Influences Of Different Crosslinking Agents On Properties Of Edible Collagen Film

Due to its good biocompatibility and degradability,as well as low cost and abundant sources,gelatin films have gained increasing interest recently.However,being similar to other protein films,gelatin films have some disadvantages,such as inferior strength,low barrier capacity and so on.Crosslinking can effectively improve the mechanical and barrier properties,as well as thermal stability of the gelatin film.In this study,riboflavin,tannin and smoked liquid were used to crosslink gelatin or collagen film for improvement of its properties.Compared with other chemical crosslinking agent,these crosslinking agents are with low toxicity,mild reaction,and provide special chemical and pHysical properties to filmsFirst,the use of riboflavin as pHotosensitizer in the UV-A induced crosslinking process was studied to iprove the water resistance and strength properties of cellulose nanocrystals-reinforced fish gelatin(CG)films.The fluorescence spectroscopy results supported the conclusion that crosslinkings occurred in the film at a riboflavin charge of 0.1%or higher.The viscosity of the CG solution increased as the riboflavin charge increased.The FTIR spectrum of the films showed that the riboflavin mediated UV(RmUV)irradiation caused the formation of new chemical bonds occurring at 1583 cm-1.The water contact angel of the RmUV radiated CG films was significantly improved compared with the control CG films at 60 s.Moreover,the increased hydropHobicity of the films from the RmUV process,decreased the amount of water absorption at a high humidity.Furthermore,a strong dependence of the resulting film solubility in water after 30 min,on the riboflavin content was observed for the RmUV treated CG films.The tensile strength and tensile modulus of the radiated CG films at a high humidity condition were significantly higher than those of the control CG films,thanks to the improved water resistance,while the elongation at breakdecreased.Based on the above results,the UV/riboflavin irradiation is a potential effective process concept for improving the properties of CG films.Second,adding tannin to gelatin solution can improve the mechanical properties and water resistance of the film.When tannins is 30 mg/g(on the dry basis of gelatin),the properties of gelatin film was improved well;the tensile strength is 22.10±0.81 MPa,breaking elongation rate is 40.12±0.03%,water vapor permeability is 1.49293±0.01(g·Pa-1·s-1·m-1×10-11),and Minimum oxygen transmittance is 21.63±0.624 Meg/kg.From the results of differential scanning calorimetry(DSC),FTIR and electron microscope,it was suggested that crosslinking between the tannin and edible film happened.Lastly,the influence of liquid smoke on gelatin film was investigated.The results showed that adding smoke fluid into gelatin film will led to a significant increase in tensile strength and water vapor permeability(P<0.05).The addition of 3%HSLS,gelatin film had the best strength of 13.98±1.25 Mpa.Furthermore,when 2%of AWLS are added to the film-forming solution,edible film get the lowest elongation at break 87.69±15.42%.In addition,the degree of hydrolysis of gelatin film in different liquid smoked have a significant decrease(P<0.05),when adding 3%AWLS,composite film of minimum degree of hydrolysis reached 11.96±1.03%.In addition,enhanced mechanical properties and low degree of hydrolysis may be relation to formed stable covalent bond between smoked fluid and gelatin protein molecules by DSC,FTIR and SEM analysis.Additionally,the addition of all liquid smokes at 5%led to a significant increase in tensile strength(P<0.05),but a decrease in elongation at break under room temperature.Among them,the tensile strength of HSLS reached to 51.80±2.12MPa and 12.99±1.13MPa,and elongation at break as low as 56.47±11.21%and 59.53±10.35%for both natural casing and collagen casing,respectively.Compared with the control group,the smoke liquid treated casings showed a significant deeper color:L*value of the casings decreased,and the a*and b*values increased.Under different temperature,the mechanical properties of casing soaking with HSLS decreased with the rise of temperature.In conclusion,these crosslinking agents:smoke fluid,riboflavin and tannin can well improve the mechanical and barrier properties of the edible film and has a great potential application for special enforcement of edible protein film in food packaging,preservation and functionality.