Physiochem Profiles

For countries like Nigeria and Ghana, cassava provides a reasonable yield under marginal soil conditions and is drought tolerant. For this reason, it has and continues to be a good reliable staple food in many parts of Africa. However, cassava roots cannot be stored for too long hence, cassava is best stored in the form of flour. High-quality cassava flour (HQCF) can conveniently replace maize or wheat flour. HQCF can be included in wheat flour to make many different products such as bread or baked goods.

 

 

 

Peeling cassava roots immediately after harvesting is a difficult operation and is mostly done by women. Hand peeling was and still is the only feasible option while, grating cassava roots to mash can effectively be done with powered graters.

The dewatering process however, is another tedious operation. The traditional method involves packing the mash inside a polypropylene sack and pressing with heavy stones for 24-48 hours. Improved dewatering is done with a mechanical press to apply pressure on polypropylene sacks that contain the grated cassava mash for 2-4 hours. These mechanical press machines are usually not available at the village level and thus, their absence is a constraint to cassava processing.

The traditional dewatering method allows skin contact with cassava mash and since all cassava tissues contain toxic cyanogenic glycosides, the mash process stages expose workers to ailments and disorders of ergonomic origin.

Raffia sieves are used for pulverizing and sifting cassava cake during the flour making process; an unhygienic and hazardous process.

 

The high-quality cassava flour available at the time, was made from different varieties of cassava that were available to processors and which might not have met the required parameters of HQCF. Therefore, the objective in this component of the project was to determine which varieties of cassava are suitable for the production of high-quality cassava flour that would meets its quality parameter in terms of functional property, proximate composition and cyanide content.

 

 

 

PHYSIOCHEMICAL PROFILES OF FLOUR & STARCHES OBTAINED FROM PROCESSORS

To assess the proximate composition, functional properties and chemical properties of high-quality cassava flour in Nigeria, HQCF was sourced from small medium enterprises (SMEs) in Ogun and Ondo states with a view of providing information on whether they met quality standards that would ensure the enhancement of their end use. HQCF obtained from six different SMEs was screened to check for specific chemical properties to ascertain if quality levels were met. These chemical properties included: –

• Residual cyanogenic potential
• Carbohydrate value
• Mineral content

 

 

 

 

To assess the residual cyanide level (total cyanogens) of the flours of the cassava varieties, the alkaline picrate method with modifications was used. The minerals (Calcium, Magnesium, Potassium, Sodium, Copper, Manganese, Iron, Zinc, Phosphorus and Cobalt) in each SME sample were analyzed using atomic absorption spectrophotometer (AAS) fitted with a hollow cathode lamp and fuel-rich flame (air acetylene) following the Association of Analytical Chemist (AOAC) procedure.

Total cyanogens left after the processing of high-quality cassava flour were determined for each sample with SME5 having the highest cyanide content (1.82mg/kg) and SME6 with the lowest (1.06mg/kg). Since SME6 showed a slightly lower level of residual cyanide compared to the other samples, it was found to be an appropriate HQCF for partial substitution of wheat flour in the production of bakery products. The difference in cyanide values could have been a result of the cassava variety used (whether it was bitter or sweet), the agronomic conditions, the age at harvest or the processing methods used.

 

 

 

There was no significant difference (p<0.05) in the cyanide content of the flours except for SME5. SME1, 6 and 4 were similar and showed no significant differences from each other while SME2 and SME3 were similar and also showed no significant difference. SME5’s value however, was significantly higher compared to the other samples’ values. This could have been a result of varietal differences, agronomic factors or processing conditions.

Prior studies had shown that the cassava variety used to obtain HQCF whether bitter or sweet, affects the amount of residual cyanogenic content; HQCF made from sweet cassava varieties was shown to usually have less residual cyanogens when compared to HQCF process from bitter cassava varieties.

 

With regards to carbohydrate levels in the HQCF samples, all samples showed relatively high carbohydrate values with SME1 having the highest value of carbohydrate on dry matter basis at 84.17% while SME4 had the lowest at 81.35%. The high carbohydrate levels made the samples an excellent choice for using as partial substitutes to wheat flour in bread making and for the production of high energy snacks for teenagers and adolescents.

All values obtained for carbohydrates showed very little significant differences from each other with SME4 and SME5 showing slight significant differences in values. SME2, 1 and 3 were similar and also showed slight significant differences. The slight variation in values of carbohydrate on the basis of dry matter of the HQCF samples may be a result of varietal differences, drying conditions or certain processing operations such as pressing and milling.

