9.1.6.1 Production of Achu
Achu can be prepared by:
1. Traditional method: Taro corms are cooked until softened, then peeled and pounded in a mortar to obtain a smooth paste locally called achu, herein referred as taro traditional achu (TTA).
2. Flour method: Flour is mixed with water in the ratio of 1: 3 (w/v) and cooked to obtain a paste. During cooking, water is added occasionally and the paste is gently mixed and cooked until a desired consistency is obtained (Figure 9.1.4). The paste obtained from taro flour is referred as taro flour achu (TFA).
3. Chips method: Taro chips are placed in warm water for 30 min and then pounded to form achu, which is referred as taro chips achu (TCA).
A flow diagram for the production of TTA, TFA and TCA is given in Figure 9.1.4.
Figure 9.1.4 Flow diagram for the production of TTA, TFA and TCA.
In Asia, taro paste is prepared with cooked taro, which is mashed into a smooth paste, followed by mixing with sweeteners, shortening and/or seasoning. For the preparation of achu, the cooking of taro corms is carried out at 98 °C for 20 min and then cooled to 20 °C for 20 min followed by slicing (0.5 cm cubes). The slices are then lyophilized for 48 h (Njintang et al., 2008). The dried slices (chips) are further used for the preparation of achu by the chips method.
For TTA, the cooked corms are peeled and pounded in a mortar to obtain a smooth achu. Njintang et al. (2006) prepared TTA in which taro corms (2 kg) were hand peeled and pounded in a mortar for 30 min to obtain a smooth paste. However, for the preparation of achu from TFA, the flours are mixed with distilled water in the ratio of 1: 3 (w/v) and cooked while stirring to obtain a paste. During cooking, water is added occasionally and the paste gently mixed until it is ready (Njintang et al., 2007). The standard procedure from the flour method consisted of mixing 30 g of taro flour with 89 ml of boiling water, followed by stirring in a mortar and the moisture content equilibrated to 76.3 % before further stirring for 20 min to obtain a smooth paste (Njintang et al., 2007).
Achu from TCA is prepared by placing the chips in warm water for 30 min followed by pounding in a mortar to form achu. Njintang et al. (2008) prepared achu by placing chips (6 g) in a porcelain mortar followed by the addition of a defined volume of water according to suitable design. After 30 min hydration, the chips are pounded for 10 min, enough to obtain a homogeneous paste. The time of hydration and pounding may vary, depending upon the changes in process. The paste of TTA and TCA contain starch-filled cells, covered in a continuous amylose-amylopectin gel, which may have some vascular elements and mucilage (Njintang et al., 2008). The cooking of taro corms and cormels before drying is a good approach in the processing of the flour for the preparation of achu (Njintang et al. 2008). The very soft achu texture obtained from taro flour could be due to broken starch grains. The different analysis (functional, rheological and microscopic) reflects the higher degree of starch gelatinization in TCA as compared to TTA. The difference in the properties of achu, prepared from different methods, may be due to particle size (Njintang et al., 2006).
9.1.6.2 Quality Requirements
The acceptability of achu is mainly attributed to colour, texture and flavour. The texture of achu is the most determinant parameter, which is closely dependent on the processing method (Njintang et al., 2000). Achu texture is characterized by its elastic behaviour and average hardness (Njintang, 2003) (Table 9.1.7). The traditional and reconstituted achu of the six cultivars had similar creep recovery values showing an instantaneous deformation (Njintang et al., 2006). The immediate deformation resulting from the applied load per unit surface area is termed as instantaneous elasticity. After sufficient time, deformation per unit time becomes constant, showing steady state creep. Instantaneous recovery during unloading of TTA and TFA reveal the elastic properties of TTA and TFA. The creep viscosities of TTA and TFA were negatively correlated to other visco-elastic parameters (Table 9.1.7). Among the five taro culti-vars, TTA is found to be the more viscous from the varieties Sosso, Ngaoundere yellow and Ekona red, as compared to TFA. Higher values of creep viscosities in maximum cultivars indicated lesser elasticity of TTA as compared to TFA (Table 9.1.7). The trend in creep viscosities of TTA and TFA is reversed with respect to creep steady state compliance, creep compliance, recovery compliance, creep instantaneous compliance and recovery instantaneous compliance (Njintang et al., 2006) in Sosso, Ngaoundere yellow, Ekona white, Ngaoundere yellow and Ekona red varieties. The consumers in general like to have the colour of achu as creamy white as possible. Therefore, the application of taro flour in the preparation of achu becomes a limiting factor due to the browning reactions that may take place during reconstitution (Njintang et al., 2006). Achu prepared from the flour and chips methods generally does not impart the similar texture and flavour like the traditional method. These limitations need to be addressed and corrected in order to obtain good taro flour performance as an ingredient for the preparation of achu.
Table 9.1.7 Comparative visco-elastic characteristics of traditional and reconstituted-flour achu
Parameters
Cultivars | Creep viscosity (104 Pas) | Creep steady state (10-1) | Creep compliance (10-3 Pa-1) | Recovery compliance (10-3 Pa-1) | Creep instantaneous compliance (10-4 Pa-1) | Recovery instantaneous compliance (10-4 Pa-1)
Ekona red | TFA | 89.1±29.6 | 1.7±0.6 | 0.11±0.01 | 0.12±0.02 | 0.46±0.01 | 0.46±0.0
―"― | TTA | 210.5±55.6 | 1.4±0.4 | 0.07±0.01 | 0.08±0.02 | 0.43±0.02 | 0.46±0.03
Ekona white | TFA | 109.7±49.9 | 1.6±0.7 | 0.10±0.01 | 0.10±0.00 | 0.45±0.00 | 0.45±0.02
―"― | TTA | 76.9±9.6 | 2.2±0.2 | 0.10±0.01 | 0.10±0.01 | 0.43±0.01 | 0.45±0.02
Ngaoundéré white | TFA | 662.0±55.2 | 2.0±0.2 | 0.13±0.02 | 0.15±0.03 | 0.58±0.07 | 0.57±0.05
―"― | TTA | 117.4±36.3 | 1.5±0.2 | 0.10±0.01 | 0.11±0.01 | 0.46±0.00 | 0.47±0.01
Ngaoundéré yellow | TFA | 64.2±15.3 | 3.2±0.7 | 0.07±0.01 | 0.08±0.01 | 0.44±0.01 | 0.46±0.01
―"― | TTA | 169.5±16.3 | 1.6±0.2 | 0.06±0.00 | 0.08±0.00 | 0.39±0.02 | 0.40±0.00
Sosso | TFA | 122.7±41.5 | 2.1±0.5 | 0.06±0.00 | 0.07±0.00 | 0.47±0.01 | 0.46±0.01
―"― | TTA | 301.3±64.4 | 1.5±0.2 | 0.04±0.01 | 0.04±0.00 | 0.25±0.08 | 0.24±0.05
TFA = reconstituted achu; TTA = traditionally prepared achu
Source: Njintang (2003)
9.1.6.3 Properties
Reconstituted achu is generally softer in consistency and less appreciated than traditional achu. The estimated water absorption capacity, bulk density, blue value index and penetrometric index are lower in traditional achu than reconstituted achu. In contrast, the viscosity of traditional achu is significantly higher than reconstituted achu (Njintang et al., 2006).