Keywords: cassava peels, cyanide, fermentatio, protein.

Two important biological wastes, that may cause damage to environment, are generated during the traditional processing of cassava starchy storage roots for ‘gari' production in Africa, namely, the cassava peels and the liquid squeezed out of the fermented parenchyma mash. Cassava peels derived from gari processing are normally discarded as wastes and allowed to rot in the open, thus resulting in health hazards. As a rough estimate, about 10 million tonnes of cassava are processed into gari annually in Nigeria alone. Since these peels could make up to 10% of the wet weight of the roots, they constitute an important potential resource for animal feeds if properly processed by a bio-system (Antai and Mbongo, 1994). The peels contain toxic levels of cyanogenic glucosides, while the liquid contains a heavy load of microorganisms capable of hydrolyzing the glucosides. The resulting products of fermentation of cassava peels with squeezed out water can be dried and used as animal feeds (Tweyongyere and Katongole, 2002). This study therefore sought to investigate the effect of the fermentation of cassava peel on the nutritional quality of the fermented product.

In the production of nutrient enriched cassava peels; sweet variety of cassava tubers (less than 50mg/kg cyanide content) were freshly harvested from the Research farm of the Federal University of Technology, Akure, Nigeria. The whole roots were peeled, washed, grated, after which 1 kg of the processed pulp was spread in a tray (about 50cm diameter) to an average layer thickness of 2cm, a 10g mixture of freshly sub-cultured pure strains of Lactobacillus delbruckii, Lactobacillus coryneformis and Saccharomyces cerevisae(2:1:1) was carefully added to the solid matrix in order to obtain a well homogenized mixture. The mash was allowed to ferment for three days; the incubation temperature and the relative humidity of the air were 30ºC and 90-93%. After the fermentation the waste-water was pressed out, while the second treatment was fermented naturally without any inoculum. 150 ml of the wastewater was carefully mixed with 200 g of washed, dried and ground cassava peels, the mash was subsequently spread in a tray to an average thickness of about 2 cm and allowed to ferment for seven days, the incubation temperature and the relative humidity of the air were 30ºC and 90-93%. The fermented peels were subsequently analyzed for their proximate composition (Cordenunsi et al. 2004), antinutrients: phytate (Preet and Punia, 2000) and the cyanide (Oboh et al. 2002); and mineral (Zn, Na, Ca, and K) composition using a Perkin-Elmer atomic absorption spectrophotometer (Model 372). The unfermented cassava peels serve as control.

The result of the analysis of the fermented cassava peels revealed that, there was an increase in the protein content of the cassava peels fermented with waste-water from fermented cassava pulp when compared to unfermented peels (8.2%). This increase was highest in the peel fermented with waste-water from the inoculated cassava pulp (21.1%). The increase in the protein content of the cassava peels fermented with waste water from the inoculated fermented cassava pulp could be attributed to the possible secretion of some extracellular enzymes (proteins) such as amylases, linamarase and cellulase (Oboh and Akindahunsi, 2003) into the cassava mash by the fermenting organisms (Raimbault, 1998), as well as increase in the growth and proliferation of the fungi/bacterial complex in the form of single cell proteins (Antai and Mbongo, 1994; Obohet al. 2002). Conversely, there was a decrease in the carbohydrate content of the cassava peels fermented with waste water from the inoculated cassava pulp (51.1%), when compared to the unfermented cassava peels (64.6%). The decrease could be attributed to the ability of the fungi/bacterial complex to hydrolyze starch into glucose and ultimately the glucose will be used by the same organisms as a carbon source to synthesize fungi/bacterial biomass rich in protein (Oboh et al. 2002). However, there was no discernable trend in the fat, crude fibre, ash and the mineral content of the cassava peels. 

Cassava peels usually have higher concentration of cyanogenic glucosides than the parenchyma (pulp); this makes the peel unsuitable as animal feed. Fermentation of the cassava peels with waste water from the fermented cassava pulp reduced the cyanide content of the cassava peels (6.2 - 23.5 mg/kg), when compared with the unfermented cassava peels (44.6 mg/kg). However, the cassava peels fermented with waste water from cassava pulp fermented with a mixture of Saccharomyces cerevisee, Lactobacillus delbruckii and Lactobacillus coryneformis had a lower cyanide content (6.2 mg/kg) than those cassava peels fermented with waste water from the naturally fermented cassava pulp (23.5 mg/kg).It is also evident from the results that waste-water from the inoculated cassava pulpwas very efficient in cyanide detoxification than that of naturally fermented cassava. The fermented cassava peels could be considered safe in terms of cyanide poisoning in view of the fact that the cyanide was below the deleterious level of 30 mg/kg (Tweyongyere and Katongole, 2002). Furthermore, there was a decrease in the phytate content of the fermented cassava peels (705.1 - 789.7 mg/100g), this decrease was more in cassava peels fermented with waste water from naturally fermented cassava pulp (705.13 mg/100g), while the unfermented cassava peels had 1043.56 mg/100g phytate content. The decrease in the phytate content of the fermented cassava peel could be attributed to possible secretion of the enzyme phytase by the microorganismsin the waste-water. This enzyme is capable of hydrolysing phytate thereby decreasing the phytate content of the fermented cassava peels (Oboh et al. 2003). In view of the increase in protein content of the cassava peels fermented with waste-water from fermented cassava products (inoculated and natural) and the significant decrease (P < 0.05) in the antinutrients (residual cyanide and phytate), this by-product could be a good supplement in compounding animal feed provided that it is acceptable and highly digestible.

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