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Journal of Food, Agriculture & Environment, Vol.6 (2), April 2008 251

Proximate composition and cyanide content of cassava peels fermented with Aspergillus niger and Lactobacillus rhamnosus

C. E. Okpako, V. O. Ntui *, A. N. Osuagwu and F. I. Obasi Department of Genetics and Biotechnology, University of Calabar, Calabar, Nigeria.

*e-mail: [email protected]

Received 14 December 2007, accepted 28 March 2008.

AbstractCassava ( Manihot esculenta ) is an important root crop in the tropics, providing energy for more than 500 million people. Cassava and its productsare widely used in tropical areas to feed farm animals. The effects of Aspergillus niger and Lactobacillus rhamnosus on the proximate compositionand cyanide content in peels of cassava variety ADP3(4) were investigated using solid media fermentation. The objective of the study was toincrease the nutritive value of cassava peels in order to make them good component for animal feeds. Six treatment samples viz: T 1 (peels fermentedwith a mixture of A. niger and L. rhamnosus ), T 2 (peels fermented with A. niger ), T 3 (peels fermented with L. rhamnosus ), T 4 (naturally fermented

peels), T 5 (soaked and unfermented peels) and T 6 (non-soaked and unfermented peels) were used in the study. The experimental design was thecompletely randomized design with 3 replications. Results obtained showed significant (P

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252 Journal of Food, Agriculture & Environment, Vol.6 (2), April 2008

content of the peels. Such base line information will be useful foranimal breeders.

Materials and Methods Materials: Cassava tubers of sweet variety ADP 3(4) was obtainedfrom the Cross River State Agricultural Development Programme(ADP).The microorganisms were collected from Federal Instituteof Industrial Research Oshodi (FIIRO) Lagos, Nigeria.

The microorganisms used were As perg il lu s ni ge r and Lactobac il lu s rhamnosus . These microorganisms weresubcultured in nutrient agar and MRS media in the MedicalMicrobiology Laboratory, University of Calabar Teaching Hospital,Calabar, Nigeria.

Treatment preparation: Six treatment samples were preparedfollowing the methods of Oboh 13 with some modifications.For treatments 1, 2, 3 and 4 freshly harvested cassava tubers ofthe variety ADP 3(4) were peeled, washed and soaked in water 16

for 2 days (initial fermentation), after which they were removedand grated. Four kg of the processed pulp were spread in 4 trays,each tray containing 1 kg of the pulp.

Tray 1 (Treatment 1) was mixed with 10 g of a mixture of freshly

subcultured pure strains of As perg il lu s ni ge r an d Lactobacillus rhamnosus . Tray 2 (Treatment 2) was mixed with10 g of Aspergillus niger and Tray 3 (Treatment 3) had 10 g of

Lactobacillus rhamnosus . Tray 4 was not inoculated with anymicroorganism. These were allowed to ferment for 7 days.The incubation temperature and relative humidity of air were 30Cand 90-93% respectively 13. In Treatment 5, peels which were soaked for 2 days were gratedand used for analysis without fermentation. Treatment 6, whichserved as the control contained peels which were not soaked inwater but grated and analyzed without fermentation.

Proximate compos ition ana lys is of samples: Proximatecomposition (moisture, ash, protein, fat, crude fibre andcarbohydrates) of the 6 treatments was determined using standardanalytical methods 17, 18 and official and standard method ofanalysis 19. The moisture content of the sample was determinedgravimetrically by drying 5 g of the sample in a crucible to aconstant weight at 120C. The ash content of the sample wasdetermined gravimetrically by ashing 2 g of each sample in a clean

pre-weighed crucible in a furnace at 550C for 24 hours.The protein content was determined using Kjeldahl method ofnitrogen (N) analysis. Approximately 2 g of each sample wasdigested with concentrated H 2SO 4 using K 2SO 4 catalyst.The ammonia in the digested sample was then distilled into astandard boric acid and titrated with 0.1 M HCl. The crude proteinof the sample was obtained using the formula: crude protein =

titre value x 1.4 x 50 x 100 x 65/(1000 x 10 x 1)N 2. The crude fibre was determined using an acid alkaline hydrolysismethod involving boiling 2 g of the sample with 0.1 M H 2SO 4 and0.1 M NaOH in a beaker. The content of the beaker was filteredthrough a Bchner funnel, dried and ashed at 550C. The total fatcontent of each sample was determined gravimetrically by Soxhletsolvent extraction technique and the residue was dried to aconstant weight and calculated as % of ether extract = (wt of

extract/wt of sample) x 100. Carbohydrate content was determinedas the difference: 100 (moisture + ash + protein + fat + crudefibre).

