Pasting Properties of Ohmically Heated Rice Starch and Rice Flours

ABSTRACT:  Pasting characteristics were examined for conventionally or ohmically heated rice starch and rice flours. Brown rice flour showed the greatest cooking stability and least retrogradation potential. Brown rice flour also showed the greatest pasting temperature and lowest peak viscosity, whereas commercial starch had the lowest pasting temperature. Nonstarch components of the brown rice flour, such as fat and protein, may have acted as stabilizers delaying water access into the granules and reducing swelling of the starch. Ohmic heating reduced pasting temperature for commercial rice starch, resulting in a starch that swelled faster. Furthermore, ohmic heating produced better cooking stability in white rice flour 1 and 2 than in the native sample, and caused white rice flour 2 to have less potential for retrogradation than the conventionally heated sample. At lower electric field strength (20 V/cm), ohmic heating resulted in the greatest cooking stable starches compared to higher voltages (40 and 70 V/cm) because more starch granules were disrupted from a longer cooking time, so there were fewer intact granules for pasting. Ohmic heating has been shown to alter rice starch and flour pasting characteristics with an added influence of lipids, proteins, and amylose contents.