Composite Bread
In this final component of the project, composite bread was made from the combination of various high-quality cassava flour varieties with wheat flour. This high-quality composite flour was then used to bake different loaves of bread. Additionally, studies were conducted to determine ways in which the nutritional content of the HQCF composite bread could be improved.
Audit of High-Quality Cassava Flour Producers and Usage in Southeast Nigeria
A total of forty-three (43) bakers responded to the questionnaires that were administered with ten (10) bakers responding from Abia State, seven (7) from Enugu State and eight (8) each from Anambara, Imo and Ebonyi States. While forty- one of the bakers were sole proprietors, two of the bakeries were found to be in partnership.
Additionally, 35% of the bakeries confirmed that they did indeed use HQCF in their bread production while 65% did not use HQCF.
With respect to HQCF inclusion in products, only 9 bakeries met the government mandatory 10% inclusion rate while the majority (28 bakers) did not make use of any HQCF in their products.
Twenty-six (26) bakers indicated that they had interest in HQCF inclusion in their products while fifteen (15) bakers responded no.
Physiochemical attributes of HQCF composite bread
The objectives here were to:
- Produce high-quality cassava flour from improved cassava varieties available in Southeast Nigeria and formulate flour from them
Determine the physiochemical properties of the formulated composite flour - Produce bread from flour blends of wheat and cassava flours
Evaluate the properties of the bread produced - Determine sensory qualities of the bread produced from them in order to analyze the suitability of the composite flour in bread making
- Ascertain the effect of proofing time, cassava composite and variety on the sensory characteristics of bread from HQCF
- Use a Response Surface Methodology (Central Composite Design) to determine the effect of various factors on the bread made from composite flour
- Evaluate biochemical properties of the bread produced from cassava-wheat flour blends
- Use Response Surface Methodology to evaluate the interactions between cassava varieties, composition of flour and improvements in the properties of bread produced
HQCF was produced from improved selected cassava varieties which included:
- TME 98/419
- TMS 98/0581
- TMS 98/1632
- NR 98/8082
- TMS 98/87164
To produce the above high quality cassava flour hybrids, healthy, mature, firm and fresh cassava roots were harvested from the cassava programme farm in the National Root Crops Research Institute (NRCRI) in Umudike, Nigeria. Tremendous care was taken to make sure that the roots had no bruises during harvesting and transportation. The fleshy roots were then taken to the cassava processing unit of the NRCRI for processing making sure they had few fibrous roots with no cracking. The root tubers were subsequently weighed for flour yield calculation then peeled with the stock, woody tips and any fibrous roots removed using a sharp knife.
The peeled cassava roots were then washed with clean water to remove unwanted dirt particles including sand, soil, leaves and other impurities using a mechanical grater.
The grated cassava was then packed into a clean sack that would allow water to escape following which, the bagged mash was then pressed using a screw press to remove excess water until the cassava was crumble. This dewatering process was carried out within a short time to avoid fermentation. The dewatered mash was then manually dispersed for drying.
Drying was done by spreading the pulverized cassava mash thinly on clean dry oven trays which were placed in preheated oven cabinets set at 100°C for 4 hours with frequent turning. The dried cassava was milled to flour using a 9FC-360A hammer mill and sieved afterwards to remove excess fibre and lumps leaving free-flowing flour. The flour was then packed in double airtight moisture-proof black coloured high-density cellophane bags which were then stored in a deep freezer until the flour needed to be used for baking and analyses. The entire process is shown in the flow diagram provided.
The functional properties of the flour investigated included bulk density, water and oil absorption capacities, wettability, gelation capacity, foaming capacity and stability, emulsion and gelatinization temperature.
Pasting characteristics of the flour samples once again determined using the Rapid Visco Analyzer (RVA). Total running time was 13mins and the viscosity values were recorded every 4 seconds by Thermocline Software as the temperature increased from 50°C to 95°C before cooling back to 50°C. The rotation speed was set to 960rpm for the first 10sec and then 160rpm until the end. Three grams (3g) of flour and 25ml of distilled water were placed in a canister where a paddle was then inserted and shaken through the sample before the canister was inserted into the RVA.
While determination of hydrogen cyanide using the alkaline picrate method was done on the cassava flour alone, proximate analyses using the Association of Analytical Chemist (AOAC) procedure were conducted on the composite flour and bread samples (made from various blends of the flours previously listed). Particle size analysis of the HQCF from the different cassava varieties was done using a particle shaker with a set of standard sieves of different aperture sizes while pH of the flours was measured with a Hanna pH meter (Model HI1270).
Bread was baked using varying proportions of cassava flour ranging from 10-40% using the improved cassava flours from the five previously listed cassava varieties. Production of bread was based on a 5×3 composite design resulting in 25 formulations/runs. Bread was baked with improvers (Panok, Carboxyl methyl Cellulose (C8H16O8) and ascorbic acid (C6H8O6))) for the cassava varieties TMS 98/87164, TMS 98/1632 and TME 98/419, based on acceptable functional and sensory characteristics.
