Water-soluble and alkali-soluble protein concentrates from Chaetomorpha sp.: chemical composition and functional properties
Abstract
This study was aimed to evaluate the proximate composition and functional properties of algae protein concentrate (APC) derived from brackish algae Chaetomorpha sp. and compare them with those of soy protein concentrate (SPC). Two APC fractions, watersoluble (APC-W) and alkali-soluble (APC-A), were sequentially extracted using cellulase with phosphate buffer and 0.1M NaOH. The extracted proteins were precipitated with ammonium sulfate, desalted by dialysis, and freeze-dried to a moisture content below 12% w/w. Their chemical composition, amino acid profile (analyzed by HPLC), microstructure (examined using scanning electron microscopy, SEM), and functional properties were evaluated. Results showed that APC-W and APC-A had protein contents of 72.8±1.26% and 76.3±0.41%, respectively, comparable to SPC (73.2±0.98%), with a high and wellbalanced essential amino acid (EAA) profile. SEM images revealed a porous microstructure in APC-A and a sheet-like, less porous microstructure in APC-W. APC-W had a higher content of hydrophilic amino acids (serine, tyrosine, cysteine, proline) and greater solubility at pH 7 (49.92±1.79%) compared to APC-A (41.23±1.12%) and SPC (22.81±1.57%). APC-A exhibited water absorption capacities 1.43 and 1.17 times lower than APC-W and SPC, respectively. Both APCs demonstrated stronger gelation ability, with a minimum gelation concentration of 10%, compared to SPC. Rich in hydrophobic amino acids (valine, alanine, leucine, isoleucine), APC-A exhibited superior foaming and emulsifying properties, with foam stability (90.0±2.0%), emulsifying activity index (75.7±0.90 m²/g), and emulsion stability index (45.1±1.02 min), which were 1.15–1.2, 1.13–1.4, and 1.3–2.86 times higher than those of APC-W and SPC, respectively. Thus, both APC fractions exhibited certain functional properties that were superior to those of conventional plant-based SPC, highlighting their potential for food applications.