| Collagen and gelatins were extracted from channel catfish (Ictalurus punctatu) skin, and properties of collagen and gelatins were studied. Furthermore, collagenous peptides were derived from channel catfish skin gelatin digested using Alcalse and trypsin. Those collagenous peptides showed protective effects on mice skin by removing free radicals for its strong antioxidant. A peptide with 9 amino acids was purified and characterized.Acid-soluble and pepsin-soluble collagens (ASC and PSC) were extracted from the skin of channel catfish (Ictalurus Punctaus) and partially characterized. The collagen obtained in the experiment contained more than 23% glycine, 7.3% hydroxyproline. The denaturation temperature of acid-soluble collagen was 34°C, about 5°C lower than that of the porcine skin collagen. SDS-PAGE showed that the collagens were composed of two distinct alpha chains. This is similar to the porcine type I collagen. The contents of the skin ASC and PSC, on a dry weight basis, were 25.8% and 38.4%, respectively. These results suggest that channel catfish skin has protential as a supplement to the sources of vertebrate collagens.The gelatin extraction from channel catfish (Ictalurus punctatus) skin using alkali and acid treatment methods was optimized. Response surface methodology was adopted in gelatin processing for extracting optimization. Concentration of alkali, treatment time, extracting temperature and extracting time were adopted as independent variables. The main dependent variable was gel strength, the secondary dependent variable were yield and viscosity. Optimal conditions of alkali pre-treatment process were the concentration of Ca(OH)2 =1.6g/L,treatment time=67h, extracting pH=5.0-5.5, extracting temperature=43.2°C and extracting time=5.75h. Optimal conditions of acid pre-treatment process were the concentration of H2SO4=0.5mL/L, treatment time=17.3h, extracting pH=3.5-4.0, extracting temperature= 54.3°C, extracting time= 5.89h.Physical and chemical properties of gelatin extracted in the optimal conditions were determined. The Bloom strength of A-type and B-type gelatin were 271 Bloom and 265 Bloom, respectively. A-type and B-type gelatin have different isoionic points (pI) which were 7.3 and 4.1 respectively. Gelatin of type B exhibited higher viscosity (10.52±0.5 mPa.s) than gelatin of type A (8.38±0.3 mPa.s), but lower gelling and melting points than gelatin of type A. The gelatin from channel catfish skin also has a higher gelling ability and a lower thermo-stability than porcine skin gelatin. So we can assume that the skin of channel catfish can be a possible material for gelatin industry as the replacement of porcine and bovine skin.Channel catfish skin gelatin was hydrolyzed to obtain antioxidant peptides and assessed for scavenging effects on·OH and O2·-. The results showed that scavenging effect on·OH and O2·- of hydrolysates digested by Alcalse was higher than those of hydrolysates produced by acid or alkali. The experiment deals with the effects of hydrolysis temperature, optimum pH, substrate concentration, enzyme amount and hydrolysis duration carried out with Alcalse on the hydrolysis proportion of the gelatin. The suitable hydrolysis conditions of this enzyme are hydrolysis temperature of 60°C, optimum pH 7, substrate concentration of 45g/L, enzyme amount of 2000U/g, hydrolysis duration of 45min. Under such conditions, the scavenging effects on·OH and O2·- were 88.33% and 41.1%, respectively. A great deal of activity peptide was prepared while hydrolysate was enzymatically hydrolyzed by trypsin for 45min, and the scavenging effects on·OH and O2·- roared to 95.24% and 53.7%, respectively. Hydrolysate has good solubility and ability of moisture retention, a lower molecular weight below 2,000 Da.Protective effects on mice skin damaged by exposing to ultraviolet B were studied. The skin of mice was exposed to UVB to establish the oxidative damage model. The thickness of epiderm was observed after the experiment, and the activities of GSH-Px, SOD, contents of hydroxyproline and MDA were detected with biochemical methods. The epiderm in UVB exposure group became thick, however, that in protective group did not became thick obviously. Activities of GSH-Px, SOD and content of hydroxyproline in UVB exposure group were less than that in protective group. On the contrary, the MDA content in UVB exposure group was higher than that in protective group. It could be concluded that collagenous peptides from channel catfish skin showed some protective effects on photoaged skin, which might mediated by inhibiting the activity of NOS, by eliminating the free radicals and by increasing the activity of antioxidative enzymes to inhibit the oxidative damages of UVB.Peptides derived from hydrolysate of channel catfish skin gelatin were assessed for their antioxidant properties in different in vitro assay systems. One representative peptide with comparatively higher antioxidant potency was separated by the consecutive chromatographic methods including ion-exchange chromatography (through SP-Sephadex C-25), gel filtration (through SP-Sephadex G-25) and reverse-phase high performance liquid chromatography. The isolated peptide was composed of Gly - Pro - Leu - Ser - Gly - Pro - Gly -Hyp- Arg (855.44Da).
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