Study On Effects Of Protein On Pasting Viscosity Properties Of Rice Flour And Stability Of Its Maltose Syrup Product

This paper mainly focused on the effect of protein derived from rice on the pasting viscosity of rice flour and stability of thermal flocculate heated from maltose syrup. Long-grain rice flour and waxy rice flour were the raw materials in this experiment.T he rice flour samples with low gelatinization temperature and high peak viscosity were produced respectively with the method of alkali, protease, and acetic anhydride esterification. The paper also studied the effect of protein content of rice flour on the pasting properties of the samples treated by alkali and protease and explored the thermal flocculate composition and formation mechanism of tranditional maltose syrup, and further investigated the influence of protein on the stability of maltose syrup products.The aforementioned rice flour samples were produed by removing a part of protein of rice flour with sodium hydroxide and neutral protease to make a comparison as for pasting properties. The result suggested that the treated rice flour samples by alkali showed lower gelatinization temperature and higher peak viscosity. The ones treated by protease, lower gelatinization temperature but lower peak viscosity. Neither the alkaline nor enzymatic approaches changes the crystal structure type of rice starch, but alkali can destroy the crystal structure of rice starch.The paper continued to measure the pasting properties, granule morphology and microscopic properties of the waxy rice flour treated by alkali. It found that gelatinization temperature of alkaline treatment products decreased by 1 4℃; the peak viscosity increased significantly, in the range of 130% 260%, compared to native waxy rice flour. With the increase of alkaline concentration, duration or temperature, or the decrease of slurry concentration, waxy rice flour protein removal decreased. The removal efficiency was lower when the residual protein content was under 2%. Correlation analysis showed that the protein content is not the only factor that affects gelatinization temperature and peak viscosity of waxy rice flour products. Alkaline conditions（slurry concentration, alkaline concentration, duration and temperature, represented respectively by X₁, X₂, X₃, X₄） also affect its pasting properties. Generated from the experiments of response surface design, the multiple quadratic regression equation of peak viscosity of waxy rice flour products treated with alkali is as follows:Y=-5421.43+325.62X₁-14242.30X₂+125.74X₃+479.07X₄+303.50X₁X₂-1.21X₁X₃-11.95X₁X₄+45.50X₂X₃+757.5X₂X₄-7.7X₃X₄-5.13X₁X₁+10503.03X₂X₂-1.07X₃X₃-2.74X₄X₄.The physicochemical properties of low substituted acetylated rice flour products synthesized by the reaction of long-rice flour with acetic anhydride（AA） in an aqueous medium were investigated. The result showed that the better preparation condition was to let it react 2 hours at the p H value of 9.0 with acetic anhydride dosage of 5%. The DS of the low substituted acetylated rice flour was 0.066. The pasting temperature of acetylated rice flour decreased about 6 ℃; the peak viscosity increased by 35%⁴0%. Furthermore, paster clarity, retrogradation and swelling power all get enhanced, however, the relative crystallinity decreased, just because of the introduction of acetyl group in the actylated rice starch molecule.The paper lastly studied the effect of the protein on the stability of maltose syrup products. The result showed that protein in maltose syrup played a leading role in the process of thermal-floc formation; and the content of protein mainly derived from rice in the floc was 81.79%, other elements such as calcium, iron, silicon, or ions of substance with the content of 17.66% also promoted the flocculation of protein. Adding a little more amount of calcium ions in liquefaction process, increasing the heating strength before filtration and prolonging the heating time in production can eliminate or reduce thermal flocculation heated from maltose syrup products.