Samples of experimental rice breads baked in a home bread machine were evaluated by physicochemical methods and compared with a local commercial whole-wheat bread. The results showed that rice breads had less specific volume, harder texture, and were more prone to retrogradation during storage than whole wheat bread. All stored breads showed a peak at about 52 Њ Њ Њ Њ ЊC by differential scanning calorimetry (DSC) analysis, which is characteristic of retrograded starch. However, the ⌬ ⌬ ⌬ ⌬ ⌬H for rice bread was about 3 times the value of whole-wheat bread, suggesting its strong tendency to retrograde. X-ray diffraction (XRD) evaluation also indicated the appearance of a strong 2 peak between 16.7 Њ Њ Њ Њ ЊC to 17.0 Њ Њ Њ Њ ЊC in rice bread than in whole-wheat bread, which is consistent with starch retrogradation.
Effects of nonwaxy (21% amylose, 79% amylopectin) and waxy (100% amylopectin) rice starch‐lipid complexes on the rate of in vitro digestibility were determined. Long‐chain (≥C:18) saturated emulsifiers reduced digestibility more than short‐chain (
Waxy (short grain), long grain, and parboiled (long grain) rice flours were extruded using three different temperatures and five different water feed rates. The water absorption and water solubility index of the extrudates was 0.67–5.86 and 86.45–10.03%, respectively. The fat absorption index was similar to that of unextruded flours with an average value of 0.96 g/g ± 0.12. Bulk density decreased with an increase in moisture, except waxy rice, which had a quadratic relationship. The viscosity profiles for long grain and parboiled rice were similar. Both initially increased in viscosity (>130 RVU), then decreased to ≈40 RVU. The final viscosity was ≈60 RVU. Waxy rice viscosity remained low (<20 RVU), then doubled upon cooling. The main difference in the digestion profiles was due to temperature. The flours extruded at 100°C digested significantly slower than those extruded at 125 and 150°C. Significant differences were not detected for a given temperature and moisture (P > 0.05) except for long grain and parboiled rice extruded at 100°C and 15% added moisture (F = 4.48, P = 0.03) and 150°C and 20% added moisture (F = 3.72, P = 0.05). Moisture appeared to have little effect for a given temperature, except when parboiled rice was extruded at 150°C. The digestion rate for 11 and 25% added moisture was significantly less than that for 20% (P ≤ 0.05).
The functional properties of a long-grain and a short-grain rice flour extruded at 70 to 120 °C and 22% moisture are reported. The bulk densities essentially stayed unchanged. Both water absorption and water solubility indices increased with an increase in extrusion temperature. The fat absorption indices decreased only at 55 °C. The cold-paste viscosities progressively increased, whereas the peak, breakdown, setback, and final viscosities decreased with an increase in extrusion temperature. A substitution of 25% of unextruded or 70 °C extruded long-grain rice flour into a wheat flour-based fried snack decreased its fat absorption by 35% to 50% without affecting the overall texture.
A commercial long-grain rice flour (CRF) and the flours made by using a pin mill and the Udy mill from the same batch of broken second-head white long-grain rice were evaluated for their particle size and functional properties. The purpose of this study was to compare the commercial rice flour milling method to the pin and Udy milling methods used in our laboratory and pilot plant. The results showed that pin milled flour had more uniform particle size than the other 2 milled flours. The chalky kernels found in broken white milled rice were pulverized more into fines in both Udy milled flour and CRF than in the pin milled flour. The excessive amount of fines in flours affected their functional properties, for example, WSI and their potential usage in the novel foods such as rice breads (RB). The RB made from CRF collapsed more than loaves made from pin milled Cypress long-grain flours.
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