Sanderson, Philip John (2018) Evaluation of biomass from the halotolerant microalga Dunaliella salina as an animal feed additive with immune-modulatory activity. PhD thesis, University of Greenwich.

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Abstract

The work presented in this thesis sought to evaluate the potential of microalgal biomass sourced from Dunaliella salina for use as an animal feed additive. Dunaliella salina is the richest known source of carotenoid pigments and anti-oxidants, and these have a variety of uses including as food colourants, additives for cosmetics, and nutritional or health supplements for veterinary and human use. The total global market of carotenoids from all sources is ~$1.5 billion, 10 % of which is β-carotene from algae, and this is growing at ~4 % p.a.

Supercritical CO2 extraction of high-value carotenoids yields a solvent-free defatted powder. This material was sourced from biomass cultivated across different seasons from two different cultivation sites, namely a coastal Mediterranean site, which used seawater and pressurised CO2 for cultivation, and an inland site, which used underground mined solution salt and flue gas for CO2. Each was home to different strains of D. salina. Biomass at both sites was harvested with either a disc-stack or spiral-plate centrifuge and batches were analysed for their nutritional content both before and after extraction of lipids and carotenoids with supercritical CO2.

Ash, protein and lipid contents varied significantly between batches of D. salina biomass harvested across different seasons but not glycerol, carbohydrate or carotenoid contents. Variability in batch composition between sites was only significant for ash, glycerol and carotenoid content.

Powders harvested using a disc-stack centrifuge were found to contain a full complement of essential amino acids. Heavy metals present were found to be below the maximum permitted levels for foodstuffs. The presence of residual carotenoids (0.42 ± 0.012 % AFDW), starch (54.13 ± 0.81 % AFDW) and long-chain polyunsaturated fatty acids (LCPUFAs) such as α-linolenic acid (11.54 % of total fatty acids) provide additional nutritional value. Poultry feeds were formulated at additive level (0.01 - 0.5 %) and ingredient level (1 – 20 %). Data from analysis of the formulated diets were compared to industry recommendations and found to meet the nutritional requirements of poultry with no significant difference between their nutritional profiles.

In an in-vivo study (1180 chicks) chicks supplied with up to 0.1 % defatted D. salina algal biomass as a feed additive displayed a significantly improved feed conversion ratio and gained significantly more weight compared to those fed without the algal additive. However, chicks that were supplied with more than 1 % defatted D. salina algal biomass i.e. as a feed ingredient, performed less well compared to those fed without algal supplements.

Preliminary bioactivity analysis showed antioxidant activity in lipid extracts that had been prepared from defatted material using methyl-tert-butyl-ether and methanol. Galactolipids which may have bioactivity, were also detected. Antibacterial effects were not observed, although these cannot yet be ruled out.

Item Type:	Thesis (PhD)
Uncontrolled Keywords:	Dunaliella salina; biochemistry; microalgae;
Subjects:	Q Science > QK Botany
Faculty / School / Research Centre / Research Group:	Faculty of Education, Health & Human Sciences Faculty of Education, Health & Human Sciences > School of Human Sciences (HUM)
Last Modified:	09 Oct 2021 04:45
URI:	http://gala.gre.ac.uk/id/eprint/24801

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