| Abstract | Proximate, amino acid and elemental composition, total phenolic content (TPC), and in vitro protein digestibility (IVPD) of microalgal biomass were determined. Microalgae contained low to moderate ash (5–17 %), moderate to high carbohydrate (18–46 %), crude protein (18–46 %), high crude lipid (12–48 %), and energy (19–27 MJ kg−1). Characteristic of microalgae, non-essential amino acids (AAs), aspartic and glutamic acids, were predominant (20–30 % of protein; 8–12 % of dry weight). Microalgae had favorable essential AA profiles with high essential amino acid (EAA) indices (0.9–1.2). Expressed as g EAA 100 g protein−1, Porphyridium aerugineum was rich in leucine (11.9), lysine (8.0), arginine (8.6), and tryptophan (3.3); Nannochloropsis granulata (A) in leucine (11.0), lysine (8.5), and tryptophan (2.8); Tetraselmis chuii and Botryococcus braunii in arginine (9.4 and 20.5, respectively); and Phaeodactylum tricornutum in lysine (6.4) and tryptophan (2.6). Mineral compositions (%) were calcium (0.1–3.0), magnesium (0.3–0.7), phosphorous (0.7–1.5), potassium (0.7–2.4), sodium (0.8–2.7), and sulfur (0.4–1.4), and trace element compositions (mg kg−1) were copper (18–102), iron (1,395–11,101), manganese (45–454), selenium (0–0.5), and zinc (28–64). Microalgae contained low TPC (6–13 mg gallic acid equivalents (GAE) g−1 DW), except T. chuii (20 mg GAE g−1 DW). IVPD was high (>90 %) for B. braunii (A), P. aerugineum, and lipid-extracted N. granulata (B); mid-range (80–89 %) for P. tricornutum, N. granulata (A), B. braunii (B), Neochloris oleoabundans, T. chuii, and whole N. granulata (B); and lower (<80 %) for Acutodesmus dimorphus. Microalgal species P. tricornutum, B. braunii, N. granulata, and T. chuii had high protein (40–52 %), IVPD (82–97 %), and digestible protein (35–50 %), comparable to plant proteins used in animal feeds and aquaculture. |
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