To produce the bread samples, each ingredient was carefully weighed and kept in separate well-labelled bowls with lids for use. The bread samples were baked in batches according to the proofing time or according to the level of different improvers added, by mixing and kneading manually each of the flour blends with the ingredients in a stainless-steel bowl. After each case of thorough kneading, the dough was moulded into cylindrical shapes and placed in a well-oiled baking pan and proofed for 40-80mins at room temperature before baking for 25mins in a cabinet oven which had been pre-heated and set at 230°C. After baking, the baked dough was then removed from the oven and immediately de-panned by knocking on the bread pan before it was placed in a clean tray to cool while avoiding condensation. Below is a flow chart describing the cassava-wheat bread production process.
Loaf volume, weight, specific volume, the oven spring, the organoleptic properties, as well as crumb moisture of the breads were evaluated. The sensory evaluation of the bread samples was carried out using 20 panelists to asses the organoleptic attributes of the bread samples such as taste, crumb appearance, crust appearance, softness of feel (texture), bread height (volume) and overall acceptability. Panelists were instructed to rank the samples based on the highly preferred samples in order of 1 (most preferred) to 5 (least preferred) with the Hedonic scale later adopted when evaluating the acceptance of the bread samples.
To determine the protein solubility indices at different pH levels, a 2g ground portion of each bread sample, milled in a blender, was dispersed in 100ml of deionized water and agitated again in the blender. At least 10ml of the suspension was poured into a set of six beakers for the six different pH values studied; the pH solution was adjusted to 2,4,6,8,10 and 12 with 1mol hydrochloric acid (1M HCl) or 1mol sodium hydroxide (1M NaOH). The mixture was then stirred at room temperature for 15mins using a magnetic stirrer, and then centrifuged at 4000rpm for 20mins. The protein content in the supernatant was determined according to to the Kjeldahl method and the formula is provided below:
Approval was obtained fro the Research and Ethics Committee of the Federal Medical Centre, Abia State, Nigeria for the use of humans as test subjects to determine the glycemic response from composite bread consumption. Fifty healthy human test subjects (aged between 16 and 40) were randomly selected and offered a single meal which was one of the twenty-five bread samples. Blood samples were collected before feeding and during the 180mins after the meal. The test subjects were clinically normal, non-smokers and non-diabetic who were appraised verbally and gave their consent.
The bread samples used to determine blood glucose were baked a day prior to glycemic testing and stored as previously described. Following a 12hr overnight fast, test subjects ate 50g, available carbohydrate portions of the standard/reference food (glucose D) or the bread samples at random on different days.
The standard food was repeated three times in each subject and their Incremental Area Under Curve (IAUC) was calculated as the IAUC of the glucose. Table water was given to each of the volunteers so that total meal volume was greater than 400ml to stimulate stomach emptying and reduce the variability of glycemic responses.
The foods were consumed within 10-15mins and the volunteers were asked to remain seated for the duration of the test. Finger prick capillary blood samples were taken from the volunteers using blood lancets before eating the meals (0min) and at 15, 30, 45, 60, 90 and 120min intervals after consumption of the meals.
Whole blood glucose was measured by dropping the volunteers’ blood at each of the intervals in a test strip and inserting the test spot of a glucometer (a one touch basic system glucometer) and the reading taken immediately. IAUC was measured geometrically using the data obtained from the blood glucose concentration-time graph ignoring the area beneath the fasting level.
The IAUC for the bread samples was expressed as percentage of the IAUC of the glucose (standard food) while the Glycemic Index (GI) of each subject was calculated as follows:
The average of the two measures for each subject was taken as the GI for that food for the subject. The GI for each food was finally calculated as the mean of the averages of the GIs of the subjects in each composite bread sample group.
IAUC was calculated for each meal for each subject as the sum of the surface triangles and trapezoids between the blood glucose curve and the horizontal baseline running in parallel to the time axis from the beginning of the curve to the point at 120mins. This was done to reflect the total rise in blood glucose concentration after eating the test food. The IAUC for reference (standard food) i.e. 50g of pure glucose (IAUCS), was obtained in a similar way.
The hydrogen cyanide values obtained fro TMS 98/0581 and TMS 98/1632 were not significantly different from each other but were significantly different (p<0.05) from those values obtained from NR 8082 and TMS 98/1632, which also had no significant difference between their values. The values obtained were within the permissible limit of 10mg/kg specified by the World Heath Organisation (WHO) and maintained by the Standard Organisation of Nigeria (SON), except for TME 98.419 (10.42mg/kg) which was slightly higher than the acceptable limit. However, it was normal to expect that further processing such as baking would reduce this level to an acceptable and safe limit.
The moisture contents of the flour samples and composite flour blends ranged from 4.15 to 11.90% indicating that the samples would keep well if properly stored in good conditions. Results also showed a higher protein content of flours containing wheat which was an indication that wheat was a better source of protein when compared to cassava. It was also evident from the results that increasing the level of wheat flour increased protein content of the cassava flours hence, the reasoning behind composite technology. Furthermore, cassava blends compared favourably in bulk density thus, bulk density of the flours could be used to determine their handling requirement because it is a function of mass and volume.
