Effect of Mechanised Shredding of Cassava Roots on The Hydrogen Cyanide and Moisture Contents of The Shreds: A Response Surface Analysis

Effect of Mechanised Shredding of Cassava Roots on The Hydrogen Cyanide and Moisture Contents of The Shreds: A Response Surface Analysis

*Etoamaihe U. J. ,Dept. of Agricultural and Bioresources Engineering, Michael Okpara University of Agriculture Umudike, Iwe M.O. Dept. of Food Science and Technology, Michael Okpara University of Agriculture Umudike, *Corresponding Author.

Abstract

Cassava roots in different states (fresh, steamed and dried) were shredded with a mechanized shredder. The hydrogen cyanide (HCN) and moisture contents of the shreds produced were evaluated. The results were subjected to regression analysis using response surface methodology. The moisture content of the shreds produced was influenced significantly (P0.05) by only the state of the cassava roots used. The highest moisture content obtained was 69.84% from fresh cassava roots at a shredder speed of 975rpm.The linear and quadratic effects of the state of cassava roots had significant effects (P0.05) on the HCN content of the shreds. The lowest HCN content was obtained from 3mm shredder aperture and from steamed cassava roots.

Keywords: shredder, moisture content, hydrogen cyanide, response surface analysis

1.0 Introduction

Cassava is one of the most important crops in Africa. It derives its importance from the fact that its starchy roots are a low cost source of calories, especially in African countries where protein-calorie deficiency related malnutrition is widespread. The leaves and tender shoots of cassava are also consumed as vegetables that are rich in vitamins and proteins (Krochmal and Hahn, 1991).

Cassava varieties are often classified according to the levels of hydrocyanic acid (HCN) in their roots and leaves (IITA,1990). Hydrogen cyanide is a colorless extremely poisonous liquid that boils slightly above room temperature at 260C. Hydrogen cyanide is a linear molecule with a triple bond between carbon and nitrogen.

Cassava consists of 60 to 70% water (IITA, 1990). Processing it into dry form reduces the moisture content and converts it into a more durable and stable product with less volume which makes it more economically transportable and storable. Processing is also necessary to

eliminate or reduce the level of cyanide in cassava and to improve the palatability of the food products (Agriga and Iwe, 2008).

The response surface methodology (RSM) are a collection involving experimental strategy, mathematical methods, and statistical inferences which when combined, enable the experimenter to make an efficient empirical exploration of the system in which he is interested, (Myers and Montgomery, 1995; Agriga and Iwe, 2008). RSM uses a sequential philosophy of experimentation the ultimate goal of which is to optimize a process. Response surface methodology uses the fewest possible number of experimental runs to achieve process optimization. It is therefore efficient for both experimentation and optimization (Lah et al., 1980.,Iwe, 2008).

The objective of the present work was to apply statistical methods to optimize the HCN and moisture contents of cassava shreds produced from a locally developed cassava shredding machine.

1

2

3

1. Hopper 6

2. Shredding plate

3. Collector 7

4. Frame

5. Pulley 4

6. Shaft 8

7. Slider disc

8. Bearings

9. Sprocket 9 5

Fig.1 : Isometric View of The Cassava Shredding Machine

1. Materials and Methods

2. Determination of the HCN Content

   A mechanized cassava shredder (Fig.1) was used for the tests. Three samples of the same cassava roots in different states, namely fresh, steamed and dried, were peeled, washed and separately shredded with the machine at three different speeds of operation, using three different shredding disc apertures of the machine. The same specie of cassava roots obtained from the University of Agriculture Umudike (TMS 30572), farm was used for all the tests. The experiments were planned using the Central Composite Design of Response Surface Methodology with fifteen runs. The steamed specimens for the tests were obtained by boiling fresh cassava root in water for about 20 minutes on a standard 80cm diameter gas ring and later cooled, while the dried specimens were obtained by drying fresh cassava roots in an

   oven at 1000C for six hours.The method used for the determination of the HCN content of the

   cassava shreds produced by the machine was the one outlined by Onwuka (2005).In this method, 5gm of each cassava shred sample was ground into a paste and dissolved in 50ml of distilled water in a conical flask. This was allowed to stay overnight for solubilization of cyanide ions. The solution was later filtered. 2ml of the filtrate solution was transferred into a conical flask. 4ml of alkaline picrate solution was added to the mixture and then incubated in

   water bath for 5mins at a temperature of 60oC for colour development (reddish brown) and

   absorbance was taken at 490nm with a Jenway spectrophotometer.

   The cyanide content was extrapolated applying a cyanide standard curve by using the equation;

   HCN

   Vf

   1 100 1000

   (1)

   mg / kg

   a

   a

   V 106 W 1

   When Vf = Total volume of extract (ml) Va = Volume of extract used (ml) W = Weight of sample used (mg)

   The cyanide standard curve was obtained by preparing concentrations of KCN solution containing 5 to 50µg cyanide in a 500ml conical flask. 25ml of 1N HCL was added to the mixture. Using different concentrations of this mixture a cyanide standard curve was prepared.

