Effect of cassava variety, fertiliser type and dosage on the physicochemical, functional and pasting properties of high-quality cassava flour (HQCF)

S.A. Rasaq1, T.A. Shittu1, G.J. Fadimu2, A.B. Abass3,4, and O. Omoniyi3

1Department of Food Science and Technology College of Food Science and Human Ecology, Federal University of Agriculture, P.M.B. 2240, Abeokuta, Ogun State, Nigeria; 2Department of Food Science & Nutrition, College of Food and Agricultural Sciences, King Saud University, P.O. Box 2460, Riyadh, Saudi Arabia; 3International Institute of Tropical Agriculture (IITA), P.M.B. 5320, Oyo Road, Ibadan, Nigeria; 4International Institute of Tropical Agriculture (IITA), Plot 25, Light Industrial Area, Coca cola Road, Dar es Salaam, Tanzania

Corresponding Author: G.J. Fadimu, [email protected]

Received: 25 March 2019 / Accepted: 24 November 2019 / Published: 31 December 2019


The increase in the dry matter content of cassava due to fertiliser application has been widely reported. However, information on the effect of cassava variety, fertiliser compounding ratio and dosages on physicochemical, functional and pasting properties of high-quality cassava flour (HQCF) is scarce in the literature. This study was conducted to investigate the effect of cassava variety (TME 419 and TME 30572), fertiliser compounding ratios (NPK ratio 15-15-15, 20-10-10 and 12-12-17) and dosage (150 and 300 kg/ha) on some quality parameters of HQCF, and the influence of independent factors on HQCF was determined using general linear model (GLM) analysis. The result revealed that all the independent variables had significant (p < 0.05) effect on the physicochemical, functional and pasting properties of HQCF. The proximate composition of the flour was mostly affected by variety and fertiliser type, while the interactive effect of fertiliser type and dosage as well as the fertiliser type and variety was significant (p < 0.05) on the total starch content. Varietal influence was the main factor that significantly affected the amylose content of the flour samples and swelling power as well as least gelation concentration was significantly affected by fertiliser compounding ratio. In addition, interaction of fertiliser type and dosage had significant effect on swelling power. Pasting properties of the flour samples were mostly influenced by fertiliser type and cassava varieties, while dosage did not show significant influence on the flour properties. Peak viscosity value, which varied from 462.58 to 534.67 RVU, is the pasting property that was mostly affected by the independent factors. This study clearly indicates that cassava varieties and fertiliser treatment could influence the functionality of HQCF in food systems.

Keywords: cassava varieties; fertiliser compounding ratio; fertiliser dosage; HQCF; quality attributes


1. Introduction

Cassava (Manihot esculenta Crantz) is an important tropical root crop. Its starchy roots are an important source of calories in the tropics, providing energy nourishment for more than 500 million to 1 billion people worldwide (Sornyotha et al., 2010). Nigeria is the leading producer of cassava roots in the world. In the year 2017, Nigeria produced 59 million metric tons of cassava roots, which was about 18% of the total world production (FAOSTAT, 2019). With rising wheat prices on the global market, there is an interest to promote the utilisation of local sources of flour for the partial substitution of wheat flour in food products in order to reduce the dependency on wheat imports and also to increase the livelihoods of local farmers. Current status of research in West Africa and in Nigeria has focused on the production of high-quality cassava flour (HQCF) for use in the food industry. HQCF provides the best alternative to flour production for baked products. Several food products prepared from wheat, rice and corn starches can be made using cheap and readily available stable product such as HQCF as a partial or total substitute. Cakes, cookies, bread and other confectioneries have been successfully made from HQCF.

HQCF is one of the numerous products that are obtained from cassava roots. HQCF is unfermented, white, smooth and odourless cassava flour with no gluten and has been used as a local inclusion into wheat flour for use in the baking industry (Oti et al., 2010). It is produced from freshly harvested sweet cassava variety and rapidly processed cassava roots. Optimum utilisation of cassava flour in composite bread production could be a catalyst for rural industrial development by raising the income levels of farmers, processors and traders as well as ensuring the nutrition and food security status of Nigerians (Balagopalan, 2002; Plucknett et al., 1998). Cassava flour has been reported to contain 0.2% fat, 0.5% fibre, 1.7% ash, 85% starch and 0.7% protein (Darkwa and Jetuah, 2003). In addition to its high-energy content, it is also a rich source of minerals and vitamins. However, these nutrients usually exist in lower concentrations in cassava flour when compared with flour from cereals such as wheat and corn. Generally, cassava flour is processed from the sweet variety of cassava, a variety known to contain very low level of cyanogenic glucoside, and elimination of cyanogenic glucoside is achieved during peeling, grating and dewatering operations. The starch of cassava is capable of forming a strong gel and could be used as a composite flour of good binding property (Oparah et al., 2013).

