Biological and Agricultural Engineering Department, North Carolina State University, Raleigh, NC 27695, USA

Biograph
Dr. WENQIAO (Wayne) YUAN is currently a professor and University Faculty Scholar in the Biological and Agricultural Engineering Department at North Carolina State University (NCSU), U.S.A. Dr. Yuan previously was an assistant/associate professor at Kansas State University for five years. He has made outstanding contributions to the field of biofuels and bioproducts development, and is the recipient of many prestigious awards and honor, such as the Alexander von Humboldt Research Fellowship, the U.S. National Science Foundation CAREER award, NCSU University Faculty Scholar, the American Society of Agricultural and Biological Engineers New Holland Young Researcher Award, Rain Bird Engineering Concept of the Year Award, Graduate Research Award, Superior Paper Award, and Scholarly Achievement Award etc.

Speech Title: Antioxidant Production from Marine Brown Algae

Abstract: Bioactive compounds of marine organisms have gained attention because of their various bioactivities and abundance in ecosystems. Among these organisms, marine brown algae are a potential source of bioactive compounds such as phlorotannins, polysaccharides, unsaturated fatty acids, and proteins. Phlorotannins are polyphenolic compounds that are only found in brown algae and are known for various bioactivities, e.g., antioxidant, antimicrobial, anticancer, anti-diabetes, anti-HIV, etc. Thus they have a great potential to be applied as medicines or nutraceuticals.

Two solvent-extraction methods were utilized to obtain soluble phlorotannins (SPs) from five edible brown algae species Ascophyllum nodosum, Fucus vesiculosus, Alaria esculenta, Laminaria digitata, and Saccharina latissima. The leftover algae powder was then treated with sodium hydroxide to release the membrance-bound phlorotannins (MPs). Folin-Ciocalteu method using phloroglucinol (1,3,5-benzenetriol) as the standard was applied to quantify SP and MP contents. MP samples were further purified with solvents to obtain the extracted MP (eMP). F. vesiculosus and A. nodosum showed the highest SP content (4.66 and 4.90 mg/g algae, respectively) by the first extraction method. The highest MP content was observed in A. nodosum (68.55 mg/g algae) followed by F. vesiculosus (62.58 mg/g algae). For every algal species tested, the content of MP was greater than eMP, suggesting the great potential for harvesting value-added products from the leftover algae powder after SP extraction. The two algal species were then extracted by the second extraction method. SP yields from A. nodosum and F. vesiculosus were 6.59 and 3.07 mg/g algae, respectively. Method 1 was better on F. vesiculosus but method 2 was better on A. nodosum in terms of SP yield, indicating that the effectiveness of extraction methods was algal species dependent.

The DPPH radical scavenging activity was applied to evaluate the antioxidant activity of phlorotanins. The yields and antioxidant activity of F. vesiculosus (yield = 14.83 mg-extract/g-algae, IC₅₀ = 0.0038 mg/ml) and A. nodosum (yield = 12.80 mg-extract/g-algae, IC₅₀ = 0.0072 mg/ml) were the highest among the five algae species. Moreover, the SP, MP and eMP extracts of F. vesiculosus and A. nodosum showed equal or higher DPPH radical scavenging activity than commercial antioxidants butylated hydroxytoluene (IC₅₀ = 0.051 mg/ml) and ascorbic acid (IC₅₀ = 0.0063 mg/ml). Different extraction processes also showed effects on the antioxidant activity of the phlorotannin extracts.