| Due to the complex growth environment, most marine microalgae could produce bioactive metabolites during their growth and metabolism process, and many of these substances have been demonstrated to possess interesting biological activities. The research on microalgaes and its metabolites is becoming hot topic around the world in recent years. In this thesis,15microalgaes strains separated from the Hainan tropical natural water were tested the antibacterial activity and antioxidant activity, and identification was performed for part of algal species with stronger activities. Whereafter, the cultivation conditions and cells harvesting with flocculants, its nutrients, chemical composition and biological activity of the target microalgae were investigated.The results showed that five microalgal strains had stronger antibacterial activities, and five microalgae strains had better antioxidant activities. Four species presentied stronger antibacterial activity and antioxidant activity were identified by morphological observation and molecular classification as Chlorella sp. C14, Chlorella sorokiniana C74, Scenedesmus armatus C79and Chlorella sp. SY01, respectively.The effects of different culture media, nitrogen source, concentrations of nitrogen and concentrations of phosphorus on growth and intracellular nutrients of microalgae C. sorokiniana C74were investigated by the bath cultivation. TAP and BBM were more conducive to the accumulation of biomass, while BG-11Medium was suit for the polysaccharide accumulation. The best nitrogen source based on BBM for the test strains was glycine, with which the biomass, content of lipid, protein and polysaccharose were higher than other nitrogen sources. The best concentration of glycine was13.33mmol·L-1. The lower concentration would not conducive to produce more biomass and the lipid, protein content accumulation. Different phosphorus concentration had no significant difference on growth and nutrients accumulation of C. sorokiniana C74based on BBM. The optimum concentration of phosphorus was1.72mmol·L-1.Three kinds of flocculants were investigated for harvesting cells of C. sorokiniana C74. The results showed that chitosan was the best one among the tested flocculant, due to less dosage, and non-damaging effects on the cell integrity.Determination of C. sorokiniana C74nutrients, the results showed that C. sorokiniana C74contains kinds of nutrients, crude protein, carbohydrates, fat, ash, crude fiber and pigment was accounted for20.4%,34.28%,22.16%,12.20%,20.22%and4.50%by algae powder dry weight respectively. Fatty acid analysis showed that algae powder contains a variety of unsaturated fatty acids, and linoleic acid and linolenic acid contents were22.73%and14.87%; Contents of amino acid in C. sorokiniana C74was17.50%, of which the essential amino acids was6.17%. Through essential amino acid index evaluation, indicating that C. sorokiniana C74is an excellent source of protein; C. sorokiniana C74was rich in vitamins, especially vitamin B1, B3and B6; Algae powder contains a variety of trace mineral elements, and potassium, magnesium, calcium, iron and zinc was higher, the heavy metal lead, mercury, arsenic and cadmium was no more than the national standard.To study the chemical constituents from the petroleum ether extract of C. sorokiniana by silica gel column chromatography, Sephadex LH-20chromatography and recrystallization method, and seven compounds were isolated. The compounds were identified as:(22E,24R)-5α,8α-epidioxiergosta-6,22-dien-3β-ol (1),(24S)-ergosta-7-en-3β-ol (2), loliolide (3), stigmasta-7,22-dien-3(3,5α,6α-triol (4),3β-hydroxy-5α,6α-epoxy-7-megastigmen-9-one (5), Dipropyl phthalate (6), and isololiolide (7). The main liposoluble constituents from C. sorokiniana C74were esters of fatty acids, alkyl acids and olefine acids, and components1-7were isolated from the C. sorokiniana for the first time.The antibacterial and antioxidant activity of the extracts of petroleum ether, ethyl acetate, n-butanol, water phase and some of the compounds from C. sorokiniana C74were studied. The results showed that the crude extract of petroleum ether and ethyl acetate from C. sorokiniana C74was showed stronger antibacterial activity, and the DPPH radical scavenging of C.s-EtOAc showed the best antioxidant effect, followed by C.s-MSO. Compounds1and5showed antibacterial activity to the tested bacteria, and both have some antioxidant activity. |
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