Variability in nutrient composition and in vitro crude protein digestibility of 16 microalgae products

The chemical composition of 16 microalgae products of four genera, Arthrospira (n=2), Chlorella (n=8), Nannochloropsis (n=4) and Phaeodactylum (n=2), was assayed to evaluate the intra- and inter-genera variation of nutrient profiles of commercial microalgae products. Crude protein was the main component in all genera, followed by ether extract and crude ash. Mean crude protein concentrations were 690, 502, 431 and 446g/kg dry matter, and mean ether extract concentrations were 63, 157, 188 and 113g/kg dry matter for Arthrospira, Chlorella, Nannochloropsis and Phaeodactylum respectively. However, there was considerable inter- and intra-genera variation. The concentration of -linked glucose was low (0-143g/kg dry matter). There was high variation between and within genera in the crude ash concentration (22-237g/kg dry matter), which was also observed for the mineral composition. In contrast to the crude protein concentration, the amino acid composition of the protein (g amino acid/16g N) was less variable. The investigated samples possessed high concentrations of Glx, Asx and Leu, and low concentrations of Cys and Met. The mean concentration of non-protein nitrogen compounds was highest in Phaeodactylum (110g/kg dry matter) and lowest in Nannochloropsis (47g/kg dry matter) products, and as with proximate nutrients, high variability between and within genera was observed. In vitro crude protein digestibility varied between 54% (non-cell-disrupted Nannochloropsis) and 84% (cell-disrupted Chlorella). Inositol phosphate isomers were not detectable in any sample (concentration <1mol/g dry matter). The predominant fatty acids were C16:0 in Arthrospira products, C18:2 n-6+ C19:1 t7 and C18:3 n-3 in Chlorella products, and C20:5 n-3 in Nannochloropsis and Phaeodactylum products; however, the relative proportions of fatty acids varied within genera. Commercially available microalgae products appear to be valuable alternative food and feed products. However, because of the high variability in nutrient profiles, attention should be given to the analytical characterization of the products.