| As a natural antibacterial agent for food,thymol is easily degraded by external conditions and reduces its bioavailability.Microencapsulation of thymol can broaden its application in the field of food packaging.In this study,thymol/zein/shellac(TZS)microcapsules were prepared by encapsulating thymol with different thymol concentrations and different core-shell flow rate ratios by coaxial electrospray method;Then,the obtained TZS microcapsules were added to the sodium alginate/pectin coating solution under the optimal process conditions,and the antibacterial ability of the coating solution with different addition amounts was measured;Finally,the group with the best antibacterial performance was used to wrap the fresh-cut cantaloupe,and its fresh-keeping effect on fresh-cut cantaloupe stored at 25℃ for 4 days was discussed.The following research results were obtained:(1)The viscosity of the electrostatic spray precursor solutions with different components is lower than 0.0050 Pa·s and have suitable conductivity,which can form stable electrospray microcapsules.(2)The microcapsules formed by the coaxial electrostatic spray process have a tight three-dimensional network structure,which provides the protection and controlled release ability of thymol,and the encapsulation of zein and shellac can improve the long-term storage stability of thymol.Among them,B2 nano-capsules have the best comprehensive performance.Scanning electron microscope results showed that B2 nano-capsules(thymol concentration was 5.0%;electrospray shell-core flow rate ratio was 0.6:0.3 m L/h)were encapsulated spheres with small particle size,uniform dispersion and high encapsulation efficiency(81.34±0.69%),with clear shape and outline,and the lowest degree of agglomeration.Transmission electron microscopy and infrared spectroscopy confirmed good interactions and successful formation of the composite structure,with thymol uniformly distributed in the zein/shellac matrix.The average particle size of B2 nano-capsules is 606.53±21.01 nm,and the range of polydispersity index is low.The retention rate of thymol in B2 after 30 days of storage is68.74±2.14%,and the retention rate of thymol after heat treatment is 47.27±1.66%,with high stability and the best comprehensive performance.(3)The B2 nano-capsules were mixed into the sodium alginate/pectin coating solution with the addition amount of 0%,5%,10%,20% and 30%,and the antibacterial ability and thymol release rate of different solutions were determined.The experimental results showed that the SA/PEC/TZS-20% group showed the largest inhibition zone diameters against E.coli and S.aureus,which were 14.67±0.02 and 14.74±0.02 mm,respectively.The minimum colony diameter of Alternaria alternata was 26.57±0.39 mm,and the effect on the colony size of Penicillium was not significantly different from SA/PEC/TZS-30%.Based on its inhibitory ability to four kinds of bacteria,the SA/PEC/TZS-20% group was selected for fresh-cut cantaloupe pulp preservation.(4)The preservation effects of blank unwrapped group,SA/PEC/TZS-0% and SA/PEC/TZS-20% groups on fresh-cut cantaloupe were studied at 25℃.The SA/PEC/TZS-20% coating containing 20% B2 nano-capsules had the best fresh-keeping effect,and could effectively maintain fruit firmness,weight loss rate,titratable acid and Vc content,etc.After storage for 4 days,cantaloupe pulp still maintained good quality,in which the weight loss rate was only 12.65±1.44%,the hardness was 6.07±0.43 N,the titratable acid content was 0.093±0.01%,the soluble solid content was 9.87±0.37%,and the Vc content was 7.68±0.22 mg/100 g.Thymol also has antibacterial properties,which can destroy the cell walls and cell membranes of microorganisms and produce bactericidal effects,which directly affects the changes in the total number of colonies of fresh-cut cantaloupe within 3days.The addition of 20% B2 nano-capsules can effectively inhibit the growth of bacteria in fresh-cut cantaloupe and reduce the loss of nutrients,indicating that the prepared SA/PEC/TZS-20% coating can effectively prolong the edible period of fresh-cut cantaloupe. |
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