidase enzyme. About 13.74, 43.12 and 63.19 % loss of ascorbic acid when blanched at 98 °C for 10s, 1 min and 3 min resp. | Kaushal et al. (2013)
3 | Processed taro | Pressure cooking For 7 min and Blanching at 65 °C for 1 h | Oxalate loss (35.58 %), Dash and protein loss (24.56 %), Calcium loss (3.57 %), phosphorous loss (0.05 %) and iron loss (4.76 %) | Gurumoorthi (2011)
Drying The drying time can be reduced by increasing the surface area of the slices in relation to their volume. Therefore, the drying properties of the larger slices can be improved by reducing the size. The rate of drying during the first stage is dependent on the ability of the air passing over the material to absorb and remove moisture. The slices, once dried, should not crumble, but rather should break easily.
A range of driers are available for the drying of taro corms, but their selection depends on the cost of the drier and type of the product being dried. Traditionally, taro is dried in the open air under the sun. Artificial drying is suggested under different climatic conditions, because then the operating parameters can be precisely controlled. Taro slices can be dried overnight in a hot air oven at 50 °C (Adane et al., 2013). Opara (2003) suggested drying of taro corms at 57–60 °C, whereas Nurtama and Lin (2010) dried taro corms at 45 °C for 24 h.
Milling Traditionally, dried pieces of taro roots are ground in mortars and pestles. At the large scale, a range of manual or powered plate, disc mills are available (www.fao.org). Dried taro slices are passed into a milling machine (hammers mill, grinder, etc.) to obtain taro flour, which is further passed through a screen to achieve the desired particle size. After grinding, the flour is sieved to remove large particles, which are returned to the mill for further grinding. By using a vibrating or rotating sieve, sieving can be mechanized. The dried taro samples can be ground into a fine powder by a hammer mill to pass through a 250 pm sieve (Amon et al., 2011). Other milling machines used for producing taro flour are the Kenwood mill/blender (Darkwa and Darkwa, 2013), hammer mill equipped with a 500 pm sieve (Aboubakar et al., 2010) and a laboratory grinder (Kaur et al., 2013).
Packaging and Labeling The taro flour obtained is then packed into polythene bags or other packaging materials to prevent adsorption of moisture. Packing and sealing should be done immediately by removing as much air as possible from inside the package, to avoid rehydration and insect infestation. The requirement of packaging material for the product is based on transportation requirements and shelf life. The labeling should have all the information specified by the national/international regulatory agencies.
9.1.5.2 Methods for Production of Taro Flour
Taro flour can be produced by the method shown in Figure 9.1.3. In this process, taro corms are peeled, sliced (5 mm) for air drying (60 °C/20 h) and freeze drying (60 °C/24 h), followed by milling (Fitz mill) to 0.18 mm (Nip et al., 1989). The taro flour produced can be slow in the size reduction process due to the thickness and hardness of the dried taro slices. Traditionally, in the Pacific area, precooked taro flour is prepared by boiling tubers to a soft texture, followed by drying and grinding. Uncooked taro flour is more stable during drying than precooked flour (Njintang and Mbofung, 2003). The drying of taro flour, especially that obtained from gelatinized slices at high temperatures, affects the colour and is more susceptible to gelatinization (Njintang and Mbofung, 2003). The drying at higher temperatures is more efficient, but it adversely affects product quality, functionality and performance of the flour during reconstitution (Njintang et al., 2001a, c). Taro flour has been prepared by different researchers. The chronological progression for the production of taro flour is given in Table 9.1.5.
Figure 9.1.3 Production of taro flour.
Table 9.1.5 Chronological progression for the production of taro flour
S. No. | Salient features | Reference