Study on denaturation of whey protein isolate and its control in convective and spray drying processes
Creators: name: Haque, Md. Amdadul
Publisher: name: RMIT University
Year: 2024

description: In their native state whey proteins possess unique globular configuration which is important in imparting functional properties such as solubility, emulsification, foaming and gelling. Whey proteins have to pass through a series of processing steps such as filtration, evaporation and drying when they are converted into powders. Spray drying is the most commonly used drying method to produce whey protein isolate (WPI) powders and it is known to exert denaturing stresses such as thermal, dehydration and interfacial stresses to proteins. These stresses denature whey proteins and the resultant WPI powders show poor functional activities. Presently there is a lack of information in the literature regarding the relationship between denaturation kinetics and drying kinetics (moisture content, temperature histories and drying rate) and development of morphology during particle formation process of whey proteins. In addition, there is inadequate information regarding the efficacy of protectant solids such as lactose, trehalose and polysorbate-80 in minimising the denaturation of whey proteins during drying at an individual droplet level. Single droplet dryer was used in this study to obtain these properties in WPI and WPI-protectant droplets and particles. This fundamental information can be used to produce less denatured and functionally superior whey protein powders through spray drying.<br><br>The denaturation was measured using reversed phase high performance liquid chromatography (RP‑HPLC), differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR). The drying and denaturation kinetics of WPI droplets were simulated by using Reaction Engineering Approach (REA) and first order reaction kinetics, respectively and they were integrated into a single model. The extent and nature of denaturation of WPI in spray drying process was measured using a laboratory scale spray dryer.<br><br>It was found that, WPI was denatured about 68.5±0.05% by convective drying for 600 s at 65 oC and 80 oC. The moisture, temperature and denaturation histories of WPI during convective drying at single droplet level were successfully predicted using REA and first order reaction kinetics models. It was also found that the whey protein bovine serum albumin had the highest, β-lactoglobulin had the lowest and α-lactalbumin had intermediate stability under convective drying conditions. Addition of 20% trehalose resulted into almost complete protection of WPI from loss due to irreversible denaturation, while addition of 30% lactose could protect only up to 70% of WPI. The secondary structural features (β-sheet, β-turn and random coil) of WPI were significantly altered even in the presence of these two sugars. There was no loss of WPI through denaturation induced aggregation when WPI was spray dried at inlet and outlet temperatures of 180 oC and 80 oC, respectively. However, the secondary structural features were found to be altered significantly. Addition of up to 0.01% polysorbate‑80 with WPI as an excipient effectively protected the α-helix and β-sheet from alteration. The spray dried WPI powders produced in the presence and absence of lactose, trehalose and polysorbate‑80 had characteristic wrinkled surface morphology and were amorphous in nature.