Optimized Degradation and Inhibition of α-glucosidase Activity by Gracilaria lemaneiformis Polysaccharide and Its Production In Vitro

Gracilaria lemaneiformis polysaccharide (GLP) exhibits good physiological activities, and it is more beneficial as it is degraded. After its degradation by hydrogen peroxide combined with vitamin C (H2O2-Vc) and optimized by Box–Behnken Design (BBD), a new product of GLP-HV will be generated. While using GLP as control, two products of GLP-H (H2O2-treated) and GLP-V (Vc-treated) were also produced. These products chemical characteristics (total sugar content, molecular weight, monosaccharide composition, UV spectrum, morphological structure, and hypolipidemic activity in vitro) were assessed. The results showed that the optimal conditions for H2O2-Vc degradation were as follows: H2O2-Vc concentration was 18.7 mM, reaction time was 0.5 h, and reaction temperature was 56 °C. The total sugar content of GLP and its degradation products (GLP-HV, GLP-H and GLP-V) were more than 97%, and their monosaccharides are mainly glucose and galactose. The SEM analysis demonstrated that H2O2-Vc made the structure loose and broken. Moreover, GLP, GLP-HV, GLP-H, and GLP-V had significantly inhibition effect on α-glucosidase, and their IC50 value were 3.957, 0.265, 1.651, and 1.923 mg/mL, respectively. GLP-HV had the best inhibition effect on α-glucosidase in a dose-dependent manner, which was the mixed type of competitive and non-competitive. It had a certain quenching effect on fluorescence of α-glucosidase, which may be dynamic quenching.

Experimental Study of the Environmental Effects of Summertime Cocultures of Seaweed Gracilaria lemaneiformis (Rhodophyta) and Japanese Scallop Patinopecten yessoensis in Sanggou Bay, China

The shellfish–algae mode of integrated multitrophic aquaculture (IMTA) is a sustainable aquaculture method that benefits the environment and the carbon cycle. However, most current shellfish–algae aquaculture modes are based on the expansion of kelp aquaculture. Due to the low tolerance of kelp to high temperatures, integrated shellfish–algae aquaculture areas often become shellfish monocultures in summer, which may lead to both high mortality rate of shellfish and to economic loss while causing serious environmental harm via eutrophication, decreases in dissolved oxygen (DO), and decreases in pH. In this study, we investigated the effects of different ratios of seaweed (Gracilaria lemaneiformis), which is tolerant of high temperatures, to Japanese scallop (Patinopecten yessoensis) on water quality and environmental parameters. A two-day small-scale enclosure water body experiment was conducted in Sanggou Bay (Shandong, China) in August 2019. The results demonstrated that culturing shellfish alone significantly affected pH, DO, eutrophication, and other environmental indicators, as well as the carbonate system. The negative environmental impact of the shellfish–algae aquaculture system was much smaller. However, too high a proportion of algae might consume excessive amounts of dissolved inorganic nitrogen (DIN) and nutrients, while too low a proportion of algae might not fully absorb the nutrients released by the cultured shellfish, in turn leading to an increased risk of eutrophication. The shellfish–algae aquaculture system not only improved the inorganic carbon system, but also the organic carbon system. At the end of the experiment, all the parameters of the inorganic carbon system had decreased significantly, while all the parameters of the organic carbon system had increased significantly. The results of this study illustrate the need to include macroalgae rotations in summer, and that an appropriate ratio of shellfish to algae is necessary to achieve a sustainable aquaculture system. Moreover, this research has also confirmed the importance of the future and related research in the actual production, which will provide useful information to guide governmental strategies for summer aquaculture rotations and insight into the controversy concerning whether aquaculture is a carbon source or sink.

The Biological-promoting Function of Dietary Nano-selenium, Seaweed Gracilaria Lemaneiformis and Nano-selenium-enriched Gracilaria Lemaneiformis on Growth Performance, Antioxidant and Immunity Systems and Meat Quality of Grouper (Epinephelus Coioides)

Background: Nano-Se-enriched Gracilaria lemaneiformis (G. lemaneiformis) as feed ingredient on aquatic animals remained largely unknown. Feeding experiment was conducted for a total of 45 days to research the biological impacts of nano-selenium (Nano-Se) (group N), G. lemaneiformis (group G) and Nano-Se-enriched G. lemaneiformis (group NG) on growth, selenium concentration, oxidation, immunity and nutrition of Epinephelus coioides.Results: At each tested time point, the weight gain rate, specific growth rate and feed conversion rate of group N, group G and group NG were significantly increased in contrast to those of the control group (group C). A remarkable increase of the hepatosomatic index (HSI) and viscerosomatic index (VSI) was observed in group N and group NG. The activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) of fish in group N, group G and group NG were significantly enhanced relative to those in group C. The immune system was also activated by showing an elevated expression level of various immunological genes including Immunoglobulin M, tumor necrosis factor-α and Interleukin -8. The muscle Se content in group N and group NG was 31- and 40.5-fold that of the control group (group C), respectively. The liver Se value of group N and group NG was 1.06 and 2.50 times higher than that of group C, respectively. The lipid and moisture values of group N and group NG are increased and reduced, respectively, in comparison to that of group C. The diet supplementation of Nano-Se-enriched G. lemaneiformis led to significant increase of the protein content, delicious amino acids along with total amino acids content in grouper. Conclusions: Our results demonstrate a great application potential of Nano-Se-enriched G. lemaneiformis as dietary additive in grouper.