Contribution of process parameters to the particle size distribution and apparent viscosity properties of soy protein isolate- and hydrolysate-based infant formula emulsions

Oil-in-water emulsions were manufactured with commercially available soy protein isolate (SPI 1500 and SPI 1651) and soy protein hydrolysate (SPH 1761 and SPH 1762) ingredients. In addition to SPIISPH, the model emulsions contained corn syrup solids (CSS) and a proprietary vegetable fat blend. The ingredients mixture was pasteurised at 77°C for 30 sec, followed by homogenisation (double pass) using a first stage pressure of 30 bar and a second stage pressure of 170 bar. The objective of the study was to quantify the effect of ingredient composition (SPIISPH and CSS), and lecithin inclusion on the particle size distribution of the emulsions. The effects of variation in total solids (TS, 12.5 - 26 % w/w), pH (6.4 - 7.5) and homogenisation pressure (110 - 360 bar) on the particle size distribution, and apparent viscosity (llapp) of the emulsions was also evaluated. The exclusion of CSS in the emulsions manufactured with SPH 1762 resulted in an increased proportion of smaller particles, compared to the same emulsion containing CSS. There were no real differences in particle size distribution profiles for emulsions manufactured with the fat blend containing varying amounts oflecithin (0 - 2 % [w/w)). However, the absence of added lecithin resulted in model emulsions manufactured with SPI sample 1651 and SPH sample 1761, having particle size distribution profiles with a greater proportion of larger particles. The addition of lecithin to emulsions generated with SPH sample 1762 resulted in a decrease in the average particle size. No TS related effects were observed on the particle size distributions of model emulsions generated with the SPI samples 1500 and 1651 and SPH sample 1761. However, emulsions made with SPH sample 1762 at low TS (12.5 - 14 %) contained more particles having a lower size distribution than those made at high TS levels (23 - 26 %). Increasing homogenisation pressure generally resulted in a decrease in the mean particle size of SPI emulsions. Emulsions generated with SPH sample 1761 had a bimodal particle size distribution profile at the higher homogenisation pressures. For emulsions generated with SPH sample 1762, an increase in homogenisation pressure resulted in an increase in llapp. The particle size distribution and llapp profiles of SPI sample 1500/1651 and SPH sample 1651 model emulsions were unaffected by pH . changes between pH 6.4 and 7.5. However, an increase in pH resulted in a general decrease in average particle size and an increase in llapp of the SPH sample 1762 emulsion. The results demonstrate that ingredient composition and processing conditions have significant effects on the properties of soy protein-based model emulsions.