| In this paper,White Guanxi honey pomelo was used as experimental material,the pomelo peel essential oil was extracted by hydro-distillation,after all the pomelo peel essential oil was purified by molecular distillation combined with GC-MS Real-time analysis for obtaining various fractions with different boiling points.The characteristic aroma components of pomelo peel oil were identified through the evaluation of artificial sensory evaluation and OAVs value calculation.At the same time,the antioxidant activity and antimicrobial activity for each fraction were investigated to study the active ingredients for examining the enrichment effect of the molecular distillation process in the peel essential oil of pomelo.The study main results are focused on:1.The peel essential oil of pomelo was extracted by hydro-distillation,the extraction technique was optimized by response surface methodology combined with Box-Behnken design.Based on the results of the single-factor experiments,solvent-to-sample ratio,NaCl concentration and distillation time were identified as the significant factors that are influencing the yield of the pomelo peel crude oil(Co).These parameters were further optimized through a central composite design and the results revealed that the optimum conditions were the sample-to-solvent ratio =1:11.75 g/mL.The NaCl concentration was 2.71%and the distillation time was 60 min with this operating condition,the yield of the pomelo peel crude oil was(2.8410.04)%,which was close to 2.85%of predicted value.The chemical composition of pomelo essential oil was analyzed using Gas Chromatography-Mass Spectrometry(GC-MS)and Gas Chromatography(GC).The results demonstrated that thirty-three compounds were identified representing approximate 99%of the pomelo peel crude oil(Co).The principal constituents in crude oil were geraniol(156.52 g/L),D-limonene(66.33 g/L)and β-caryophyllene(41.05 g/L),respectively.2.Pomelo peel essential oil is refined by molecular distillation combined with GC-MS.The first-stage in molecular distillation of pomelo crude oil was carried out by adjusting the evaporator temperature,vacuum degree and the temperature of the primary condenser,and the chemical composition of each fraction was analyzed in Real Time with GC-MS.Under the conditions of the evaporation temperature was 20℃,the operating pressure was 1～10 Pa,the temperature of the primary condenser was-10℃,finally,the separation effect was successfully,and three primary fractions were obtained:heavy residue 1RH7,middle distillate 1DM7 and light distillate 1DL7,the yields of them were 45.78%,34.52%and 17.96%,respectively.In order to obtain the relatively concentrated fractions of the boiling point,the second-stage in molecular distillation was acomplished to the first-stage fractions by changing the distillation conditions,and six fractions in the second-stage were obtained.The concentration of geraniol and β-caryophyllene in 2RH1 was significantly increased,which was 2.2-fold and 2.3-fold that of 1RH7,respectively.The middle distillate 2DM2 was enriched in components with a boiling point in the middle,such as a-terpineol.The light distillate 2DL3 had removed the high boiling point component,and number of compounds decreased from 25 types of 1DL7 to only 12 types and the boiling point distribution range was diminnished,whereas D-limonene can be suitable to the light distillate 2DL3 with concentration ration close to 1.3 than the light distillate 1DL7.After these,for the two-stage molecular distillation,the main components of heavy residue 2RH1 were mainly geraniol and β-caryophyllene,and the major components enriched in light fraction 2DL3 was D-limonene.3.The characteristic aroma components of pomelo peel crude oil were identified.The aroma changes of the fractions after the molecular distillation were studied.Through the evaluation of the artificial senses and the calculation of the OAVs,were preliminarily determined that the overall odor intensity,odor sensitivity and pomelo peel smell of heavy distillate(2RH1,2RH2)were higher,and the total OAV value was 2-fold that of crude oil.After analyzing the components of each fraction and according with the literature analysis,we found that the components which contributed to the essential oil flavor of pomelo peel could be on account of geraniol,decanal and a-terpineol-based oxygenates and β-caryophyllene together.4.The inhibition ability of pomelo crude oil and fractions to Gram-negative bacteria(Escherichia coli,ATCC NO.8739 and Pseudomonas aeruginosa,ATCC NO.27853),Gram-positive bacteria(Bacillus subtilis,ATCC NO.14579 and Staphylococcus aureus,ATCC NO.6538)and fungi(Candida albicans,ATCC NO.10231 and Aspergillus niger,ATCC NO.16888)were detected by broth microdilution method.The experimental results show that the crude oil didn’t have inhibitory effect on Gram-negative bacteria and on the other hand,the minimum inhibitory concentration(MIC)against Bacillus subtilis and Staphylococcus aureus were 312.5μg/mL and 1250 μg/mL,and 39 μg/mL and 19.5 μg/mL for Candida albicans and Aspergillus niger,respectively.Light distillate(1DL7,2DL3)had significant influences on Escherichia coli,Pseudomonas aeruginosa and Staphylococcus aureus,and the inhibitory effect of 2DL3 on Escherichia coli and Staphylococcus aureus was increased by 2-fold and 1-fold than 1DL7.It is possible that the fraction 1DL7 and 2DL3 enrich more antibacterial compounds,such as D-limonene,sabinene and pinene.5.In vitro the antioxidant activity of different fractions was investigated.By measuring the free-radical scavenging activity of fractions obtained by two-stage molecular distillation to DPPH and ABTS,the results show that the order of antioxidant activity was 2RH1>2RH2>2RH3>1RH7>2DMi>Co(Crude oil)>1DM7>2DM2>1DL7>2DL3-Moreover,free-radical scavenging activity was determined for all fractions and was highest in 2RH1,increasing by 60%in DPPH and 75%in ABTS greatly higher than pomelo crude oil.The compounds that are playing a role are likely the result of the combination of various high-boiling components,mainly geraniol and β-caryophyllene. |
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