A study by Nweke (1996) reported that cassava root has the potential to bridge the food security gap in Africa. However, cassava yield is generally low due to poor soil fertility (Nweke, 1996). The poor soil fertility is also accelerated by failure of farmers to apply fertilisers. To increase the yield potential of cassava, the crop had been reported to respond to good soil fertility and adequate fertiliser. Fertiliser application supplies the major soil nutrients such as nitrogen, phosphorus and potassium needed for plant growth. NPK fertiliser, which contains the three macro-nutrients, nitrogen, phosphorus and potassium, needed by plants, is the most commonly used fertiliser in cassava cultivation. Addition of these soil nutrients will translate to starch synthesis and expressed in variation of starch and flour quality (Gomez et al., 1980). Many previous works were devoted to determining the effect of cassava genotype and the level of wheat flour substitution with cassava flour on their bread-making quality (Adeyemi and Idowu, 1990; Defloor et al., 1993). However, fewer studies considered the effect of nitrogen treatment on chemical composition and the quality of food product from such roots (Mensah, 2013; Shittu et al., 2008).

Shittu et al. (2008) showed that the quality of flour from cassava varieties was affected by the application of NPK fertiliser. However, the author reported only one fertiliser type and compound dosage ratio of 15/15/15 at 150 kg/ha. Information on the effects of several fertiliser compounding ratio and dosage on physicochemical, functional and pasting properties of HQCF is scarce. This study was therefore conducted to evaluate the effects of different cassava varieties, fertilisers compounding ratio and dosage on physical, chemical and functional properties of HQCF using general linear model (GLM) analysis.

2. Materials and methods


Two varieties of cassava grown with three different fertiliser protocols were obtained from the research site of the International Institute of Tropical Agriculture (IITA) experimental station in Ikenne, Ogun State, Nigeria. The varieties were: TME 419 and TMS 30572. The cassava varieties were harvested at 12 months after planting. Immediately after harvest, the cassava roots were transported to the processing laboratory for processing in order to prevent fermentation. All chemicals used were of analytical grade and procured from Sigma Aldrich Co. (St Louis, MO, USA).

Preparation of high-quality cassava flour

Freshly harvested cassava roots from the two varieties and different fertiliser treatments were processed into HQCF using Adekunle et al.’s (2012) method within 24 h from the time of harvest to drying in order to produce good-quality flour that conforms to the set standard. The cassava tubers were peeled, thoroughly washed and grated into a mash with a grater (model SD-500, Henan, China). The mash was then dewatered by manual pressing in clean woven sacks, the lumps were pulverized and the mash was solar dried on a raised platform in a solar house (direct natural convection solar drier). The dried mash was then milled into flour using the disc attrition milling machine. The flour was sieved with a 0.25-mm sieve to obtain very fine HQCF. The flour was packaged in a polythene bag stored at 4°C for analysis.

Experimental design to produce HQCF

A 2×3×2 factorial design involving two cassava varieties (TMS 30572 and TMS 419) and three compounding fertiliser ratios (NPK 15-15-15: N = 15, P = 15, K = 15; 20-10-10: N = 20, P = 10, K = 10; and 12-12-17: N = 12, P = 12, K = 17) at two dosage levels of fertiliser (150 and 300 kg/ha) was designed using general linear model (GLM) analysis. In each case, the compounding ratios 15-15-15, 20-10-10 and 12-12-17 represent the percentage of nitrogen, phosphorus and potassium in the fertiliser. The 12 experimental runs and two control samples (unfertilised TMS 30572 and TMS 419) generated are presented in Table 1.

Table 1. Experimental design.
Cassava variety Fertiliser type (NPK) Fertiliser dosage (kg/ha)
TMS 30572 15-15-15 150
TMS 30572 15-15-15 300
TMS 30572 20-10-10 150
TMS 30572 20-10-10 300
TMS 30572 12-12-17 150
TMS 30572 12-12-17 300
TMS 30572 NF -
TME 419 15-15-15 150
TME 419 15-15-15 300
TME 419 20-10-10 150
TME 419 20-10-10 300
TME 419 12-12-17 150
TME 419 12-12-17 300
TME 419 NF -
NF, no fertiliser (control sample).

Proximate composition of HQCF samples

The proximate composition (moisture content, crude protein, crude fibre and ash) of the HQCF samples was determined as described by AOAC (2000), while the carbohydrate content was calculated by difference method using the following formula:


Determination of physicochemical properties of HQCF


Five gram of flour (dry basis) was taken in a clean dried beaker and 25 ml of distilled water was added into it and stirred to obtain a homogenous mixture. The mixture was left to settle for 10 min. A calibrated pH meter (Model HI 2210, HANNA Instruments, Romania) was immersed into the water phase of the mixture and the pH reading was recorded (AOAC, 2000).

