| Gelatin is one of the most widely used natural biopolymers which is produced by the irreversible degradation of collagen.Traditional gelatin is mainly produced from the bones of livestock such as cows and pigs,however,in recent years,the scope of its use has been limited due to diseases and religions.Therefore,exploring new raw materials for gelatin production has become popular.In the process of finding new raw materials,rabbit skin was found not only to be gelatinized faster than other mammalian skins,but also the gelatin it produced was of good quality and could be used as a new source of gelatin raw materials.However,the mechanism of its rapid gelatinization has not yet been clarified,which is not conducive to the industry.Gelatin production process mainly includes gelatinization and hot water extraction.Previous study demonstrated that except the triple-helix,the existence of secondary structure during gelatin preparation has correlation with gelatin yield and gel strength,but no studies have been reported on the mechanism of changes in structure of collagen on the release of subunit components.Therefore,this study mainly studied the molecular mechanism of rapid gelatinization of rabbit skin collagen and the changes of secondary structure of collagen during the preparation of gelatin in order to further clarify the gelatinization mechanism of collagen and provide a theoretical basis for the development of new gelatin raw materials and the determination of extraction processes.The results are as follows:(1)The molecular mechanism of rapid gelatinization of rabbit collagen was studied.The results showed that rabbit skin collagen could achieve gelatinization with1%(w/v)HCl treatment for 5 min,and got gelatin with higher gel strength and yield.Later,in order to analyze the gelatinization mechanism,rabbit skin collagen was purified,and gelatin was used as a raw material to extract gelatin.Comprehensive analysis of the yield and gel strength of gelatin,and SDS-PAGE,FTIR,SEM of the gelatinized collagen,found that the covalent bond of rabbit skin collagen was verysensitive to acid;A brief acid pretreatment will cause a considerable amount of cleaning losses;Acid pretreatment first destroys the covalent cross-linking between collagen molecules and covalent bonds in non-helix crystallization,thus promoting the release of subunits.Only when the collagen spatial structure is changed and subunit components are exposed,will the peptide bonds be destroyed;Most of the easily gelatinized collagen has been destroyed at 5 minutes acid treatment,and the original hydrogen bond equilibrium has been broken,so the appearance of the collagen has changed from flat to wave-like;As the acid treatment time increased,the wavy folds on the collagen surface gradually became smaller and flattened again,indicating that the hard gelatinized collagen began to expose.(2)The relationship between the presence of collagen secondary structure and gelatin yield and gel strength during gelatinization was studied using rabbit skin and fish skin as raw materials.The results showed that the sum of ?-helix and ?-sheet contents in gelatinized collagen is highly correlated with the yield of gelatin,indicating that the higher ?-helix and ?-sheet in gelatinized collagen are beneficial to the release of subunits in the subsequent extraction process.However,the ?-helix content in gelatinized collagen is strongly negatively correlated with the gelatin gel strength,indicating that the higher ?-helix content is not conducive to the extraction of gelatin with higher gel strength.(3)Based on the above study of gelatinization,the molecular simulation of rabbit skin collagen was carried on to further analyze the molecular mechanism in this process.The RMSD results showed that the acid treatment allowed the non-helical regions of multiple collagen molecules to separate,but had less effect on the conformation of a single non-helical region,but had a greater influence on the triple helix region.The results of the hydrogen bonds showed that the acid treatment resulted in the rapid reduction of the triple helix hydrogen bond in a short time;after 50 ns,the number of hydrogen bonds remained relatively stable.These results were consistent with the results of the infrared spectrum of gelatinized collagen after acid treatment for 1 h,indicating that for rabbit skin collagen acid treatment <1 h is the most effective gelatinization time.The results of secondary structure showed that as the simulation time increased,there was almost no change in the secondary structure of the non-helical region,but the spatial structure of triple helix was immediately broken with acid treatment,and then the peptide chains were loosened into a disordered state,so thesecondary structure was gradually exposed;With the simulation time increased,the content of triple helix gradually decreased,and the content of irregular coils increased.The sum of ?-helix and ?-sheet content increased first and then decreased,which was consistent with the change of gelatinized collagen that was actually treated with acid for1 h.(4)The relationships between the presence of secondary structure of gelatin and the yield as well as the gel strength of gelatin were studied respectively using rabbit skin and fish skin collagen.The results showed that the formation of triple helix-like structures in dilute solutions affected the gel strength of the final gelatin,and the triple helix formation ability of rabbit skin gelatin solution was stronger than that of fish skin;With the extraction time increased,the yield of gelatin gradually increased,which resulted in the increase of irregular coils,but this phenomenon was not conducive to the formation of good gel strength.Therefore,in the gelatin extraction process,the formation of irregular coils should be controlled. |
PDF Full Text Request