Results revealed that 100% cassava flour achieved wetness faster than its composite flours. In addition, higher water absorption capacities (WAC) as well as higher oil absorption capacities (OAC) were recorded for the cassava varieties used compared to their composite flours. This showed that 100% cassava flour could be a good retainer of flavour and could also give a better mouth feel when used in food preparation. The higher WAC of the high-quality cassava flours observed compared with composite flours could have been an indication of higher polar amino acid residues of proteins having an affinity for water molecules and this was an advantage for it in this regard.
In terms of pasting properties, values for peak viscosity for the five cassava varieties ranged from 66.08 RVU to 358.08 RVU. Peak viscosity increased with an increase in the ratio of cassava flour with the highest peak viscosity (358.08 RVU) obtained with 50% TMS 98/0581. Given that peak viscosity is indicative of ease of cooking, the increase in peak viscosity given an increase in the ratio of cassava flour could be attributed to the high degree of swelling of cassava starch granules.
Cassava-Wheat Functional Properties
Rapid drop in viscosity at 95°C was observed which corresponded to almost half of the peak viscosity, suggested a large extent of breakdown of the paste and hence, low stability. As all cassava flours were high in amylose (≈90%), they exhibited a high retrogradation tendency with a high final viscosity upon cooling compared to peak viscosity. The final viscosity (a parameter commonly used to determine a sample’s ability to form a gel after cooking and cooling) ranged from 123.58 RVU to 413.82 RVU. 100% cassava flours from the five improved varieties showed an increase in final viscosity and lower peak viscosity compared to wheat flours.
The pasting profiles of flour from TME 98/419 and its composite flours were verifiably different from the other four flour samples and their wheat flour composites with the addition of cassava flour to wheat affecting some pasting properties of the composite flours The onset of gelatinization occurred faster for flours with a high inclusion level of cassava and retrogradation decreased as proportion of cassava flour increased. The increasing substitution level would have been undeniably felt in the eating quality of food prepared from this composite flour as the paste stability was consistently reduced. Nonetheless, 20% replacement of wheat flour with cassava flour showed paste stability which was akin to 30% substitution level. This effect of cassava flour on the composite flour is explained by the increase in amylose-gluten or amylose-lipid complexes.
Results showed high moisture content of the bread samples which may have been attributed to the amount of water added during baking. However, this may have also been simply due to the fact cassava flour tends to retain more moisture than wheat flour. Also evident from the results was that increasing the level of wheat flour increased the protein of the cassava flours while, the increase in the substitution level of cassava flour showed a decrease in the fat content of the bread sample; this indicated that cassava tubes are not an oil rich crop.
Specific volume ranged from 2.26 to 4.94cm3/g. Observation showed that the specific volume increased with a reduction in the level of cassava flour substitution (10 to 20%) with the highest value obtained from bread baked with 10% TMS 98/87164 at 40mins proofing while the least value was obtained from the sample bread baked with 50% TMS 98/8082 at 70mins proofing.
Consumers were often attracted to a loaf by its size and volume believing that it had more substance for the price. Studied independent variable showed that only cassava variety and the interaction of proofing time had significant (p<0.05) effect on the specific volume of the loaf. Analysis of variance showed that flour composition also had significant effect on the specific loaf volume.
Regression results showed the linear and quadratic interaction between cassava variety and proofing time had significant effect (p<0.05) on the loaf volume and this accounted for 79.48% of the total variation. Additionally, response surface curve showed the interactions between the three variables quadratic effects on the loaf volume.
Loaf density results ranged from 0.20 to 0.51cm3/g and showed that with an increase in the substitution level of cassava flour and longer proofing time in, loaf density increased. This could have been due to the fact that cassava flour absorbs more moisture that wheat flour and longer proofing time could lead the dough to collapse after rising which may have made the bread compact together allowing no further expansion for gas evolution.
The regression coefficient showed that cassava variety only had significant effect on the loaf density while flour composition and proofing time had quadratic effect on load density. The model was significant (p<0.05) and accounted for 65.71% of total variation. Additionally, the response surface curve showed that the interactions between the variables had quadratic effects on the loaf density.
Flour composition was found to have significant effect on the crumb moisture parameter. At a higher substitution level (30-50%) of cassava flour, an increase in the crumb moisture was observed. This could have been due to the fact that cassava flour has the ability to retain or absorb more water than wheat flour. Additionally, results showed that the interaction terms of cassava variety, flour composition and proofing had significant (p<0.100) effect on the crumb moisture.
Oven spring is the difference between the height of dough after proofing and height of loaf after baking and was found to range from 0 to 0.8cm. Results showed that at 10 to 20% inclusion of cassava flour and 40 to 50mins proofing time, an increase in the oven spring was observed in all samples except for those baked with NR 98/8082. Some results showed a negative result representing a collapse in the bread height. This showed that an increased substitution level and increased time of proofing decreased oven spring of the bread which was undesirable at the retain end as consumers prefer bread with firm height.
Sensory evaluation of the loaf volume showed that bread samples from 10% TME 98/419 at 40mins proofing had lower sensory mean scores (1.44) showing that these samples were mostly preferred by the panelists. The observed reduction in the loaf volume with an increase in the substitution level was significantly obvious as bread with 40% TMS 98/8082 at 60min proofing recorded the highest sensory mean score of 4.60 showing least preference by the panelists and it was well known that cassava flour lacks gluten protein which is required for the leavening of dough.