Determination of total titratable acidity of HQCF

Titratable acidity was determined using AOAC (2000) method, where 25 ml of the filtrate obtained from 5 g of HQCF sample dissolved in 50 ml of distilled water against 0.1 N NaOH using phenolphthalein as indicator was titrated. An amount of 1 ml of 0.1 N NaOH will be taken as equivalent to 9.008×10−3 g lactic acid. A flour sample of 1 g was added into a conical flask and 20 ml of ethanol was added to it and mixed together; then 0.2 ml of phenolphthalein indicator solution was added to the mixture. It was titrated while shaking with 0.1N NaOH until pink colour appeared and persisted for about 10 s. A blank titration was also carried out. The percentage TTA was calculated using the following formula:



V = Volume of the titrant (NaOH) consumed for sample

B = Volume of the titrant consumed for blank

N = Normality of the titrant (NaOH)

W = Weight of the sample

Determination of amylose content of HQCF

The formation of helical complex between amylose and iodine gives rise to the typical deep blue colour of starch dispersion stained with iodine, and this forms the basis for quantitative determination of amylose content (Williams et al., 1970); 100 mg of the flour sample was added into a flask, and 1 ml of distilled ethanol and 10 ml 1N/0.1 N NaOH were added and the mixture was heated for 10 min; 20 ml of distilled water and three drops of phenolphthalein indicator were added to 2.5 ml of the extract. After this, 0.1 N HCL was added drop by drop until the pink colour disappears. 1 M iodine reagent was added and the volume was made up to 50 ml, and the colour was read at 590 nm; 0.2, 0.4, 0.6, 0.8 and 1 ml of standard amylose were taken, and the colour was developed as in the case of the sample. The amount of amylose present in the sample was calculated using the following formula, and 1 ml of iodine reagent was diluted with 50 ml distilled water to obtain the blank:


Determination of starch and sugar contents of HQCF

The starch and total sugars content were determined using a colorimetric method described earlier (Onitilo et al., 2007). This involved weighing 0.02 g of the sample in a centrifuge tube with 1 ml cold ethanol, 2 ml distilled water and 10 ml hot ethanol. The mixture was vortexed and centrifuged at 2000 rpm for 10 min. The supernatant was decanted and used for the determination of the sugar content, while the sediment was hydrolysed with perchloric acid and used to estimate the starch content. Phenol-sulphuric reagent was used for colour development, and glucose standards were used for the estimation of sugar. The absorbance was read with a spectrophotometer (T60 UV Visible) at 490 nm.

Determination of hydrogen cyanide

Quantitative determination of hydrogen cyanide was carried out using Essers et al.’s (1993) method. An extract was made from the flour blends and extrudates using cold orthophosphoric acid. The extract was treated with an excess amount of exogenous linamarase; the pH was raised to convert all cyanohydrins and hydrogen cyanide to cyanide ions. Cyanide ions were quantified using a specific and stoichiometric reaction with chloramine T, isonicotinate and dimethyl barbituric, which produces a coloured dye. The absorbance of the colour produced is proportional to the concentration of cyanide ions in the reaction mixture.

Functional properties of HQCF

Determination of bulk density

Bulk density of plantain flours was determined using Fadimu et al.’s (2018b) method; a 100 ml measuring cylinder was filled with the sample to mark 100 ml; the cylinder was tapped 50 times and then reweighed. Bulk density was calculated as the ratio of the bulk density and the volume of the container (g/ml).

Determination of water absorption capacity

Water absorption capacity of the plantain flour was determined as described by Sathe and Salunkhe (1981). One gram of the sample was mixed with 10 ml of distilled water. The mixture was allowed to stand at room temperature for 30 min and then centrifuged at 1.073 × g for 15 min. The water absorption capacity was expressed as percentage increase in the weight of the sample.

Determination of swelling power and solubility index

Swelling power and solubility index were determined as described by Leach et al. (1959); 1% flour solution was prepared and heated in a water bath (Gallenkamp Water bath Model BKS-350-030), maintained at 90˚C for 30 min with constant stirring and cooling. The suspension was centrifuged at 3000 rpm for 20 min, and the supernatant was decanted into a pre-weighed can and dried at 100˚C to constant weight. The dried can was weighed for solubility calculation, while the weight of wet sediment in the centrifuge tube was used to determine the swelling power.

Determination of dispersibility

Dispersibility of the plantain flour was determined using Kulkarni and Ingle’s (1991) method. Ten grams of the flour sample was suspended in a 100 ml measuring cylinder and distilled water was added to reach a volume of 100 ml. The mixture was stirred vigorously and allowed to settle for 3 h. The volume of the settled particles was recorded and subtracted from 100, and the difference was reported as percentage dispersibility.

Determination of least gelation concentration of HQCF

Gelation property was determined according to Coffman and Garcia’s (1977) method. Sample suspensions of 2–20% (w/w) were prepared in distilled water, and the dispersions were transferred into a test tube. It was heated in a boiling water bath for 1 h, followed by rapid cooling in a cold water bath. The test tubes were further cooled at 4°C for 2 h. The least gelation concentration was determined as the concentration when the sample from the inverted test tube did not slip or fall.

Pasting properties of HQCF

Pasting characteristics were determined by using a Rapid Visco Analyser (RVA TECMASTER, Perten Instruments North America, Springfield, IL, USA). Parameters estimated were peak viscosity, setback viscosity, final viscosity, pasting temperature and time to reach peak viscosity. About 3.50 g of the sample was weighed to the nearest 0.01 g in the test canister and 25 ml of distilled water was dispensed into the canister. The canister was thereafter lowered into the RVA system and the slurry was heated from 50 to 95°C and then cooled rapidly to 50°C within 12 min, rotating the can at a speed of 160 rpm with continuous stirring of the content with a plastic paddle. Parameters estimated were peak viscosity, trough viscosity, breakdown viscosity, setback viscosity, final viscosity, pasting temperature and pasting time.

