Title:Nutritional Evaluation of Whole and Lipid-Extracted Biomass of the Microalga Scenedesmus sp. AMDD Isolated in Saskatchewan, Canada for Animal Feeds: Proximate, Amino Acid, Fatty Acid, Carotenoid and Elemental Composition
VOLUME: 4 ISSUE: 4
Author(s):Sean M. Tibbetts, Ronald J. Melanson, Kyoung C. Park, Arjun H. Banskota, Roumiana Stefanova and Patrick J. McGinn
Affiliation:National Research Council of Canada, Aquatic and Crop Resource Development, 1411 Oxford Street, Halifax, Nova Scotia, B3H 3Z1, Canada.
Keywords:Amino acids, carotenoids, composition, fatty acids, microalgae, minerals, proximate.
Abstract:Background: While a major driver for technological innovation, microalgae-based biofuels remain
economically non-viable. However, as microalgae cultivation continues to scale-up to industrial production
levels, algal biorefinery strategies must emerge in order to effectively valorize the biomass (crop) and help
stabilize the economic viability of a microalgae-based industry. Of the numerous potential markets for
microalgae (co) products, the animal nutrition and aquaculture sectors may be highly promising areas to
focus for generating revenues. The aim of this paper was to generate novel primary chemical and
biochemical composition data on whole and lipid-extracted algal biomass produced from a proprietary
freshwater strain of Scenedesmus sp. AMDD.
Methods: Scenedesmus sp. AMDD biomass was produced in a ‘Brite-Box’ photobioreactor and half was
lipid-extracted by automated Soxhlet solvent extraction. Using established and new methods, both fractions were characterized
for their chemical and biochemical composition including proximate, amino acid, fatty acid, carotenoid and elemental
composition. The data are discussed with an emphasis towards their application to terrestrial livestock and aquaculture feeds.
Results: Under the particular cultivation conditions employed in this study, Scenedesmus sp. AMDD had a growth rate of 0.8±0.1
d-1, biomass production of 0.4±0.0 g DW L-1 and daily productivity of 40.0±2.9 mg DW L-1 d-1. On a DW basis, whole algal
biomass (WAB) contained low ash (3%), moderate protein (32-35%), esterifiable lipid (11-13%) and starch (8-9%), high total
carbohydrate (35-38%), fibre (26-29%) and energy (23 MJ kg-1). Lipid-extracted biomass (LEB) contained higher protein (40-
44%), total carbohydrate (40-48%), starch (10-12%) and fibre (30-35%) and lower residual esterifiable lipid (<1%) and energy
(20 MJ kg-1). Scenedesmus sp. AMDD protein had favorable amino acid profiles with high essential amino acid indices (0.9-1.0);
was rich in first-limiting essential amino acids lysine (1.8-2.3%), methionine (0.7-1.0%) and tryptophan (0.2-0.7%). Algal lipid
(% of total fatty acids) was predominantly composed of polyunsaturated fatty acids (PUFA, 45-52%), high in monounsaturated
fatty acids (MUFA, 31-38%) and low in saturated fatty acids (SFA, 16%). Scenedesmus sp. AMDD lipid was particularly rich in
α-linolenic acid (18:3n-3; 18-23%), total n-3 PUFA (30-38%) and lower in total n-6 PUFA (13-15%); which resulted in attractive
n-3:n-6 ratios (2-3:1). Scenedesmus sp. AMDD biomass was rich in potassium (0.6-0.7%), phosphorous (0.5-0.7%), iron (1081-
1777 mg kg-1) and lutein (0.3% [WAB only]) and was virtually absent of contaminating heavy metals. A species-specific
nitrogen-to-protein conversion factor of N×5.55 was validated for use with Scenedesmus sp. AMDD harvested during
exponential growth phase.
Conclusion: Due to its relatively high contents of protein (32-44%) and carbohydrate (35-48%), Scenedesmus sp. AMDD
biomass could be considered a protein-rich algal meal with a market value similar to those produced from terrestrial oilseed crops
such as soy, canola and corn. However, the carbohydrate fraction contained low levels of starch (23-26% of total carbohydrate)
and a high proportion of fibre (74-77% of total carbohydrate). As a result, relatively unprocessed Scenedesmus sp. AMDD
biomass may not be well digested by monogastric animals and may be better suited for ruminant animals that have a higher
capacity for digestion of cellulosic materials. In order to enter the higher-value monogastric animal feed sector, the biomass
would likely need to be upgraded to produce algal protein concentrates (APCs) with higher protein levels, concomitant with
reduced total carbohydrate and fibre levels. In vitro investigations are currently underway to evaluate Scenedesmus sp. AMDD
biomass for nutrient digestibility, metabolizable energy content, ruminal gas production, enteric methane abatement potential,
ruminal fatty acid biohydrogenation and assessment for potential consumption risk by monogastric and ruminant animals.
