Concentration of whey proteins using the Pressurized Gas eXpanded (PGX) liquid technology and their characterization
Creators: Wong, Emily Y
Publisher: name: University of Alberta Library
Year: 2024

<p>The Pressurized Gas eXpanded (PGX) liquid technology utilizes CO2-expanded ethanol to simultaneously dry and purify high molecular weight biopolymers, producing micro/nanosized powders and fibrils with low bulk densities and high surface areas. The fractionation, concentration and drying of whey proteins directly from sweet- and acid-type whey was investigated using the PGX technology as a single unit operation to produce concentrated whey protein powders. The feasibility of processing a complex feedstock such as whey was first investigated using sweet whey on a laboratory scale system, followed by a 5x scale up to a bench-scale system and varied mass ﬂow rate ratios (θPGX). Efficiently defatting and removing &gt; 50% lactose from the dairy waste stream, whey powders containing ≥ 45% protein were obtained through the single-step concentration process. The concentrated whey powders were characterized in terms of their physicochemical attributes, specifically untapped bulk density, particle size distribution, specific surface area and pore size, surface morphology as well as the compositional analysis, protein composition and structure by determining the soluble protein content, analyzing the protein secondary structure, intrinsic protein fluorescence and protein hydrophobicity. PGX whey powders were primarily composed of major whey proteins, β-lactoglobulin, α-lactalbumin, and bovine serum albumin in the presence of amorphous lactose and milk minerals such as Ca, K, Mg, Na, P and S. The physicochemical attributes of the PGX whey powders were affected by the varying θPGX linked to the anti-solvent interaction with the biopolymer stream at the nozzle. At intermediate θPGX ratios, the whey proteins had similar protein structures to freeze-dried proteins, indicating that the PGX process is mild. At lower θPGX ratios, a reduced amount of PGX fluid (the CO2-expanded EtOH that breaks up the biopolymer stream) limits the anti-solvent-polymer interaction, thereby favouring biopolymeric polymer-polymer interactions, and overall resulting in fewer disruptions to the protein secondary structures (β-sheet and α-helix). With improved jet breakup at higher θPGX ratios, protein exposure to the solvent is increased, resulting in rearrangements of proteins to more compact configurations with increased protein hydrophobicity. <br>
To assess the potential of the PGX technology for commercial applications to produce whey protein concentrates, ultrafiltration and spray drying were introduced as reference methods in the second study. To evaluate the versatility of the PGX technology, a second type of whey feedstock was also introduced. The results demonstrated that the PGX technology was comparable to a one-step ultrafiltration process in terms of protein concentration. Whey protein concentration up to 4.4x was achievable utilizing sweet whey, while only 2.7x protein concentration was possible with acid whey feedstocks. Lactose reduction ranged from 25-50% with more effective reduction in sweet matrices compared to acid matrices. This indicated that while it is possible to concentrate whey proteins from various whey feedstocks, obtaining high protein content products from acid whey was more challenging compared to sweet whey due to the high level of ash content and lower amounts of protein in the feed material. Overall, these research findings are significant in the continued application of the PGX technology for the development of value-added ingredients for nutraceutical applications. </p>