| In virtue of its health benefits, soybean is now attracting more and more attention throughout the world. It brings those traditional oriental soybean-based food great chances and challenges. The objective of this dissertation was to prepare instant sugar-free soybean milk powder. We chose it both for catering to the mainstream of modern food industry-"fast food" and for meeting the demands of the special group. Firstly, the dissertation established the soaking and blanching conditions in terms of the flavor and the solubility of soybean milk powder. Soybean could gain sufficient absorption of water when soaked in 0.5% NaHCO3 aqueous solution for about twelve hours under room temperature. After the process of blanching, grinding, preheating and spray-drying, the soybean milk powder thus prepared tasted palatable and had no off-flavor. After the process of soaking, beany flavor of soybean milks prepared with different blanching temperature or at various grinding conditions was extracted by SDE. The constituents of the beany flavor were separated and identified by gas chromatography-mass spectrometry(GC/MS). Based on the NBS standard mass spectral data and by integrating peak area method, the main constituents of beany flavor (hexanal, 1-hexanol, 2-hexenal, 2-pentylfuran) in each sample were quantified. Combined with sensory evaluation, optimal processing parameters were determined as: soaked soybean was blanched at 90℃ for 5 minutes, then grinted with hot water at the same temperature, soy powder thus prepared was almostly beany-free, the content of hexanal was only 1:20 to that of control. Secondly, after research of four kinds of proteinases ( Neutrase,AS1.398,Alcalase and Trypsin) frequently used in food industry, this dissertation found that Neutrase was the ideal proteinase, which was used to hydrolyze protein in soybean milk in production of soybean milk powder. When Neutrase was used, the total quantity of the proteinase added was about 0.4%(Neutrase/soy protein, w/w) and the temperature under which the proteinase was added was 65℃... When hydrolyzing was finished, the degree of hydrolysis of protein in soybean slurry was about 4.37%. After homogenizing and spray-drying, the remaining proteinase activity in soybean milk powder was zero. At the same time, the dissertation also did some research on glutin's debitterness. The result indicated that glutin could mask the bitterness brought by proteolytic product if the glutin was hydrolyzed together with soybean milk slurry.Thirdly, the dissertation also gave regards to the influence of emulsifier and hydrophilic colloid on instant property of soybean milk powder. The research suggested that the addition of emulsifier and hydrophilic colloid to soybean slurry could benefit the physical aspects of soybean milk powder. The hydrophilic colloid added was glutin, and its quantity was about 1.0%( glutin/ solid in soybean milk, w/w). The glutin could not only bring about a bed of hydrophilic pellicle on the surface of soybean milk powder particles to increase hydrophilicity, but also increase the viscosity of milk to avoid or postpone delaminating and precipitating. The emulsifiers added were Hydrophilic Glycerol Monostearate and Tween-80. Hydrophilic Glycerol Monostearate could increase the flowability of soybean powder, while Tween-80 could increase the soybean powder's dispersibility because of its strong solubility in water. The two emulsifiers increased the soybean milk powder's physical properties in different aspects. The total quantity of the two emulsifiers was 2.0%( emulsifiers/solid in soybean milk, w/w) and the proportion of Hydrophilic Glycerol Monostearate to Tween-80 was 3:2.Finally, the dissertation attached great importance to the research of spray-drying conditions. The optimal conditions were: when spray-drying, the concentration of soybean milk was about 12.60%, the air pressure of atomizer was 0.20MPa, and the inlet temperature was 185℃, the outlet temperature was 85℃. The moistability of the soybean milk powder thus prepa...
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