Preparation Of Cinnamaldehyde Micro-capsule Polylactic Acid Antibacterial Film And Its Preservation On Papaya

Cinnamaldehyde(CA)has strong antibacterial activity against foodborne pathogens and fungi,but it is unstable and easily denatured under light and temperature.The Paste method is a simple Microencapsulation,and the raw material β-cyclodextrin(β-CD)is cheap.The inclusion prepared by paste method can effectively protect CA from the influence of external environment,improve its stability and prolong its antibacterial period.Polylactic acid(PLA)has good mechanical and physical properties,but it lacks antibacterial properties,which limits the application of PLA film in fruit preservation.Papaya is one of the characteristic fruits in Guangxi province,which is a rich resource of many nutritional active components such as vitamin C,carotene,and protease.Moreover,papayas have high medicinal and industrial value.However,papayas are susceptible to fungal infections and easily ripen at room temperature after harvest and quickly enter the senescence stage,with browning of the skin accompanied by dark spots and soft flesh.These adverse changes lead to its loss of edible and commercial value,resulting in huge economic losses.In this study,CA/β-CD microcapsules were prepared by paste method,and the microcapsules were added into PLA to prepare antibacterial films.Finally,the antibacterial films were applied to papaya preservation.The main contents and results are as follows:(1)CA/β-CD microcapsules were prepared based on the paste method.The optimum process of the microcapsules was obtained by single factor experiment: the molar ratio of β-CD to CA was 1:1,the inclusion temperature was 50 ℃,the volume of ethanol was 5 ml,the stirring time was 4 h,and the stirring rate was 1000 R/min.Under the optimum preparation conditions,the encapsulation efficiency(EE)and loading capacity(LC)of CA/β-CD microcapsules was 63.26% and 6.46%,respectively.The prepared CA/β-CD microcapsules were multi-layer crystals with uniform size and regular shape,and had good thermal stability.The CA/β-CD microcapsules had a sustained-release period of 18 days(at 37 ℃.)(2)The PLA antibacterial films with different concentrations(0,5%,10%,20% and 30%)of CA/β-CD microcapsules were prepared.When the content of CA/β-CD microcapsule was 10%,the surface and cross-section of antibacterial film were smooth,the crystallinity was increased,the tensile strength was increased,and the barrier property was enhanced.However,the addition of CA/β-CD microcapsules reduced the elongation at break of the antibacterial film,and did not significantly improve the thermal stability of the antibacterial film.In addition,the antibacterial film with 10% microcapsule has 100% antibacterial rate against Gram-positive bacteria(Listeria)and Gram-negative bacteria(E.coli).The sustained-release rate of the antibacterial film containing 10% CA/β-CD microcapsules was relatively stable,and the sustained-release period was 20 days(at 37 ℃.)(3)In order to prolong the shelf life of papaya,the prepared antibacterial film was made into a bag to preserve fresh papayas.The bagged papayas were stored at 25 ℃ and 50%bagged or packed with polylactic acid film.Compared with the control group,the antibacterial film bagging treatment reduced the weight loss,softening,color change and decay rate of papaya,delayed the decrease of titratable acidity and ascorbic acid content,and maintained the respiratory rate,p H value and soluble solid content.The results showed that CA/β-CD microcapsule PLA antibacterial film could effectively maintain the postharvest quality of fresh papaya and prolong its shelf life.