Effects of variety, harvest age and pre-treatment on the drying characteristics and baking quality of cassava flour

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July, 2016
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Cassava is an important tropical crop that is widely grown and consumed in different forms across various countries in the tropics. It has great potentials for use in the bakery and other food industries for the production of value added products. The effects of harvest age, chipping, grating, toasting and citric acid pre-treatments on drying characteristics and baking quality of Ampong, Broni and Otuhia cassava varieties were investigated. Pre-treatment had the greatest influence on the drying characteristics as more than 50 % of the drying time was saved by toasting and grating pre-treatments. Henderson and Pabis, Page and Newton models adequately predicted the drying behaviour of the cassava varieties but the best prediction was achieved with the Page’s model. The proximate composition of the cassava flour was significantly (p ≤ 0.05) affected by harvest age, variety and pre-drying treatments. The flours obtained had satisfactory quality attributes in terms of protein, fat, fibre, ash, carbohydrate, moisture content, pH and cyanogenic potentials. The three cassava varieties produced flours with low cyanide contents of 2.48 mg HCNeqv/kg to 6.99 mg HCNeqv/kg dry matter. These values are below the WHO recommendation of cyanide content which is not to be greater than 10 mg HCNeqv/kg dry matter of cassava flour (WHO/FAO, 2013). Hence the flours could be safely consumed by humans without any concern of cyanide toxicity. The water binding capacity, swelling power, water and oil absorption capacities of the cassava flours were significantly (p ≤ 0.05) affected by variety, harvest age and pre-treatment while solubility was affected by only harvest age and pre-treatment. The Otuhia cassava variety had relatively lower gelatinization temperature and peak time values while Otuhia and Ampong varieties had higher peak and final viscosity values. The setback viscosity values of the flour from the three cassava varieties did not differ iv from each other. Grating pre-treatment had the highest peak viscosity value while the setback and final viscosity values of toasted and grated samples were higher than the others. The early gelatinization, high peak viscosity, setback and final viscosities generally exhibited by the flour samples were good indicators of their suitability for use in the bakery industry. Results from the baking experiment indicated that the specific volume and sensory attributes of bread samples containing 20% cassava flour produced from five different pre-treatments of Otuhia variety harvested at 14 months compared very well with the control sample. Composite bread with acceptable sensory qualities were produced from flour containing up to 40% toasted and 30% grated cassava which was not significantly different (p ≤ 0.05) from bread containing 100% wheat flour.
A Thesis Submitted to the Department of Agricultural Engineering, College of Engineering in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food and Post-Harvest Engineering.