The estimated regression coefficient showed that at 40mins proofing, the entire variable did not have significant effect on the sensory effects of the loaf volume parameter, but that that cassava variety and proofing time did indeed have quadratic effect. At 50mins proofing, results from regression analysis showed that proofing time and flour composition had significant quadratic effect on the loaf height. Cassava variety, the interaction terms, flour composition and proofing time also had significant effect on the loaf height.
While at 60mins proofing, flour composite was observed to have significant effect on the parameter with interaction of flour composition having a strong significant effect on load height, at 70mins proofing, it was observed that all the variables except for the interaction between cassava variety and proofing time had significant effect on the load volume.
At 80mins proofing, significant effects existed between cassava variety and flour composite which had quadratic effect on the parameter. The model at 40, 50, and 60mins proofing were not significant and did not account for 17.81%, 42.66% and 23.68% of the total variation respectively. However, the model at 70 and 80mins proofing were significant and accounted for 93.19% and 83.42% of the total variation respectively. The significance of the data could have been as a result of experimental conditions. Additionally, the response surface curves showed that the interaction between the three variables had linear and quadratic effects on the loaf volume for all levels of proofing.
With regards to softness of feel (texture) of the HQCF composite bread, 10% TME 98/419 at 60mins proofing had the least mean sensory score of 1.08 which indicated that it was the sample mostly preferred on the Hedonic scale by the panelists. Some panelists showed likeness to some bread samples baked with 20 to 30% TMS 98/1632 and TME 98/419 with sensory mean scores of 1.56 and 1.44 at 70 and 80mins proofing respectively. These results agreed with previous findings which reported that inclusion of up to 30% cassava flour in wheat flour could still give an acceptable fresh loaf. This observation could also have been attributed to personal choices as food texture sometimes embraces appearance.
While the estimated regression coefficient showed that at 40mins proofing time, cassava variety, flour composition and proofing time had significant effect on the softness of feel, the interactive effect of cassava variety, flour composition and proofing time were not significant.
At 50mins proofing time, flour composition and proofing time also had a significant effect on texture as well as the interaction terms. Similarly, at 60mins proofing, observations showed that cassava variety, flour composite and proofing time also had significant effect on the parameter and that the interactive influence between cassava variety, flour composite and proofing time had significant effect on the softness of feel parameter.
At both 70 and 80mins proofing, the variables cassava variety, flour composition and proofing time had significant effect (p<0.05) on the parameter and the interaction terms in the model all had significant effect on the variable when regressed.
The values of glycemic indexes obtained ranged from 16.00 to 134.50 with the processing method known to cause variation of the GI of foods. However, the variability was also partly introduced by the composition of the flour. Botanical source of flour and composition or presence of other nutrients are also important factors affecting the glycemic index of a particular food.
For the cassava variety TME 98/419, it was observed that the glycemic index increased proofing time when the composition of the flour was the same. At 10% cassava flour inclusion in the bread formulation, the glycemic index increased from 45.50 after 40mins proofing to 105.00 after 50mins proofing. Similarly, the GI of 20% cassava-wheat composite bread increased from 33.00 after 60mins proofing to 65.00 after 70mins proofing.
The glycemic index model obtained was not significant (p>0.05), although reliable (R2= 0.7928) with a mean GI of 61.44 (an intermediate GI value). The glycemic indices were significantly affected by cassava flour inclusion level, quadratic interaction of cassava variety and substitution ratio and the cubic term of inclusion level. The level of inclusion was therefore, the only independent linear variable that significantly affected the GI of the bread. This was shown by the large F-value of 6.38 and small p-value of 0.0354. The coefficient of variation showed reliability of the experiment with its value of 36.96% considered to be low, giving an acceptable precision level, given the possible and common wide inter-subject.
The tables above show the regression coefficient of the polynomial fit and the analysis of variance (ANOVA) with coefficient of variation respectively, for the adjusted GI values. The adjustment measured of the GI here refer to the elimination of subject glycemic index values that were outliers and measures the maximum effect of the independent variables on the response (GI). Due to variability in the glycemic responses among the individuals, some subjects at times showed unrepresentative, “idiosyncratic” responses. This is when the standard deviation from the mean (SD) is more that twice that of their GI values. After the adjustment, significant effects of more variables as well as their interactions then became evident.
From the p-values obtained, it was observed that the glycemic indices of the wheat-cassava bread were significantly (p<0.05) affected by the substitution level, proofing time, quadratic interaction of cassava variety and substitution level, quadratic effect of cassava variety and proofing time and the cubic effect of cassava flour inclusion level. The glycemic model was not significant and fitted the response, with an R2 value of 0.6615. Better reliability was also obtained with CV of 35.07%.
Generally, dependent variables (response) continue to increase or decrease as the case may be, with simultaneous change in interacting independent variables until the optimum point is reached. After attaining the optimum response level, any continuous change in the interacting independent variables causes the response to start changing in the opposite direction. The steepest ascent was observed in the surface curve depicting the effect of cassava variety and cassava flour inclusion on the GI of wheat-cassava bread.
