Effect of Gamma Irradiation on the Physicochemical and Functional Properties of Cassava Starch

Cassava (Manihot esculanta Crantz) is popularly consumed as a staple food crop in many tropical countries in Africa, South America and Asia. In Africa the crop has been recognized as more than a subsistence crop. The crop is very important and commercially serves as a raw material for industries with significant effect on the economy of a country. Cassava roots contain high starch content and approximately half of the total roots produced is used for the production of starch for industrial purposes. Limitation to utilization of cassava roots by processors is due to its high perishability and bulkness, while native starches are structurally too weak and funtionally restricted for a wide variety of industrial applications. The objective of the project was to determine the effect of gamma irradiation as a modifying agent on native starch from three cassava varieties namely Ankra, Bosome nsia and TME419. Gamma radiation doses applied ranged between 0 - 20kGy and changes in physicochemical, functional and pasting indices of the starch were measured. Physicochemical indices measured were moisture content, amylose content, carbohydrate content, pH, ash content, fat content, protein content and L*a*b* values. Functional indices mesured were water absorption capacity, solubility index, bulk density, swelling power, fat absorption capacity, emulsion capacity, emulsion stability and least gelation concentration. Pasting indices measured were gelatinzation temperature, peak viscosity, viscosity at 92 degrees C and 50 degrees C, breakdown viscosity and setback viscosity. The pH, amylose content, carbohydrate content and ash content of native starch from Ankra, Bosome nsia and TME 419 were respectively 8.06, 7.80 and 7.18, 17.62%, 19.46% and 23.54%, 56.11%, 52.43% and 35.70%, 0.11%, 0.19% and 0.12%. The water absortion capacity and least gelation concentration of native starch from Ankra, Bosome nsia and TME 419 were 12.3%, 13.0% and 10.0%, respectively, least gelation concentration had values of 5%, 6% and 8% and swelling power also had values of 13.60g, 7.63g and 9.02g. The setback and breakdown viscosities of native starch samples from Ankra, Bosome nsia and TME 419 were respectively 292BU, 265BU and 262.5BU, 1358BU, 1325.5BU and 1122BU. Analysis of variance treatment means indicated that irradiation significantly decreased amylose content and carbohydrate content,PH, L* and a* values but increased b* values. PH, amylose and carbohydrate contents were 7.98, 20.2% and 48.1% respectively for non-irradiated starch to 7.03, 13.3% and 27.5% for 20kGy starch. L*a*b* values were 96.7,-0.17,1.39 for 0kGy starch and 90.6,-0.38,2.98 for 20kGy starch. All the physicochemical indices were significantly influenced by the variety of cassava. The amyclose content of TME419, Ankra and Bosome nsia wer 14.5%, 16.4% and 18.2% respectively. Irradiation significantly increased starch water absorption capacity, solubility index, fat absorption capacity and least gelation concentration but decreased swelling power. These functional indices of starch were significantly influenced by the variety of the cassava. Irradiation had significant effects on the pasting indices measured. Peak viscosity, breakdown viscosity, setback viscosity and paste stability at 92 degrees celcius were 1822.3BU, 1268.5BU, 273.2BU, 269.5BU for native starch and 483.7BU, 397.5BU, 42.7BU and 185.3BU for starch treated with 20kGy. Paste stability at 50 degrees celcius for native starch was -110.5BU and -33.7BU for starch treated with 20kGy radiation. The properties of irradiated cassava starch were significantly different from non-irradiated starch and could be exploited for specific industrial applications. (au)