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Fish skin is a potential source of collagen and collagen is a protein source of bioactive peptides including iron chelating peptides. The aim of this study is to compare physicochemical properties of collagen extracted from fresh and dried cod skin and the ferrous ion chelating properties of collagen hydrolysates. Then the fresh and dried cod skin extracted collagen was hydrolyzed with collagenase to obtain collagen peptides. The collagen peptides chelated ferrous ion. The results showed that cod skin is a good source of collagen which is accounted for 95.17% of the total proteins. The collagen from fresh cod skin was slightly easier to be hydrolyzed than that from dried cod fish. Respectively, at the same hydrolysis conditions the maximum degree of hydrolysis were 13.64 and 12.57%. The collagen from fresh cod skin had better iron chelating ability than that from dried cod skin, the iron chelating abilities were 32.16 and 23.12%. The UV-Vis spectroscopy of collagen peptides obtained from fresh or dried cod skin showed the same maximum absorption peaks near 230 and 250 nm. When combined with ferrous ion, the maximum of absorption peak is migrated. SDS-PAGE proved that the molecular weight of collagen is 180k Da more or less. The electron microscopy and infrared spectra showed that collagen peptide could chelate with ferrous ion through -NH and C = O. Fresh cod skin extracted collagen has a higher degree of hydrolysis and is more favorable to chelate ferrous ion to produce peptide ferrous chelate, but they have a similar structure.

Collagen is the most abundant protein in nature and widely exits in animals. However collagen usage is not good enough, which is a waste of natural resources and an environmental burden. Collagen peptides have some special characters and functions. These functions can decide their usage. Therefore producing, discovering and using new functional collagen peptides are promising way to deal with this issue. Collagen peptides are produced by hydrolysing collagen or gelatin via chemical or biochemical methods. Biochemical hydrolysation is more proper to produce functional collagen peptides than chemical hydrolysation. The collagen hydrolysates or peptides have four levels of functions: Nutrition, basic functions, special biological functions and other useful properties. The nutrition is providing amino acids and small peptides. The basic functions are improving the state of connective tissues, such as skin and bone. The special biology functions include antioxidant, antihypertensive and other bioactive benefits. Other useful functions include antifreeze, metal chelation and forming edible film. All these functions decide that they can be used in food as well as other fields. The present work is a compilation of current information on the preparations and functions of collagen peptides. At last, recommendation for the further research of collagen peptides is proposed.

Tenebrio molitor larvae was hydrolyzed by pepsin and trypsin for preparing high antithrombotic activity hydrolysate. The significant variables were selected according to the Plackett-Burman design and further optimized by the Response Surface Methodology (RSM). Four factors, including substrate concentration, pepsin digestion time, pepsin amount and trypsin amount, respectively, influenced significantly on the hydrolysis effectiveness. The best hydrolysis conditions obtained using RSM experiments are as following: substrate concentration of 19.8 mg/mL, pepsin digestion time of 1.8 h, pepsin amount of 1634 U/mL and trypsin amount of 126 U/mL, respectively. Under the optimal hydrolysis conditions, the antithrombotic activity was 82.8% predicted by the RSM model, which was basically consistent with the 80.6% obtained in the three verification experiments. Moreover, the antithrombotic activity of the hydrolyzate had no linear relationship with the degree of hydrolysis.

Total 24 isolates with antimicrobial activity against Staphylococcus aureus, Escherichia coli, Bacillus cereus and Shigella castellani, out of 259 strains, were isolated from the internal of seven marine fishes. The extracellular metabolites of strain S14, isolated from the internal of shark, showed stronger inhibition against the four tested bacteria, including G- and G+ bacteria. Based on the 16S rDNA the sequencing analysis, the strain S14 belonged to a member of Staphylococcus epidermidis with 99% DNA similarity and named to Staphylococcus epidermidis S14. The Staphylococcus epidermidis S14 secreted rarely antibacterial substance in the stabilization period and the antibacterial active substances might be the secondary metabolites. The antibacterial metabolites were not hydrolyzed by pepsin, trypsin and lysozyme. The antibacterial metabolites were stable for 30 min to high temperature treatment at 100°C and had higher antibacterial activity at neutral pH.

The scad (Decapterus maruadsi) processing byproduct (SPB) was hydrolyzed by four commercial enzymes, namely, trypsin, flavourzyme, protamex and alcalase, for preparing high Iron-Binding Capacity (IBC) hydrolysate. Alcalase was the best choice for obtaining high IBC hydrolysate from SPB. Response surface methodology using a central-composite design was employed to optimize the enzymatic hydrolysis conditions with alcalase to obtain a maximum hydrolysate yield from the SPB with high iron-binding capacity. The best alcalase hydrolysis conditions were as following: Hydrolysis temperature of 46°C, enzyme substrate ratio of 6040 U/g-protein and hydrolysis time of 66 min, respectively. Under these optimal hydrolysis conditions, the predicted iron-binding capacity was 317.2 µg g-1, which was consistent with the average of three replicates of 296.2 µg g-1 obtained in the validation experiments. The IBC of hydrolysate did not displayed linear relationship with antioxidative ability or the Degree of Hydrolysis (DH). Results indicated that the alcalase hydrolysate from scad processing byproduct can be developed into iron supplant ingredients in functional foods.