As the glycemic index is based on 50g of carbohydrate, an amount that does not always coincide with the amount of carbohydrate ordinarily eaten per typical serving size, the glycemic load (GL) was developed to resolve this problem. It takes serving size into account, thereby offering a more realistic measure of a food’s effect on blood sugar and predicts the glycemic response/impact when different amounts of carbohydrate are eaten.
The glycemic load values ranged from 8g for 50% TMS 98/0581 proofed for 80mins to 67.25g recorded for 30% TMS 98/87164 baked after 60mins proofing. The serving portions here all compared to a standard glucose meal of 50g with GI 100 and GL 50g. One unit of GL approximates the glycemic effect of 1g of glucose.
Most samples had low glycemic load per serving, with results lower than 60g. Furthermore, apart bread made with 100% wheat flour, only six samples had GL above 45g (which is considered as the upper limit of low GL on a 1000kcal basis). Although GL here showed the glycemic weight or “metabolic burden” a serving would pose to the system, the term load, as in GL, refers to a total accumulation, usually per day.
Nitrogen solubility indices of the wheat-cassava bread samples were determined at different pH levels. The pH with maximum and minimum protein solubilities int he bread widely varied. Generally, the solubility values of TME 98/419 were highest at pH 2 when used at 10% with 50mins proofing and lowest at pH 8 at 20% inclusion and 70mins proofing. For bread baked after 40mins proofing time, TMS 98/87164 at 10% inclusion and 40mins proofing had the highest solubility of 11.24% at pH 6. For 50mins proofing time, TMS 98/1632 at 10% inclusion showed the highest solubility of 12.07% at pH 2. The highest solubility value of 8.86% was recorded for NR 8082 at 40% inclusion after 60mins proofing. For 70mins proofing, NR 8082 at 50% inclusion showed the highest solubility value of 13.24% at pH 10. This sample also showed the highest nitrogen solubility across all pH values studies. The highest solubility value for breads baked after 80mins proofing time was 7.75% recorded for TME 98/410 at 30% inclusion.
Overall, the protein solubility values obtained for the bread samples were low. The low solubility values could have been as a result of protein denaturation caused by the high baking temperature of 210°C. However, this also suggested high protein digestibility.
Improving the nutritional content of HQCF composite bread
After the sensory experiments, three cassava varieties (TMS 98/1632, TMS 98/87164 and TME 98/419) had the best sensory performance and thus, were subsequently used for the experiment with the improvers Ascorbate (conjugate base of L-ascorbic acid, Panok (a conventional bread improver) and Carboxyl methyl cellulose (CMC).
Values obtained for oven spring of the bread samples ranged from -0.3cm (30% TMS 98/1632/CMC and TME 98/419/ascorbate) to 0.8cm (TMS 98/87164/CMC). Results showed that oven spring was highest for bread samples baked from TMS 98.87164 despite the improver used. Increase in cassava flour substitution led to a decrease in the oven spring and negative results were obtained for some samples showing a fall on loaf height after baking. This fallen effect is undesirable for bread loaves where firm and increased loaf height is anticipated by consumers and indicates quality of the food.
Linear and quadratic interaction between flour composited and improvers only showed significant effect on oven spring amongst the studied independent variables, and this accounted for a total of 89% of the variation in oven spring. The final equation in terms of actual variable for oven spring resulted in an R2 of 89.04 and conferred goodness of fit. Effects of cassava variety (X1), level of cassava flour substitution (X2) and improvers (X3) on oven spring are visualized using the response curves provided above.
The predicted model and level of cassava flour substitution in wheat significantly (p<0.01) affected the oven spring. Furthermore, linear interactions between cassava varieties and the level of cassava flour substitution significantly affected oven spring. It was observed that while the linear interaction of the three factors significantly affected oven spring, the effect was more significant (p<0.01) with respect to the level of cassava flour substitution, which showed quadratic influence with both cassava varieties and improvers.
The oven spring is a good indicator of not only the crumb but also how light and airy the interiors of the composite breads are. Low oven spring values indicated a dense and compact crumb with optimization showing that the maximum oven spring that was obtainable from bread samples was 0.9cm and it was attained in the bread made from 10% TMS 98/87164 baked with panok.
Loaf volume is affected by the quantity and quality of protein in the flour as well as proofing time while loaf weight is basically determined by the quantity of dough baked and the amount of moisture and carbon dioxide (CO2) diffused out of the loaf during baking. Higher loaf weight and volume have a positive economic effect on bread at the retail end. Therefore, loaf weight reduction during baking is an undesirable quality to the bakers as consumers often get attracted to bred with higher weight and volume believing that it has more substance for the same price.
Studied independent variables showed that interactions between cassava variety and flour composition had significant (p<0.01) effects on the load volume and weight. Final equation in terms of actual variables for loaf volume and weight resulted in R2 of 92.75% and 89.45% respectively. The predicted models were significant for the loaf weight and volume, while combined effects of cassava varieties and flour composites only showed significant (p<0.05) effects in loaf weight and volume.
Furthermore, results revealed that the linear interaction of the three factors significantly affected loaf weight, but the effect was more significant with respect to cassava varieties and the level of cassava flour substitution to wheat flour, which showed quadratic influence in responses.
