Food Structure


Corn starch samples containing 0, 25, 50 and 70% amylose irradiated with -y -radiation dosages of 0 (native) , 5 , 10, 20 (containing 0, 2.5 or 5% potassium persulfate , hydrogen peroxide or eerie ammonium nitrate) or 30 kGy were extrusion cooked using a C. W. Brabender single-screw extruder at a barrel temperature of 140 °C, a screw speed of 140 rpm and 18% moisture content. Increasing irradiation dosages from 0 to 30 kGy gave consistently increased expansion ratios from 2.9 to 7.9 for 25% amylose starches and from 6.5 to 14.5 for 50% amylose starches, while the expansion ra tios consistently decreased from 6.0 to 2.1 for 0% amylose starches. The expansion ratios for 70% amylose starches remained more or less constant at 10 irrespective of irradiation dosage. Expansion ratios of all the 20 kGy irradiated starch samples treated with chemical agents, however, decreased to 5 or below. The patterns of bulk densities and expansion ratios of the products were generally similar. Increasing irradiation dosages caused darkening of the product color. The water solubility increased from < l% for native starches to almost 100% for certain irradiated starches processed with chemical additives. Overall, increasing amylose contents of the starches appeared to be resistant to changes that otherwise occurred due to irradiation modifications and chemical treatments. Molecular weights and iodine binding capacities of starches were significantly reduced with irradiation dosages and chemical treatments.

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