Apparent viscosity by irradiation dose-effect relationship for starch-based materials

There are analysed and presented, in terms of dose-effect relationship, the experimental results on the investigation of the rheological behaviour of gelatinized suspensions of irradiated starch and starch-based materials, as well as the variation with the dose value of the apparent viscosity and the shear stress. Irradiation has been performed using a linear accelerator, with the following parameters: electron mean energy, ∼6 MeV; mean bean current, 10 μA ; pulse period, 3.5 μs and repetition rate, 100 Hz. The main experimental parameters were: irradiation dose in the range of 0-25 kGy; dose rate 1.5-2.0 kGy/min and dose uniformity less than 10 %. Doses were checked by standard procedures for electron beam dosimetry. Some starch-based materials were ground and sieved to obtain similar particle sizes, necessary to eliminate the influence of particle size on the apparent viscosity variation with the dose. The rheoviscometric measurements have been carried out using a rotationally viscometer on gelatinised suspensions of starch-based materials, into equivalent starch concentration and alkalinised suspensions for pepper. For the considered materials the variation of apparent viscosity by irradiation dose is described by exponential equations and the apparent viscosity decreases with the dose. These equations fit very well the experimental data for starch and starch-based materials, the correlation coefficient values being, r ≥ 0.93 for all cases of dose-effect relationships for starch suspensions. The coefficients of these equations could also be obtained by analyzing the data from viscometric measurements and they strongly depend on the shear rate values, Dr. The starches and starch-based materials obviously present the same rheological behaviour under irradiation and this fact should be attributed to starch degradation and depolymerization due to the ionising radiation action and confirms one of this study main assumption. This property should be used to develop an identification and control method for the ionising treatment of starch-based food materials. (authors)