The Application Of Chitosan/Whey Protein/Nanometer TiO₂Composite Film To Fresh-cut Bamboo Shoots Preservation

In order to find the suitable modification method, nanometer TiO2was modified byusing lauryl sodium sulfate (SDS) and sodium laurate (SL) in this experiment, respectively.The better modifier was chosen and the modification conditions were optimized by usingthe settling time experiment, fourier infrared spectrometer (FTIR), and scanning electronmicroscope (SEM), respectively. Chitosan/whey protein isolate/nanometer TiO2compositeFilm (CWFT) was prepared by a casting technique mixing chitosan (CTS), modifiednanometer TiO2dissolved in0.1N acetic acid, and whey protein isolate (WPI) dissolved indeionized water under continuous stirring. The preparation conditions of CWTF includingdegree of deacetylation and relative molecular weight for CTS, content of WPI andnanometer TiO2, and ultrasonic time were optimized by analysis of the tensile strength(TS), breaking elongation rate (E), and water vapor permeability (WVP). Under theoptimum conditons, The chromatic aberration, mechanical properties, WVP, and waterabsorption property of CWTF was determined by colorimeter, texture analyzer, the cupmethod and moisture adsorption isotherm method, respectively. The thermodynamic andmorphology properties, and secondary structure of CWTF was analyzed by usingdifferential calorimeter scanner (DSC), scanning electron microscopy (SEM), X-raydiffraction (XRD), and fourier infrared spectrometer (FTIR), and the mechanism of filmswere speculated according to the experiment results. Surfactants including TW20, TW60,TW80, and TW85were added to CWTF, respectively. The suitable surface-active agentwas chosen and its better amount was optimized by the analysis of mechanicalperformance, waterproof performance, FTIR and SEM, and the weightlessness rate offresh-cut bamboo shoots coated with CWTF, respectively. The weightlessness rate,activities of phenylalanine ammonialyase (PAL) and peroxidase (POD), contents of MDA,lignin, soluble solids, and total number of colonies and coliform of fresh-cut bambooshoots stored at4℃were measured during the storage to evaluate the effect of CWTF with thesurfactantonfresh-cutbambooshootspreservation. The results were showed as follows:(1) The results of the settling time experiment showed that the dispersion ofnanometer TiO2modified by SDS and SL was improved compared to the unmodifiednanometer TiO2. The results of FTIR indicated that the bonding ways of nanometer TiO2modified by SL, including the change of hydroxyl numbers and the formation of newbonds were different from that of SDS. SEM results showed that nanoparticles aggregationdegree increased in the light of the following order: unmodified nanometer TiO2,nanometer TiO2modified by SDS, and nanometer TiO2modified by SL. Therefore, SL waschosen as the surface modifier of nanometer TiO2and the optimum conditions were pH5ofthe solution,40℃of mixing temperature,30min of reaction time.(2) The preparation conditions of the CWTF including90%of degree deacetylationand300,000of relative molecular weight for CTS,0.75g/100mL of WPI,0.01g/100mLof nanometer TiO2,15min of ultrasonic time were optimized.(3) Compared to CWF and CF, the chromatic aberration of CWTF increasedobviously and the transparency decreased lightly, and11.51%and25.97%of the tensilestrength and12.01%and13.29%of breaking elongation rate of CWTF increased,respectively. Moreover,7.60%and1.45%of the water vapor transmission rate of CWTFdecreased, respectively. The results of water sorption isotherm found that the hydrophobicproperty of CWTF is the strongest among three films. The analysis of XRD, FTIR, DSC,and SEM showed that the molecules of CWTF crosslinked more compact than the othertwo kinds of films, which makes the film more stable.(4) Surfaces of CWTF with surfactants including TW20, TW60, TW80, and TW85were much rougher than which without surfactants, and mechanical performance andwaterproof performance of CWTF-TW20were the best, second was CWTF-TW85andCWTF-TW80, and CWTF-TW60was the worstest among CWTFs with surfactants. FTIRand SEM analysis showed that regularity of the network structure of CWTFs was differentamong them probably due to the different intermolecular crosslinking degree between surfactants and CWTF, respectively. The weightlessness rates of fresh-cut bamboo shootsgroups coated with films were lower than uncoating group during4℃freezing storage.There was a negative correlation between properties of film and the weightlessness rate.Surfaces of CWTF with different surfactants were all damaged. CWTF-TW20was damagedat a minimum degree, and the most appropriate concentration of TW20was0.1%.(5) Compared to fresh-cut bamboos uncoating group and coating group with CWF, theweightlessness rate and POD activity of fresh-cut bamboos coating group with CWTF wassignificantly low, the content of lignin and MDA, and PAL activity were much lower.Moreover, bacterial growth rate was also inhibited during4℃freezing storage. It wasshowed that the fresh-keeping effect of CWTF on fresh-cut bamboo shoot was significant,which was better than that of CWF. It was indicated that CWTF adding with nanometer TiO2and TW20could extend shelf life of fresh-cut bamboo shoots, which was a properpreservation method.