Study On Isolation And Functional Properties Of Collagens From The Skin Of Cobia (rachycentron Canadum)

In this study, collagens from cobia (Rachycentron canadum) skin were prepared, purified, and physicochemical characters, subunit compositions, functional characteristics were studied. Thereby, it provided theoretical basis for the comprehensive utilization of fish skin. The results were as follows:The skin of cobia was rich in the crude protein, which were up to 28.53% on the basis of wet weight, however 81.59% on the basis of dry weight. The glycin, alanine, glutamic acid and proline was most abundant in protein of cobia skin, contents were 4.45, 2.28, 2.27, 2.23%, respectively. The amina acid composition was expressed as residues per 1000 total amino acid residues, the content of glycin was 32.8%, approximately occurs uniformly, at every third residue throughout most of collagen molecules, which was consistent with the character of Gly-X-X. The content of collagen from the cobia skin was up to 20.09% on the basis of wet weight. The content of collagen accounted about 72.4﹪of the crude protein. The yields of ASC and PSC were 35.5% and 12.2%, respectively, on the basis of dry weight.The amino acid composition of ASC and PSC were similar. The glycin was rich in ASC and PSC (32.9% and 34.2%), The amounts of imino acids, proline and hydroxyproline in ASC and PSC were 213, 197 residues per 1000 residues, respectively. A strong UV absorption peak were obtained at 219nm, 221nm,respectively. This result was in accordance with the characterization of the typeⅠ. The denaturation temperature of ASC and PSC were 38.17℃, 36.03℃from the curve of DSC, respectively, which was lower 5℃than that of calf skin collagen. Maximum solubility in 0.5M acetic acid was observed (0.75 mg/mL and 0.78mg/mL) at pH 3 and pH 4 for ASC and PSC, respectively. Solubility reached the minimum when the pH was 7. A sharp decrease in solubility was observed in the presence of NaCl, above 2% and 3% (w/v) for ASC and PSC, respectively. Reflectance Fourier transform infrared (FT-IR) microspectroscopy was applied to show relatively complete helix of collagens was preserved.Judging from chromatographic and electrophoretic patterns, ASC, PSC from cobia skin accorded with typeⅠcollagen, which were composed of threeαchains. Strongly suggesting the coexistence of (α1)2α2,α1α2α3 heterotrimers of type I collagen. An understanding of their functional difference must await further studies, because the isolation of theα1α2α3 heterotrimer had not been achieved so far. Tissue-specific existence ofα3 in cobia collagen was apparent. Judging from amino acid composition, the composition ofα1 andα2 of ASC and PSC was quite similar, but not identical.The moisture absorption of ASC and PSC was worse than glycerol, but PSC better than the ASC in temperature 25℃, under RH 43%, 81% conditions. In vitro, 0.2% PSC, 0.2% ASC could well reduce the water loss rate, indicating the good moisture. All the formulas were good in surface moisture retention, PSC was superior to propylene glycol, but more better than ASC. But to only propylene glycol, the moisturizing effect was much better by inputting ASC, PSC.When Collagen concentration was 0.25%, the foamability of were the highest. The foamability was the highest in pH5. PSC was better than ASC in the foamability with indifferent salt conditions or temperature, in general. Both ASC and PSC arrived at highest at temperature 30℃. On different pH conditions, ASC and PSC were similar in having the higher foam stability. Along with the increase of NaCl, foam stability of ASC and PSC reduce. At temperature 30℃, it was the best.ASC and PSC's ESI decreased along with increasing the ionic strength, the best emulsifying capacity was found in 0.25mol/L of sodium chloride system. ASC and PSC's emulsifying capacity was higher in acid or alkaline solution, but it was the lowest around the isoelectric point. Regardless of increasing rotational speed, enhancing temperature or raising the density of sodium chloride, the emulsifying capacity of ASC and PSC increased to varying degrees. At pH 4 and pH 9, emulsion stability were the best; ASC changed little in emulsion stability with speed increasing, when the speed was up to 18000 r/min, PSC reached the maximum of emulsion stability; the emulsion stability of PSC was the best at 40℃, but ASC did not change significantly. ASC and PSC had the higher oil absorption, high up to 19.97 mL/g, 21.65 mL /g, respectively.