Study On Extraction Technology And Composition Of Essential Oil From Pomelo Leaves

Citrus maxima Merr.is an important bulk fruit of Rutaceae and citrus.China is the largest producer of grapefruit around the world,and its planting area reached 96000 hectare in 2018,among which the existing planting area of grapefruit in Meizhou City,Guangdong Province is 40053 hectare.A large number of abandoned grapefruit leaves are generated due to pruning in the planting process of grapefruit,which not only causes great waste of resources,but also greatly increases the breeding opportunities of pests and diseases.As a Rutaceae plant,pomelo leaves have unique flavor.In this paper,the potential of extraction and comprehensive utilization of essential oil from pomelo leaves were evaluated based on the extraction process and chemical composition of essential oil from pomelo leaves.The main results are as follows.1.A rapid analysis method of volatile components in grapefruit leaves based on headspace-solid phase microextraction-gas chromatography/mass spectrometry was established.The optimized headspace extraction analysis conditions were as follows:DVB/CAR/PDMS extraction head,extraction temperature 60℃,extraction time 30 min and equilibrium time 30 min.2.The composition,content and aroma characteristics of volatile components in 17 pomelo leaf samples were compared,and 52 volatile components were isolated and identified,including 7 kinds of compounds:14 monoterpenes,9 sesquiterpenes,17 aldehydes,8 alcohols,2 furans,1 ketone and other compounds.In terms of volatile components,there were 42-47 species of sour pomelo,30-38 species of C.grandis.cv.MiYu,and 31-37 species of C.maxima cv.ShatianYu.In terms of the total peak area,C.maxima cv.ShatianYu and sour pomelo were the largest,followed by Citrus paradisi,and Cgrandis.cv.MiYu was the smallest.The aroma characteristics are mainly divided into three categories.C.maxima cv.ShatianYu and sour pomelo can be classified into one category,showing Ffruit aroma,C-citrange aroma and G-green aroma.Citrus paradisi is classified as K-cedar fragrance,M-bell orchid fragrance and H-herb fragrance.C.grandis.cv.MiYu is classified as a class,G-green,A-fat,M-bell orchid fragrance.3.The differences of content and composition of volatile components in pomelo leaves in different harvest seasons were investigated.The results showed that the peak area of C.maxima cv.ShatianYu leaves was higher than that of C.grandis.cv.HongxinmiYu leaves in the same period,which was about 1.44-6.14 times that of C.grandis.cv.HongxinmiYu leaves in the same period.The content of volatile components in C.maxima cv.ShatianYu was the highest in March,which was 6.14 times of C.grandis.cv.HongxinmiYu.It is suggested that the essential oil content of C.maxima cv.ShatianYu leaves is higher than that of C.grandis.cv.HongxinmiYu,which is suitable for extracting essential oil.March is the most suitable harvest time.Metabonomics method was used for comparative analysis,and the results showed that the composition of essential oils in C.maxima cv.ShatianYu and C.grandis.cv.HongxinmiYu leaves was significantly different.The characteristic volatile substances in C.maxima cv.ShatianYu leaves were β-citral,α-citral,Geraniol and Citronellal,while those in C.grandis.cv.HongxinmiYu leaves were(E)-3-Hexene-1-ol.4.The effects of different drying conditions and storage conditions on volatile components of C.maxima cv.ShatianYu leaves were evalutaed.The results showed that different drying methods caused more than 50%loss of volatile components in pomelo leaves,and the loss rate from high to low was freeze drying(72.93%)>sun drying(68.36%)>shade drying(63.15%)>drying(51.01%).At room temperature storage environment for 3 days,the loss rate of volatile compounds in C.maxima cv.ShatianYu leaves was about 85.00%;when stored at 4℃ for 15 days,the loss rate was 30.00%;when stored at-20℃for 30 days,the volatile components almost had no loss,with no significant difference in comparison with fresh leaves.The above results suggested that low-temperature preservation was an effective way to reduce the loss of volatile components in C.maxima cv.ShatianYu leaves during storage.5.The extraction conditions of essential oil from C.maxima cv.ShatianYu leaves by steam distillation were optimized by Box-Behnken experimental design.The optimum conditions were as follows:extraction time 8h,sodium chloride concentration 2%and solidliquid ratio 1:6.Under this process,the yield of essential oil from grapefruit leaves was 0.071±0.01%,which was basically consistent with the predicted value of 0.069%.6.GC-MS analysis showed that the essential oils extracted by steam distillation were mainly β-pinene(13.30%),α-citral(10.31%),and β-citral(11.54%).The activity test showed that C.maxima cv.ShatianYu leaf essential oil had good inhibitory activity against all tested bacteria such as methicillin-resistant Staphylococcus aureus,S.aureus,Escherichia coli,Bacillus subtilis and Pseudomonas aeruginosa.The MIC was between 0.61 and 5.00%(v/v),and MBC was between 1.25 and 10%(v/v).The MIC was 0.61%(v/v),and MBC was 1.25%(v/v).