| Essential oils have antibacterial,anti-inflammatory,anti-cancer and other biological activities,especially antibacterial properties,which show potential application value in food,medicine and other fields.However,the existence of problems such as volatilization and instability of essential oil limits the practical application.At present,the problems of essential oils are mainly solved by encapsulation.Cyclodextrin inclusion technology has achieved good results,but it has the defects of high cost and low load.In this paper,we introduced a one-step method:Inclusion of hydrophobic guests duringβ-cyclodextrin glycosyltransferase-catalyzed cyclodextrin synthesis.Essential oils are added directly in cyclodextrin enzyme production.The reactant was directly emulsified and spray dried when the cyclodextrin yield was stabilized.The objective of this study is to obtain essential oil microcapsules with low production cost and excellent antibacterial properties,and to provide a new idea for the preparation of inclusion compounds.The main contents of this paper are as follows:First,the antibacterial activities of thymol,carvacrol,eugenol and cinnamaldehyde were determinated.The results showed that carvacrol has the strongest inhibitory effect on bacteria and cinnamaldehyde has the strongest inhibitory effect on fungi.Then the best mass ratio of these 2 components is 6:4(cinnamaldehyde:carvacrol).The minimum bacteriostasis concentration of compound oil under 6:4(w/w)was determined,which was compared with single component essential oils,found that the broad-spectrum antimicrobial effect of compound oil is 2-4 times as much as the single component essential oils.Secondly,the system of enzymic production of cyclodextrin with inclusion of essential oils was established.The addition of different essential oils significantly increased the yield of cyclodextrins,indicating the effective inclusion interaction,the yield ofβ-cyclodextrin increased the most significantly.The optimum conditions were determined as follows:Wheat starch as substrate,substrate concentration of 20%,the cyclization enzyme amount 2U/g,core-wall ratio of 1:6(w/w),emulsifier amount 5%,shear rate 1.4×10~4 r/min,shear time2 min,spray drying air inlet temperature of 180°C,feed flow rate of 0.4 L/h.Under the optimal conditions,the total yield of cyclodextrin was 49.53%,the oil loading of microcapsules was 11.25%,the encapsulation yield was 82.81%,and the encapsulation efficiency was 93.29%,which was significantly better than before.Compared with pure cyclodextrin inclusion compounds,the yield of microcapsules in this study was increased.Then,the structure of the inclusion complex was studied.The inclusion modes were studied by means of microscopic morphology,determination of the stability constants and nuclear magnetic resonance.The results showed that the inclusion complexes were spherical and hollow,and particle sizes ranged 1-10μm.Carvacrol withα-,β-,γ-cyclodextrin inclusion stability constants were respectively 397.21,2103.13,996.35 L/mol,cinnamaldehyde were respectively 382.79,1902.57,1183.60 L/mol.The inclusion stability constant ofγ-cyclodextrin with two essential oils is greater thanα-cyclodextrin.The reason may be due to that carvacrol and cinnamaldehyde were able to form inclusion withγ-cyclodextrin at the molar ratio of 2:1.This conjecture was confirmed by the ~1H NMR and2D ROESY study.Then,the inclusion model was established.The essential oil microcapsules may have two layers of encapsulation structure.Besides the oils-cyclodextrins inclusion,the residual substrate of the enzymatic system formed wall layer during the spray drying process,to form the secondary encapsulation of essential oil.This unique structure played an important role on the improvement of essential oil application.Finally,the bacteriostatic properties of the microcapsules were determined from two aspects of direct contact bacteriostasis and fumigation bacteriostasis.The results showed that the MIC of the essential oil microcapsules was 0.1295 mg/ml,which was significantly lower than that of the compound essential oil(0.3125 mg/ml),and that of the microcapsules with maltodextrin as wall material(0.5016 mg/ml)and the microcapsules with maltodextrin-β-cyclodextrin as wall material(0.2550 mg/ml),indicating that the direct contact antibacterial of the essential oil against fungi could be significantly enhanced by enzymatic encapsulation method.The results of volatilization curve showed that the retention rate of essential oil increased by 2 times after exposing 30 d at room temperature.The results of fumigation showed that the microcapsules(containing fumigated MIC essential oil content)could still completely inhibit the growth of Aspergillus niger after exposing for 32 d,indicating that the slow release significantly improved the fumigation antibacterial property of essential oil and prolonged the effective antibacterial time. |
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