Optimization showed that the maximum loaf volume that was obtainable from the bread samples was 711.18cm3 and was obtained from 10% TME 98/419 with panok, while optimum loaf volume was 664cm3 and was obtained from 10% TME 98/1632 baked also with panok. Furthermore, optimization also showed that the minimum loaf weight that is obtainable from bread samples was 122. 56g and was attained using 10% TME 98.87164 baked with panok improver.
With regards to sensory evaluation, results showed that interactions between variation in cassava varieties, composition and improvers produced acceptable bread with respect to overall acceptability. Bread from TMS 98/87164 with panok was preferred mostly in terms of general acceptability. It is also worth noting that acceptance decreased with the increasing level of cassava flour inclusion.
Bread from 10% TME 98/419 ascorbate was significantly different (p<0.05) in loaf volume with a mean score of 1.44 which translated to extremely liked. This could have been as a result of ascorbic acid used as an improver for the baking which contributed to the high volume of the loaf. However, bread samples from other improvers and varieties at 10% substitution recorded similar results and differed significantly from other samples. While the decrease in loaf volume with increasing cassava flour is obvious, previous studies established that cassava gluten protein which is essential for the leavening of loaves and thus consistent with loaf volume results in this study.
Regression analysis and analysis of variance (ANOVA) showed that the interaction between cassava varieties, composition and improver as well as the equation accounted for a total of 85.07% variation in loaf volume, which conferred goodness of fit. Among the three studied factors, the effect of cassava variety exerted more influence on the loaf volume of cassava-wheat bread with response curves showing little quadratic effect in loaf volume.
Optimization showed that the maximum obtainable loaf volume value was 8.21 from10% TME 98/419 baked with panok improver on loaf volume which conferred goodness of fit. Among the three studied factors, the effect of cassava variety exerted more influence on the loaf volume of cassava-wheat bread. The response graphs once again showed quadratic effect on loaf volume.
General acceptability is an overall assessment of the sensory characteristics of the bread samples as well as the combination of all the other sensory parameters. If a product records acceptability quality levels in most of the other parameters, it is expected that such a product will have good overall acceptability.
Panelists preferred bread sample 10% TMS 98/87164 panok (2.64) in terms of overall acceptability followed by 20% TMS 98.1632 CMC (2.84). Acceptability decreased with the increased level of cassava flour substitution. However, all the flour samples produced bread that were generally accepted by the panelists except for bread samples form 30% TME 98/419 ascrobate (5.00), 30% TMS 98/87164 ascorbate (5.28) and 30% TMS 98/1632 CMC (5.44), that were neither liked or disliked.
To conduct the nutritional evaluation of bread from cassava-wheat composite flours, experimental rats were used as test subjects in this part of the project. Analysis of variance showed significant difference (p<0.05) in all the parameters evaluated. Results also showed comparable data with control (bread from whole wheat flour) had better results when compared to the control sample.
Data obtained from nutritional evaluation of bread samples fed to experimental animals showed that increase in cassava flour reduced acceptability of the feed by the test animals which agreed with previous studies which demonstrated that animals are known to eat more food when such food has good organoleptic appeal.
Linear interaction of the three factors significantly (p<0.01) affected general acceptability of the bread samples. The interactions of the studied variables were more significant (p<0.01) with respect to improvers which showed quadratic response, and this accounted for a total of 96% of the variation in general acceptability and conferred goodness of fit.
Previous studies reported preference of cassava-wheat bread with lower concentration of wheat flour. They also observed that panelists’ preferences decreased with increasing levels of non-wheat flours in the bread samples. In this study, optimization showed that maximum general acceptability obtainable from the cassava-wheat bread samples was 4.21 from 10% TMS 98/87164 panok, while an optimum value of 3.84 was recorded from 10% TMS 98/1632 baked with panok.
Net protein utilization (NPU) is used to describe the value or usefulness of certain proteins in a diet. NPU is similar to biological value except that it involves a direct measure of retained nitrogen. A range of 60.06% (10% TMS 98.87164 with ascorbate) was recorded for net protein utilization. A streamline increase was observed with increasing wheat levels and blends with 10% cassava flours recorded values similar to bread from whole wheat (control).
The predicted model was significant (p<0.01) on NPU of rats fed cassava-wheat bread. It was observed that interactions between cassava varieties and flour compositions showed a skewed figure. However, the influence of cassava flour on NPU had a significant quadratic effect, while the influence of variety and improvers was linear.
Results also revealed that interaction between cassava flour, improvers and cassava varieties had significant (p<0.05) effect on NPU. However, regression on net protein utilization showed no significant effect on the studied independent variables but final equation in terms of actual variables accounted for 60.84% R-squared which conferred goodness of fit. Optimization showed that the maximum NPY that was obtainable from the bread samples fed to the experimental rats was 91.23% from 10% TMS 98/1632 baked with panok improver. An optimum value of 90.74% was also recorded for the same bread sample.
Statistical results regarding true digestibility (TD) indicated that it differed significantly (p<0.05) among different experimental diets. Data obtained showed that bread from wheat (control) recorded the highest TD value ( 91.83%) and that there was no significance (p>0.05) between bread samples 20% TMS 98/1632 baked with carboxyl methyl cellulose (CMC) as improver and 10% TMS 98/87164 panok with 69.30% and 69.81% respectively which recorded the least TD values. These results provided good information that improvement in the nutritive value of diet occurred as a result of what flour incorporation in cassava flour and not from the use of improvers. A steady increase was observed with increasing levels of wheat.
