Study On Preparation And Properties Of Active Packaging Films Based On Porous Starch

Food packaging is essential to prevent food contamination and waste,and active packaging can provide better protection for food by changing its external conditions.Antimicrobial packaging and antioxidant packaging are common active packaging,which can play a better role in preserving food through the interaction of active agents such as antimicrobial agents and antioxidants with food.If the slow release of active agents can be achieved,they can provide a longer protection for food.In this subject,slow release active packaging films were prepared based on porous starch which was used as slow release carrier of tea polyphenols.The films were characterized,and the release behavior of tea polyphenols and antioxidant activity of films were studied.The main contents can be divided into the following three parts:（1）Study on preparation and adsorption properties of porous starch.With corn starch as substrate,porous starch was prepared by enzymatic hydrolysis with α-amylase and amyloglucosidase,and single factor experiment was carried out to determine the optimal preparation conditions of porous starch.The particle size of porous starch was about 10 μm observed by SEM,and there are many pores with a diameter of about 1 μm distributed on porous starch,extending from the particle surface to the interior.The specific surface area,oil adsorption and water adsorption of porous starch were 31.16%,121.91% and 131.02% larger than those of corn starch,respectively.（2）Study on corn starch/PSTP active packaging films.Porous starch loaded with tea polyphenols（PSTP）was prepared by using porous starch to adsorb tea polyphenols and added to corn starch matrix.Active packaging films were prepared by solution casting method and characterized.The release behavior,release mechanism and antioxidant activity were also studied.It was found that the interactions between the components of films are mainly physical interactions,and no new chemical bonds were generated.The addition of PSTP can increase the crystallinity of films.The film is smooth,uniform and compact,and the compatibility between the components is good,without obvious phase separation.After adding PSTP,the tensile strength of films increased by 28.54%,swelling degree decreased by 11.17%,the thermal stability of films was slightly improved,the ultraviolet barrier properties and antioxidant activity of the films were greatly improved,but the water vapor barrier properties and transparency of films slightly decreased.The addition of PSTP can slow down the release rate of tea polyphenols from films and prolong the time they take to reach release equilibrium by 33.33%.The release kinetics of tea polyphenols can be described by Fick’s second law.The films have excellent antioxidant activity and can achieve sustained release of tea polyphenols,which can be used as active food packaging films to extend the shelf life of food.（3）Study on PVA/PSTP@MD active packaging films.In order to improve the mechanical properties and overcome the water sensitivity of starch films,polyvinyl alcohol（PVA）was used as matrix for the preparation of films.In order to further enhance the slow release effect of tea polyphenols,PSTP@MD microcapsules were prepared by freeze drying method with PSTP as core material and maltodextrin（MD）as wall material to realize the slow release of tea polyphenols.PSTP@MD microcapsules were added to PVA matrix and the active packaging films were prepared by solution casting method,which were characterized and their release behavior and antioxidant activity were investigated.It was found that the interactions between the components of films were physical interactions,without new chemical bonds.The addition of PSTP@MD microcapsules can decrease the crystallinity of films,and the compatibility between PSTP and PVA film can be improved after the formation of microcapsules.After adding PSTP@MD microcapsules,the ductility of films was enhanced,water content decreased by 46.74%,swelling degree decreased by 54.38%,water vapor barrier and ultraviolet light barrier properties of films were improved,the transparency was high and the transmittance at600 nm was 76.02%,the thermal stability of films was improved and the maximum thermal decomposition temperature increased by 83.83 ℃,the antioxidant activity of films was high and the DPPH radical scavenging rate was 58%,but the tensile strength of films decreased,solubility and hydrophilicity increased.Encapsulation of tea polyphenols with porous starch or microcapsules can achieve slow release effects,and microcapsules have better slow release effects.In addition,the release of TP from films follows Fickian diffusion mechanism.