Determination of cyanide content: For cyanide content, 10.0 g ofthe sample was weighed into a round bottle flask and left to soakfor about 4 hours. It was then steam distilled into 20 ml of 2.5%(w/v) NaOH contained in an Erlenmeyer flask. The distillationcontinued until 250 ml of the distillate was collected. Then 8.0 mlof 6 N NaOH and 2 ml of 5% ( w/v) potassium iodide were added tothe distillate and the distillate was titrated with 0.02 N AgNO 3 untilthere was a faint but permanent turbidity.

Statistical analysis: All data were subjected to analysis of variance

test using completely randomized design with 3 replications.Significant means were separated using least significant difference(LSD) test at P< 0.05. Simple linear correlation coefficients weredetermined for proximate composition parameters and cyanidelevel. A linear regression model which fitted into the equation;y = a+bx, where y = proximate composition parameters, x = cyanidelevel, was used to predict the relationship between significant

proximate composition parameters and cyanide level 20.

ResultsThe results of the proximate composition of the different treatmentsare presented in Table 1. The moisture, ash, protein and fibrecontents of cassava peels fermented with a mixture of

Aspergillus niger and Lactobacillus rhamnosus were significantly(P < 0.05) higher than those fermented with either of themicroorganisms, naturally fermented or unfermented peels.

Non-soaked unfermented cassava peels recorded the lowestmoisture, protein and fat contents (Table 1). Cassava peelsfermented with either of the microorganism did not differsignificantly (P > 0.05) from each other in most of the parametersstudied. A significant (P 0.05). Key: -T 1 (peels fermented witha mixture of A. niger and L. rhamnosus ), T 2 (peels fermented with A. niger ), T3 (peels fermented with L rhamnosus ), T 4 (naturally fermented

peels), T 5 (soaked unfermented peels), T 6(non-soaked unfermented peels).

Sample Moisture Ash Protein Fat Crude fibre CarbohydrateT1 10.34d0.2 7.52c 0.5 24.40e 0.46 2.50a0.2 10.62d0.12 44.62a1.211T2 9.09c0.01 6.87b0.15 20.60d0.46 3.10b0.52 7.80c0.3 52.54b4.31T3 9.05c0.23 6.92b0.34 19.95d0.43 2.72a0.31 7.52c0.51 53.84b2.26T4 8.60b0.21 6.54a0.32 10.60c 0.33 3.52c0.3 6.23b0.2 64.51c 3.01T5 7.81a0.32 6.51a0.32 8.61b0.25 3.32b0.24 4.90a0.45 68.85d2.51T6 7.50a0.2 6.50a 0.2 5.50a 0.22 3.31b0.34 4.69a0.4 72.50e 3.03

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Cyanide contents of the different treatments are presented inTable 2. Low cyanide level of 7.350.81 mg/kg was obtained incassava peels fermented with a mixture of A. niger and

L. rhamnosus while non-soaked unfermented cassava peels produced significantly (P0.05) differences in thecyanide levels of peels treated with either of the microorganisms.

The results presented in Table 3 show that cyanide level

correlated positively and significantly with carbohydrate atP < 0.001 and negatively with moisture (P

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254 Journal of Food, Agriculture & Environment, Vol.6 (2), April 2008

content increases cyanide concentration (Fig. 1a). However, thecyanide content was below the deleterious level of 30 mg/kg infermented peels (Treatments 1-4) indicating that fermentedcassava peels could be considered safe in terms of cyanide

y=39,65+0.861x

R=0.9917y=39,65+0.861xR=0.9917

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Cyanide level (mg/kg)b)

y=10.26-0.151xR=-0.9134

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poisoning 5, 13 . It was also noted that increase in fibre content,moisture content and ash content of cassava peels significantlyreduced the cyanide level (Figs 1b-d) as these correlated negativelywith cyanide (Table 3) suggesting that this by-product could be agood supplement in compounding animal feed.

ConclusionsCassava peels fermented with the microorganisms recorded

significant increase in the protein, ash, moisture and fibre contentswith a subsequent reduction in the cyanide level compared to thenaturally fermented and the unfermented peels. It is thussuggested that cassava peels which are regarded as having noeconomic value could be engineered by microorganisms toincrease nutritive value, reduce cyanide content and used as feedfor farm animals provided it is accepted and highly digestible.

AcknowledgementThe authors gratefully thank the Cross River State AgriculturalDevelopment Programme for providing the cassava variety andthe Federal Institute of Industrial Research Oshodi for themicroorganisms.

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y=7.355-0.025xR=-0.8682

Figure 1. Relationship between proximate composition parameters andcyanide content: a) carbohydrate and cyanide, b) crude fibre and cyanide,c) moisture and cyanide, d) ash and cyanide.

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