Given that the human body requires micronutrients in smaller quantities, micronutrients in cassava roots (iron, magnesium, copper, zinc and manganese) are ideal for ingestion as they are available in minute quantities and thus, they are perfect for HQCF processing. Cassava roots also contain high levels of macronutrients (phosphorus, potassium, calcium) making them again ideal for human consumption. Cassava leaves on the other hand, have higher levels of both micro- and macro-minerals (iron, zinc, manganese, magnesium, calcium) when compared to cassava roots and are thus, less ideal for human consumption

 

This all shows the importance of the presence of phosphorus in the human diet hence, the need for its intake in areas where cassava and its products are used as staples is of the utmost importance. HQCF should contain phosphorus not less then 15mg/100g; the phosphorus statistical analysis in this study showed similar observations as all values obtained were above 15mg/100g.

Additionally, all mean values obtained for phosphorus showed little significant difference except for SME1 and SME6 as these samples showed more significant differences from other sample values in that SME1 and 6 phosphorus values were higher which may have been due cassava varietal differences or varied drying conditions.

 

 

 

With regards to the magnesium results, SME4 was significantly different from the values of other HQCF samples which could have resulted from mineral content variations with cassava varieties, agronomic conditions or drying conditions. Studies previously conducted prior to this HQCF processing study had showed that sun drying cassava cakes during the drying process has an adverse effect on vitamins and minerals including magnesium.

 

 

 

The results of this physiochemical study showed that the potassium values obtained from were all high with SME4 having the highest value (90mg/100g). This high value in potassium indicated that an effective processing method was used to produce SME4. Additionally, all potassium values varied significantly with high numerical differences. The decrease in potassium values could have emanated from processing conditions which can cause reduction with every process operation.

 

 

 

For the micro-minerals examined in this study (copper, manganese, iron, zinc, cobalt) their values were found to be minimal with most having little or no health implications in minute quantities and absence of quality levels. However, if some of these micro-minerals are consumed in high quantities, they show certain harmful effects.

 

 

 

Functional Properties of HQCF Samples

Bulk density is an important parameter that determines the ease of packaging and transportation of certain foods. Usually, the lower the bulk density of a food powder such as high-quality cassava flour, the higher the moisture content thus, flours with good bulk densities are useful in the preparation of confectionary products. As shown in the table above, HQCF SME2 had the highest bulk density (0.65g/ml) and HQCF SME3 had the lowest bulk density (0.53g/ml). While SME 5, 1, 6 and 4 were not significantly different, SME3 and SME2 were found to be significantly different (p<0.05).

 

 

 

Results showed that the swelling power of the HQCF samples ranged from 7.20% in SME2 to 9.82% in SME4. While SME4 and SME6 were found to be significantly different, SME 5, 1, 3 and 2 were not significantly different (p>0.05), Swelling capacity is regarded as a quality criterion in the making of certain products in the baking industry such as bread. It is evidence of non-covalent bonding between molecules within starch granules and is also a facto fo the ratio of α-amylose and amylopectin ratios.

With regards to foaming capacity, SME2 had the highest capacity (5.96%) while SME5, SME1 and SME6 had the lowest (0.00%). SME 5, 1 and 6 were also not significantly different however, SME2 and SME4 were significantly different (p<0.05). These differences could have been due to variation in the processing methods adopted for the production of each of the samples. Additionally, SME3 (86.60%) had the highest foaming stability while SME6 (29.96%) had the lowest.

Soluble proteins can reduce surface tension at the interface between air bubbles and any surrounding liquid. Thus, the coalescence of the bubbles is obstructed. In addition, protein molecules can unfold and interact with one another to form multilayer protein film with an increased flexibility at the air liquid interface. As a result, it is more difficult for air bubbles to break and the foams are more stabilized.

 

 

 

 

 

 

As per the table above, water absorption capacity of the HQCF samples ranged from 75.15% in SME1 to 153% in SME4. The WACs of these HQCF samples were useful indications of whether protein could be incorporated with aqueous food formulations, especially those involving dough handling. Interactions of protein with water is important to other flour functional properties such as hydration, swelling power, solubility and gelation.

