Improvement of the pasting properties of yam flour/cassava starch blend enriched with soybean flour for preparation of yam meal

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1 American Journal of Food Science and Nutrition Research 2015; 2(2): Published online February 10, 2015 ( Improvement of the pasting properties of yam flour/cassava starch blend enriched with soybean flour for preparation of yam meal Anuonye J. C. *, Saad M. F. Department of Food Science and Technology, Federal University of Technology Minna Niger State Nigeria address (Anuonye J. C.), (Anuonye J. C.), M. F.) To cite this article Anuonye J. C., Saad M. F.. Improvement of the Pasting Properties of Yam Flour/Cassava Starch Blend Enriched with Soybean Flour for Preparation of Yam Meal. American Journal of Food Science and Nutrition Research. Vol. 2, No. 2, 2015, pp Abstract Yam (Dioscorea rotundata) and soybean (Glycine max) were cleaned of dirt and other foreign materials. Soybean was tempered and cracked, winnowed manually and soaked overnight (12-72 hrs).the soaked grits were washed, boiled (100 0 C) for 5 mins and dried at ambient temperature ( C). Yam was also peeled, washed, sliced, blanched, dried and milled to pass a sieve mesh of 1mm. Cassava was peeled, washed, grated, and sieved and allowed to settle (30mins-1hr). The water was drained, and the starch obtained was oven dried at c for 4-6 hrs and milled into flour. Yam flour (65%) was firmed-up with cassava starch (25%). The firmed-up yam flour was then fortified with soybean flour (10%). The pasting properties of yam flour, cassava starch, yam flour/cassava starch, yam flour/cassava starch fortified with soy flour (65:25:10) and poundo yam (commercial yam flour) flour were analyzed. Conventional pounded yam meal pasting profile (peak viscosity 5069 RVU, trough 1899 RVU, break down RVU, final viscosity 2878RVU and setback RVU) differed significantly (p 0.05) from all the other samples. Pasting time and pasting temperature of all the samples also ranged from min and C respectively, with yam flour having the highest value while cassava starch and conventional pounded yam meal had the lowest values. Addition of 25% cassava starch improved the pasting characteristics of the yam flour while the addition of soybean for improved the nutritional status. The product would remove the drudgery associated with pounding yam. The new product stands a good chance for commercialization. Keywords Pounded Yam Meal, Cassava Starch, Yam Flour, Soybean Flour, Pasting Properties 1. Introduction According to Lasisi (2010) yam has high potassium and low sodium contents which produces a good potassiumsodium balance in the body and so protect against osteoporosis and heart disease. Apart from being a good calorie source, yam is also a significant source of vitamin C, iron, calcium and nicotinic acid. Its low level of saturated fat is also helpful in protecting against heart disease. It has also been reported to occupy a place in many traditional marriage ceremonies and in special diets for fetish priests in sacrificial ceremonies. Nevertheless, as a result of the combination of high degree of perishability, bulkiness and distance from production area to the consuming centers and the seasonal nature of production, attention has therefore been drawn to the processing of yam tubers into flour which depends on some vital functional properties of yam varieties Production of Yam flour and subsequent reconstitution however leads to a dumpling lacking in firmness, texture and rigidity of the conventional pounded yam meal. This witling down of the conventional pounded yam meal s consistency makes many not to accept reconstituted yam flour meal as pounded yam meal. Preliminary evaluation (Lasisi 2010) established that cassava starch added at 25% levels to yam flour restored some of its textural profile of reconstituted yam meal and was organolepticaly rated higher than conventional pounded yam meal. The report also indicated that the fortified yam