   Based on the experimental design used, cassava shreds that emerged from the three different shredding apertures of the machine at three different speeds of operation were tested for their HCN contents. Each test had 3 replications.

3. Determination of Moisture Content

   The moisture contents of the cassava shreds were determined using the static gravimetric method (James 1996). In each case 5gm of the cassava shreds were put into a weighed sample can. The can and its sample contents were dried in the oven at 1050C for 3

   hours. The can and its sample contents were later removed from the oven and cooled and later reweighed. The drying, cooling and weighing were repeatedly done until a constant weight was obtained. The percentage moisture content on wet basis was determined using the equation.

   MC W3 W2 100

   (2)

   W

   W

   1

   1

   wb

   0

   when, W2 = Weight of can before drying.

   W3 = weight of can + sample after drying. W0 = weight of sample used.

   The three cassava shred, samples that emerged from the different apertures of the shredder at the three different speeds of operation of the machine had their moisture contents determined. In each case three replications of the moisture contents of each sample were determined, and the mean value was used.

4. Experimental Design, Statistical Analysis and Optimization

   Response surface methodology (RSM) was used to investigate the effects of the state of cassava roots, speed and shred aperture of the cassava shredding machine on the hydrocyanic acid and the moisture content of the shreds produced. A central composite design including 15 experiments with a centre point of three factors at three levels was used (Table 1).

   Experimental data were fitted to a second order polynomial model and regression coefficients obtained. The generalized second order polynomialmodel used in the response surface analysis was as follows:

   3

   3

   Y

   3

   3

   i Xi

   3

   X

   X

   2

   ii i

   ii Xi X j

   (3)

   i1 i1

   i j 1

   Where o, i and, ii are constant coefficients and Xi ,Xj are coded independent variables linearly related to speed of machine, shred aperture and state of cassava roots.

   Mathematical models were evaluated for each response by means of multiple regression analysis using Minitab software. The modeling included linear, quadratic and the interaction terms. Significant terms in the model for each response were found from the analysis of variance (ANOVA). The response curves were drawn with Matlab software.

5. Results of the HCN and Moisture Contents of the Shreds Produced

Table 1: Experimental Results Data of Machine Parameters, Versus HCN/MC Contents in Coded Terms.

Coding

Speed: 1=975rpm, 0=650rpm,-1=325rpm Shred Aperture: 1=10mm, 0=6mm,-1=3mm

State of Cassava Roots: 1=Fresh, 0=Steamed,-1=Dried

1. Results and Discussion

2. HCN Content of the Cassava Shreds

   The estimated regression coefficients associated with the HCN content of different cassava shreds produced with the machine are shown in Table 2. The linear and quadratic effects of state of the cassava were significant (P 0.05). The other variables had no significant effects on the HCN content. From the analysis of variance Table 3, linear and

   quadratic effects of the state of the cassava accounted for 97.7% of the total variation in the response (HCN) content, with the highest overall values from fresh cassava roots. This shows that fresh cassava roots obviously have more HCN content than other samples. The result is in line with the works of (Kay et al, 1987,Okoli et al.,2012, and Enyenihi et al., 2009.), which showed that a lot of the hydrocyanic acid in fruits and vegetables is lost during soaking and cooking, so that its content in the vegetable and fruits poses no danger of toxicity, after such processing. From Figure 2, the HCN content of the cassava shreds had the lowest value of 14.6mg/kg from a shred aperture of 3mm and a speed of 650rpm. In Figure 3, the lowest value of HCN content (16.32mg/kg) was obtained when the cassava was steamed and shredded at machine speed of 650rpm. This also confirms that processing operations such as steaming, washing etc, can reduce the HCN content of cassava (Morgan and Julius 2012, Cardozo et al., 2005, Brainbridge et al., 1998). Finally from Figure 4, the lowest value of HCN content was 5.47mg/kg and it was obtained when the cassava was steamed from a shred aperture of 3mm.

   Table 2: Estimated Regression Coefficients For HCN Contents Versus Speed, Shredding Aperture and State of Cassava Roots.