 

 

 

 

Solubility is the ability of solid substances to dissolve in an aqueous solution usually water thus, solubility is an important parameter in baking since flour with a high solubility may give soggy and less cohesive dough. Solubility could be influence by granular size as studies have reported lower solubility in smaller granules of starch from botanical sources. SME2 (20.80%) had the highest solubility value while SME3 (13.81%) had the lowest. SME5 and SME3 were not significantly different perhaps because their sample granular sizes were same while the other HQCF samples were not.

 

 

 

Viscosity is a main component of flour and is needed to predict behaviour under a given processing condition. Higher viscosities demonstrate a weaker binding force, low resistance to shear during heating and less paste stabilities, making these flours potentially useful raw materials in the production of thickeners, jelly or in other products where high viscosities are recommended. However, lower viscous flour samples are useful in the production of weaning food and in the paper and textile industries. In this study, viscosity of the HQCF samples ranged from 42.33% (SME3) to 32.78% (SME4). While the samples most of the samples were found to be significantly different, statistical analysis showed that SME6 and SME4 were not significantly different (p>0.05).

 

 

 

Gelatinization is the temperature at which starch molecules in a food substance lose their structure and leach out from the granules as swollen amylase and this affects the time required for the cooking of the food substance. The sample with the highest gelatinization capacity was SME5 (21.82°C) while that with the lowest was SME6 (15.34°C) with all samples found to be significantly different (p<0.05).

 

 

 

Wettability of the HQCF samples ranges from SME1 (47mins) to SME4 (22.66min). SME5 was found to be the only sample that was significantly different (p<0.05) while SME 3, 2, 1 and 6 were not significantly different (p>0.05). The wettability results implied that SME1 required a much longer time to become completely wet when compared to the other samples.

Dispersibility is a measure of the degree to which flour or flour blends reconstitute in water; the higher the dispersibility, the better the flour reconstitutes in water. HQCF dispersibility amongst the samples ranged from 73% in SME2 to 64.6% in SME4. The samples of the HQCF with higher dispersibility values indicated their ability to produce smooth dough in composite with wheat flour.

 

 

 

HQCF – Proximate Composition

The six HQCF samples selected from small and medium enterprises in Ondo and Ogun states were studied to determine their moisture, fibre, ash, fat, protein and carbohydrate content. Results from the proximate compositions showed that the HQCF SME5 had the highest moisture content (13.2%) while SME1 had the lowest (10.43%). SME5 was the only sample that was found to be significantly different (p<0.05). This may have been as a result of varying drying efficiency or it could also have been due to improper packaging or the variation in cassava roots used. With regards to the ash content, SME4 had the highest content (1.04%) and accordingly had the highest amount of minerals while SME4 had the least ash content (0.64%).

 

 

 

 

While SME6 had the least fat content (0.05%), SME3 had a far greater content (0.68%) when compared to the other HQCF samples. Both SME5 and SME4 were found to be significantly different from the other samples. This could have been as a result of heat and mass transfer during drying. In addition, the pressing techniques used to separate the fibrous material and liquid may have explained the fact content variation amongst the HQCF samples.

Moreover, the results of the crude protein content of the HQCF samples showed that SME4 had the highest protein content (2.15%) while the least crude protein content was found in SME3 (1.19%). SME1 was the only sample that was found to be significantly different.

 

 

 

 

 

 

Pasting Properties of HQCF Samples

When starch-based foods are heated in an aqueous environment, they undergo a series of changes constituting gelatinization and pasting. There are two of the most important properties that influence quality and aesthetics in the food industry as they affect the texture and digestibility of the foods as well as the end-use of starchy foods.

 

 

 

The table above displays the pasting properties of the HQCF samples selected from the SMEs in Ogun and Ondo states. The peak viscosity determined for the HQCF samples ranged from 169.92 RVU (SME6) to 337.88 RVU (SME3) with no high-quality cassava samples found to be significantly different. These high peak viscosities found between SME2 (313.46 RVU) and SME3 (337.88 RVU) could be attributed to the high degree of swelling of cassava starch granules.

 

 

 

Similarly, the final viscosity of the HQCF samples ranged between 176.17 RVU (SME2) to 245.25 RVU (SME6) with again significant differences observed between samples. Conversely, no significant differences were observed for the setback viscosity values which ranged from 42.45 RVU in SME2 to 68.21 RVU in SME3.

