Construction And Performance Of Intelligent Color Responsive Coatings On The Surface Of Polvlactic Acid Film

Recently,intelligent packaging that can detect food freshness in real-time has attracted increasing attention.Anthocyanin(ANT)has a certain potential in food freshness detection because of its natural and safe water-soluble material with pH response.At present,polylactic acid(PLA)is one of the current researching focuses on packaging film due to its rich sources,biodegradability,easy processing and molding.The application of ANT in PLA film to construct a safe and reliable intelligent color film will be a new exploration of intelligent packaging for food freshness detection.However,hydrophobic PLA can not be mixed with hydrophilic ANT to form a film.Therefore,in this paper,the PLA film is endowed with a color response function through the construction of intelligent color indicative coating on the surface of the PLA film,whose properties are optimized by adjusting the components of the coating.The main research contents and results are as follows:Firstly,purple sweet potato was used as raw material,and the volume ratio of glacial acetic acid and anhydrous ethanol was changed by organic solvent extraction to explore the effect of different extractant ratios on ANT extraction.FT-IR,UV-vis absorption and pH differential method were used to characterize and analyze.The results showed that when the volume ratio of glacial acetic acid to anhydrous ethanol was 1:1,the content of ANT in the ANT extract was the highest,24.38 mg/L.Through the research on the color response performance of ANT extract,it was found that ANT extract had better color response performance when the volume ratio of glacial acetic acid to absolute ethanol was 1:0.5,1:1,and 0.5:1.Secondly,the intelligent color response coating on the surface of PLA film was prepared by mixing sodium alginate(SA)and ANT extraction solution.And the effects of SA concentration and the mixing ratio of SA and ANT extract on coating performance were investigated.It was found that when the SA concentration was 5%and the mass ratio was 1:1,the ANT content in the coating was higher and the coating had a better coating effect.Then,the influence of the coating layer number on film performance was investigated.Through the research on the color response performance and oxidation resistance of the films,the results showed that the color response performance and oxidation resistance of the films were continuously improved with the increase of the number of SA/ANT coating layers.When the number of coating layers was 5,the film had the most obvious color response performance and the brightest color;the final scavenging rate for free radicals reached 82.76%.Through UV-vis spectrum testing,the results showed that as the number of SA/ANT coatings increased,the transmittance of the film decreased at 600 nm.When the number of coating layers was 5,the light transmittance was 85.23%,which was 8.22%lower than the PLA film,and still had a higher light transmittance.At the same time,the transmittance of the film to UV was also reduced compared with PLA film.In the range of 250?350 nm,the UV transmittance was 34.52%around.Finally,tannic acid(TA)was added to improve the oxidation resistance of the film,and the effect of the addition ratio of TA in the coating on related performances of the film was discussed.Through the antioxidant performance test,the results showed that the free radical scavenging ability of the film increased with the increase of the TA addition ratio.When the TA addition ratio was 5%,the free radical scavenging ability of the film was 4 times that of the film prepared by SA/ANT coating with the same layer number.According to the research on the color response performance,although the color response performance of the film decreased with the increase of the TA addition ratio,when the TA addition ratio was 5%,the film still had a good color response performance.In addition,with the increase of the TA addition ratio,the film's UV absorption capacity also improved to a certain extent.When the addition ratio of TA was 5%,the UV transmittance in the wavelength range of 250?300 nm was almost 0.In summary,the addition ratio of 5%TA in the coating improved the film's oxidation resistance,and also had a good color response performance,as well as enhanced the film's UV absorption ability.