Within the parent protein molecule, most peptides are inactive, and they are released with biofunctionalities after enzymatic hydrolysis. Marine algae have high protein content, up to 47% of the dry weight, depending on the season and the species. Recently, there is an increasing interest in using marine algae protein as a source of bioactive peptides due to their health promotion and disease therapy potentials. This review presents an overview of marine algae-derived bioactive peptides and especially highlights some key issues, such as in silico proteolysis and quantitative structure-activity relationship studies, in vivo fate of bioactive peptides, and novel technologies in bioactive peptides studies and production.

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Spirulina platensis is a blue-green algae with potential anti-obesity effects. In this study, the anti-obesity effects of whole Spirulina platensis (WSP), Spirulina platensis protein (SPP) and Spirulina platensis protein hydrolysate (SPPH) were compared in high-fat diet fed mice, and the potential acting mechanism of SPPH was also investigated. Totally, SPPH exhibited good anti-obesity effects (reducing 39.8%±9.7% of body weight), lowering 23.8%±1.6% of serum glucose, decreasing 20.8%±1.4% of total cholesterol, while positive drug Simvastatin had the corresponding values: 8.3%±4.6%, 24.8%±1.9% and -2.1%±0.2%, respectively. Subsequently, PCR array was used to conduct gene expression analysis in brain and liver tissues of SPPH-treated mice, which displayed distinctly different expression pattern. The most markedly changed genes included: Acadm (-34.7 fold), Gcg (2.5 fold), Adra2b (2 fold) and Ghsr (2 fold) in brain; Retn (39 fold), Fabp4 (15.5 fold), Ppard (6 fold) and Slc27a1 (5.4 fold) in liver. Further network analysis demonstrated that the significantly expressed genes in brain and liver tissues were mapped into an interacting network, suggesting a modulatory effect on brain-liver axis, major pathways were involved in the axis: PPAR, adipocytokine, AMPK, non-alcoholic fatty liver disease and MAPK. This study showed that Spirulina platensis protein hydrolysate possessed anti-obesity effect in mice.

The total flavonoids from Hemerocallis citrina baroni are regarded as a green and natural health care product with many beneficial impacts on human health. In this study, ultrasound-synergized electrostatic field extraction (UEE) of the total flavonoids (TF) from H. citrina was investigated. Significant independent variables of the extraction, including the electrostatic field, ultrasonic power, ethanol concentration and extraction time, were optimized using the Box-Behnken (BB) method, and the optimal extraction conditions were obtained by response surface methodology (RSM). The extraction yield using UEE was compared with the yields obtained using only ultrasound extraction (UE) and water bath extraction (WE), using a UV-vis spectrophotometer. The best extraction yield of 1.536% using UEE was achieved under the following optimal conditions: electrostatic field of 7kV, ultrasonic power of 500W, ethanol concentration of 70% and extraction time of 20min. The optimal solid-liquid ratio (1:25g/mL) and extraction temperature (55°C) were determined by single factor experiments. Compared to other extraction methods, UEE not only increases the extraction yield of TF but also exhibits an excellent antioxidant activity in assays of the scavenging capacity for DPPH, hydroxyl and superoxide anion radicals. The availability of the UEE method can be supported by the ultrasonic cavitation effect, which plays the most important role in the UEE method. The electrostatic field can be regarded as a random disturbance for sonication, which can strengthen the cavitation effect and increase the cavitation yield. Moreover, the amount of iodine release in potassium iodide solution well validated the synergetic effect between the ultrasound and electrostatic field.