Properties of Normal and Glutinous Black Rice Flours Prepared by Different Milling Methods
2013
Lee, Y.T., Gachon University, Republic of korea
Two black rice samples, normal and glutinous black rice, were milled by different milling methods, and the physicochemical properties of the black rice flour samples were tested. Total anthocyanin content in the black rice decreased during soaking in the process of wet milling. The particle size of the black rice flour prepared by dry milling (DM) using a pin mill was smaller than that by wet milling (WM) using a roll mill. Damaged starch contents in the dry milled black rice flour were 16.2 and 14.2% for normal and glutinous samples, respectively, whereas these were only 2.7 and 5.9% for the wet milled samples. The particle size was further reduced by successive dry milling of the flour after wet milling and drying (WDM). However, WDM resulted in a lower damaged starch (%) than DM, despite reduced flour particle size. Little differences in the water absorption index (WAI) of the black rice flour were observed among the different milling methods. Water solubility index (WAI) was in the following order: DM, WDM, and WM, and was higher in glutinous black rice flour than in normal black rice flour. Determined by Rapid Visco Analyzer (RVA), glutinous black rice flour appeared to have significantly higher gelatinization temperature and pasting viscosities including peak, trough, breakdown, and final viscosities. Compared to dry milled black rice flour, wet milled black rice flour showed lower peak viscosity and higher final viscosity, resulting in increased setback value.
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