Preparation,isolation and identification of iron-chelating peptides derived from Alaska pollock skin

Alaska pollock skin as aquatic by-product was usually discarded in food processing. Iron deficiency has been a nutritional problem for a long period. In this study, Alaska pollock skin was used to generate iron-chelating peptides after being treated by commercial enzymes. Sequential chromatography, including immobilized metal affinity chromatography (IMAC) and reversed phase high performance liquid chromatography (RP-HPLC), was used for capturing and purifying iron-chelating peptides. One tripeptide, with high iron-chelating activity, was obtained and identified by electrospray ionization tandem mass spectrometry (LC–ESI-MS/MS). The amino acid sequence of the iron-chelating peptide was identified to be Ser-Cys-His (MW: 345 Da). These results show that Alaska pollock skin could be utilized to generate iron-chelating peptides as an iron supplement in functional food industry.     

Preliminary studies on the chemical characterization and antihyperlipidemic activity of polysaccharide from the brown alga Sargassum fusiforme

A polysaccharide (SFP) extracted from the brown alga Sargassum fusiforme (Harv.) Setch. was purified by chromatography on DEAE-Sephadex A50 and Sephadex G-100. Studies using paper chromatography (PC), electrophoresis and infrared spectroscopy (IR) indicated that SFP was a kind of alginate with a molecular weight of 16 000 and a molar ratio of mannuronic acid (M) to guluronic acid (G) of 2.75. Pharmacological experiments showed that SFP could markedly decrease the content of total cholesterol (TC), triglyceride (TG) and low density lipoprotein-cholesterol (LDL-C) in the serum of experimental hyperlipidemic rats, and significantly increase the level of high density lipoprotein-cholesterol (HDL-C).

     

Characterization of Acid- and Pepsin-Soluble Collagens from the Cuticle of <Emphasis Type="Italic">Perinereis nuntia</Emphasis> (Savigny)

To extend the practical applications of collagen, alternatives to mammalian sources are needed. In this study, acid-soluble collagen (ASC) and pepsin-soluble collagen (PSC) were extracted from the cuticle of Perinereis nuntia (Savigny), and their physicochemical features and structures were examined. The yields of ASC and PSC were 3.89% and 6.74%, respectively. The glycine contents of both collagens accounted for approximately one-third of the total amino acid residues, and the sum totals of proline and hydroxyproline in ASC and PSC were 212 and 214 residues/1000 residues, respectively. However, the proline hydroxylation rates of ASC and PSC were 84.0% and 83.6%, respectively. The maximum absorption peaks of both ASC and PSC were detected at 233 nm. Zeta potential studies indicated that ASC and PSC have a net zero charge at pH 4.89 and 4.95, respectively. Fourier-transform infrared spectroscopy, circular dichroism, and X-ray diffraction confirmed the triple helical structure of the collagen. The denaturation temperatures (T_d) of ASC and PSC were 36.5 °C and 33 °C, respectively. Moreover, the collagens appeared to be loose, fibrous, and porous by scanning electron microscopy. These results suggested that collagen from the cuticle of Perinereis nuntia (Savigny) has potential commercial applications in the food, nutraceutical, and pharmaceutical industries.     

Antihypertensive effect and purification of an ACE inhibitory peptide from sea cucumber gelatin hydrolysate

Gelatin from the sea cucumber (Acaudina molpadioidea) was hydrolyzed sequentially with bromelain and alcalase. The hydrolysate was fractionated into three ranges of molecular weight (GH-I, <10 kDa; GH-II, <5 kDa; GH-III, <1 kDa) using an ultrafiltration membrane bioreactor system. The GH-III brought about a high angiotensin-I-converting enzyme (ACE) inhibitory activity, with IC₅₀ value of 0.35 mg/ml. An ACE inhibitory peptide was isolated from the GH-III, using the chromatographic methods including ion-exchange chromatography, gel filtration and reversed phase high-performance liquid chromatography. The purified ACE inhibitory peptide with a molecular weight of 840 Da consisted of five main amino acids (Glu, Asp, Pro, Gly and Ala), and its IC₅₀ value was 0.0142 mg/ml. This sea cucumber gelatin hydrolysate (GH-III) was used as drinks administered to renal hypertensive rats (RHR) for 1 month. The systolic blood pressure and diastolic blood pressure of the RHR were significantly reduced, which indicates an antihypertensive effect by oral administration.     

Effect of molecular weight on the antioxidant property of low molecular weight alginate from Laminaria japonica

In this study, three alginate fractions with different molecular weights and ratios of mannuronic acid (M) to guluronic acid (G) were prepared by enzymatic hydrolysis and ultrafiltration to assess the antioxidant property of alginates from Laminaria japonica with molecular weight below 10 kDa. The antioxidant properties of different molecular weight alginates were evaluated by determining the scavenging abilities on superoxide, hydroxyl, and hypochlorous acid and inhibitory effect on Fe²⁺-induced lipid peroxidation in yolk homogenate. The results showed that low molecular weight alginates exhibited high scavenging capacities on superoxide, hydroxyl, and hypochlorous acid radicals and good inhibition of Fe²⁺-induced lipid peroxidation in yolk. By comparison, alginate A1 with molecular weight below 1 kDa and M/G of 1.84 had better scavenging activity on superoxide, hydroxyl, and hypochlorous acid radicals in vitro than A2 (1–6 kDa), A3 (6–10 kDa), ascorbic acid, and carnosine. With similar M/G ratio, A2 exhibited better antioxidant activity on superoxide and hypochlorous acid radicals than A3. However, fraction A3 with molecular weight of 6–10 kDa exhibited higher inhibitory ability on lipid peroxidation in yolk in vitro than A1 and A2. The results indicated that molecular weight played a more important role than M/G ratio on alginate to determine the antioxidant ability. By comparison, low molecular weight alginates composed of guluronic acid and mannuronic acid exhibited better antioxidant ability on oxygen free radicals than sulfated polysaccharides from L. japonica in our previous study and represent a good source of marine polysaccharide with potential application as natural antioxidant.