Chemical composition and nutritional properties of freshwater and marine microalgal biomass cultured in photobioreactors

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.