Statistical analysis

All analyses were conducted in triplicate. The results were expressed as mean ± standard deviation. Statistical analysis was carried out using one-way analysis of variance (ANOVA) with IBM SPSS 21.0 version (Michigan State University, East Lansing, MI). Duncan’s multiple range test was used for mean separation.

3. Results and discussion

Effect of cassava varieties, fertiliser type and dosage on the chemical composition of HQCF

Table 2 shows the effect of cassava variety, fertiliser compounding ratio and dosage on the chemical composition of HQCF. The values of moisture content, ash, crude fat, crude fibre, protein, carbohydrate and dry matter for the flour samples varied from 7.50 to 11.39%, 0.46 to 1.05%, 0.53 to 0.70%, 0.91 to 1.52%, 1.20 to 2.76, 83.62 to 88.43 and 88.61 to 93.00%, respectively, and were significantly different (p < 0.05) from each other. The values reported for some of these parameters are consistent with those reported in previous studies (Moorthy, 2002). The moisture content of the flour obtained in this study was lower than 10% maximum recommended for dried products, and the lower the moisture content of a stored product, the better the storage stability (Sanni et al., 2005). The level of moisture observed in this study may be attributed to varietal influence and/or fertiliser uptake. The protein content of the flours ranged from 1.20 to 2.76% with the highest value reported in TME 419 variety with 20-10-10 NPK compounding ratio at 300 kg/ha. HQCF from unfertilised TME and TMS cassava varieties had significantly lower protein content than the flour from fertilised cassava roots. This implies that fertiliser application to the cassava root could enhance the protein content of the flour from the root. Compared to flour from cereals including wheat, corn and rice, the protein content of cassava flour is generally low.

Table 2. Effect of variety, fertiliser type and dosage on the chemical composition of HQCF.
Variety Fertiliser type (NPK) Dosage (kg/ha) Moisture (%) Ash (%) Fat (%) Fibre (%) Protein (%) CHO (%) Dry matter (%)
TMS 30572 15-15-15 150 9.03±1.05c 0.71±0.02h 0.58±0.00abc 1.19±0.01abcd 2.38±0.03bc 86.61±0.97bc 90.97±1.89d
TMS 30572 15-15-15 300 10.06±0.58de 0.73±0.01i 0.61±0.02abcd 1.46±0.02def 2.33±0.04bc 84.81±1.45ab 89.94±1.58bc
TMS 30572 20-10-10 150 9.00±0.05c 0.460.01a 0.59±0.01abc 1.23±0.00bcd 2.57±0.01bc 86.15±1.08bc 91.00±2.48d
TMS 30572 20-10-10 300 11.39±1.05f 0.57±0.00c 0.53±0.02a 1.52±0.00ef 2.37±0.00bc 83.62±0.36a 88.61±2.75a
TMS 30572 12-12-17 150 10.32±0.26e 0.67±0.00f 0.59±0.01abc 1.17±0.00abcd 2.51±0.02bc 84.74±1.79ab 89.67±1.49b
TMS 30572 12-12-17 300 7.50±0.25ab 1.05±0.00j 0.61±0.02abcd 1.30±0.00cde 2.17±0.00bc 87.37±3.48cd 92.50±2.78ef
TMS 30572 NF - 8.50±0.15bc 0.61±0.00d 0.57±0.01abc 1.21±0.00bcd 1.90±0.00a 87.21±2.47cd 92.00±1.68e
TME 419 15-15-15 150 8.00±0.47b 0.69±0.00g 0.65±0.00bcd 0.91±0.00a 2.67±0.04bc 87.08±0.94cd 92.00±2.73e
TME 419 15-15-15 300 8.00±0.67b 0.66±0.01ef 0.56±0.02ab 1.13±0.01abc 2.28±0.00bc 87.37±0.71cd 93.00±0.36f
TME 419 20-10-10 150 7.00±0.02a 0.62±0.00d 0.62±0.01abcd 1.29±0.02bcde 2.44±0.01bc 88.03±2.46d 90.66±0.36cd
TME 419 20-10-10 300 9.34±0.56cd 0.71±0.00h 0.66±0.02cd 1.10±0.02abc 2.74±0.02bc 85.45±0.46b 91.60±2.48de
TME 419 12-12-17 150 8.41±0.47bc 0.65±0.00e 0.63±0.01abcd 1.01±0.02abc 2.10±0.02bc 87.20±2.89cd 92.50±2.37ef
TME 419 12-12-17 300 7.50±0.47ab 0.58±0.01c 0.61±0.01abcd 1.00±0.01ab 2.76±0.02c 87.55±1.09cd 91.50±1.79d
TME 419 NF - 7.50±0.42ab 0.56±0.01b 0.70±0.01d 1.61±0.02f 1.20±0.10a 88.43±0.89d 92.50±2.70ef
The superscript is used to show significant differences among the samples.
Values are means of triplicate determination.
Mean values with different superscripts within the same column are significantly different (p < 0.05).
HQCF, high-quality cassava flour; NF, no fertiliser (control sample); CHO, carbohydrate.