2 American Journal of Food Science and Nutrition Research 2015; 2(2): flour /cassava starch blend could be commercially produced. The blend would provide more sustainable energy and give better protection against obesity and diabetes but may not be adopted as growth and development food because it is poor in protein. The report recommended that firmed- up yam flour required supplementation with available protein rich legumes or oilseeds. Soybean is considered an increasingly important crop in Asia, several African countries and at present has a tremendous potential for alleviating proteinenergy malnutrition (Osho and Dashelli, 1995). According to (Alabi 2008) soybean is an important source of high quality, inexpensive protein and oil, compared to other protein- rich foods such as meat, fish and eggs. The oil is low in cholesterol; therefore its intake reduces the incidence of cardiovascular diseases. Yam flour firmed up with cassava starch had been developed (Lasisi, 2010). Adetutu (2011) fortified yam/cassava starch with soybean flour. This current work was aimed at evaluating the pasting characteristics of the raw and blended yam flours/ cassava starch fortified with soybean flour. 2. Materials and Methods Yam flour, cassava starch and soybean flour was prepared as reported by Lasisi(2010) and Adetutu (2011). Wholesome tubers (Dioscorea rotundata) yam was selected. The selected tubers were washed to remove adhering sand and other foreign materials and then peeled and cut with stainless steel knife into slices of 0.50 cm thick by 0.80 cm long into water containing 0.001M sodium metabisulphite (NaHSO 3 ). The yam slices were washed and blanched in boiling water (100±2 0 C) for 10 minutes. The blanched yam slices were dried in an air oven (Uniscope SM9053 Laboratory oven, Surginfriend Medicals, England) at 50 0 C for 5-6 hours. The dried yam chips were pulverized (milled) into flour using attrition milling machine. The cassava tubers were peeled and wet milled using attritional milling machine. The starch was extracted after sedimentation and dewatered in muslin cloth packs of 500grams each. The starch was evenly spread on the oven (Uniscope SM9053 Surginfriend Medicals, England) trays and dried at C for 2-3hrs. The dried cassava starch was milled into flour using an attritional milling machine. Soybean was prepared according to Anuonye (2006). It was sorted, washed in clean tap water and then sundried for 3-4 hrs (tempering). The tempered grains were cracked in an attrition mill. Soybean hulls were removed by manual winnowing and the grits was soaked in water overnight (12-17) hours. The soaked grits was rinsed in tap water, washed and boiled for 5minuites (100 0 C), decanted and dried at ambient temperature (25 0 C-27 0 C) until millable. The blend was reconstituted as described by Lasisi (2010) by mixing 65% yam flour to 25% cassava starch to 10% soybean flour. A commercial yam flour blend was purchased from the Minna Central Market (Niger state Nigeria). Pasting properties of the yam flour, cassava starch, soybean flour and the blend of yam flour(65%) plus 25% cassava starch flour and 10% soybean flour along with the commercial yam flour were evaluated by the use of the Rapid Visco Analyzer (RVU) (Newport Scientific, Rapid Visco Analyzer Super 3) according to the method described by Anuonye (2006). Conventional pounded yam meal was used as a check. 3. Results Pounded yam and cassava starch depicted normal tuber native starch characteristics (Figures 1and 2). With high peak, set back trough and final viscosities the viscograms showed that much of the native starch remained intact. The viscogram of the yam flour (Figure 3) did not show any visible trough and exhibited very low setback indicating that most of the starch has been modified. It is this modification that affects the texture of the yam flour meal. Addition of cassava starch to yam flour (Fig4) showed a clear trough and recovery of the pasting profile. Figure (5) shows the soybean pasting profile. The viscogram was expected; lacking in both peak viscosity and final viscosity without a trough and no actual point of gelatinization. The addition of soybean to yam flour/ cassava starch mixes did not significantly alter the pasting profile. The viscogram (Figure 6) showed distinct trough and high peak viscosity normal for native tuber starches. 4. Discussion The pasting characteristics of conventional pounded yam meal and cassava starch (Figures 1 and 2) showed that as expected these native starches had the highest peak and final viscosities. This could be attributed to the rapid rise in viscosity of the native starches with the onset of gelatinization (Anuonye etal, 2009). Peak viscosity is the ability of starch to swell freely before their physical breakdown. According to Baah etal (2009) Peak viscosity, as the name implies, is the maximum viscosity attained soon after starch slurry becomes viscous due to starch granule swelling and leaching out of soluble component into solution. Odedeji and Adeleke, (2010) and Rickard et al.(1991) had reported that cassava starch has high peak viscosity because it exhibits high degree of swelling. High peak viscosity has been suggested to contribute to good texture of pounded yam, which basically depends on high viscosity and moderately high gel strength. High peak viscosity is an indication of high starch content and also related to water binding capacity of starch. High peak viscosity observed in conventional pounded yam meal and cassava starches were therefore expected because cassava and yam starches have been reported to have high peak viscosity due to high swelling ability on heating (Abioye et al. 2011). The result for cassava starch was also consistent with those reported in literature (Adeleke and Odedeji 2010). The peak and final viscosities obtained for conventional pounded yam and cassava starch respectively were higher than the values (90.20RVU and RVU) reported by Adetutu (2011) but lower than ( and RVU)

