Screening Of Antioxidant Active Components Of Essential Oil From Boesenbergia Rotunda (L.) Mansf. And Its Application In Fresh Cut Grass Carp

Boesenbergia rotunda(L.)Mansf.belongs to the Boesenbergia genus of the Zingiberaceae family.It is wildly distributed in Thailand and Indonesia and is cultivated in Xishuangbanna Dai Autonomous Prefecture,Yunnan Province,China.B.rotunda is one of the natural spices.B.rotunda essential oil(BEO)is major bioactive components in the rhizome of ginger,but there are no detailed reports about BEO at home and abroad.Based on the exploration of the antioxidant mechanism of BEO,the composition and structure of the natural antioxidant active components in BEO were studied,and the application of inclusion complex(BEO-K-?-CD-MOF)to improve the oxidation stability of fresh-cut grass fish was also studied.In order to make full utilization of the plant resources,it provides more possibilities for the development of natural antioxidants.The research includes four parts:(1)Ultrasonic-microwave-assisted extraction of BEO and evaluation of antioxidant activity.The ultrasonic-microwave assisted method is used to extract BEO,and the best crushing conditions(microwave power,microwave temperature,and microwave time)of BEO are determined by single factor experiment combined with response surface method.Under the crushing conditions,the best extraction process conditions(material-to-liquid ratio,extraction power,extraction time)are determined.The results showed that the optimal conditions for ultrasonic-microwave-assisted extraction were microwave crushing power600 W,microwave crushing temperature 96?,microwave crushing time 3 min,the ratio of solid to liquid 1:15(g/m L).And the extraction power 500 W,extraction time 25 min.The essential oil extraction rate is 2.86%.At the same time,the antioxidant activity of BEO was studied regarding to total antioxidant capacity,scavenging capacity for DPPH,ABTS⁺,OH radicals,comparing with antioxidant propyl gallate(PG)and butylated hydroxytoluene(BHT)by calculating the half-maximal inhibitory concentration(IC₅₀).The experiments showed that in a certain concentration range,BEO had certain antioxidant activity,and the total antioxidant activity of BEO was weaker than that of PG and BHT,and the scavenging ability of DPPH and ABTS⁺was also weaker than that of PG and BHT,while the scavenging ability of OH free radical was stronger than that of PG and BHT.(2)The component analysis and antioxidant activity screening of BEO.The chemical composition of BEO was analyzed by GC-E-nose and GC-MS.Twenty-five constituents including the higher content of?-ocimene(38.56%),1,8-cineole(24.81%),myrcene(13.14%),and?-terpineol(11.57%)were identified in BEO by GC-E-nose technique.By comparison with the GC-MS results,the coincidence reached 86.2%.In addition,GC-E-nose combined with the chemical method was used to screen the active ingredients of BEO to scavenge DPPH,ABTS⁺,and OH radicals.Principal component analysis(PCA)results showed that the content of volatile components after the reaction between BEO and DPPH,ABTS⁺,and OH radicals are significantly different,and among active components of BEO,?-terpineol(65.17%),1,8-cineole(60.35%),and geranial(64.67%)had the strongest radical scavenging ability for DPPH,ABTS⁺,and OH radicals,respectively.According to the structure of the active ingredient,the scavenging reaction mechanism is further clarified.The corresponding structure-activity relationship was established.(3)The preparation,characterization,and stability of the inclusion complex of BEO(BEO-K-?-CD-MOF)were studied.Because BEO is mainly composed of terpenes containing more conjugated double bonds and has strong activity,and it is volatile and unstable at room temperature,the application of essential oil is limited..BEO-K-?-CD-MOF was prepared using?-cyclodextrin potassium metal organic framework(K-?-CD-MOF)as the wall material to improve the stability of the essential oil.The inclusion complex was characterized by infrared spectroscopy and X-ray diffraction,and its light,heat and acid-base stabilities were also evaluated.The results showed that the inclusion ratio of the essential oil from BEO to the material was 1:1.The reaction was an exothermic spontaneous reaction.The saturated aqueous solution method was adopted to carry out the inclusion of BEO,the inclusion rate is the highest when the core-wall ratio of the inclusion is 1:10,reaching 71.70%.The different methods were used to study the light,heat,and acid-base stability of the inclusions,and the light and heat stability were increased by 50.0%and 76.0%,respectively.The stability was better under the conditions of p H=3and p H=7 to compare with physical mixture.And the retention rate was increased by 33.9%and 17.4%,respectively,indicating that BEO-K-?-CD-MOF is more suitable for use in acid to neutral environments.(4)Application of BEO-K-?-CD-MOF in fresh cut grass carp.In order to explore the application value of inclusion compound in practice,BEO-K-?-CD-MOF was added as a preservative to fresh grass carp meat to evaluate the quality change and stability of grass carp meat by measuring the water loss rate,thiobarbituric acid value(TBARS),texture and color changes of grass carp meat under different treatment methods.The results showed that,compared with the control group(untreated),the water loss rate TBARS of the fresh cut grass carp with inclusion complex were reduced by 35.0%?64.0%and 46.0%?71.0%,respectively.The hardness,elasticity and chewability were lower than 6.8%?24.1%,15.4%?28.2%and 45.8%?70.6%,respectively.The color change of fresh cut grass carp(to produce color no.2712,light grayish brown)was lower than 59.6%?80.0%.It indicates that BEO-K-?-CD-MOF had obvious preservation effect on the fresh cut grass carp.