Final equation in terms of actual variables showed that linear and quadratic interactions between cassava varieties, composite flour and improvers accounted for 60% variation in true digestibility and conferred goodness of fit. Response surface graphs provided above revealed that studied independent variables showed no patter of response. It was observed that the impact of the level of cassava wheat flour substitution in wheat flour had greater impact on true digestibility among the studied variables.
In addition, linear interactions of the three factors showed no significance (p>0.01). However, effects of cassava flour substitution had greater significant (p<0.01) effect on TD which showed quadratic influence with respect to cassava varieties and improvers; while the effects of cassava varieties and improvers showed linear responses. Optimization showed that the maximum true digestibility value was obtainable from the bread sampled fed to the experimental rats was 88.61% from 10% TMS 98/1632 with panok improver, while an optimum value of 86.95% was obtained from the bread sample.
Biological value (BV) provides a measurement of how efficient the body utilizes protein consumed in the diet. BV was highest for the group of rats fed bread from 10% TMS 98/87164 baked wit CMC as improver with a mean value of 99.16% and lowest for bread baked from TMS 98/87164 panok with a value of 86.06%. Values obtained for samples from cassava variety TMS 98/87164 recorded biological values that were higher than the control sample. However, it was observed that bread samples baked from the flours TMS 98/1632 had low BV values. The high BV generally recorded by these samples were an indication that the amino acid patterns were comparable with the control sample.
There was significant difference (p<0.05) in the biological values of the bread samples. The predicted model had significant (p<0.01) effect while the interaction of independent variables had no significance. The plot responses (provided above) sowed linear responses with respect to flour substitution and cassava varieties, while the effect of cassava varieties showed little quadratic response. Furthermore, from the graphs it was observed that the effect of level of cassava flour substitution in wheat flour showed a more pronounced quadratic influence with respect to cassava varieties and different improvers.
However, the predicted model and final equation for BV accounted for a total of 62% variation in biological value and conferred goodness of fit. Optimization showed that the maximum and optimal values for BV obtainable from cassava-wheat bread samples fed to experimental animals were 105.76% and 105.03% respectively, from 10% TMS 98/1632 bread baked with panok improver.
The blood glucose of rats fed samples from cassava-wheat flours baked with different improvers ranged from 88mg/dL to 165.25mg/dL. The glucose recorded for the bread samples was slightly higher than the values termed normal for rats after overnight fast of 60-130mg/dL and humans’ normal range of 80-120mg/dL. The results obtained were a clear indication that the inclusion of cassava flour up to 30% did not result in diabetic glucose levels given that a value of 240mg/dL and above is considered diabetic.
The interaction between independent variables studied showed no significance (p>0.01) and the final equation for blood glucose accounted for 70% of the variation. Response surface graphs displayed above, revealed gradual increase (quadratic response) in blood glucose with increasing cassava flour substitution, while cassava varieties and different improvers showed linear responses in the blood glucose of rats fed wheat-cassava bread. However, the results also revealed that the influence of varietal effect had greater significance (p<0.01) among the studied variables. Optimization showed that the minimum value for blood glucose obtainable from cassava-wheat bread samples was 93.61mg/dL from 10% RMS 98/87164 baked panok, an optimum value of 112.77mg/dL was obtained from 10% TMS 98/1632 panok, while the maximum obtainable value for blood glucose was 136.78mg/dL from 30% TMS 98/87164 baked with ascorbate.
Nitrogen intake accounts for the total amount of nitrogen taken within the period of balance study. The result obtained in this project showed that nitrogen intake was highest for the control sample (wheat bread) with a value of 3.62 and lowest for bread baked from 20% TMS 98.1632 with CMC improver (0.67). There was a steady increase in nitrogen intake with increasing levels of wheat flour. Given that the higher nitrogen intake recorded for the group of rats who were fed the control sample against the composite flours was a function of their feed intake and also that of the protein composition of the blend consumed, the results revealed that feed intake had a direct influence on nitrogen intake. The values obtained were however, lower than those recorded studies where wheat flour was supplemented with legumes.
As visualized in the response curves above, nitrogen intake increased with respect to combined effects of cassava varieties and increasing cassava flour substitution, while improvers showed linear response. The results of regression analysis and ANOVA of nitrogen intake of experimental rats fed sample breads showed no significant difference (p>0.01). However, interactions of studied variables accounted for 92.47% variation on nitrogen intake of rats fed cassava-wheat bread with conferred excellent goodness of fit. Optimization showed that the minimum nitrogen intake value of 0.56 was obtained fro 10% TME 98/419 baked with ascorbate, while an optimum value of 1.58 was obtained from 10% TMS 98/1632 baked with panok.
Digested nitrogen was also highest for the group of rats fed control diet (3.33) and least for rats fed 20% TMS 98/1632 with CMC (0.47). Higher values obtained for the control sample was an indication of a superior protein quality. Additionally, a visible relationship was observed between feed intake, nitrogen and digested nitrogen suggesting that higher intakes resulted in higher digestibility which could imply that high feed intake affected these parameters.
