Preparation And Properties Of Chitosan Edible Films Incorporated With Hexahydro-?-acids And Prolongation Of Shelf Life Of Fresh Meat

With the increasing attention of people to environmental issues and food safety,it is particularly important to use natural polymers to prepare environment-friendly,healthy and safe alternatives to replace traditional plastic packaging.In the paper,edible chitosan films were prepared using glycerol and hexahydro-?-acids(the reduced derivatives from hops ?-acids)as plasticizer and antibacterial/antioxidant agents,respectively.Based on the optimum conditions of preparing film,the properties of chitosan-hexahydro-?-acids edible films were evaluated.And also,the release of hexahydro-?-acids in ethanol aqueous solutions and the preservation effect of edible films on fresh meat were investigated.The main results of research were as follows:1.The effect of chitosan concentration,glycerol concentration and drying temperature on mechanical properties including tensile strength and elongation at break of films were studied.The optimized the preparation process of chitosan-hexahydro-?-acids edible films were obtained by using single factor and orthogonal test.Results indicated that chitosan concentration was the biggest factor on the mechanical properties,followed by the interaction between the concentration of chitosan and glycerol,while drying temperature showed the minimal influence.The optimized conditions were determined as follows: chitosan concentration 1.75%(w/v),drying temperature 40 ?,and the glycerol concentration 1.4%(v/v).Under these conditions,the chitosan-hexahydro-?-acids edible films showed the best mechanical properties,and the tensile strength and elongation at break were up to 29.26 MPa and 81.29%,respectively.2.Based on the optimized preparation conditions,the effect of hexahydro-?-acids contents of 0.1%,0.2%,0.3%(w/v)on the microstructure of chitosan edible films,as well as its properties was investigated.Fourier transform infrared spectroscopy testified that hexahydro-?-acids had been successfully added into the chitosan films,and scanning electron microscopy showed that the edible films containing hexahydro-?-acids had rougher surface and cross-section.Compared with plain chitosan film,the thickness and opacity of prepared films significantly increased with the addition amount of hexahydro-?-acids.The peak values of tensile strength and elongation at break were found at 0.1%(w/v)dosage of hexahydro-?-acids,and the minimum values at 0.3%(w/v).Within the test dosage,incorporation of hexahydro-?-acids did not affect moisture contents and solubility.Moreover,chitosan-hexahydro-?-acids films exhibited better antioxidant and antibacterial activities,and the activities increased with the concentractions of hexahydro-?-acids.3.The release behavior of hexahydro-?-acids from chitosan-hexahydro-?-acids films into ethanol aqueous solutions of 95%,75%,and 55%(v/v)were studied.The results indicated that the release of hexahydro-?-acids gradually increased with the increase of time and temperature,until the equilibrium was reached.According to the Peppas and Peleg equations,the release of hexahydro-?-acids in 95% ethanol followed by Fick diffusion,while 75% and 55% ethanol accorded with Peleg equation.The diffusion coefficient increased with temperature rising,and the maximum was found in 55% ethanol,which indicated that the major factors on diffusion of hexahydro-?-acids was the moisture contents of simulator and temperature.4.The preservation of fresh meat were applied to evaluate the prepared chitosan-hexahydro-?-acids edible films,and commercial film and plain chitosan film were used as control.The results showed that edible chitosan-hexahydrobeta-acids films could effectively inhibit the growth of bacteria in fresh meat,such as reduce TVB-N value,malondialdehyde content and p H value,which demonstrates that chitosan-hexahydro-?-acids films exhibited better fresh-keeping effect.In particular,when fresh meat was treated with 0.2% chitosan-hexahydro-?-acids films and stored at room temperature for 6 days,all indictors of fresh meat had no significant differences compared with initial values,which suggested the prepared film could effectively extend the shelf life of fresh meat.Meanwhile,the other chitosan films added with different doses hexahydro-?-acids also showed fresh-keeping effect compared with control.