The ash content provides information about the mineral composition of a sample. The ash values obtained in this study were lower than the values reported by Shittu et al. (2008), who reported a mean ash value of 1.5% for HQCF from fertilised roots. The highest ash value was found in the HQCF sample from cassava variety TMS 30572 with NPK 12:12:17 at 300 kg/ha, suggesting an increase in the potassium content of the soil following fertiliser application. Dry matter is an essential chemical indicator of food quality in root and tuber crops (Assanvo et al., 2006), and it determines the textural quality of foods (Izutsu and Wani, 1985). The values obtained for dry matter in this study are consistent with those reported by Moorthy (2002). Differences in chemical composition of cassava flour due to varietal differences have been reported (Aryee et al., 2006), and this may influence the utilisation of the flour for food and industrial use.

Effect of cassava varieties, fertiliser type and dosage on physicochemical properties of HQCF

Effect of cassava varieties, fertiliser type and dosage on physicochemical properties of HQCF is presented in Table 3. Significant difference (p < 0.05) was observed in total titratable acidity (TTA), pH, total starch, soluble sugar, amylose and hydrogen cyanide (HCN) content of the flour samples. The TTA and pH of the flour samples ranged from 13.90 to 17.68% and 5.09 to 6.24, respectively. Total starch, soluble sugar, amylose and HCN content of the HQCF samples ranged from 66.82 to 83.23%, 2.67 to 4.42%, 20.29 to 24.00% and 0.46 to 1.15%, respectively. From the GLM analysis, it was observed that the main effect of cassava variety had significant (p < 0.05) effect on the amylose content of the flour samples (Table S1), while the two-way interactive effects of cassava variety and fertiliser type as well as fertiliser type and dosage had significant (p < 0.05) effect on the total starch content of the samples (Table S2). HQCF from cassava variety TMS 30572 without fertiliser had significantly lowest TTA among the samples. Among the fertilised cassava varieties, TMS 30572 with NPK 15-15-15 at 150 kg/ha had the highest total starch (Table 3). The three-way interactive effect of the independent variables studied had no effect on any of the parameters studied (Table S3).

Table 3. Effect of variety, fertiliser type and dosage on the titratable acidity, pH, starch, sugar, amylose and cyanide content of HQCF.
Variety Fertiliser type (NPK) Dosage (kg/ha) Titratable Acidity pH Total starch (%) Soluble sugar (%) Amylose (%) HCN (mg/kg)
TMS 30572 15-15-15 150 15.27±0.02g 6.12±0.23gh 83.23±0.36n 3.77±0.01def 20.94±0.02b 0.95±0.00h
TMS 30572 15-15-15 300 15.16±0.08f 5.09±0.86a 72.31±0.47f 3.92±0.00f 23.54±0.89ef 0.85±0.02fg
TMS 30572 20-10-10 150 16.20±1.02j 6.19±0.02h 82.59±0.02m 4.42±0.10g 20.29±0.48a 0.50±0.00a
TMS 30572 20-10-10 300 16.95±0.59k 6.15±0.00gh 72.90±1.56g 3.75±0.43cde 21.28±0.39b 0.73±0.01e
TMS 30572 12-12-17 150 16.90±0.48k 5.97±0.01ef 75.50±0.78j 3.61±0.07c 20.94±0.78b 0.63±0.00bc
TMS 30572 12-12-17 300 15.70±0.79h 6.24±0.02h 79.79±0.57k 2.70±0.12a 21.76±0.27c 0.46±0.00a
TMS 30572 NF - 9.37±0.56a 6.23±0.04h 74.33±0.79i 4.40±0.01g 23.33±0.95e 0.81±0.01f
TME 419 15-15-15 150 15.74±0.79h 5.87±0.00e 69.43±0.04b 3.75±0.02cde 22.67±0.42d 0.66±0.02bcd
TME 419 15-15-15 300 13.90±0.37b 5.83±0.01de 66.82±0.36a 3.70±0.07cd 23.58±0.39ef 0.88±0.00g
TME 419 20-10-10 150 14.79±0.48d 5.96±0.02ef 70.14±0.56d 3.54±0.03b 24.00±0.12g 0.71±0.01de
TME 419 20-10-10 300 14.95±0.03e 6.01±0.00fg 69.89±0.36c 3.90±0.00ef 21.67±0.78c 0.68±0.23cde
TME 419 12-12-17 150 16.07±0.28i 5.72±0.03d 72.07±0.48e 2.67±0.00a 22.83±0.99d 0.48±0.18a
TME 419 12-12-17 300 17.68±0.48l 5.23±0.00b 82.05±1.09l 3.72±0.00cd 23.72±0.14fg 1.15±0.02i
TME 419 NF - 14.61±0.71c 5.44±0.00c 73.70±0.75h 4.67±0.00h 22.77±0.39d 0.61±0.00b
The superscript is used to show significant differences among the samples.
Values are means of triplicate determination.
Mean values with different superscripts within the same column are significantly different (p < 0.05).
HQCF, high-quality cassava flour; NF, no fertiliser (control sample); HCN, hydrogen cyanide.

