| Based on the problems such as long production period and serious pollutionexisting in the processing of the gelatinization of collagen that induced by tradition acid or/and alkali-base, this study treated the porcine collagen by acid and ultra-high pressure (UHP) respectively. The microstructure of collagens before and after gelatinized and also the extraction yields of gelatins were studied, to make it more clear that how does the collage microstructure changes during the process of gelatinization and what’s the mechanism of UHP treatment. A regression model to predict the extraction yield of gelatin was established lastly. So as to provide theoretical basis and data reference for the industrialization of gelatin preparation.The preparation processes of the porcine collagen with pepsin were firstly researched. And the optimum conditions for preparation were that pH of the solution:2.2; dissociation time:18h; quantity of enzyme:0.5%. Under these conditions the extraction of porcine collage arrived to the maximum (84.35±0.33)%. The purity of collagen was(82.5±1.6)%after it was purified and dried. All the results of the studies of DSC、FTIR、CD、SDS-PAGE and SEM for collagen microstructure showed that, porcine collagen that extracted under the optimum conditions maintained the native triple helix.Results of the analysis of DSC、FTIR、CD and SDS-PAGE for the porcine collagens that gelatinized by traditional acid and the extraction yields of its gelatins indicated that, after treated by1or4hours the microstructure of collagens were slightly broken;8hours were appropriate;12or24hours were over. During the gelatinization, the complicated network of collagen was firstly loosened, and then the high molecular weight subunits were degraded.The high pressure cooperated with pressure medium, which was water, NaOH, or HCl, to induce the gelatinization of collagens. According to the results of DSC、FTIR、 CD、SDS-PAGE、SEM and the yield of gelatins, some conclusions could be drew as follows:①when treated by UHP with water as the pressure medium, the destroy of collagen structures were mainly caused by high pressure, which majorly break the non-covalent bonds such as hydrogen bonds.The covalent bonds in collagen were little affected, and the triple helixes were relatively integrated.Therefore, this treatment lowered the loss rate of gelatins, the content of high molecular weight submits in gelatins were higher than other groups, and molecules were highly ordered. But it contributed little to the preparation of gelatin. The extraction yields of its gelatins were only about5percent higher than the untreated one.②when treated by UHP with NaOH as the pressure medium, the covalent and non-covalent bonds in collagen were rapidly damaged, some regions especially the pyrrolidine-rich region were over loosen and degraded. The solubility of collagen in alkali sharply increased. As the loss of collage increased, T1values were significantly decreased, and the differences between T1and T2were up to the maximum. But other regions were little affected, and its microstructure was relatively completed. Furthermore, content of high molecular weight components in its gelatins were the lowest, this means that the gelling properties of gelatins would tend to be the worst. In conclusion, using NaOH as a pressure medium would not benefit for the preparation of high-yield and high-quality gelatin.③whentreated by UHP with HCl as the pressure medium, covalent crosslinks between triple helixes could be broken effectively; and then the non-spiral crystal zones were destroyed; triple helixes tended to unwind; the gelatinization of collagen could be finished in a short time. What’s more, high pressure can not only damage the network of collagen, but also promote the aggregates of molecules. As the result of obstructing the deep damage of acid to hydrogen bonds and covalent bonds especially peptide bonds between the a-peptide chains. So the peptide chains of collagens were still connected by some hydrogen bonds after treated by HC1/UHP although they were unwound. Thus all the losses of gelatins were greatly lowered, yields increased, differences between T1and T2decreased. Content of high molecular weight components in HCl/UHP-treated gelatins were very close to the water/UHP-treated ones, indicating that these gelatins would have good gelling properties. In conclusion, using UHP cooperated with acid as a replacement for traditional acid method could effectively loosen triple helixes and also maintained the integrity of submits, it would beneficial to the preparation of gelatins with high yield and good quality. Among the HCl/UHP conditions,300MPa cooperated with HCl which concentration was1%for15min was the best, for the collagen was most gelatinized, and it obtained the highest level of gelatin yield. For traditional acid-treated collagens, the Tm and absorption areas of amide I band were both quadratically related to the T1, but for the HCl/UHP treated ones, they were linearly related. Moreover, Tm, absorption intensity of amide I band, and the loss rate of gelatin in group U3, which had the highest gelatin yield, were all lower than those in8h acid-treated group. These further proved that high pressure had a protection effect on submits, which made it possible for HCl/UHP treatment to loosen triple helixes to the most extent and with little damage to the integrity of peptide chains, resulting in a significant drop of gelatin loss.There were a significantly correlation between Tm and T1in traditional acid-treated groups, the regression model was:Y=8.564X-0.07X2-185.951(R2=0.899). Differences between the corrected prediction values and true values of T1were all within5percent, and they were linearly related. Thus the above regression model could be used as a prediction model for the extraction yield of gelatins directly or after corrected. But the loss rate of gelatins caused by different treatments differ from each other, so the prediction model established by this research would mainly suitable for traditional acid treatment, UHP treatment cooperated with acid, and other treatments whose gelatin loss rate close to them. |
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