| In this thesis,fresh grapes were studied and pepper and oregano essential oils were used as antibacterial and preservative agents.The microcapsules of pepper,oregano and compound essential oils were firstly prepared by spray drying method,and the preparation process of microcapsules was optimized by single-factor and response surface tests.Then the microcapsules were characterized by scanning electron microscopy and Fourier infrared spectroscopy for encapsulation and release.Finally,the three microcapsules were placed in non-woven fabric combined with spontaneous air-regulated packaging film to store grapes at 12 ℃ and 90% RH,so that the pepper,oregano and the compound essential oil could be released slowly to achieve long-lasting antibacterial and freshness preservation.The results showed that(1)when the essential oil microcapsules were prepared with sodium alginate as the wall material,the highest encapsulation rate of 58.79%(v/v)was achieved at the core-to-wall ratio of 1:3(w/w),homogenization time of 50 s and spray drying inlet temperature of 180 ℃.The FTIR spectra showed that the characteristic absorption peaks of pepper essential oil at 2856 cm-1 and oregano essential oil at 2960 cm-1 could be found in the corresponding microcapsules,indicating that pepper,oregano and the compound essential oils were successfully encapsulated;the release test showed that the release rates of pepper,oregano and compound essential oils in the microcapsule group were31%,32% and 33% lower than those in the unencapsulated group after 20 days of storage,respectively.The in vitro inhibition test showed that the inhibition rate of E.coli was 71.97%,77.41% and 71.13% after 15 days of storage for the prepared pepper,oregano and compound essential oil microcapsules,respectively.It showed that the spray drying operation did not significantly affect the antibacterial properties of the essential oils,and the microencapsulation operation could achieve long-lasting antibacterial effects.(2)The prepared essential oil microcapsules were applied to the postharvest storage and preservation of jasmine grapes.The results showed that the essential oil microcapsules with the introduction of pepper and oregano and their combination on the basis of PCL/PLLA package could effectively delay the respiratory metabolism of grapes and improve the sensory quality.In terms of physicochemical indexes,the PCL/PLLA+CEOM group reduced the decay rate of grapes after 24 days of storage from 14.87%(w/w)to 2.97%(w/w)in the PCL/PLLA gas-conditioned group;meanwhile,the PCL/PLLA+CEOM group was also able to increase the retention rate of total phenols and flavonoids by 23.89%(w/w)and 18.26%(w/w),respectively,compared with the CK group after 20 days of storage.and 18.26%(w/w),and 2.91%(w/w)and 2.03%(w/w)higher than the PCL/PLLA+PEOM group.In terms of microbial indicators,the PCL/PLLA+CEOM group was able to reduce the abundance of Penicillium and Rhizopus,the dominant bacteria causing spoilage after 28 days of storage,from 34% and 38% to 0,with the total number of species reduced from 204 to 111,while the PCL/PLLA+PEOM and PCL/PLLA+OEOM groups groups reduced the abundance of Penicillium spp.to 1% and 2%.In addition,the phenylalanine aminolytic enzyme activity of grapes in the PCL/PLLA+CEOM group only reached a maximum value of 33.64 U/g at20 days of storage,significantly improving the disease resistance of grapes compared to the PCL/PLLA group(P<0.05).In summary,pepper,oregano and compound essential oil microcapsules were successfully prepared by spray drying method.Meanwhile,the introduction of pepper essential oil,oregano essential oil and compound essential oil microcapsules in PCL/PLLA packaging environment could inhibit the growth of major spoilage bacteria of grapes for a long time,while maintaining good organoleptic and physicochemical quality of grapes after harvest,and the effect of PCL/PLLA+CEOM group was better than PCL/PLLA+PEOM and PCL/PLLA+OEOM treatment groups. |
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