pH is an important parameter in determining the quality of cassava flour. Flour pH of 4 or less indicates appreciable fermentation and starch breakdown. Fermented flour also imparts a characteristic aroma and flavour to the flour, making it less preferred in baking. In spite of fertiliser application, the flour pH values obtained in this study were comparable with those reported by Dziedzoave et al. (2006) and fall within the standard specification for HQCF by Africa Regional Standard Organization (ARSO). Apea-Bah et al. (2011) reported pH range between 5.07 and 6.65 for unfertilised HQCF. Starches/flour with high pH has been reported to have better solubility. This is as a result of increased hydrophilic role of starch at high pH values (Adebowale et al., 2005). pH value close to 7 has been reported to stimulate retrogradation because of the absence of salts of monovalent anions and cations (Chen et al., 2011). Therefore, the pH range of 5.09 to 6.24 obtained in this study further revealed that fertiliser application does not have any adverse effect on the usability of the HQCF in food systems.

Amylose and starch have been reported to be the major dry matter constituents of roots (Cadavid et al., 1998). Low amylose composition in starch contributes to an increased relative crystallinity owing to the reduction in the amorphous regions inside the starch granule (Tukomane et al., 2007). Amylose is also an essential factor to attain desirable structure in products and thought to influence the eating quality of starchy food like noodles as well as the sticky properties of pasta (Grant et al., 1993). The amylose and HCN content of HQCF from TMS 30572 cassava variety decreased with fertiliser application, and they increased in TME 419 roots after fertiliser application. Generally, the HCN values obtained in this study are below 10 mg/kg safe level established for HCN in cassava flour (FAO, 2013). Cassava variety as well as fertiliser compounding ratio had varying effects on HCN contents of HQCF. The total starch content for HQCF from TMS 30572 increases with fertiliser application and a reduction in the starch content after fertiliser application was observed in the flour from TME 419 variety. The observed variations may be due to varietal differences.

Effect of cassava varieties, fertiliser type and dosage on functional properties of HQCF

Table 4 shows the effect of cassava variety, fertiliser type and dosage on functional properties of HQCF. GLM analysis indicates that the most significantly affected functional property is the swelling power (Table S4). The swelling power ranged from 7.12 to 9.95% and was lower than the values reported by Shittu et al. (2008) for fertilised cassava roots, and higher swelling power has been linked with improved digestibility and ability to use the flour in varied dietary applications (Moorthy, 2002). The variations observed may be due to differences in fertiliser compounding ratio and dosage used in the studies. Cassava samples of both varieties fertilised with NPK 15-15-15 at 150 and 300 kg/ha gave significantly higher swelling power compared with other fertilised and unfertilised samples. The least gelation concentration (LGC) that ranged from 9.77 to 13.97% was only affected by fertiliser type and not by cassava variety or fertiliser dosage (Table S5). This may be due to the different fertiliser treatments applied to the cassava roots used in this study. Generally, the interactive effects of fertilizer-type, variety and dosage did not have significant effect on the functional properties of the composite flour (Table S6).

Table 4. Effect of cassava varieties, fertiliser type and dosage on functional properties ofHQCF.
Variety Fertiliser type (NPK) Dosage (kg/ha) WAC (%) Disp. (%) BD (g/ml) SP (%) SI (%) LGC
TMS 30572 15-15-15 150 103.85±1.05f 71.30±0.96e 0.58±0.00b 9.06±0.07h 9.81±0.75f 13.97±0.45f
TMS 30572 15-15-15 300 114.56±0.98i 73.25±0.57g 0.61±0.00f 9.94±0.20l 10.13±0.37i 12.13±0.29b
TMS 30572 20-10-10 150 120.79±0.56k 68.06±0.59c 0.62±0.00g 7.81±0.08e 9.55±0.48d 12.93±0.26c
TMS 30572 20-10-10 300 117.41±0.79j 72.15±0.56f 0.58±0.00b 8.05±0.01g 10.36±0.47j 13.10±0.27cd
TMS 30572 12-12-17 150 121.03±1.39l 74.90±0.36h 0.60±0.00e 7.93±0.36f 10.99±0.23k 13.20±1.05cde
TMS 30572 12-12-17 300 125.26±2.78m 68.35±0.75c 0.59±0.00d 7.26±0.44c 12.71±0.71l 9.78a±0.00
TMS 30572 NF - 104.88±0.78h 67.30±0.27b 0.66±0.00j 7.13±0.58a 15.71±0.52n 13.48±0.08de
TME 419 15-15-15 150 125.93±1.04n 68.15±0.77c 0.58±0.00b 9.60±0.37j 9.51±0.76c 13.00±0.47c
TME 419 15-15-15 300 77.45±0.67a 67.25±0.94b 0.56±0.00a 9.95±0.76l 9.26±0.53b 13.35±0.48cde
TME 419 20-10-10 150 89.87±0.39b 65.02±1.07a 0.64±0.00i 9.69±0.65k 9.74±0.58e 13.59±0.07ef
TME 419 20-10-10 300 96.32±0.37d 70.80±0.51de 0.59±0.00d 9.23±0.37i 9.95±0.46h 12.36±0.48b
TME 419 12-12-17 150 99.00±1.78e 70.35±0.79d 0.60±0.00e 7.12±0.89a 14.42±0.94m 9.77±0.20a
TME 419 12-12-17 300 104.00±0.56g 74.30±1.05h 0.61±0.00f 7.20±0.91b 4.63±0.48a 10.17±0.05a
TME 419 NF - 92.16±0.89c 74.25±0.51h 0.63±0.00h 7.41±0.71d 9.90±0.35g 10.13±0.35a
The superscript is used to show significant differences among the samples.
Values are means of triplicate determination.
Mean values with different superscripts within the same column are significantly different (p < 0.05).
HQCF, high-quality cassava flour; NF, no fertiliser (control sample); WAC, water absorption capacity; Disp, dispersibility; BD, bulk density; SP, swelling power; LGC, least gelation concentration; SI, solubility index.

