The object is to provide an enriched liquid food which comprises a soybean protein material, which has a low viscosity, which produces little aggregates, and which has good physical properties. An enriched liquid food can be prepared by using a soybean protein material having the following physical properties a) to d): a)an aqueous solution containing the soybean protein material in an amount of 5 g in terms of solid content relative to 100 g of the aqueous solution and also containing calcium lactate in an amount of 30 mg in terms of calcium content has a viscosity of 10 mPa·s or less at 20°C after the aqueous solution is heated at 121°C for 10 minutes, and produces precipitates in an amount of 1 vol% or less after the aqueous solution is centrifuged at 1,300 × g for 5 minutes； b) a 12-wt% aqueous solution of the soybean protein material has a viscosity of 1,000 mPa·s or less at 5°C； c) the soybean protein material can be solubilized in a 0.22 M TCA at a solubilization ratio of less than 11%； and d) the soybean protein material has a PSI (protein solubility index) value of 70 or more. The soybean protein material can be produced by heating an aqueous solution or an aqueous dispersion solution of a soybean protein raw material at pH 5.7 to 7.4 and at a temperature of 110 to 160°C for 15 to 70 seconds.
