Reparation Of Oxindized Starch Antibacterial Composite Membrane And Study On Its Fresh-keeping Performance

Coating preservation is one of the effective preservation techniques for fruits and vegetables and has been gained more and more attention due to its good safety and convenience to use.The preparation of the safe membrane-forming solution,with broad-spectrum antimicrobial properties and membrane forming abilities,has become one of the research hotspots in recent years.In this paper the antimicrobial membrane-forming solution has been prepared with the nano-silver as an antimicrobial agent and oxidized starch as the base.The effects of the membrane forming process and the components on the properties of the membranes have been explored systematically.And then,its fresh-keeping effects on cherry tomatoes were investigated.The main results are as follows.The nano-silver sol was prepared by chemical reduction method in aqueous solutions.Transmission electron microscopy and UV-visible absorption spectroscopy detected uniformly dispersed Ag particles with sizes of about 22 nm.Nano-silver sol indicated well stability in the temperature range of 4-65? and could be stored stably for at least 1 month under dark and room temperature conditions.Both the content of the main components of the nano-silver oxidized starch composite film and the drying temperature affect the performance of the film,while glycerol can increase the toughness of the membrane and reduce its brittleness.The optimum conditions for the preparation of the membrane was determined by single-factor test and orthogonal test as follows:concentrations of starch,sodium carboxymethyl cellulose,glycerol and nano silver were 0.05 g/mL and 4 mg/mL,2%and 0.038 mg/mL,respectively,and the membrane should be dried at 55? for 6 hours.After being immersed in 2%NaOH solution for 3 hours or being microwave treated with medium and high power for 9 seconds,the composite membranes showed enhanced mechanical properties.The tensile strength of the membrane enhanced nearly 82.37%by alkali treatment and 102.03%by microwave treatment respectively.In addition,the elongation of the membrane was increased by alkali treatment,but decreased by microwave treatment.The appearance,microstructure and thermal stability of oxidized starch composite membrane and raw starch composite membrane were analyzed by scanning electron microscope and differential scanning calorimeter.Compared with the raw starch membrane,the oxidized starch membrane had smoother surface,more compact and uniform structure and better thermal stability.Fresh cherry tomatoes were used as the test material to study the preservation effect of the nano silver-oxidized starch coating solution.The coating treatment was found to remarkably reduce and delay the weight loss of the fruit,Vitamin C contents,as well as soluble solids,and total sugar content in the tomatoes.These effects were beneficial to preserve the quality of tomatoes and prolong their preservation time.In addition,the concentration of nano-silver in the coating solution had an effect on the preservation effect of cherry tomatoes.The best preservation effect was obtained when the concentration of nano-silver in the coating solution was 0.038 mg/mL.