The least gelation concentration (LGC) of flour is an important functional property that determines the minimum flour/water ratio needed to produce gel from cooked flour/water suspension (Shittu et al., 2008). The gelation process is the main avenue for the hydration of protein/carbohydrate polymer system during baking. In this study, the water absorption capacity of HQCF from fertilised root was higher than the control. This indicates that fertiliser application may influence the water absorption tendency of cassava flour. However, a contrary trend was observed in bulk density of HQCF from TMS 30572 and TME 419 as bulk density reduced following fertiliser application, with exception of flour from TME 419 with NPK 20-10-10 at 150 kg/ha whose bulk density increased after fertiliser application. Generally, the functional properties of HQCF improved following fertiliser application regardless of the compounding factor and dosage used, and this is an indication that fertiliser application to cassava roots could improve the functionality of HQCF in food systems.

Effect of cassava varieties, fertiliser type and dosage on pasting properties of HQCF

When starchy foods are heated in water, they undergo several changes including gelatinisation and pasting. These are the two most important factors that influence the quality and aesthetic considerations of HQCF application in food industry, since they affect the texture and digestibility as well as the end use of starchy foods (Adebowale et al., 2005). The pasting properties of the HQCF samples as influenced by cassava variety, fertiliser type and dosage are presented in Table 5. GLM analysis revealed that the main effect of cassava variety and the interactive effect of fertiliser type and dosage had significant effect on the peak and pasting temperature of the flour samples (Table S7). In addition, the interactive effect of cassava variety and fertiliser dosage had significant effect on pasting temperature, while the interaction of fertiliser type and cassava variety significantly affected the breakdown viscosity and pasting temperature of the flour samples (Table S8). Also, the three-way interactive effect of cassava variety, fertiliser type and dosage had significant effect on the peak viscosity of the HQCF flours (Table S9).

Table 5. Effect of cassava varieties, fertiliser type and dosage on pasting properties of HQCF.
Variety Fertiliser type (NPK) Dosage (kg/ha) PV (RVU) Trough (RVU) Breakdown (RVU) FV (RVU) Setback (RVU) Peak time (min) Pasting temp. (°C)
TMS 30572 15-15-15 150 499.17±0.56c 216.33±2.36g 282.83±1.09b 305.75±1.58i 89.42±1.25l 4.467±0.01c 75.85±027c
TMS 30572 15-15-15 300 530.75±2.69e 213.67±2.52f 317.08±1.03f 280.17±0.68f 66.50±0.87b 4.333±0.02b 75.85±1.24c
TMS 30572 20-10-10 150 529.08±1.78e 199.92±1.58d 329.17±0.29gh 274.75±1.43e 74.83±0.35e 4.333±0.03b 76.70±1.08d
TMS 30572 20-10-10 300 531.57±0.99e 194.25±0.98c 337.42±1.03h 280.92±1.60f 86.67±1.58k 4.400±0.00c 76.75±0.47d
TMS 30572 12-12-17 150 515.83±1.74d 188.83±1.23b 327.00±2.57gh 273.83±1.57e 85.00±0.74j 4.467±0.02c 76.70±0.68d
TMS 30572 12-12-17 300 524.58±1.68de 211.50±1.05e 313.08±2.68e 284.00±2.48g 72.50±0.13de 4.267±0.04a 75.90±1.58c
TMS 30572 NF - 534.67±1.06f 195.33±2.46c 339.33±0.76hi 238.67±1.42a 73.58±1.97e 4.400±0.25c 76.70±0.02d
TME 419 15-15-15 150 466.08±1.08a 172.08±0.64a 294.00±2.48d 249.17±1.81b 77.08±0.67g 4.333±0.00b 75.10±0.48b
TME 419 15-15-15 300 515.25±2.36d 189.67±0.39b 325.58±3.68g 267.75±2.30d 78.08±0.10h 4.267±0.25a 75.90±0.57c
TME 419 20-10-10 150 489.25±1.48ab 215.17±1.34g 274.08±0.79a 299.50±1.75h 84.33±1.07i 4.533±0.35d 75.90±0.39c
TME 419 20-10-10 300 483.00±2.36b 210.00±0.48e 273.00±2.76a 286.08±2.97g 76.08±0.38f 4.467±0.48c 76.70±0.58c
TME 419 12-12-17 150 480.92±1.89b 194.00±2.35c 286.92±0.38c 265.00±0.78d 71.00±0.48d 4.333±0.59b 74.25±0.74a
TME 419 12-12-17 300 500.75±0.58c 186.33±1.47b 314.42±2.57e 255.00±3.47c 68.67±0.37c 4.267±0.15a 74.95±0.48a
TME 419 NF - 462.58±2.74a 174.67±0.68a 287.92±3.97c 238.67±1.68a 64.00±1.58a 4.267±0.35a 75.90±0.99c
The superscript is used to show significant differences among the samples.
Values are means of triplicate determination.
Mean values with different superscripts within the same column are significantly different (p < 0.05).
HQCF, high-quality cassava flour; NF, no fertiliser (control sample); PV, peak viscosity; FV, final viscosity.

