Rice starches of long grain and waxy cultivars were annealed (ANN) in excess water at 50°C for 4 hr. They were also modified under heat‐moisture treatment (HMT) conditions at 110°C with various moisture contents (20, 30, and 40%) for 8 hr. The modified products were analyzed by rapid‐viscosity analysis (RVA), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD). Generally, these hydrothermal treatments altered the pasting and gelling properties of rice starch, resulting in lower viscosity peak heights, lower setbacks, and greater swelling consistency. The modified starch showed increased gelatinization temperatures and narrower gelatinization temperature ranges on ANN or broader ones on HMT. The effects were more pronounced for HMT than for ANN. Also, the typical A‐type XRD pattern for rice starch remained unchanged after ANN or HMT at low moisture contents, and the amorphous content increased after HMT at 40% moisture content.

In this study, the effects of ozonation and the addition of amino acids on rice starches were determined in terms of pasting properties using a rapid visco-analyzer. Results from viscosity analysis showed that 30-min ozone treatment on commercial rice starch exhibited the greatest swelling extent among the treatments and least retrogradation tendency. The control pure oxygen treated sample had the best cooking stability. The addition of lysine (6%) to 30-min ozonated commercial rice starch significantly reduced peak viscosity (PV), minimum viscosity (MV), and final viscosity (FV) by 918, 1024, and 1023 cP, respectively. Moreover, it decreased Ptime, resulting in the faster swelling upon heating and less rigid gel formation upon cooling. Furthermore, the presence of lysine in 30-min ozonated starch isolate (WSI) also significantly reduced PV, MV, FV, pasting time, and total setback (TSB) and produced starch gel with the best cooking stability and the least retrogradation tendency. Ozonated starch exhibited similar pasting properties to those from oxidized starches treated with low concentrations of chemical oxidizing agents. The combination of lysine with ozonation resulted in pasting properties similar to starches treated with high levels of chemical oxidizing agents. The ozonated starch could be used as a thickening agent, whereas ozonated starch with lysine might be an alternative for a highly chemically oxidized starch. Therefore, ozonation alone or the combination of ozonation and addition of lysine might be used to develop new starch ingredients with various functionalities without using typical chemical modifications.

Thermal properties of conventionally and ohmically heated rice starch and rice flours at various frequencies and voltages were studied. There was an increase in gelatinization temperature for conventionally heated rice starches since they were pregelatinized and became more rigid due to starch-chain interactions. In addition, there was a decrease in enthalpy (energy needed) for conventionally and ohmically heated starches during gelatinization; thus, the samples required less energy for gelatinization during DSC analysis. Ohmically heated commercial starch showed the greatest decrease in enthalpy probably because of the greatest extent of pregelatinization through ohmic heating. Brown rice flour showed the greatest gelatinization temperature resulting from the delay of starch granule swelling by lipid and protein. Enthalpy of ohmically heated starches at 20 V/cm was the lowest, which was most likely due to the lower voltage resulting in a more complete pregelatinization from a longer heating time required to reach 100 degrees C. Ohmic treatment at 70 V/cm decreased onset gelatinization temperature of white flour; therefore, it produced rice flour that swelled faster, whereas the conventionally heated sample showed a better thermal resistance.

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.

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