The Journal of Food Technology in Africa Innovative Institutional Communications ISSN: 1028-6098 Vol. 6, Num. 3, 2001, pp. 101-103

The Journal of Food Technology in Africa, Vol. 6, No. 3, July-Sept, 2001 pp. 101-103

Changes in carbohydrate fractions of cassava peel following fungal solid state fermentation.

Eustace A Iyayi¹* and Dorothy M. Losel ²

¹Department of Animal Science, University of Ibadan, Nigeria,
²Department of Animal and Plant Sciences, The University of Sheffield, S10 2TN, Sheffield, U. K
* Corresponding Author

Code Number: ft01027

Introduction

Cassava peels continue to constitute wastes in the cassava processing industry. This is in spite of the potential of the by-product as an animal feedstuff. Considerable evidence has emerged in recent times of the possibility of using processed cassava peel as an energy source for pigs and poultry (Longe et al, 1977; Tewe, 1981; Iyayi, 1986;). Higher inclusion of the by-product in monogastric feed or formulation of diets with cassava peels, as sole energy source is limited because of its fibrous nature. Fakolade (1977) and Arowora et al (1999) have reported the occurrence of high amounts of non-starch polysaccharides in cassava peels. Degradation of these carbohydrate compounds to simple sugars will further increase the energy value of cassava peels. Since the monogastric industry constitutes the largest consumer of commercial livestock feeds in Africa, it is imperative to find alternative feed sources to the expensive energy ingredients like the cereals. The enhancement of the nutritive value of cassava peels by the use of fungi to break down the unavailable carbohydrates in them is desirable and is the subject of this study.

Materials and Methods

Processing and inoculation of Cassava peels

Cassava peels were obtained from the International Institute of Tropical Agriculture, IITA, Ibadan, Nigeria. They were washed free of sand and screened for removal of all non-organic materials. They were then shredded and dried to constant weight. Slants of Aspergillus niger, Rhizoctonia solani and Phanerochaete velutina were obtained from the culture bank of the University of Sheffield's Department of Animal and Plant Sciences, U.K. They were sub-cultured on 2% malt extract agar after the medium was sterilized at 121⁰C for 15mins. Spore suspensions were then prepared with distilled water. About 30grams of the cassava peel samples were added to each of 3 sets of flasks and the moisture content was adjusted to 25%. All flasks and contents were autoclaved and asceptically inoculated with each of organisms and properly labelled. Thereafter, the flasks were incubated at 25⁰C and samples withdrawn at days 7, 14 and 21 from the R.solani and P. velutina flasks and at days 5, 10, 15 and 20 from the A. niger flasks for analyses. Cellulose was estimated by the technique of Bath (1960), starch by the method of Pucher et al (1948) and soluble sugars by the method of Deriaz (1961). The General Linear Model for significant effect and means separated by the least significant difference analyzed results.

Results and Discussion

Changes in the cellulose, starch and soluble carbohydrates of cassava peels by A. niger, R. solani and P. velutina are shown in Figures 1, 2 and 3 respectively. Percentage changes in the carbohydrate fractions with time due to fermentation by the fungi are shown in Table 1.

There was a significant (P<0.05) and rapid increase in the percentage reduction of the cellulose content of the peels by A. niger and P. velutina within 10-14 days and by R.solani within 21 days. In 10 days, A.niger reduced the cellulose level by 83.09% and in 15 days by 90.26% while P.velutina caused an 85.65% and 88.04% reduction of the cellulose content in 14 and 21 days respectively.

Starch build up was very rapid. It was most rapid within the first 2 weeks by about 379% increase by A.niger compared with 33% increase by P.velutina and 51.0% by R.solani within the same period. Beyond the 15^th day, the rate of starch build up began to fall (see figures). There was a significant (P<0.05) rapid increase in the soluble carbohydrates in the substrate within the first 10-14 days. Again the percentage change in the soluble carbohydrate in the substrates began to fall after this period. With R. solani, starch increased slowly up to day 14, then fell to a low level while the sugar levels increased rapidly to a higher value than for A. niger and P.velutina. Optimum soluble carbohydrate levels were obtained in 14days for P. velutina and R. solani and in 10 days for A. niger. Figure 1 (peels + A. niger) shows a slow rise in soluble sugars which was followed on day 5 by a rapid increase in starch reaction. The three microorganisms showed potential for breaking down the complex cellulose and rapid convension to soluble sugars. The microorganisms helped to break down the cellulose to soluble sugars, some of which appeared to be used in the accumulation of a polysaccharide presumably glycogen, giving a starch-like reaction in the I-based assay used. This was eventually converted to the soluble sugars. With A. niger, cellulose breakdown was very rapid in the first 5 days but starch and sugar build up was slow, reaching an optimum between 10 and 15days. In the case of R.solani, starch build up was rapid, reaching an optimum at about the 14^th day and coinciding with that of sugars (Figure 2). But after this period, the levels of both compounds began to fall, also suggesting a possible utilization of the products of cellulose breakdown by the microorganisms. It appears that the system in R. solani forms relatively little polysaccharide and produces mainly sugars. This probably explains the higher sugar levels obtained with R. solani than with A. niger. Fermentation for optimum sugar yield with A. niger can be attained in 10 days and for starch in 15 days. But the optimum period for production of both, using R. solani was found to be 14 days.

Much of the cellulose of the peels using P. velutina was significantly degraded in the first week and thereafter decrease in cellulose was not significant. Optimum build up of starch was obtained in 14 days. There was a decline in the levels of the starch and sugars after 14 days, again suggesting a utilization of these compounds by the fast growing organism. It follows therefore that for P. velutina, optimum sugar and starch yields can be obtained in 14 days. Balagopalan (1996) who used Trichoderma pseudokoningii to demonstrate the cellulolytic potential of fungi has reported similar results to these. The author reported maximum starch and sugar yield in 12 days. The earlier work of Ofuya and Nwajiuba (1990) pointed out the potential degradability of cellulose of cassava peel by Rhizopus sp, Aspergillus niger and Trichophyton sp. According to the authors, fungi do produce cellulase, lignocellulase, amylase and other polysaccharidases by which they are able to break down complex polysaccharides.

This study reports the ability of R. solani, P. velutina and A.niger to degrade the cellulose of cassava peels to starch and sugars. The optimum period of degradation of the by-product by A. niger is 10 days and 14 days when R. solani and P. velutina are employed.

References

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Copyright 2001 The Journal of Food Technology in Africa, Nairobi

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