The Influence Factors Of Application Quality Analyzing And Its Mechanism Studying For Collagen Casings

The continuous development of the sausage products industry has put forward higher requirements on the properties of collagen casings.According to the evaluation method of the application characteristics of collagen casings mentioned by the current researches,most of the modification researches focused on improving the mechanical properties and thermal stability.However,such evaluation methods are not systematic and deviate from the actual application,and the reported methods for improving the basic properties of collagen casings have not improved the application quality well.Based on the above problems,this study aims to establish the correlation between the basic characteristics of collagen casings and their application characteristics,and analyze the basic properties and microstructure characteristics of casings with good application performance.In view of this,the microstructure of the collagen casing is changed by changing the drying temperature and the pH value of the cross-linking to further clarify the mechanism of the influence of casing internal structure on its basic properties.By analyzing and measuring the basic characteristics of the casing,the correlation can be used to accurately evaluate collagen casings’ application characteristics so as to make the researches on improving the basic characteristics of casings more targeted and accurate.The specific contents are as follows:Establishment of correlation between the basic properties and application performance of collagen casings and analysis of structure analysis.The application experiment,composition and physicochemical properties of 7 commercial collagen casings were carried out firstly,and then the results were analyzed by the means of PCA and PLS.The data showed that the Young’s modulus(YM)and tensile strength(TS)under wet condition were negatively correlated with the degree of sausage deformation(P < 0.05).When TS < 4 MPa,the sausage had irreversible deformation after loading on the shelf,when the length of sharp head reached more than 0.5 cm,obvious sharp head phenomenon can be observed,and even lead to the sausage falling down in serious cases.The thermal swelling characteristics were positively correlated with the sausage’s boiling performance(P < 0.05),while the heating shrinkage rate,thermal stability,and changes in mechanical properties during boiling were negatively correlated(P < 0.05).In order to explore the root causes of the differences among casings,FTIR,XRD,SEM and fluorescence microscope were used to characterize the structures of the above 7 casings,and analyzed their basic properties and application performance.The results showed that the size and stacking structure of collagen fibers coupled with the network structure formed by crosslinking were the two main structures of casing.The structural differences resulted in the differences in macroscopic properties,such as thermal swelling,heating shrinkage,thermal stability and the change of mechanical properties,which further affected its application characteristics.Study about the influence of drying temperature on the microstructure and properties of collagen casing.By changing the drying temperature,the effects of drying temperature on glutaraldehyde cross-linking and the influence rule of the two on the collagen fiber structure and the basic characteristics were investigated.The results showed that when GA was not added,the increase of the drying temperature lead to the denaturation of collagen,disintegration of the large collagen fibers and bundles,and the internal structure become more compact,the network structure formed by collagen fibers was reduced,but the degree of heat crosslinking was enhanced.Therefore,compared with the casing film dried at 55oC,the thermal swelling rate of the films dried at 85oC decreased by 80% and the thermal shrinkage rate decreased by 20%,while the YM and TS were both increased by 10% under wet and boiled condition,of which the wet TS reaches 4 MPa,and the thermal stability was also significantly improved.When GA was added,as the drying temperature increased,the cross-linking rate was accelerated,and the degree of cross-linking was also greater.Compared with the uncross-linked casings at the same temperature,the thermal swelling rate and the shrinkage were the lowest at 85oC,while the YM and TS wet and cooked were increased by 2~3 times.The crosslinks formed in the early drying stage hinders the collapse of the collagen fiber structure due to heat and the unwinding of the triple helix.At the same time,more covalent bonds were formed between collagen molecules to form denser network structure,which will change the basic properties.Study about the effect of pH on the structure and performance of the collagen casings.The influence of pH on the characteristics of cross-linked and uncross-linked collagen films were analyzed.The results showed that when not crosslinked by GA,the content of the triple helix and the integrity of the collagen fiber structure both increased first and then decreased with the increase of pH value.At pH 6.0,the fiber packing structure inside the casing film was the most compact,the thermal swelling rate was 190%,the thermal shrinkage rate was 55%,the wet and boiled tensile strength was maximum,and thermal stability was 145oC.The pH also affected the cross-linking reaction of GA and the formed cross-linking network structure.When the pH was lower than 7.0,it was not conducive to the cross-linking reaction of GA,and the degree of cross-linking of GA was lower as the pH decreases.The cross-linking of GA was the most effective at pH 8.5,and the thermal swelling rate and shrinkage rate were reduced by 50% and 40% respectively compared to the films uncross-linked.The thermal stability,YM and TS under wet and boiled state were also significantly improved.Combined with the change of sausages during cooking,it can be speculated that the casing films crosslinked at pH 4.5 and 6.0 can meet the requirements of mechanical strength,and part of the thermal degradation occurs quickly during cooking,which will provide cushioning properties to the changes of sausage.Thereby the collagen casings have potential to demonstrate good application performance.This study is of great significance for guiding the modification research and industrial production of collagen casings.