Alternative Extraction Strategies for Recovering Proteins and Carbohydrates from Red Macroalga Gracilaria birdiae

Growing demand for alternative food sources has increased interest in macroalgae as raw materials because of their high protein and polysaccharide content. This study evaluated extraction strategies for recovering total soluble protein (TSP) and total soluble carbohydrate (TSC) from the red macroalga Gracilaria birdiae, considering particle size and comparing water-based extraction with ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) under the specific operating conditions evaluated. Particle size influenced the recovery of soluble compounds, while thermal treatments achieved higher yields than ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) under the specific operating conditions evaluated. TSP reached 19.21 mg/g with autoclave-assisted extraction (AAE), whereas TSC reached 114.14 mg/g with heat-assisted extraction (HAE). Sequential extraction showed potential for biomass reuse, with pretreatment affecting TSP and TSC recovery differently. The enzyme-assisted extraction (EAE) protocol involving cellulase resulted in the highest observed TSP and TSC yields among the conditions tested, achieving 101.09 mg/g TSP and 193.60 mg/g TSC at low biomass loading (3 g, 1:67 w/v). However, extraction efficiency decreased at higher biomass loading (7 g, 1:29 w/v), even when comparing assays at an equivalent enzyme dosage (~48 IU/g biomass). Nevertheless, the specific contribution of cellulase still needs investigation. Functional characterization of the polysaccharide-rich precipitated fraction showed a water-holding capacity of 18.18 g/g, water solubility of 44.74%, oil-holding capacity of 2.14 g/g, and limited emulsifying and foaming performance. Overall, these findings highlight the potential of G. birdiae as a source of protein- and carbohydrate-rich materials for further investigation in food applications.