The use of a single controlled bead milling step of the microalga Tetraselmis suecica resulted in a soluble fraction, rich in functional proteins. This was achieved by fine-tuning the processing time, thereby exploiting the difference in rates of protein and carbohydrate release during milling. Soluble proteins were extracted under mild conditions -room temperature, no addition of chemicals, pH 6.5-, with a yield of 22.5% and a specific energy consumption of 0.6 kWh kg, which is within the recommended minimum energy for an extraction step in a biorefinery process. The resulting protein extract contained 50.4% (DW) of proteins and 26.4% carbohydrates, showed light green color and displayed superior surface activity and gelation behavior compared to whey protein isolate. The proposed process is simple (only one bead milling step), scalable, and allows the mild extraction of functional proteins, making it interesting for industrial applications in the food industry.
A mild
fractionation process to extract functional biomolecules
from green microalgae was implemented. The process includes bead milling,
centrifugation, and filtration with several membrane cut-offs. For
each fraction, the corresponding composition was measured, and the
surface activity and gelation behavior were determined. A maximum
protein yield of 12% was obtained in the supernatant after bead milling
and between 3.2 and 11.7% after filtration. Compared to whey protein
isolate, most of the algae fractions exhibited comparable or enhanced
functionality. Surface activity for air–water and oil–water
interfaces and gelation activities were notably superior for the retentate
fractions compared to the permeates. It is proposed that such functionality
in the retentates is due to the presence of hydrophobic compounds
and molecular complexes exhibiting a similar behavior as Pickering
particles. We demonstrated that excellent functionality can be obtained
with crude fractions, requiring minimum processing and, thus, constituting
an interesting option for commercial applications.
Macroalgae are a promising feedstock for several industries
due
to their large content of proteins and carbohydrates and the high
biomass productivities. A novel extraction and fractionation concept
based on ionic liquids (ILs) using Ulva lactuca as model organism is presented. Biomolecules are first extracted
by means of IL-assisted mechanical shear, followed by two-phase partitioning
or ultrafiltration in order to fractionate proteins and carbohydrates
and to recover the IL. Ethyl methyl imidazolium dibutyl phosphate
([Emim][DBP]) is strongly selective to proteins, leading to extraction
yields up to 80.4% for proteins and 30.7% for carbohydrates. The complete
process, including extraction and ultrafiltration, allowed protein
recovery of up to 64.6 and 15.4% of the carbohydrates in the retentate
phase, while a maximum of 85.7% of the IL was recovered in the permeate
phase. The native structure of the extracted proteins was preserved
during extraction and fractionation as shown by gel electrophoresis.
Selective extraction of proteins from macroalgae under non-denaturing
conditions using ILs followed by the recovery of IL using ultrafiltration
is for the first time reported. The proposed extraction–fractionation
approach is simple and can be potentially applied for the biorefinery
of macroalgae at the commercial scale.
The disintegration of three industry relevant algae (Chlorella vulgaris, Neochloris oleoabundans and Tetraselmis suecica) was studied in a lab scale bead mill at different bead sizes (0.3 mm-1 mm). Cell disintegration, proteins and carbohydrates released into the water phase followed a first order kinetics. The process is selective towards proteins over carbohydrates during early stages of milling. In general, smaller beads led to higher kinetic rates, with a minimum specific energy consumption of ≤ 0.47 kWh kgDW-1 for 0.3 mm beads. After analysis of the stress parameters (stress number and stress intensity), it appears that optimal disintegration and energy usage for all strains occurs in the 0.3-0.4 mm range. During the course of bead milling, the native structure of the marker protein Rubisco was retained, confirming the mildness of the disruption process.
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