Valorization of some microalgae from different aquatic environments for animal feed and other applications

Abstract

This study focused on the isolation, purification, morphology, and molecular characterization of local microalgae species and studied their growth in culture media at different salinity levels. In addition, qualitative and quantitative analyses of their polyphenolic compounds with some biological activities (antioxidants and antimicrobials) were performed. The isolated microalgae species and yeast were used as feed for Artemia (Artemia franciscana) and Daphnia magna to study their effect on their growth. Three species, Chlorella sp. CHL11, Chlorella sp. CHL15, and Limnospira fusiformis TL03, have been isolated, purified, identified, and deposited in the NCBI, with accession numbers of MZ970329, ON799438.1, and ON799439.1, respectively. The results of the growth evolution, chlorophyll a, chlorophyll b, and carotenoid contents of the three species at different salinity levels showed their tolerance to different salinity concentrations, and their growth was inversely proportional to the increase in salinity. The polyphenol and flavonoid contents of the hydromethanolic extracts showed that the three algal extracts were rich in polyphenols and flavonoids, with higher amounts of total phenolic content (18.41±0.32 mg GEA/g) recorded in L fusiformis TL03 and higher total flavonoid content (3.59±0.06 mg QE/g DW) in Chlorella sp. CHL11. High-performance liquid chromatography (HPLC) analysis of the hydromethanolic extracts revealed the presence of different classes of phenolic compounds (phenolic acid, flavanols, flavanones, hydroxy-flavones, flavonols, and flavones). Regarding the biological activity part, the results of antioxidant activities evaluated by DPPH radical scavenging activity and beta-carotene bleaching activity showed that the highest percentages of DPPH inhibition (86.19 ± 1.61%) and beta-carotene bleaching (60.35 ± 1.10%) were recorded in L. fusiformis TL03. The results of the antibacterial activity of the crude hydromethanolic extract against six strains of pathogenic bacteria (Bacillus subtilis, Staphylococcus aureus, Listeria monocytogenes, Escherichia coli, Pseudomonas aeruginosa, and Klebseilla pneumoniae) showed that all the extracts had strong activity against B subtilis and S. aureus, with different effects recorded against other bacteria. The results of Artemia feeding during 12 days ,showed that, the highest values for body length(5030.13 ± 189.82 ìm) and survival rate(78.33 ±0.88% ) were registred in Artemia fed on L. fusiformis TL03. For the Daphnia magna feeding trial lasting two weeks, the highest body length values (2997.63 ± 60.04 ìm) were recorded in those fed on Chlorella sp. CHL15, and the highest survival rate (67 ± 1.15%) was recorded in Chlorella sp. CHL11.