Extraction And Thermal Stability Of Collagen From Jellyfish(Rhopilema Esculentum)

As a traditional aquatic product, jellyfish(Rhopilema esculentum Kishinouye) have been exploited commercially by Chinese as an important food for more than a thousand years. For the past few years, there was steady economic growth in the jellyfish industry. In 2013, the national output of jellyfish reached 27.8 kilotons, of which about a quarter was taken by Liaoning province. According to the traditional eating habits, jellyfish was usually divided into four parts, umbrella, scapulet, oral arms and column. The umbrella, scapulet, oral arms were used as edible parts, and the gastric column was often treated as waste. Jellyfish protein contents are very high in the four tissues on dry basis, and the collagen is the major ingredients. It can be inferred that the changes of the special texture features of jellyfish in the heating processing, such as hardness, spring and tenderness were likely related to the physical and chemical properties and thermal stability of the collagen.In this study, we first investigated the physical and chemical properties and secondary structure information of the crude collagen fibers(CCF) and the pepsin-solubilized collagen(PSC), which were extracted from fresh jellyfish umbrella, by infrared spectroscopy(IR), circular dichroism(CD), differential scanning calorimetry(DSC), high performance liquid chromatography and SDS-PAGE electrophoresis. And the results of the amino acid composition analysis showed that CCF and PSC possessed a distinct amino acid profile of collagen. The glycine, possessing approximately 1/3 of the total amino acid residues, was the most abundant amino acid in umbrella collagen and there were relatively high contents of hydroxyproline, proline which possessed 5%, 7% respectively. Amino acids with aromatic ring, such as Phe, Tyr were much less than others. This kind of composition resembled with the bovine tendon collagen and conforms to the feature of aquatic product collagen composition. This collagen was comprised of α, β, γ- heterotrimers. DSC analysis showed that the denaturation temperatures of CCF and PSC were 46.74°C and 32.36 °C, respectively. PSC was characterized by an absorption peak at 230 nm by ultraviolet spectrum, but it was indistinct for CCF which was rare dissolved in acetic acid solution. In the FTIR spectra analysis, the composition of CCF and PSC was similar.Finally, we revealed the different biochemical, structure and rheological properties of PSC extracted from different tissues of jellyfish(umbrella, gastric column, scapulet and oral arm). As the results showed, there was slight difference in amino acid compositions in different PSC samples. Four PSC showed an evident α–chain band in SDS-PAGE analysis, indicating the PSC extracted were type I collagen. The UV-vis absorption spectra of the PSC showed that their maximum absorption wavelength was at 233.4 nm, which is comparable to that of type I collagen. IR spectroscopy analysis showed that the PSC from four parts have different secondary structure, the amide A and I were slightly different and the amide II and III were similar; Their thermal denaturation temperature range in consecution–heat tests were 31–40 ℃; The thermal denaturation curves obtained by rheometer indicated the thermal denaturation temperature were in coincidence with the results of IR spectroscopy analysis. PSC extracted from different tissues showed different viscosity and elasticity. PSC extracted from gastric column and scapulet were dominated by elasticity, while the PSC extracted from umbrella and oral arm expressed dominated by viscosity.