| Based on the problems such as long production period and serious pollution issued from acid and alkali existing in the traditional acid or/and alkali-base production process, this study improved the traditional porcine gelatin production process by using ultra-high pressure(UHP) technology to replace traditional acid method to induce porcine collagen gelatinizing. In order to provide a technical reference and theoretical basis for UHP technology application and establishment of clean and efficient production process in gelatin preparation, the gelatinizing process induced by UHP was optimized and the quality of gelatin prepared from the gelatinized collagen was analyzed, then the gelatinizing mechanism was investigated.The extraction yield and gel strength of gelatin were used to evaluate the gelatinizing effects of collagen to select an optimal UHP method. Then some factors such as pressure level and time of UHP and concentration of transmitting media in gelatinizing process were optimized. The results showed that UHP could induce collagen gelatinizing, and UHP treatment with HC1as transmitting media could significantly improve gel strength of gelatin while the extraction yield kept high. The optimal conditions were that UHP level was250MPa, UHP time was10min and HC1concentration was0.75%, under which condition the extraction yield and gel strength of gelatin were up to88.62%and384.43g, respectively. The UHP process had great advantages in pollution treatment investment and production period by contrast with traditional method, as the gelatinizing time was greatly shortened and the pollution was greatly reduced by decreasing the quantity of acid wastewater.The basic physical and chemical properties, amino acids composition, the subunits composition and molecular weight distribution, gelling/melting temperature, viscosity characteristics and spectral characteristics of UHP gelatin were analyzed by comparison with commercial gelatin. The results showed that the moisture and ash contents, pH and gel strength of UHP gelatin reached A-degree standard of edible gelatin. Its transparency and color were much better than the commercial one’s. The characteristics of amino acid composition of UHP gelatin were tally with that of collagen, glycine content was largest, proline and hydroxyproline contents second, aromatic amino acid and sulfur amino acid contents were very low. The gelling/melting temperatures and thermal stability of viscosity of UHP gelatin were higher, while the sensitivity of viscosity to shear rate was lower. The contents of amino acid (proline and hydroxyproline) and high molecular weight subunits (a、βand γ) were obviously higher in UHP gelatin, which were main reasons for its greater gel performance. The UV absorbance spectrogram and the infrared spectrogram further proved that UHP gelatin had the characteristics of amino acid composition and vibration mode of collagen. The integrity of characteristic structure of collagen in UHP gelatin was poorer than that in the commercial one, which might be good for gelatin structure rearrangement during the gelation process, thus enhanced the gelling properties of gelatin.The thermal stability of gelatinized collagens and the molecular weight distributions of the extracted gelatins were analyzed to evaluate change in structure of collagens gelatinized under different UHP conditions. The gelatinizing mechanism of UHP conditions on collagen gelatinizing was investigate, combined with the results of extraction yield in single-factor test. The rheological characteristics of UHP gelatins weTe analyzed, then the influence mechanism of UHP conditions on gelling properties was investigated combined with preliminary results of gel strength and molecular weight distribution. As following was the main conclusion:(1) UHP treatment could break the inter-triple helix hydrogen bonds, destabilize the spatial structure of collagen and promote collagen gelatinizing, which is beneficial to the release of subunits. Low pressure level (100-300MPa), short time (5-15min) and low acid concentration (0.5-1%) of UHP treatment could obviously destabilize the spatial structure of collagen and induce collagen gelatinizing. Increase pressure level or prolong pressure time didn’t cause a notable change in structure of gelatinized collagen, which might be due to the denaturation and aggregation of collagen or the formation of hydration bridge (water molecule-mediated hydrogen bonds), Acid concentration had little effect on hydrogen bonds, it affected gelatinizing extent via influencing the covalent crosslinkings in collagen.(2) UHP gelatin have higher amount of subunits than tradition one, as UHP treatment had little effect on covalent crosslinkings especially peptide bonds, and could also induce aggregating. When pressure level was below300MPa and pressure time was within30min, increase in pressure level or prolong in pressure time caused an increase in aggregation, thus the relative amount of subunits increased. The relative amount of subunits especially β-component in the sample gelatinized with0.5%HC1concentration was significantly higher than that in water group (gelatinized with water), indicating this concentration was good for subunits aggregating. When increased acid concentration to1%, the breakage of covalent crosslinkings played a dominant role, thus the relative amount of subunits was decrease (equal to the water group). Further prolong pressure time to45min or increase acid concentration (>1%), the relative amount of subunits was decrease as a result of breakage of peptide bonds.(3) The trends of gel strength and gelling/melting temperatures effected by UHP level and acid concentration were consistent with that of the relative amount of high molecular weight components (subunits), as high molecular weight components could participate in forming long helical structure, which was beneficial to the formation and stability of gel network. UHP treatment affects the quality of gelatin via influencing the content of high molecular weight components. However, the trends of gel strength, gelling/melting temperatures and high molecular weight components effected by pressure time was not special consistency, which meant the gelling properties of gelatin could also affected by environmental conditions of gelation such as ionic strength.In conclusion, UHP cooperate with low concentration of hydrochloric acid can replace traditional acid method to induce porcine collagen gelatinizing, the use UHP technology to extract gelatin can shorten the production period and reduce the pollution of the environment significantly, while the yield is still high and the quality of resultant gelatin is improved. The effects of UHP cooperate with hydrochloric acid on the structure of collagen mainly include loosing helical structure by breaking the hydrogen bonds and covalent crosslinkings, inducing the collagen molecular aggregating and the degradation of collagen by breaking peptide bonds. Structure of gelatinized collagen and structure and quality of resultant gelatin are the combination of the three functions. |
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