Eva Gómez-Ordóñez

Brown and red seaweeds as potential sources of antioxidant nutraceuticals

Multifunctional antioxidant potential of several brown and red edible seaweeds was evaluated in organic and aqueous soluble extracts. The great reduction power and radical scavenging activity of Bifurcaria bifurcata—a Sargassaceae brown algal species—in both organic and aqueous extracts were emphasized. In addition, two Gigartinaceae red algal species, Gigartina pistillata and Mastocarpus stellatus showed relatively high reduction power in the aqueous extracts. When all of the variables of the aqueous extracts were combined in a principal component analysis, a clear differentiation pattern among the tested seaweeds was observed. In the Phaeophyceae, the correlation found among reduction power, radical scavenging activity and total phenolic content is in favour of the involvement of phenolic compounds in the antioxidant mechanisms, whereas in the case of the Florideophyceae, the role of sulphate-containing polysaccharides in reduction power is presumably shown. Nevertheless, the evidence of some taxonomy-based clustering (class and order levels) in this study may prove that polyphenol and sulphate content, besides multifunctional antioxidant profile, are related to specific groups of seaweeds. This evidence could help the search of suitable sources of phytochemicals from seaweeds for further nutraceutical applications.

Molecular weight distribution of polysaccharides from edible seaweeds by high-performance size-exclusion chromatography (HPSEC).

Biological properties of polysaccharides from seaweeds are related to their composition and structure. Many factors such as the kind of sugar, type of linkage or sulfate content of algal biopolymers exert an influence in the relationship between structure and function. Besides, the molecular weight (MW) also plays an important role. Thus, a simple, reliable and fast HPSEC method with refractive index detection was developed and optimized for the MW estimation of soluble algal polysaccharides. Chromatogram shape and repeatability of retention time was considerably improved when sodium nitrate was used instead of ultrapure water as mobile phase. Pullulan and dextran standards of different MW were used for method calibration and validation. Also, main polysaccharide standards from brown (alginate, fucoidan, laminaran) and red seaweeds (kappa- and iota-carrageenan) were used for quantification and method precision and accuracy. Relative standard deviation (RSD) of repeatability for retention time, peak areas and inter-day precision was below 0.7%, 2.5% and 2.6%, respectively, which indicated good repeatability and precision. Recoveries (96.3-109.8%) also showed its fairly good accuracy. Regarding linearity, main polysaccharide standards from brown or red seaweeds showed a highly satisfactory correlation coefficient (r>0.999). Moreover, a good sensitivity was shown, with corresponding limits of detection and quantitation in mg/mL of 0.05-0.21 and 0.16-0.31, respectively. The method was applied to the MW estimation of standard algal polysaccharides, as well as to the soluble polysaccharide fractions from the brown seaweed Saccharina latissima and the red Mastocarpus stellatus, respectively. Although distribution of molecular weight was broad, the good repeatability for retention time provided a good precision in MW estimation of polysaccharides. Water- and alkali-soluble fractions from S. latissima ranged from very high (>2400 kDa) to low MW compounds (<6 kDa); this high heterogeneity could be attributable to the complex polysaccharide composition of brown algae. Regarding M. stellatus, sulfated galactans followed a descending order of MW (>1400 kDa to <10 kDa), related to the different solubility of carrageenans in red seaweeds. In summary, the method developed allows for the molecular weight analysis of seaweed polysaccharides with very good precision, accuracy, linearity and sensitivity within a short time.

A simple ion chromatography method for inorganic anion analysis in edible seaweeds

A new, simple, fast and sensitive ion chromatography (IC) method, for the simultaneous analysis of fluoride, chloride, nitrite, bromide, nitrate, phosphate and sulphate in edible seaweeds was developed and reported for the first time. The validation of the analytical method was studied in terms of linearity, sensitivity, precision and accuracy. All standard calibration curves showed very good correlation between anion peak area and concentration (r>0.999). Limits of detection and quantitation ranged between 0.002-0.05 mg/L and 0.01-0.1mg/L, respectively and indicated the high sensitivity of the method. Relative standard deviation values of repeatability and inter-day precision for standard anions with the same sample were less than 2%. Anion recoveries ranged from 97 to 113% for chloride and from 87 to 105% for sulphate, respectively and showed the fairly good accuracy of the method. The method was applied to the analysis of inorganic anions in brown and red edible seaweeds. Brown seaweeds were characterized by higher chloride content up to 33.7-36.9%, while red seaweeds were characterized by higher sulphate content (45-57%). Sulphate content in seaweeds is related to the presence of sulphated polysaccharides of biological importance. The method developed was well applicable to mineral anion analysis in edible seaweeds and shows suitability and reliability of use in other food samples of nutritional importance.

Seaweed as a source of novel nutraceuticals: sulfated polysaccharides and peptides.

Seaweeds and seaweed-derived products are underexploited marine bioresources and a source of natural ingredients for functional foods. Nutritional studies on seaweeds indicate that brown and red seaweeds possess a good nutritional quality and could be used as an alternative source of dietary fiber, protein, and minerals. Moreover, bioactive sulfated polysaccharides are the main components of soluble fiber in seaweeds and also bioactive peptides can be prepared from seaweed protein. This chapter gives an overview of the main biological properties of sulfated polysaccharides and peptides from brown and red seaweeds. Recent studies have provided evidence that sulfated polysaccharides from seaweeds can play a vital role in human health and nutrition. Besides, peptides derived from algal protein are most promising as antihypertensive agents. Further research work, especially in vivo studies, are needed in order to gain a better knowledge of the relation structure-function by which bioactive compounds from seaweeds exert their bioactivity.

Effect of the red seaweed Mastocarpus stellatus intake on lipid metabolism and antioxidant status in healthy Wistar rats

Health-promoting effect of dietary supplementation with the red seaweed Mastocarpus stellatus was studied. Its major component is dietary fibre (31.7/100 g dry weight), 72% as soluble fibre, mainly formed by carrageenans, sulphated-galactans of red seaweeds. Thus, rats were fed either a basal- or an algal-supplemented diet (10%). Then, lipid metabolism was assessed in serum, and reducing power measured in serum and caecum by FRAP method. Also, caecal pH was monitored and short chain fatty acids analysed by gas-liquid chromatography. Seaweed intake reduced significantly triglycerides and total cholesterol in healthy rats, but not atherogenic index. Also, a significant increase in caecal moisture and proportion of acetic and propionic acids was obtained but no clear prebiotic effect was shown. Sulphated-galactans seemed to be related to the antioxidant status improvement in caecum and also to the 1.7-fold increase in anticoagulant capacity of plasma. Therefore, Mastocarpus could be regarded as a source of functional ingredients but its health benefits need to be further explored depending on specific use.