   Predictor	Coef	StDev	T	P
   Constant	15.956	1.568	10.18	0.000
   Speed	-0.4860	0.9223	-0.53	0.621
   Shred aper	1.6300	0.9223	1.77	0.137
   State of root	4.935	1.077	4.58	0.006
   Speed* speed	2.334	1.819	1.28	0.256
   Shred aper*shred aper	0.384	1.819	0.21	0.841
   St. of rt*st.of root	20.334	1.819	11.18	0.000
   Speed*shred aper	0.737	1.031	0.72	0.506
   Speed*st. of root	-0.003	1.244	-0.00	0.998
   Shred aper*st of root	-1.254	1.390	-0.90	0.409

   S = 2.916 R-Sq = 97.7% R-Sq(adj) = 93.5%

   Table 3: Analysis of Variance for HCN Contents

   Source	DF	SS	MS	F	P
   Regression	9	1786.76	198.53	23.34	0.001
   Error	5	42.53	8.5
   Total	14	1829.29

   21

   HCN Content (mg/kg)

   HCN Content (mg/kg)

   20

   19

   18

   17

   16

   15

   14

   1

   0.5

   0

   -0.5

   X: 0.2

   Y: -1

   Z: 14.6

   0

   -0.5

   1

   0.5

   Shred Aperture (mm)

   -1 -1

   Speed (rpm)

   Fig. 2: Response Surface Curve of Effects of Speed and Shred Aperture on the HCN Content

   45

   HCN Content (mg/kg)

   HCN Content (mg/kg)

   40

   35

   30

   25

   X: 0.1

   Y: -0.3

   Z: 16.32

   X: 0.1

   Y: -0.3

   Z: 16.32

   20

   15

   1

   0.5

   0

   -0.5

   0

   -0.5

   1

   0.5

   State of Cassava

   -1 -1

   Speed (rpm)

   Fig 3: Response Surface Curve of the Effects of Speed and State Of Cassava on the HCN Content

   35

   HCN Content (mg/kg)

   HCN Content (mg/kg)

   30

   25

   20

   15

   10

   5

   0

   1

   0.5

   0

   -0.5

   0

   -0.5

   X: -1

   Y: -0.3

   Z: 5.47

   X: -1

   Y: -0.3

   Z: 5.47

   1

   0.5

   State of Cassava

   -1 -1

   Shred Aperture (mm)

   Fig. 4: Response Surface Curve of the Effects of Shred Aperture and State Of Cassava on the HCN Content

3. Moisture Content of Cassava Shreds .

Table 4 shows the result of the regression on the data on moisture contents of the cassava shreds produced with the machine. The linear effects of state of the cassava was the only variable that was significant (P 0.05) on the moisture content. The other studied variables had no significant effects. The state of the cassava accounted for 98.8% of the variation in the response. The analysis of variance, (Table 5) showed that the variable had significant effects (P 0.05) on the moisture contents.

This result is expected as the steamed or oven dried cassava root have lower moisture content when compared to fresh roots as a result of the heat treatment causing drying, (Wilhemina et al 2009). This shows that drying is an efficient way to reduce moisture content of food materials (Igbeka,1987,). The response surface plot in Figure 5 shows that moisture content increased with shred aperture, having a maximum value of 65.43% at the speed of 975rpm from a shred aperture of 10mm.

Also in Figure 6, the moisture content increased with speed of the machine and had highest values for fresh cassava shreds. The moisture value of 69.84% was obtained at

975rpm and for fresh cassava shreds. In Figure 7, the moisture content also increased with shred aperture and had the highest overall value of 86.85% for fresh roots from 10mm shred aperture.

Table 4: Estimated Regression Coefficients for Moisture Content Versus Speed, Shredding Aperture and State of Cassava Roots.

S = 1.044 R-Sq = 98.3% R-Sq(adj) = 95.2%

Table 5: Analysis of Variance for Moisture Content

X: 1

Y: 1

Z: 65.43

65.5

65

MC (%)

MC (%)

64.5

64

1

0.5

0

-0.5

0

-0.5

1

0.5

Shred Aperture (mm)

-1 -1

Speed (rpm)

Fig. 5: Response Surface Curve of the Effects of Speed and Shred Aperture on the Moisture Content

X: 1

Y: 1

Z: 69.84

70

68

66

MC(%)

MC(%)

64

62

60

58

1

0.5

0

-0.5

0

-0.5

1

0.5

State of Cassava

-1 -1

Speed(rpm)

Fig. 6: Response Surface Curve of the Effects of Speed and State Of Cassava on the Moisture Content.

X: 1

Y: 1

Z: 86.85

88

86

84

MC (%)

MC (%)

82

80

78

76

1

0.5

0

-0.5

0

-0.5

1

0.5

State of Cassava

-1 -1

Shred Aperture (mm)

Fig. 7: Response Surface Curve of the Effects of Shred Aperture and State of Cassava on the Moisture Content

4.0 Conclusions

The moisture content of the cassava shreds (ighu) produced was influenced significantly by the state of the cassava roots used and not by speed or shredding aperture of the machine. The highest moisture content of the shred was 69.84% and it was obtained from fresh cassava shreds at 975rpm machine speed. The linear and quadratic effects of the state of the cassava roots significantly affected the HCN content of the shreds produced by the machine. The lowest HCN was obtained from 3mm shred aperture of the machine for steamed cassava roots.

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www.wikipedia.org/wiki/Hydrogen Cyanide (2010) Accessed on 12th July 2010