In conformity with the weight of the biscuit, the dough made with the Egg-like variety was weaker than that made with the Red Ibo variety, thus confirming the hypothesis of densification. The high weight of the biscuit might also be a result of difference in the spread ratio which, according to Dogan (2006), is an indication of the viscous property of the dough. It is evident that during baking as the temperature of the baking oven increases, the dough flows (spreads) until the point at which the viscosity suddenly increases, probably as a consequence of crystallization, gelatinization and gelation. The change in viscosity might presumably be a property of the flour proteins in the case of uncooked taro flour, since starches are mostly in their native form and gelatinized less. In precooked flour, as in this work, both proteins and starch might highly interact to contribute to the viscosity. From Table 9.2.4, we can see that the increase in the proportion of the taro flour in the composite flour has caused the cookies to increase in the spread factor. This result is the reverse of that observed by Teckle (2009) on composite taro wheat cookies. He inferred his observation to the increase in diameter, which was the reverse of that observed in this work. According to this author, the decrease in spread ratio and diameter is indicative of the densification of cookies. This is not the case in our study where we found a significant increase in density associated to an increase in spread ratio. The difference observed with Teckle’s report is probably due to the difference in the pretreatment of the taro corms during the flour processing. Parboiling then has caused densification of the dough and hence the biscuit.
Functional Properties of Wheat-Taro Composite Biscuits The changes on water absorption capacity and water solubility index of composite biscuits as a function of level of substitution are shown in Figures 9.2.8 and 9.2.9. Water absorption capacity is a functional property that characterizes the ability of product to rehydration. It can be seen that, irrespective of the variety, WAC of biscuits increased with increase in the level of incorporation of taro flour in dough. It varied from 119–180 % for Egg-like-based biscuits and 119–158 % for Red Ibo-based biscuits. Increase of WAC was higher with Egg-like flour compared to Red Ibo flour; it was around 44.14 % for 30 % Egg-like flour and 18.85 % for 30 % Red Ibo flour. Composite taro wheat biscuits were equally found to possess higher WSI (Figure 9.2.9) varying from 30.6-34.4 % for Egg-like-based composite and 30.6-38.0 % for Red Ibo-based composite.
Figure 9.2.8 Effect of variety and level of taro flour incorporation on water absorption capacity of biscuits.
Figure 9.2.9 Effect of variety and level of taro flour incorporation on water solubility index of biscuits.
Sensory scores reported for the composite biscuits showed that all the biscuits made from Egg-like and Red Ibo taro flours were as acceptable as 100 % wheat biscuits, except biscuits made from Red Ibo variety substituted to 5 and 10 %, which possessed higher hedonic score for all the attributes (Himeda et al., 2014). Biscuits made from precooked Red Ibo flour has induced attractive sensory attribute to the biscuits, in particular flavour and taste. Indeed, flavor is the main criterion that makes the product liked or disliked. The attractive taste and flavor of taro corm generally appeared during boiling, but this does not seem to be the case when taro is not parboiled. In fact, Teckle (2009) found that the flavor and colour of cookies significantly decreases with an increase in the proportion of raw taro flour in the cookie and also with an increase in baking temperature.
9.2.2.4 Other Recipes of Cookies and Biscuits Formulation
Payne et al. (1941) reported recipes for biscuits and cookies. For biscuit formulation, the ingredients included 1/4 cup of parboiled taro flour, 3/2 cup of wheat flour, 5 teaspoons of baking powder, 1 teaspoon of salt, 2 tablespoons full of shortening, and 1 cup of milk. The dry ingredients are sieved twice and the fat rubbed in with fingers or knife. Milk was added and the lot mixed to a consistent soft dough which was then flattened into a 1.25-1.50 cm thick sheet, cut with biscuit cutter (18 pieces) and baked for 15 min at 230 °C. The recipe proposed for cookies and the mixing procedure were different from those of biscuit. More ingredients were used and included 1 cup of taro flour, 1/2 cup of wheat flour, 1/2 cup of rolled oats, 3/4 cup of brown sugars, 1/2 cup of shortening, 1/2 cup of milk, 1 teaspoon full of salt, 2 teaspoons full of baking powder, 1/8 teaspoon full of cinnamon and 1/8 teaspoon full of ginger. Shortening and sugar are first creamed and the milk added with mixing alternately with sifted dry ingredients. The soft dough was then rolled into a sheet and cut into uniform cookie pieces (32 pieces) using a cookie cutter and baked at 190 °C for 15 min.
Ejoh et al. (2013) studied the suitability of two varieties of cocoyam (Xanthosoma sagittifolium) for making biscuits. The black and white cocoyams were transformed into flour either after blanching or not. Biscuits were obtained by substituting wheat flour at 0, 10, 20, 50 and 100 %. In the procedure of biscuits preparation, all the dry ingredients (250 g of flour were mixed with 55 g of sugars, 2.5 g of salt, 5 g baking powder, 1.5 g of grated nutmeg, 5 mL vanilla essence) were first mixed. With continuing mixing, 125 g margarine was added followed by 60–65 mL of water. The dough was then rolled out, cut into round shaped and baked at 175 °C for 30–35 min. The sensory evaluation showed that the general acceptability and all the other attributes (colour, appearance, flavour, taste and texture) of the biscuit diminished with the increase in cocoyam level in the composite with no significant difference up to 30 % substitution. In accordance with other reports on tuber/wheat biscuit composites (Adeleke and Odedeji, 2010), Ejoh et al. (2013) found significant linear correlation between the general acceptability and the taste of the biscuits. They equally found that the white cocoyam was more suited for biscuits formulation.
9.2.2.5 Boiling as a Pretreatment to Annihilate Irritation Induced by Calcium Oxalate in Taro Flour
Our laboratory started the promotion of taro flour in baking products in 2008 with the evaluation of the functional properties of taro wheat composite flour (Njintang et al. 2008). The technological test of taro flour incorporation on biscuit quality revealed that irritation induced by raw taro when it comes into contact with the body remained unchanged in the biscuits when tested organoleptically, suggesting that baking had no significant effect on taro acridity. Irritation in taro-based bakeries seems to vary with variety. In fact some studies reported no irritation of the mouth or throat during or after the sensory evaluation of taro-wheat based cookies (Ojinnaka, et al., 2009; Teckle, 2009), and this has been attributed to the very low level of oxalate in the initial taro flour and the cookies.