Baoyan Gao

Preliminary Characterization, Antioxidant Properties and Production of Chrysolaminarin from Marine Diatom Odontella aurita

A new chrysolaminarin, named CL2, with a molecular mass of 7.75 kDa, was purified from the marine diatom, Odontella aurita, using DEAE-52 cellulose anion-exchange chromatography and Sephadex G-200 gel-filtration chromatography. The monosaccharide and structural analysis revealed that CL2 was a glucan mainly composed of glucose, which was linked by the β-d-(1→3) (main chain) and β-d-(1→6) (side chain) glycosidic bond, demonstrated by infrared spectroscopy (IR) and nuclear magnetic resonance (NMR). The antioxidant activity tests revealed that the CL2 presented stronger hydroxyl radical scavenging activity with increasing concentrations, but less was effective on reducing power analysis and scavenging 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The influences of nitrogen concentration and light intensity on chrysolaminarin production of O. aurita were further investigated in a glass column photobioreactor, and a record high chrysolaminarin productivity of 306 mg L−1 day−1 was achieved. In conclusion, the chrysolaminarin CL2 from O. aurita may be explored as a natural antioxidant agent for application in aquaculture, food and pharmaceutical areas.

Effective flocculation of target microalgae with self-flocculating microalgae induced by pH decrease.

A flocculation method was developed to harvest target microalgae with self-flocculating microalgae induced by decreasing pH to just below isoelectric point. The flocculation efficiencies of target microalgae were much higher than those flocculated only via pH decrease. The mechanism could be that negatively charged self-flocculating microalgal cells became positively charged during pH decrease, subsequently attracted negatively charged target microalgae cells to form flocs and settled down due to gravity. Microalgal biomass concentration and released polysaccharide (RPS) from target microalgae influenced flocculation efficiencies, while multivalent metal ions in growth medium could not. Furthermore, neutralizing pH and then supplementing nutrients allowed flocculated medium to be recycled for cultivation. Finally, Spearmans Rank Correlation Coefficients (Rs) between flocculation efficiency and key factors were also investigated. These results suggest that this method is effective, simple to operate and allows the reuse of flocculated medium, thereby contributing to the economic production from microalgae to biodiesel.

Co-production of lipids, eicosapentaenoic acid, fucoxanthin, and chrysolaminarin by Phaeodactylum tricornutum cultured in a flat-plate photobioreactor under varying nitrogen conditions

The marine diatom Phaeodactylum tricornutum is a polymorphological, ecologically significant, and well-studied model of unicellular microalga. This diatom can accumulate diverse important metabolites. Herein, we cultured P. tricornutum in an internally installed tie-piece flat-plate photobioreactor under 14.5 m mol L−1 (high nitrogen, HN) and 2.9 m mol L−1 (low nitrogen, LN) of KNO3 and assessed its time-resolved changes in biochemical compositions. The results showed that HN was inductive to accumulate high biomass (4.1 g L−1). However, the LN condition could accelerate lipid accumulation in P. tricornutum. The maximum total lipid (TL) content under LN was up to 42.5% of biomass on day 12. Finally, neutral lipids (NLs) were 63.8% and 75.7% of TLs under HN and LN, respectively. The content of EPA ranged from 2.3% to 1.5% of dry weight during the growth period under the two culture conditions. Peak volumetric lipid productivity of 128.4 mg L−1d−1 was achieved in the HN group (on day 9). The highest volumetric productivity values of EPA, chrysolaminarin, and fucoxanthin were obtained in the exponential phase (on day 6) under HN, which were 9.6, 93.6, and 4.7 mg L−1d−1, respectively. In conclusion, extractable amounts of lipids, EPA, fucoxanthin, and chrysolaminarin could be obtained from P. tricornutum by regulating the culture conditions.

Optimum Production Conditions, Purification, Identification, and Antioxidant Activity of Violaxanthin from Microalga Eustigmatos cf. polyphem (Eustigmatophyceae)

Violaxanthin is a major xanthophyll pigment in the microalga Eustigmatos cf. polyphem, but the amount produced after propagation can vary depending upon culture conditions. In this study, the effects of cultivation time, nitrogen concentration, light intensity, and culture mode on violaxanthin production were investigated. The results showed that this microalga vigorously grew and maintained a high level of violaxanthin in the fed-batch culture, and the highest violaxanthin productivity of 1.10 ± 0.03 mg L−1 d−1 was obtained under low light illumination with 18 mM of initial nitrogen supply for ten days. Additionally, violaxanthin was purified from E. cf. polyphem by silica gel chromatography and preparative high-performance liquid chromatography (PHPLC), and identified with high-resolution mass spectrometry (HRMS). The antioxidant activity of the purified violaxanthin was evaluated by three tests in vitro: reducing power assay, 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2-azobis-3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical assays. The strongest inhibition of purified violaxanthin occurred during the scavenging of ABTS+ radicals, with EC50 of 15.25 μg mL−1. In conclusion, this is the first report to investigate the effects of different culture conditions on violaxanthin accumulation in E. cf. polyphem and provide a novel source for the production of violaxanthin that can be used for food and pharmaceutical applications.

Evaluation of oleaginous eustigmatophycean microalgae as potential biorefinery feedstock for the production of palmitoleic acid and biodiesel

This study aimed to evaluate the potential of six oleaginous eustigmatophytes for use as biorefinery feedstock for the co-production of palmitoleic acid (PA) and biodiesel under different initial nitrogen concentrations (INCs). Six eustigmatophytes were studied, the nitrogen deficiency strategy significantly stimulated the simultaneous hyper-accumulation of PA and lipids, and led to a desirable fatty acid profile (FAP), except in Vacuoliviride sp. and Nannochloropsis oculata. Particularly, Eustigmatos cf. polyphem exhibited great potential when supplied with 1 mM INC and yielded the highest PA (29.71% of dry weight (DW)) and lipid (72.01% of DW) contents, as their productivities increased to 96.26 and 232.79 mg/L/d, respectively. Furthermore, neutral lipids accounted for 91.82% of the total lipids and were rich in PA, and the favourable FAPs of C16-C18 (87.95%) and monounsaturated FAs (70.10%) ensured good biodiesel properties including the cetane number (55.69) and iodine value (92.81 gI2/100 g), and all met the standard requirements.