Analysis of variance results showed that variables had no significant effect on the digested nitrogen accounting for a total of 92% of variation in digested nitrogen of the experimental rats which conferred goodness of fit. Results of regression analysis revealed that combined linear interaction of the three factors significantly (p<0.01) affected digested nitrogen, while response surface plots provided above, showed quadratic influence of level of cassava flour substitution with respect to cassava varieties and improvers. Optimization showed that the optimum digested nitrogen value of 1.37 was obtained from bread baked from 10% TMS 98.1632.
Retained nitrogen results ranged from 0.46 (20% TMS 98/1632/CMC) to 3.09 (control). The predicted model was highly significant (p<0.01) while the effect of cassava varieties, level of cassava flour substitution to wheat flour and different improvers showed no significant effect on retained nitrogen but accounted for a total of 86% variation in retained nitrogen. Final equation in terms of actual variables showed an R2 of 85.92% which conferred goodness of fit.
The response curves obtained for retained nitrogen showed similar patterns for those obtained for nitrogen intake and digested nitrogen. Optimization showed that the minimum retained nitrogen value obtainable from bread samples fed experimental animals from 30% TME 98/419 baked with ascorbate while optimum value of 1.39 was obtained from 10% TMS 98/1632 baked with panok.
Feed intake regression analysis showed that the interaction between cassava varieties and improvers, as well as composition and improvers had significant effect (p<0.05) in the feed intakes of the experimental rats. Highest value of 226.35g was recorded for bread baked with 100% wheat flour (control sample) representing high preference of the bread by the test animals.The closest value recorded for bread baked from 10% TMS 98/87164 ascorbate with 108.01g, while the least feed intake value was recorded for bread from 20% TMS 98/1632 with CMC (41.98g) which indicated less preference of the bread samples. The results also revealed increased preference for bread samples with higher wheat levels. This also corresponded with the sensory results obtained from this project analyses, showing human preference for bread samples with lower concentration of cassava flour.
However, regression coefficients indicated that interactions between studied independent variables were highly significant (p<0.01) with respect to different improvers and the equation accounted for a total 99.9% of variation in feed intake of the rats fed bread with wheat-cassava composite flour which conferred a perfect goodness of fit. The response curves revealed quadratic responses in respect to cassava varieties and level of cassava flour substitution respectively, while the effect of improvers showed linear response. Optimization showed that the maximum feed intake value of 107.57g was obtained from 10% TME 98/419 baked with panok, while the minimum value of 49.44g was obtained from 30% TME 98/419 baked with ascorbate.
Feed efficiency ratio relates weight gain to feed consumed. The results showed that there was significant difference in feed efficiency ratio. Highest value was recorded for bread from 10% TMS 98/87164 panok (57.78) closely followed by bread samples from 10% TME 98/419 panok (51.37) and 10% TME 98/419 ascorbate (42.51), while the least value was recorded for bread from 30% TMS 98/419 ascorbate with 21.20. However, the control sample recorded value of 23.41 in feed efficiency ratio. The results indicated that those samples consumed more did not confer better efficiency of the feel while feeds consumed in smaller quantities had higher feed efficiency ratio.
Regression analysis and analysis of variance showed that the variables accounted for a total of 90% of variation although they did not contribute significantly (p>0.01) to feed efficiency ratio but conferred a goodness of fit. Response curves showed skewed figures as demonstrated above. However, it could be inferred from the figures that the combined effects of the three factors (cassava flour substitution, different improvers and cassava varieties) had quadratic influences on the feed efficiency ratio of the experimental animals. Furthermore, final equation for feed efficiency ratio accounted for 90% variation. Optimization showed that the optimum value for feed efficiency ratio of 39.96% was obtained from 10% TMS 98/1632 baked with panok.
Values of the total body weight of rats fed bread from cassava-wheat composite flour showed that the highest body weight value was attained by rats fed the control diet (10.6g) followed by brad samples from 10% TMS 98/87164/ascorbate (8.00g), 10% TMS 98/97164/panok (7.20g) and 10% TMS 98/1632/CMC (6.80g), while the least value was recorded for the bread sample baked from 30% TMS 98/1632/CMC (4.30g). Increasing cassava flour affected the body weight of the test animals and this had a direct relationship to their feed intake. It was observed that higher feed consumption showed a higher body weight and vice versa.
Interactions between cassava varieties, composite flours and improvers showed no significance while the equation accounted for a total of 55% variation maintenance body weight of the experimental animals and this conferred a goodness of fit. As expected, the influence of level of cassava flour substitution to wheat flour had great significant (p>0.01) effect on maintenance body weight of the test animals. The response curves revealed a progressive increase in body weight from 10% substitution of cassava flour through 20% while a sharp decrease was observed when the cassava flour substitution increase to 30%. Among the three factors studied, effect of cassava flour substitution had more significant (p<0.01) influence on maintenance body weight of the experimental animals. Optimization showed that the maximum maintenance body weight obtainable from cassava-wheat bread samples fed to the test animals was 8.00g from 10% TMS 98.1632 baked with panok improver.