Process Development for Plant-Dairy Protein Liquid Foods using Ultra-Shear Technology

Ultra-shear technology (UST) presents a promising way to preserve stable protein liquid foods. This dissertation investigated the effect of pressure, shear, temperature, and their interactions during UST on quality attributes and microbial inactivation. First, the impact of UST process parameters on milk was evaluated by subjecting to UST at 400 MPa/35 and 65°C. Untreated, high-pressure processed (HPP; 400 MPa/40°C/0 and 3 min) and thermal treated (72°C/15 s) milk served as controls. HPP did not cause particle size reduction but increased the viscosity up to 3.08 mPa·s compared with 2.68 mPa·s for untreated milk. 35°C UST reduced the particle diameter from 3511.76 nm (raw milk) to 291.45 nm and prevented creaming.To compare microbial safety of UST and HPP, cell suspension of Lactobacillus brevis (1.6×1010 CFU/mL) and spore suspension of Bacillus cereus (3.2×108 CFU/mL) were subjected to UST at 400 MPa/40 and 70°C. Thermal (0.1 MPa-70°C-0/5min) and HPP (400 MPa-40 and 70°C-0/5min) experiments were performed. HPP at 400 MPa /70°C/0 min resulted in 8.4 and 2.3 log reductions of L. brevis and B. cereus, respectively. After 70°C UST, L. brevis and B. cereus reduced by 7.1 and 1.6 logs, respectively. Different valve geometries, viz., ultra-shear valve, needle valve, and tubular valve, were evaluated. Ultra-shear valve produced inactivation of 2.0 and 7.1 logs for L. brevis at 40 and 70°C respectively, which was higher than needle valve and tubular valve.The ability of UST to obtain homogenous plant-dairy protein blends with varying protein and fat levels was evaluated. Milk-pea dispersions of 3 protein ratios viz., milk:pea 1:0.5, 1:1, and 1:3 were prepared. UST was performed at 400 MPa/40 and 70°C. HPP at 400 MPa/25±2°C/0 min and thermal treatment at 72°C/15s were conducted. Pea-dairy dispersions with 3 fat levels - Raw milk+Pea, Skim milk+Pea, Cream+Pea protein were prepared and UST-treated at 400 MPa/70°C. Discovery HR3-hybrid rheometer was used to determine viscoelastic properties by frequency sweep (0.1-100 rad/s), and shear viscosity by flow sweep (0.1-100 s−1). HPP and thermal treatments did not alter the particle size. UST reduced the particle size at low protein and fat concentrations although particle aggregation was observed above certain concentrations. UST increased the viscosities depending on fat and protein level. All UST-treated dispersions were stable.To understand the micro-nano structural changes in proteins, small-angle x-ray scattering (SAXS) was employed. Dispersions with animal protein - Beta-lactoglobulin (BLG), plant protein - pea lectin (PL) and their mixture–BLG+PL were processed by HPP at 400 MPa/25°C/0 and 5 min and UST at 400 MPa/70°C. HPP for 0 min showed folded proteins, however, 5 min caused partial unfolding in BLG. PL had higher pressure-resistance than BLG. UST-treated protein solutions had large protein aggregates and unordered structure. UST-treated PL produced larger aggregates than BLG.In summary, the study demonstrated that pressure, shear, heat and their interactions influenced both microbiological and functional properties of dairy-pea protein liquids. Knowledge from this study will be useful for the equipment developers, food processors and regulators to develop and evaluate safe harbor conditions for UST for treatment.