Effect of continuous flow high-pressure throttling on rheological and ultrastructural properties of soymilk

Soymilk processing uses a filtration or centrifugation step to remove coarse solids in the comminuted soy. The objective was to utilize the whole beans and determine the effect of continuous flow high pressure throttling (CFHPT) process in reducing particle size and narrowing down the particle size distribution. The rheological and ultrastructural properties of such soymilk were also determined. Whole dehulled soybeans and deionized water were ground in a food processor before comminution in a Megatron (process M) or a Fitzmill (process F) or a Stonemill (process S). The comminuted slurry was homogenized at pressures of 69, 103, 138, 207, and 276 MPa using a CFHPT system, heated to 80 degrees C in a tubular heat exchanger prior to depressurization, and held at elevated temperatures of 97, 106, 114, 131, and 148 degrees C, respectively, for each applied pressure after throttling. To avoid flashing, back pressure was applied after the holding tube and soymilk was cooled immediately. Process M produced soymilk with smallest particle size and the highest apparent viscosity. All soymilk samples showed non-Newtonian pseudoplastic flow behavior. Ultrastructural images showed a clear protein network with very small fat globules entrapped in the protein matrix. Particles were uniformly distributed when the highest pressure treatment was applied for process M, which was considered as the best process.