| Hexahydro-?-acid(HH)was one of the hydrogenated derivative of ?-acid which was an important soft resin component in hops.HH displayed a broad antibacterial spectrum against most food spoilage bacteria,especially for Listeria monocytogenes,Proteus vulgaris and Pseudomonas fluorescens.Whereas HH was so water-insoluble that limited its application in water-based food system.unlike other active ingredients from hop,the advantages of HH had not the strong taste of bitter,however,its good physiological activities not only were kept,but also obviously superior to its precursor?-acid.Therefore,it could be used in various food systems to play a role in antibacterial and anti-corrosion once the water solubility were improved,which not only explanded the application of hops,but also provided a safe preservative from natural source for the food system.In this paper,seven kinds of cyclodextrin inclusion compounds with HH were prepared and their structure were studied.The inclusion processes of hexahydro-?-acid-2-Methyl-?-cyclodextrin inclusion compound(HH-M-?-CD)and hexahydro-?-acid-?-cyclodextrin(HH-?-CD)were optimized,and then the process parameters of seven kinds of inclusion compounds were determined.Meanwhile,focused on the antibacterial activity,stability of inclusion compounds as well as their synergistic effects with the common food additives.The main research contents as follow:The process of cyclodextrin inclusion compounds were compared by water bath method,microwave method,ultrasonic method and grinding method,and the grinding method was the best one.The structure of seven kinds of inclusion compounds obtained by grinding method were identified and analyzed.The results showed that red-shift occurred at the characteristic absorption peak of the UV spectrum of the inclusion compounds compared with HH.IR spectrum showed that the characteristicabsorption peaks of HH disappeared in the inclusion compounds,but could be clearly observed in the mixture.A new absorption peaks were obsvered at 500~1000 cm-1 in inclusion compounds,which indicated that the inclusion process of HH and cyclodextrin was a combination of van der Waals force,hydrogen bond or other forms.XRD could also be observed that the crystal structure of HH disappeared in inclusion compounds,and it was existed in the mixtures of the superposition of HH and cyclodextrin.Meanwhile,different morphologies of HH,cyclodextrins,inclusion compounds and mixtures were also comfirmed by SEM.TLC could make further effects to prove that the formation of inclusion compounds and the structure of HH did not changed before and after inclusion by seven kinds of cyclodextrins.The effect of temperature,time,host-guest molecular ratio on inclusion effect were studied and the optimized preparation technology were obtained combine single factor and orthogonal design methods.In view of structural difference of cyclodextrins,the preparation processes of HH-M-?-CD and HH-?-CD were optimized by orthogonal test,respectively.The optimal condition for HH-M-?-CD was inclusion temperature 30?,grinding time 90 min,host-guest molecular ratio1:80;and for HH-?-CD was inclusion temperature 60?,grinding time 60 min,hostguest molecular ratio 1:40.Since the difference between the two optimization processes,the inclusion rate of the other six inclusion compounds were compared under the optimal condition of the two groups,respectively.Finally,the other six inclusion compounds were prepared by selecting the optimal combination of HH-?-CD except for HH-M-?-CD.The seven kinds of inclusion compounds abovementioned were soluble in water,but were different in their solubility,among HH-M-?-CD was the largest(0.821 mg/mL,calculated as HH),followed by HH-?-CD,and(hexahydro-?-acid-?-cyclodextrin)HH-?-CD was the lowest(0.147 mg/mL,calculated as HH).The result of antioxidant evaluation showed that seven kinds of inclusion compounds had different abilities in scavenging ·OH and DPPH·,and their scavenging capacities were better than HH at the same concentration as well as reference substance BHT.On the basis of above results,synergistic effect(SE)as the evaluation criteria and sodium benzoate was used as reference,studying the synergistic antioxidant activity of HH-M-?-CD,HH-?-CD,hexahydro-?-acidhydroxypropyl-?-cyclodextrin(HH-HP-?-CD),hexahydro-?-acid-2,3,6-Trimethyl-?-cyclodextrin(HH-TM-?-CD),mixed with food additives(vitamin C,sodium chloride,citric acid,and sucrose).The results showed that the bi-component combination of all kinds of inclusion compounds/vitamin C/sodium chloride/sucrose had preferable synergistic antioxidant activity,but the bi-component combination of inclusion compounds/citric acid and the multi-component combination of inclusion compounds/vitamin C-sodium chloride-sucrose had no synergistic antioxidant activity in ·OH system.Meanwhile all of the bi-component/multi-component combination had referable synergistic antioxidant activity in DPPH· system except the bi-component combination of inclusion compounds/sucrose.However,as the reference,the bicomponent combination of sodium benzoate and food additives did not exist synergistic antioxidant activity in OH and DPPH· systems.The results of the study on the stability of the seven inclusion compounds showed that the contents of them were slightly decreased but not obvious at different intensity of the various light exposure,only were the preservation rate of HH-?-CD,hexahydro-?-acid-?-cyclodextrin(HH-?-CD)and hexahydro-?-acid-2,6-Dimethyl-?-cyclodextrin(HH-DM-?-CD)lower than HH methanol solution,and others had no significant difference;the decrease rate of all the inclusion compounds were darkness<natural light<ultraviolet light,indicating that they were sensitive to ultraviolet light,it should be keep away from the light.The effect of temperature onthe stability of the inclusion compounds showed that they were stable at 50? or less;and the preservation rate of them were about 80% of the initial value after the treatment below 80? for 1 h,while when the temperature was above 80?,the stability decreased rapidly;treatment at 120? for 10 min and 1 h,the preservation rate of which were about 70% and 40%,respectively,indicating that high temperature for a long time treatment had a certain impact on the sability of the inclusionsion compounds,but high temperature for a short time treatment had no obviously effect,which indicated that the inclusion compounds could be applied to food industry.The effect of acid-alkali on the stability of the inclusion compounds indicated that preservation rates were above 95% with pH from 3~11,it demonstrated that the acidalkali had no effect on the sability.Also the addition of four kinds of food additives(Vc,NaCl,citric acid and sucrose)had no effect.Study on the antibacterial activity of the seven inclusion compounds indicated that all of them had different antibacterial effect against Staphylococcus aureus and Escherichia coli as well as the bacteriostatic effect was persistent,and also the ability of inhibiting staphylococcus aureus was stronger than that of inhibiting Escherichia coli.Among them,the antibacterial activities of HH-M-?-CD,HH-DM-?-CD and HH-HP-?-CD were significantly stronger than the other inclusion compounds and HH acetone solution,and the entire MIC were 8.0 ?g/mL.Compared with untreated group,the antibacterial activity of 3 kinds of inclusion compounds enhanced under the condition of pH>6,whereas decreased under the condition of pH<6;temperature and ultraviolet had no effect. |
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