3 42 Anuonye J. C. and Saad M. F.: Improvement of the Pasting Properties of Yam Flour/Cassava Starch Blend Enriched with Soybean for Preparation of Yam Meal reported by Baah etal (2009) for D.alata. The variation is likely due to differences in analytical viscometers and yam varieties. However the values (200RVU) obtained was higher than those reported for some cereals and tuber starches (Jideani et al.1996). Pasting temperature, time at peak viscosity, the peak time and minimum viscosity also differed. These differences are related to product structure and chemistry. Jideani and Akingbala (1993) and Jideani et al. (1996) reported that flours/ pastes that are stable to shearing at 95 o C, but increases greatly when cooled to 50 o C and remained stable to shearing at this temperature will be suitable for preparing tuwo a stiff paste. These authors reported 18.50RVU break down for acha while Anuonye etal (2009) reported 17.18RVU. The values were significantly (P< 0.05) lower than the 13.22RVU recorded for yam flour in this present study. Yam flour meal (Figure 3) lacked such abilities because of the destructurized pattern of its starch components during processing (drying and milling into flour). This is shown in its significant (P< 0.05) low peak and final viscosities compared to pounded yam meal or cassava starch viscosities indicating lack of cohesiveness and hence not easily moldable. Cohesiveness has been defined as the ease of molding pounded yam, or how moldable the pounded yam is in sensory texture profile analysis. This might be the major reason for its low acceptability. However addition of cassava starch at 25% levels led to increases in the peak and final viscosities of yam flour/cassava starch meal. The increase in peak viscosities observed is associated with the cassava starch concentration (Abiodun et al., 2010). Addition of cassava starch at 25% level of substitution to yam flour greatly affected its pasting properties due to modifications in its textural configuration. All measured parameters increased when compared to yam flour viscogramme (figure3), with the exception of the pasting temperature. The results indicated that addition of cassava starch imparted high percentage resistance to disintegration and higher abilities to resist retrogradation. However the breakdown viscosity of 40RVU recorded for the yam flour/cassava starch blend was significantly (P< 0.05) lower than the values for yam flour but more than the 17 RVU recorded for acha flour (Anuonye,2010). The implication of this result is that the yam flour/cassava flour blend will produce a dumpling stiffer than the usual cereal stuff thus recommending it to more consumers of pounded yam. While the pasting characteristics of yam flour improved with increase in cassava starch substitution addition of soya bean flour to yam flour/cassava starch resulted in reduction in the pasting values of the meal (figure 5). The decreases were however not significant. The slight changes in the pasting profile are not unconnected with the weakening of the bonding forces within the starch granules probably by the modifications in the proximate composition of meal as a result of the addition of soybean flour. Vickie and Elizabeth, (2008) reported that soybean has high protein content and its addition affects the pasting characteristic of starchy flour. Ingbian (2004) and Maria et al. (1983) reported that peak viscosity was an indication of the maximum increase in that value for the starch-water solution upon heating. The lower values of peak viscosities indicated that a greater amount of gelatinization had occurred in the initial samples or there had been fortification of flours with legumes or oilseeds. The presence of soybean flour at 30% levels therefore contributed to the increased lowering of the raw blend peak viscosity. Ingbian (2004) also reported that peak viscosity indicated the water binding capacity of starch or blends, and provides indication of the viscous load likely to be encountered by a mixing cooker. The lower peak viscosities showed that there was increased water imbibitions and increased swelling. This also would account for the reduced cooking time though this reduction was not significant (P>0.05) Trough is the minimum viscosity value in the constant temperature phase of the RVA profile and measures the ability of paste to withstand breakdown during cooling. Babajide and Olowe (2013) recorded lower trough values (108.92RVU RVU) for water yam/ cassava starch blends. High trough value recorded by samples conventional pounded yam and cassava starch represent low cooking loss and superior quality of flour samples. Low trough values recorded for yam flour and soybean flour may be due to the denatured native starch structure and the high protein content of the soybean flour. The addition of cassava starch increased the values of the trough for the yam flour/cassava starch blends. Addition of 10% soybean flour did not significantly (P< 0.05) decrease the trough of the blend. The pasting temperature and peak viscosity were the two parameters that related all the samples. They maintained similar range, even with the addition of soybean flour at 10% levels. This showed that unlike the yam flour pasting profile (lacking clear range and trough) addition of cassava starch restored significantly the pasting profile of the blend. Addition of soybean flour however did not significantly disrupt the profile of the blend. 5. Conclusions Using cassava starch as a firming agent to regenerate the pasting profile of yam flour would lead to preparation of pounded yam meal closer to the conventional pounded yam meal. The drudgery of pounding would be eliminated. The stiff paste or dumpling would be stronger texturally than the conventional cereal dumpling and hence would be more acceptable. It is concluded that cassava starch should be added to yam flour for improved yam meal preparation. To improve the nutritional status the blend should be fortified with plant protein like soybeans.

4 American Journal of Food Science and Nutrition Research 2015; 2(2): Fig. 1. Viscogramme of poundoyam Flour Fig. 2. Viscogramme of Cassava Starch

5 44 Anuonye J. C. and Saad M. F.: Improvement of the Pasting Properties of Yam Flour/Cassava Starch Blend Enriched with Soybean for Preparation of Yam Meal Fig. 3. Viscogram of Yam Flour Fig. 4. Viscogram of Yam flour and Cassava Starch

6 American Journal of Food Science and Nutrition Research 2015; 2(2): Fig. 5. Viscogram of Soybean Flour Fig. 6. Viscogram of Yam Flour/Cassava Starch enriched with Soybean Flour References [1] Abiodun O.A., Adegbite, G. A and Oladipo, T. S. (2010). Effect of cassava starch substitution on the Functional and Sensory properties of Trifoliate yam (Dioscorea dumetorum) flours. African Journal of food, Agriculture, Nutrition and development. Pp 9 [2] Abioye V. F., B. I. O Ade-omowaye, G. O. Babarinde and M. K. Adesingbin (2011). Chemical, Physico-chemical and sensory properties of soy / plantain flour. African Journal of Food Science Vol. 5(4): [3] Adeleke, R. O and Odedeji, J. O (2010). Functional properties wheat and sweet potato flour blends. Pakistan Journal of Nutrition, 9(6):

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