Yonas Gebrehiwot | ALES Graduate Seminar

A graduate exam seminar is a presentation of the student’s final research project for their degree.
This is an ALES MSc final project seminar by Yonas Gebrehiwot. This seminar is open to the general public to attend.

Project Topic: Pressurized Gas eXpanded liquid (PGX) drying of soy protein isolate and egg white

MSc with Dr. Feral Temelli.

Seminar Abstract:

As food biopolymers, carbohydrates and proteins are commonly used for the encapsulation of bioactive components. The use of high temperatures and organic solvents, minimal control on particle characteristics, low bioactive loading, and difficulties in scale-up are some of the disadvantages associated with the conventional methods used for protein micronization and drying. Pressurized Gas eXpanded liquid (PGX) technology is a novel technique that allows drying of high molecular weight water-soluble biopolymers and generates sub-micron and nano-scale particles with high porosities and high specific surface areas. It utilizes a mixture of CO₂ and anhydrous ethanol at the gas-expanded liquid conditions (100 bar, 40^oC) to dry aqueous biopolymer solutions. This study aimed to investigate the applicability of the PGX technology to micronize and dry soy protein isolate (SPI) and egg white (EW) proteins as a potential carrier for bioactive delivery systems. In the first part of the study, SPI was used to optimise the PGX process in order to obtain micronized and dried SPI particles having high specific surface area and low bulk densities. The effects of the initial concentration of soy protein isolate (1%, 2.5% and 5% w/w), aqueous solution flow rate (6, 10, 11 and 20 g/min) and flow rate ratio of aqueous solution: EtOH:CO₂ (1:3:1, 2:3:1, 1:2:1, and 0.5:3:1) on the morphology, bulk density, specific surface area, and structural conformations of the protein powder obtained were investigated. In the second part of the study, the effect of the solids content of EW (1%, 6% and 12% w/w) at the optimised flow rate ratio of EW:EtOH:CO² (20:30:10 g/min) on the morphology, specific surface area, and structural conformation of the protein powder obtained by PGX drying was investigated. Upon PGX drying of SPI and EW, agglomerates of completely dry sub-micron particles were obtained. The untapped bulk densities of the SPI powders generated ranged from 8.7 ± 0.8 mg/mL to 31.3 ± 1.1 mg/mL, which was more than an order of magnitude lower than that of the unprocessed and spray dried SPI at 276.1 ± 0.6, 272.0 ± 3.7 mg/mL respectively. The PGX-dried SPI samples exhibited much larger specific surface areas (30.2 ± 1.8 m²/g to 282.7 ± 10.3 m²/g) compared to those of the unprocessed, spray-dried and freeze-dried SPI at 8.6 ± 0.6 m²/g, 11.5 ± 1.6 m²/g and 29.2 ± 2.8 m²/g, respectively. The specific surface area of PGX-dried EW samples with initial concentration of 1%, 6% and 12% w/w were 72.33 ± 5.53 m²/g, 50.64 ± 3.35 m²/g, 34.38 ± 4.14 m²/g, respectively. Fourier transform infrared analysis on SPI and EW powders revealed that, no modifications of the protein secondary structure were induced by PGX processing. The PGX technology is a suitable scalable technique to generate egg white protein powders with increased specific surface area without affecting the protein conformation thereby providing desirable characteristics with potential use as a carrier for bioactive delivery systems.