 

 

 

 

The pasting temperatures of the HQCF samples were determined and ranged from 74.35°C (SME1) to 78.25°C (SME6), with SME6 found to be significantly different from the other HQCF temperature values. The rapid drop in viscosity at 76°C for the HQCF SME2 sample, almost half of the peak viscosity, indicated a large extent of breakdown of the paste and hence, low stability. In addition, the peak time which is essentially a measure of the cooking time, was within a close range (3.2min for SEM6 to 5min for SME3).

 

 

 

 

Cassava flour has rheological properties that slightly differ from those of cassava starch since flour contains fibres, small amounts of lipids and sugars. Therefore, cassava starch cooks to a more cohesive paste ant that the presence of the fibres in flour delay gelatinization and provides a lower peak viscosity by limiting the access of water into the granules.

During the hold period of a typical pasting test, the sample is subjected to a period of constant temperature (usually 95°C) and mechanical shear stress. This further disrupts the starch granules and the amylose molecules generally leach out into the solution and align in the direction of the shear. A gradual decrease of the paste viscosity during the hold process indicates thermal breakdown of starch and thus, can considered a measure of the starch’s stability.

 

The rate of breakdown depends on the nature of the material, the temperature and the degree of mixing and shear applied to the mixture. While cross-linked starches are more resistant to breakdown, the ability of any starch paste mixture to withstand this heating and shear stress is an important factor for many processes.

 

 

 

A high setback value indicates lower retrogradation tendency and thus, is useful if the flour is to be used in domestic products such as fufu which requires high viscosity and paste stability at low temperatures.

 

 

 

Physiochemical & functionality Properties from Different Cassava Varieties

 

 

 

 

 

 

For statistical analysis, triplicate determination was done for all samples just like that done for the SME HQCF samples. The table above shows the statistical analysis results for the proximate composition of high-quality cassava flour from four varieties of cassava (TME 419, TMS 30555, TMS 30572 and OKO IYAWO) and shows varietal influence on the composition of HQCF.

 

 

 

Moisture content of the flour ranged from 9.05% to 10.2% while protein content was relatively low as it ranged from 1.14% and 1.34%. With regards to ash content the high-quality cassava flour samples, it ranged from 0.68% to 0.91% while that of the crude fibre content ranged form 0.18-0.25% and crude fat results were between 0.68%-0.75%. Total carbohydrate ranged from 87.09% to 87.79%. Thus, all samples were found to comply with the regulatory standard of not more than 1.5% ash content recommended by the Standard Organisation of Nigeria (SON).

 

 

 

 

 

 

There was no significant difference (p>0.05) in the proximate composition of the samples however, differences were observed in crude fat content which ranged from 0.68% to 0.82% with flour from TME 419 having the lowest crude fat content and flour from TMS 30572 having the highest. Additionally, crude fibre which consists of cellulose and lignin was used as an indicator of dietary fibre content as dietary fibre is indigestible or an unavailable carbohydrate, present in the diet.

 

 

 

Functional properties of flours directly determine their end uses. The table above shows the results of the statistical analysis of some of the functional properties of the high-quality cassava flours, showing the effect of variety on the functional properties of HQCF. Results showed that there was significant difference in the water absorption capacity of the flour and that it ranged from 110 to 163% with flour from TMS 30572 having the lowest absorption capacity and that from oko iyawo having the highest value. Meanwhile, there was no significant difference in the oil absorption capacity of the samples. The higher water absorption capacity of some of the flours may have been due to the higher polar amino acid residues of proteins having an affinity for water molecules.

Foam is a colloid of many gas bubbles trapped in a liquid or solid whereby, thin liquid films surround small air bubbles. Foam can be produced by whipping air into a liquid as much as and as fast as possible. The reason flours can produce foams is that proteins in flours are surface active.

 

 

 

Statistical analysis showed there was significant difference (p<0.05) in the foam capacity of the flour samples and that it ranged from 2.1% to 3.53% with TMS 30572 having the lowest foam capacity and TMS 30555 having the highest. Similarly, there was significant difference found in the emulsification properties of the flour samples with TME 419 having the lowest capacity at 4.32g/ml and the flour from oko iyawo having the highest foam capacity 3.72g/ml. The emulsification properties of flours may have resulted from both soluble and insoluble protein as well as other components like polysaccharides.

