Studies On Preparation Of Composite Films With Collagen And Vegetable Protein

Currently collagen was a raw material of artificial edible casing on the market, but collagen had obvious disadvantage: the price was expensiven and a polluting extraction process. This paper taked two kinds of vegetable protein, soy protein isolate(SPI), wheat gluten(WG) respectively with collagen(Co) with the method of blending preparation of SPI/Co, Co/WG composite casing film, by adding plant protein to replace part of the collagen membrane to reduce casing price, reduce environmental pollution, the purpose of the study was how to improve the performance of SPI/Co, WG/Co composite casing film, and analysis the compatibility between two kinds of vegetable protein with collagen, It provided a reference in this preparation of artificial edible casing.Using full factorial design analysis method to find the optimum process condition of preparing SPI/Co composite casing film, this was the mass ratio of SPI/Co 1:2 and glycerol concentration 30%, pH value 10.0, processing temperature 40℃. Under the condition, the tensile strength and elongation at break of the protein composite casing film were respectively 21.1 MPa and 21.05%. So the optimum process conditions of WG/Co composite casing film is the solubility of ethanol 10%, pH value 10, the mass ratio of WG/Co 1:4, glycerol concentration 32.5%, processing temperature 40℃. And under that condition the tensile strength and elongation at break of the protein composite casing films can be respectively 19.56 MPa/20.18%.This paper also did research on the effect of glutaraldehyde modified on the tensile properties, water solubility, light transmittance and water vapor transmission rate of the protein composite casing film. With the dosage of glutaraldehyde increased, tensile strength of SPI/Co protein composite casing film and WG/Co composite film for sausage casing were in the trend of first increase then decrease, and become the maximum at 0.1%. But the difference was that elongation at break of SPI/Co protein composite casing film was all the way increase, while the elongation at break of WG/Co composite casing film showed first increased then decrease, with the points of 0.15%~0.2%, it reached the highest level. Over the point of 0.2%, with the glutaraldehyde addition increased SPI/Co protein composite casing film and WG/Co composite film for sausage casing water solubility, the transmittance gradually decreased. However under the same glutaraldehyde add amount, the water solubility of SPI/Co protein composite casing film was higher than WG/Co composite casing film. That was because the wheat gluten contains more hydrophobic groups. The light transmittance of SPI/Co protein composite casing film was higher than that of the WG/Co composite film. From the result we can see that, first the compatibility of Co/SPI to make protein composite casing film was better than Co/WG. Second with the amount of glutaraldehyde add increase, the water vapor transmission rate of the two kinds of protein composite casing film first decreased and then increased, and then at the point of 0.1%, water vapor transmission rate of protein composite casing film was the lowest. Water vapor transmission rate of SPI/Co composite casing film was lower than WG/Co composite casing film, which showed that the modified SPI/Co protein composite casing film molecular structure was more compact than WG/Co composite casing film. After modified the SPI can be better blended with collagen than WG, thus so it will be better for the air tightness.This paper analyzed the changes of protein molecular structure before and after glutaraldehyde modified by means of FTIR, X-RD and DSC. Collagen and two kinds of plant protein all have different degree of the intermolecular interactions during the process of blending with composite casing. Through comparison we can see that SPI has better compatibility with collagen, while the compatibility of WG was at a general degree. After modified by glutaraldehyde, we discovered that it promoted the interaction between two kinds of plant protein with collagen, and enhanced the compatibility between them due to cross-linking of glutaraldehyde. Observed by SEM, the result showed that two kinds of protein composite casing films’ surface changed after glutaraldehyde modified, before modified the protein composite casing film was rough, with stomata exist, and after modified become more smooth, uniform, and stomata disappear.During glutaraldehyde modified, the color of two kinds of protein composite casing film changed from light yellow to red orange gradually with adding the amount of glutaraldehyde. After glutaraldehyde modified, the compatibility between two types of plant protein and collagen have all increased, but because of their molecular structure, whether modified or not, the compatibility of collagen with SPI was better than collagen and WG. That is to say, in preparation of collagen to make the casing film, SPI has more advantage than WG.