Preparation And Characterization Of Ph Sensing Films Based On Tara Gum

Tara gum(TG)extracted from the endosperm of Caesalpinia spinosa tree,an abundant natrural resource.In this study,TG as raw material,glycerol(Gly)as plasticizer,cellulose nanocrystals(CNC)prepared by acid hydrolysis and PVA as reinforcing agents,extracts from grape skin(EGS and VAHE)and curcumin(Cur)as intelligent agents were used to prepare intelligent packaging films.The effects of their contents on the tensile strength,elongation at break,water vapor permeability,oxygen permeability,UV transparency of films were studied.Fourier transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),thermogrametric analysis(TGA),scanning electron microscopy(SEM)and transmission electron microscopy(TEM)were used to analysis the molecular structure,the change of crystallinity,thermodynamic properties and the microstructure of samples.The rheology properties of the film-forming solutions were also analyzed.Their optimum contents were determined through above characterizations.Besides,the effective intelligent films were obtained by studying their sensing ability to pH environment.The application of films in monitoring milk and seafood were studied as well.Gly was used to increase the feasibility of TG films due to their fragile properties.The appropriate concentration of TG film-forming solution was 0.75%-1%(w/w,based on water)first determined by viscous test.The steady rheological test revealed the TG film-forming solution exhibited a shear-thinning behavior,which was a characteristic Non-Newtonian behavior.Also,the addition of Gly did not alter the Non-Newtonian behavior but destroyed their interactions of TG molecular.Meanwhile,new hydrogen interactions were formed between TG and Gly,which was proved by dynamic rheological test and FTIR.The formation of hydrogen interactions increased the tensile strength and elongation at break of TG/Gly films,but decreased the permeability to oxygen and water vapor.Therefore,considering all the properties of films,the suitable addition of Gly was 30%(w/w,TG).CNC prepared from microstalline cellulose was blended in TG/Gly matrix to increase the mechanical properties of TG/Gly films because of their large surface area and high Young's modulus.Response surface methodology was used to study the effect of sulfuric acid's concentration,hydrolyzed temperature and time on the yield of CNC.The optimum operating condition was 55%of sulfuric acid,50? of hydrolyzed temperature and 2 h of hydrolyzed time.The resultant CNC was rod-shaped with length of 100-400 nm,diameter of 8-10 nm.The chemical structure of cellulose was not changed after hydrolysis proved by FTIR and their crystallinity was increased to 61.58%determined by XRD.The effects of CNC on the properties of films and structure were also characterized.The tensile strength increased to 65.73 MPa and the oxygen permeability of films was 0.7 cm3 mm m-2 day-1 atm-1,higher than that of polyethylene composited films with CNC content increasing to 6%.Extracts from grape skin(EGS and VAHE)were first prepared via acid/ethanol solvents.The UV-vis spectra of EGS and VAHE in the pH range of 1-10 were studied and the color clearly changed from bright red to dark green.EGS was then incorporated into TG/CNC matrix to prepare a colorimetric pH sensing films.The effect of EGS content on the properties and structure of films were studied.The results revealed that EGS was successfully introduced into TG/CNC matrix without obvious interactions.The EGS addition decreased the tensile strength and barrier permeability of films.But the tensile strength significantly increased to 54.80%.The films were immersed in different buffers to evaluate the response to pH changes.Due to the visible color change of films in different pH conditions,the effects of pH value of the film-forming solution on the properties and application of films were further studied.The addition of base and acid destroyed the compact structure of films.And the reduction of tensile strength and oxygen permeability was related to the structure of film.The films showed visible color change in monitoring the freshness of fish.The film formed at pH=6 had a better sensitivity.Considering the good biological and film-forming properties of PVA,a combination of TG/PVA was used to prepare films.The different blending ratios of TG/PVA on the properties,structure of film and rheology properties of film-forming solutions were analyzed.The viscosity measurements revealed that the blended film-forming solution exhibited a shear-thinning behavior and the dynamic tests confirmed the addition of PVA enhanced the elastic behavior.The appropriate ratio of TG/PVA was 8/2 to 7/3.The FTIR results showed hydrogen bonds formed between TG/PVA.The increase of crystallinity of films was illustrated by XRD analysis.The combination of TG/PVA=7/3 blend film possessed better proeprties.Curcumin was further added into TG/PVA matrix.The addition of curcumin decreased the tensile strength but increased elongation at break and water vapor permeability.The films also exhibited antioxidant properties.A release test in 50%ethanol/water food simulant was conducted.The release test indicated that curcumin-incorporated films were suitable for the protection of fatty foods.Moreover,the response of the intelligent films in NH3 environment under different relative humilities was studied.A color response in NH3 environment was visible within 1-3 min.High relative humidity was favorable for a color response.A shrimp spoilage test was conducted to evaluate practical application of the film and an obvious color change was observed when the total volatile basic nitrogen increased to 60.02 mg/g,indicating the film could be used as a sensor in the food industry.Because of curcumin's poor solubility in water,cetyl trimethylammonium(CTAC)brush-TEMPO-oxidized cellulose nanocrystals(TCN)colloidal systems were prepared as a delivery excipient to modulate the hosting of curcumin.The curcumin-loaded cellulose nanocrystals were incorporated in TG/PVA blend matrix to prepare antioxidant and antibacterial films.The resultant TCN was in a diameter of 5 nm with a length of 100-200 nm.And the carboxyl content of TCN was 1.1878 mmol/g and 0.71 degree of substitution of CTAC based on carboxyl groups.There was 26.57%of the curcumin bound in the brush.The prepared CQTCN was then added into TG/PVA matrix to prepare TG/PVA/CQTCN intelligent films.The results show that the mechanical and oxygen barrier properties of the films improved although water vapor permeability slightly decreased.The change of barrier properties was related to the polarity and hydrogen bonding of molecular(FTIR results).The incorporation of CQTCN made the film possessed desirable antioxidant and antibacterial properties.The release test revealed that curcumin was initially released rapidly into 50%ethanol solution,and then released more slowly into the bulk.Moreover,the resultant films showed color response to acid and base environment,indicating the film possessed antioxidant and antibacterial properties,simultaneously had sensing ability.This method provides new idea for the packaging industry.