 

 

 

 

With regards to swelling power, results showed that flour swelling power ranged from 51.23% (TMS 30572) to 54.88% (TME 419) while solubility ranged from 30.37% (TME 419) to 33.5% (TMS 30555) which implied that were was significant difference (p<0.05) in these properties of the flours processed from different cassava varieties.

 

On the other hand, dispersibility is a measure of the degree to which flour or flour blends reconstitute in water thus, the higher the dispersibility, the better the flour reconstitutes. Dispersibility results ranged from 34.56% for TMS 30572 to 34.91% for TME 419. The high dispersibility values exhibited by all the samples of HQCF analyzed were indicative of their ability to produce smooth dough in composite wheat flour.

 

 

 

Cyanogenic glucosides are compounds that yield glucose, hydrogen cyanide (HCN) and aldehydes or ketones upon hydrolysis with an acid or enzyme. The statistical analysis of cyanide content of flours developed from the different root varieties showed that there was significant difference (p<0.05) in the cyanide content of both the roots and their flours. TME 419 had the lowest cyanide content of both root and flour while TMS 30572 had the highest cyanide content for root and oko iyawo had the highest for flour. Thus, the HCN content of the flours (4.28-6.30mg HCNeqv/100g) were within the values recommended by the Standard Organisation of Nigeria (<10mg HCNeqv/100g)

 

The statistical analysis of mineral composition of the flours revealed significant different (p<0.05) in the mineral composition of the flours. While calcium ranged between 3.07mg/100g (oko iyawo) and 5.10ml/100g (TMS 30555), magnesium ranged from 20.3mg/100g (TMS 30572) to 32.46mg/100g (TME 419). TMS 30572 had the lowest potassium content while TMS 30555 had the highest. Sodium ranged from 209.53mg/100g (oko iyawo) to 250.81mg/100g (TMS 30572) while oko iyawo had the lowest phosphorus content and TMS 30555 had the highest. These results showed varietal influence on the mineral composition of high-quality cassava flour.

 

 

 

Pasting Properties

When starch-based foods are heated in an aqueous environment, they undergo a series of changes known as gelatinization and pasting. These are two of the most important properties that influence quality and aesthetic considerations in the food industry since they affect the texture and digestibility as well as end-use of starchy foods. The pasting temperature is the temperature at which the first detectable increase in viscosity is measured and is an index characterized by the initial change due to the swelling of starch. A higher pasting temperature implies higher water-binding capacity, higher gelatinization and lower swelling property of starch due to a high degree of association between starch granules.

 

 

 

Results showed that peak viscosity values obtained in this project ranged between 286.97 RVU (TMS 30572) and 342.22 RVU (oko iyawo) while the pasting temperature ranged from 75.03°C (TME 419) to 75.65°C (TMS 30555). Trough (or hot paste) viscosity HQCF sample values ranged between 144.30 RVU (TME 419) and 193.19 RVU (oko iyawo) while breakdown viscosities ranged between 140.97 RVU (TMS 30555) and 177.61 RVU (TME 419). Oko iyawo had both the highest final and setback viscosity values while, TMS 30555 and TMS 30572 had the lowest final and setback viscosities respectively.

Given that pasting temperature gives an indication of the gelatinization time during processing, the HQCFs used in this study therefore, gelatinized within a short period of time and had a higher level of gelatinization. However, pasting properties were affected by variety (p<0.05) but the pasting temperature was found to be unaffected by variety.

 

 

 

Conclusions

The quality characteristics of the four HQCF samples investigated showed significant variations (p<0.05) in some the quality parameters evaluated. Besides oil absorption capacity, the rest of the functional properties, cyanide content and mineral compositions of the flour samples wee found to be significantly different (p<0.05). Significant differences were recorded in the pasting profiles of the HQCF samples except for pasting temperature in which there was no significant difference (p>0.05) between the samples.

Cyanogenic potentials of the flours were found to be low which implied that they did not exceed toxicity levels set for cassava flour and therefore, were found to be safe for consumption. Results also showed that the flours could undergo some processes and changes in terms of their functional and pasting properties. Additionally, the flours were found to contain considerable amounts of minerals needed daily by humans and the proximate compositions were also in range. Hence, there was no varietal influence on the proximate compositions and the pasting properties of the HQCFs but there was varietal influence on the functional properties, cyanide content, mineral composition and the pasting properties. Thus, it was recommended that producers of high-quality cassava flour should use the four varieties of cassava used in processing these sample flours in order to meet their quality parameters.