Indeed, the high content of calcium oxalate crystals in some varieties of Colocasia has long been used to partly explain the acridity or irritation of taro corm, which constitutes a challenge in the use of taro flour as a value added product (Payne et al., 1941). Baking generally induced significant change in the level of calcium oxalate in wheat-taro composite cookies. Studies on Japanese taro reported that baking significantly increased the concentration of total oxalate (Catherwood et al., 2007). Conversely, Teckle (2009) observed no significant change in the oxalate content of the cookies with the increase in baking temperature while significant increase in oxalate content with increase in the taro amount in the formulation was observed. The observation by these authors suggested that baking a food causes rather an effective concentration of oxalates in the food following the loss of water (Oscarsson and Savage, 2007). Boiling taro corm has been suggested as the effective method to reduce the oxalate content and rapidly annihilate irritation of taro corm (Aboubakar et al., 2009; Catherwood et al., 2007; Nip, 1997). From these observations, the use of parboiled taro flour as starting material for food formulations has been proposed. The change in oxalate structure during precooked taro flour production has been reported (Aboubacar et al., 2009; Njintang, 2003).
Calcium oxalates crystals occurred in specific taro cells called idioblasts, within the cortex in two forms: the druses which are rosette shape form and the raphides which are needle shape form (Figure 9.2.10). The shape of druses (Sunell and Healey, 1985) is spherical, with an average diameter of 40 m, while the raphides are spindle-shaped with obtuse ends. Unlike druses, some raphides called defensive raphides are capable of ejecting their needles from their obtuse end. The difference between the defensive and non-defensive raphides is observable on the distribution of needles in the idioblast. In fact, while in defensive raphides, the needles are aligned parallel with the long axis of the idioblast and are ejected through one or both poles of the cell, the needles in the non-defensive raphides were tightly compacted into a bundle at the centre of the cell. We found in our earlier work that during boiling, the ejection of needles is annihilated, thus eliminating the acridity (Aboubacar et al., 2009).
Figure 9.2.10 Some idioblasts identified in taro corm. (a) raphide idioblast with one end ejection; (b) raphide idioblast with two end ejection; (c) druse idioblast; (d) inoffensive idioblast.
Parboiling as a pretreatment for the production of taro flour was suggested a long time ago by Payne et al. (1941), who reported that as high as 60 % precooked taro flour could be used in cookies preparation. The recommended procedure for precooked taro flour production included boiling under pressure taro corms, especially the Ibo coco variety (Figure 9.2.11) for 25–35 min. Under these conditions, the pleasant taro odour is developed; the boiled corms are then hand peeled, sliced 0.5 cm thick and powdered in a hammer grinder equipped with a ventilation system which separates coarse particles from the fine ones. The flour is then packaged in polyethylene bags to avoid adsorption of moisture.
Figure 9.2.11 Colocasia esculenta corm, ecotype Ibo coco.
9.2.2.6 Other Bakery Products
Cake Cake is a baked product liked by consumers all over the world. Soft wheat flour is the basic ingredient in cake-making. In the procedure of cake preparation, wheat flour is mixed in a bowl for a time so as to obtain an homogeneous dough with other ingredients, which include ground sugar, shortening, eggs, baking powder, vanilla essence and milk. Kumar et al. (2014) reported the effect of substitution of wheat flour with taro flour on the physicochemical and sensory characteristics of composite cake. Taro flour used in the preparation of the cake was prepared by blanching slices 0.5 cm thick for 10 min in boiling water, followed by drying and grinding to pass through a 30 m mesh sieve. Wheat flour was substituted with 5,10,15 and 20 % taro flour and the composite mixed in a single stage with ground sugar, shortening, eggs, baking powder, vanilla essence and milk. The batter so obtained was immediately poured into a previously greased baking pan, then put into a baking oven at 190 °C for 60 min. The effect of taro flour level, fat level, sugar and egg level was studied using a L16 orthogonal Taguchi design.
The results showed that the volume of cake increased with increasing taro flour up to 10 % over which a decrease in volume was observed. Generally higher volume of cake indicates higher gas retention and higher expansion of the product leads to higher volume (Gomez et al., 2008). Kumar et al. (2014) observed that as the level of taro increased, the cake could not withstand the structure during the last phase of baking and collapsed. They explained this by the lesser amount of gluten which mainly supports the structure and provided better stability. They inferred the decrease in volume to differences in the internal structure of batters, due to discontinuity in the batter caused by the high amount of taro fibre. They observed that the cake with 5 % taro exhibited the highest firmness value and finally was significantly rated best followed by that at 10 %, while the cake with 20 % taro flour had the least rating. The optimized ingredients proportion for the production of taro-wheat composite flour cake was then determined for 10 % taro flour, 60 % fat, 110 % sugar and 100 % egg, which gave nominal firmness, smaller chewiness and colour and a larger value of volume and overall acceptability.
Darkwa and Darkwa (2013) also investigated the use of taro flour in cake preparation. In their process, 450 g of margarine was weighed and added to 400 g of white refined sugar. The two ingredients were creamed together using a Kenwood cake mixer until the mixture became light and fluffy in texture. Ten eggs were cracked, flavoured with 2 teaspoons of the pineapple flavouring and whisked until foamy. The whisked eggs were added in small amounts to the fat mixture. One tablespoon (3 teaspoons) of baking powder and 3 large sized nutmegs were grated and added to the flour. The batter was divided into three and 200 g of wheat taro composite flour each of the flour samples were added to each and baked at a temperature of 180 °C for 45 min until it had an even brown colour.
The taro wheat composite flours studied consisted of 25, 50 and 75 % of taro flour. No significant differences were observed in all the sensory qualities scored except for the overall acceptability. Composite cake made from 75 % taro flour and 25 % wheat flour was selected as the best, followed by 50 % taro flour cake and lastly with 25 % taro flour. The increase acceptability of cake with increased level of taro by the Ghanaian consumers arises probably from pleasant aroma and smells induced by taro.
Payne et al. (1941) reported a recipe for taro layer cake. The ingredients were 1/4 cup of taro flour, 7/4 cup of wheat flour, 1/2 cup of shortening, 1 cup of sugar, 4 teaspoons of baking powder, 1/4 teaspoon of salt, 2 eggs, 3/4 cup of milk and 1 teaspoon of vanilla. In the procedure of preparation, shortening and sugar are creamed; the eggs are added and whisked until fluffy. The dry ingredients were sieved and mixed to the first mixture alternatively with the milk and vanilla. The dough was baked for 25 min with a temperature rising from 175–205 °C.