Antifungal Effect Of Cinnamaldehyde Microcapsule Based On Tannic Acid Cross-linked Complex Coacervate And Its Application In The Antifungal Film

With the improvement of social economy,the problem of food preservation has attracted more and more attention.Compared with synthetic preservatives,natural bacteriostatic agents such as plant essential oils and their active components have been increasingly recognized.Cinnamaldehyde has broad-spectrum antifungal properties,however it has strong volatility,poor stability and easy degradation.Microencapsulation technology could be an effective way to solve the above problems.In this paper,the complex coacervation method was used to encapsulate cinnamaldehyde.The effects of gelatin Bloom value and tannic acid cross-linking concentration on encapsulation effect,release properties and inhibition of Aspergillus brasiliensis were compared,and the antifungal mechanism was explored.On this basis,cinnamaldehyde microcapsules were added to the film matrix to prepare antifungal films,and the effect of the antifungal agent amount on the film properties was investigated.Furthermore,the anti-mildew effect of betel nut coating film was evaluated.In order to determine the suitable gelatin gel strength(Gel strength 150-240 Bloom g)for the preparation of complex coacervated cinnamaldehyde microcapsules,the effect of gelatin Bloom value on the encapsulation,release and mold inhibition characteristics of microcapsules were investigated.Results showed that the microcapsule prepared by gelatin with Bloom value of 200 had the highest encapsulation efficiency(98.86%)and loading capacity(45.90%),which was attributed to the good emulsifying activity and emulsifying stability of the complex formed with gum Arabic.In that case,the multinuclear microcapsules exhibited good dispersibility.The inhibition zone diameter of cinnamaldehyde microcapsules increased first and then decreased slightly with the increase of Bloom value,and reached 32 mm when Bloom value was 200-220.Circular dichroism and fluorescence spectrum analysis showed that the complexation of gelatin with Bloom value of 200 and Arabic gum did not significantly change the random curl ratio of the complex,but had the most obvious impact on the microenvironment of the hydrophobic amino acid side chain of gelatin,which indicated that they maintained the compactness of the capsule wall in the complex through interaction,so as to improve the antifungal property of microencapsulated cinnamaldehyde.The effect of tannic acid crosslinking concentration on the wall density of cinnamaldehyde microcapsules was investigated,and the reasons for the differences in embedding and release characteristics were explored through the analysis of intermolecular interactions.Compared with the non-crosslinked microcapsules,loading capacity of cinnamaldehyde in microcapsules increased to nearly 50%when the concentration of tannic acid was 0.1%.The further increase of the crosslinking agent concentration(0.2%-0.4%)could improve the mono-dispersity of the average size distribution of microcapsules.This might be due to the decrease of the interfacial tension of the coacervate from 21.03 mN/m to 9.70 mN/m,and the viscoelasticity and stability of interfacial layer formed by the coacervate and cinnamaldehyde were improved.The release of cinnamaldehyde microcapsules slowed down with the increase of tannic acid cross-linking concentration.Infrared spectroscopy and isothermal calorimetric analysis showed that the interaction between molecules in the process of tannic acid cross-linking complex was an enthalpy-driven spontaneous exothermic reaction dominated by hydrogen bonds.With the increase of tannic acid cross-linking concentration,helical conformation in protein molecules was reduced,which promoted the formation of the dense structure of the capsule wall and realized the sustained release of cinnamaldehyde in the microcapsules.In order to further clarify the impact of the sustained-release effect of tannic acid crosslinking on the antibacterial activity of cinnamaldehyde microcapsules,the differences in the antifungal zone diameter before and after storage were compared,and the antifungal mechanism was analyzed in combination with the decomposition of microcapsules,the release behavior of cinnamaldehyde,the microstructure of Aspergillus brasiliensis,the changes of cell membrane potential and cell apoptosis.Results showed that increase of tannic acid concentration significantly enhanced antifungal effect of cinnamaldehyde microcapsules,which was related to the compactness of the microcapsule wall and the growth cycle of Aspergillus brasiliensis.On the one hand,when the degree of cross-linking of tannic acid was higher,the microstructure of capsule wall was tighter,resulting in the slower release of cinnamaldehyde,that was,the longer the time it acted on the growth of Aspergillus brasiliensis,the better the antifungal effect.On the other hand,when the cross-linking concentration in microcapsules was between 0.2%and 0.4%,not only the germination of spores was inhibited,but also the shrinkage of hyphae could be directly observed.Under the action of tannic acid crosslinked cinnamaldehyde microcapsules,mitochondrial membrane potential in Aspergillus brazilianus was disrupted and mitochondrial function was inhibited,resulting in apoptosis.The cinnamaldehyde microcapsule based on tannic acid cross-linked complex coacervate was applied to the preparation of antifungal film,and its effects on the optical properties,mechanical properties and antifungal activity of the film were investigated.The results showed that compared with unembedded cinnamaldehyde,the addition of 1%microencapsulated cinnamaldehyde not only helped to maintain the gloss and transmittance of the film in the visible light region,effectively solved the problem of film getting yellow,but also significantly improved the mechanical properties of the film,especially flexibility with elongation at break 23%.However,increase of the addition of cinnamaldehyde microcapsules resulted in a significant increase in the water permeability of the film,which was related to its ununiform dispersion in the membrane matrix and the loose microstructure caused by poor compatibility.Compared with unembedded cinnamaldehyde,the addition of microcapsules in the range of 0.5%-2%could endow the antifungal film with better long-term inhibition of Aspergillus brasiliensis.The antifungal liquid containing cinnamaldehyde microcapsules was coated on the surface of betel nut for accelerated storage,and it was found that the water retention and appearance gloss of the coated betel nut were effectively improved.The higher the amount of microcapsules added in the antifungal coating,the more obvious the retardation of areca nut mildew in high humidity environment.Replacing more than 2/3 of the synthetic preservative with cinnamaldehyde microcapsules could achieve better anti-mildew effect of betel nut.