The peak viscosity of the flour samples ranged from 462.58 to 534.67 RVU. The highest peak viscosity was recorded in the flour from unfertilised TMS 30572, while the flour from unfertilised TME 419 had the lowest peak viscosity value. The peak viscosity of HQCF samples from TMS 30572 reduced following fertiliser application, while the peak viscosity of flour samples from TME 419 increased following fertiliser application. The peak viscosity is often related with the final product quality, as it indicates the viscous load likely to be encountered during mixing (Maziya-Dixon et al., 2004). The variations observed may be due to varietal differences as cassava roots react differently to fertiliser treatment. The values obtained for breakdown value which measures the ability of paste to withstand breakdown during cooling in this study were higher than that reported by Shittu et al. (2008) for HQCF from fertilised roots. The trough which provides information about the breakdown or stability of gel during cooking of starch (Fadimu et al., 2018) was not significantly affected by any of the independent factors.

The final viscosity is the change in the viscosity after holding cooked starch at 50°C. It is one of the most common parameters used to define the quality of a particular starch-based sample, as it indicates the ability of the flour to form a viscous paste or gel after cooking and cooling as well as the resistance of the paste to shear force during stirring (Adebowale et al., 2008). In our study, the final viscosity values were significant (p < 0.05) and the highest value of 305.75 RVU was recorded in the HQCF from TMS 30572 with NPK 15-15-15 at 150 kg/ha, while the unfertilised TME 419 and TMS 30572 flour samples had the lowest final viscosity. Pasting temperature is the temperature at which permanent swelling of starch granules takes place leading to peak viscosity (Liang and King, 2003). Reaching the pasting temperature is important in ensuring swelling, gelatinisation and gel formation during food processing (Eke-Ejiofor and Owuno, 2012). The range of pasting temperature obtained in this study was slightly higher than values of 78.03–79.30°C reported by Shittu et al. (2008) for cassava flour from fertilised roots and Oduro et al. (2000) on seven related roots and tubers.

Higher pasting temperature is associated with high paste stability usually considered as a desirable functional property. Low paste temperature and paste stability are suggestive of fewer associative force and cross-links within the starch granules. This thus indicates that the cassava flours from this study will be desirable in food applications. Usually when factorial analysis shows interactive effect of certain factors, it indicates that singular factor may not be solely responsible for the observed effect on the outcome. In this study, the significant interaction observed between fertiliser type and dosage, variety and dosage as well as fertiliser type and variety on the pasting properties indicates that the pasting characteristics may be dependent of certain biogenesis in the cassava plant tissue. However, in the analysis of the main effect, the influence of the different varieties of cassava was highly significant (p < 0.01) in the peak viscosity of the HQCF samples.

4. Conclusions

This study revealed that cassava varieties and fertiliser treatment have great impact on the functionality of HQCF in food systems. The functional and pasting properties of the HQCF samples improved following fertiliser application to the cassava varieties studied. Dosage of fertiliser did not show significant influence on the flour properties. The effect of fertiliser compounding ratio had significant effect on the swelling power and least gelation concentration of the HQCF samples, while the interaction of fertiliser type and dosage also affected swelling power. Peak viscosity was the most significantly influenced parameter of all the pasting properties by treatment factors. Pasting temperature was also affected by cassava variety, as well as by the interaction of fertiliser type and dosage. However, pasting temperature reduced in most flour samples with fertiliser application compared to their respective control samples. Contrary to an existing belief that fertiliser application during cassava growing stage could have negative effect on HQCF quality, this research has established that fertiliser application during the field cultivation of cassava root could improve the functional and pasting properties of HQCF produced from such roots.

Conflict of interest

The authors declare no conflicts of interest with respect to research, authorship and/or publication of this article.


This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

Compliance with ethical standards

This article followed all ethical standards for a research without direct contact with human or animal subjects.


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