Abstract:Rice starch has the advantages of small particles, high whiteness, and low allergenicity, but the difficulty in extraction, as well as its high cost, limits the wide application of rice starch in the food industry. The authors used three varieties of rice as raw materials and optimized the extraction conditions of alkali and protease to investigate the effects of different extraction processes on the structural and physicochemical properties of rice starches. The results showed that the protein residual rate in the alkali-extracted rice starches ranged within 0.65%~1.35% under the conditions of 0.20% alkali mass concentration, solid-liquid ratio of 1 g∶5 mL, and reaction duration of 4 h. The protein residual amount in the protease-extracted rice starches ranged from 0.58% to 0.82% with protease of 0.50% (mass fraction) at 45 ℃ under pH 4.0 for 4 h. The rice starches displayed irregularly polyhedral granules with a diameter ranging from 4 to 8 μm. Compared to the alkali-extracted rice starches, the protease-extracted rice starches had a more prominent polyhedral structure. The relative crystallinity of alkali-extracted rice starch was 22.93%~43.58%, slightly lower than that of protease-extracted rice starch (28.00%~43.81%). The solubility of rice starch (at an extraction temperature of 90 ℃) was 3%~15% higher than that of rice flour, and the swelling power was 8%~20% higher. Meanwhile, protease-extracted rice starch exhibited higher solubility and swelling power. Furthermore, compared to rice flour, rice starch showed stronger gel properties. The hardness of rice flour gels, alkali-extracted rice starch gels, and protease-extracted rice starch gels were in the range of -7.16~275.96 g, 55.09~368.43 g, and 62.37~373.45 g, respectively.
