Functional properties of rice flour from modern and traditional Philippine rice varieties

One traditional (Buenkitan) and seven modern rice varieties (IMS2, IR65, PSB Rc5, PSB Rc10, PSB Rc94, PSB Rc100, and PSB Rc72H) were processed into flour using the modified wet milling method of Patindol(1995). Four commercial rice flours were used as reference samples - Erawan Finest Rice Flour and Erawan Glutinous Rice Flour (Cho Heng Rice Vermicelli Factory Co., Ltd., Bangkok, Thailand), and Remyflo R20-T and Remyflo R200-BF-T (Remy Industries, Belgium). Dry-milled flours of PSB Rc5, PSB Rc100, and LMS2 were processed using China flourmill (CFM). Their proximate properties, particle size index, and functional properties were measured and compared with their wet-milled counterparts. Buenkitan obtained the lowest moisture content (3.38%), while PSB Rc72H (10.02%) had the highest moisture content but comparably lower than the Erawan flours. Both Remyflo Flour checks showed a notably greater ash and crude fat content than the rest of the samples, while IR65 and PSB Rc94 obtained the lowest ash and crude fat, respectively. High amylose rice flours had lower crude fat content than the intermediate rice flours. However, check samples did not follow the same trend owing to the non-uniformity of their physicochemical makeup as attributed to their composite natures. PSB Rc72H had the highest value of crude protein (10.24%). Water absorption values and swelling power of the samples were comparable with those of the references, except for Remyflo R200-BF-T, which is a pre-cooked flour. Water solubilities of the three lowest amylose-containing samples (Buenkitan, IMS2 and IR65) were comparably higher than those of the other samples and the Erawan checks (P lesser than 0.01). Remy flours had significantly higher values than all the samples, which may be due to the heat-treatment process before packaging. Oil absorption indices of both Erawan checks were slightly higher compared with all the samples except for the glutinous rice, Buenkitan and IMS2. The rest of the samples had comparable values. Waxy rice flours showed a shorter peak time and lower peak temperature, final viscosity, setback from peak, and setback from trough compared with the non-waxy rice flours. PSB Rc94 showed a lower peak viscosity and breakdown, which indicates that the starch of this variety is less susceptible to disintegration compared with other samples. Particle size index of the dry-milled rice flours ranged from hard to extra soft (50.4 to 79.6%). Among the test samples, only PSB Rc5 was categorized soft while the rest were categorized as medium-soft to hard. Dry-milled flours showed a notably greater size of particles than the wet-milled flour. Moisture content of the samples ranged from 9.6 to 13.1%, which generally fell within the safe level of microbial growth, less than 13% (Frazier and Westhoof 1988). Dry-milled PSB Rc5 had significantly higher value of water absorption index (2.61) and swelling power (0.026%) due to its low particle size index. Dry-milled IMS2 had the highest water solubility (4.22%). Wet-milled rice flours, except for PSB Rc100, obtained significantly greater oil absorption indices. Hydration properties of wet-milled flour such as water absorption index, water solubility, and swelling power were comparably lower than those of the dry-milled flours but not in their oil absorption index. Thus, milling method affected the functional properties of rice flour, which was attributed to the damaged starch particularly in dry-milled rice flour.