A Study Of Tea Scenting Technology And Mechanism By The Jasmine Essential Oil From Subcritical Extraction

Jasmine tea is a special kind of tea in China,which is popular among international customers with elegant and strong fragrance,fresh and pure taste.Currently,the traditional tea-flower mixing method is still majorly used in the processing of jasmine tea.However,there are various problems,such as complicated process,long production period,high labor intensity,low fragrance efficiency,large amount of jasmine flowers to tea base,constantly increasing cost and secondary pollution from pesticide residues.Those problems significantly slow down the sustainable development of jasmine tea industry.The aims of this study include promoting the development of jasmine tea(as featured tea of Fujian province)in accordance with the Chinese tea industry,improving the jasmine tea processing technology and equipments based on technology innovation,forming healthy and efficient jasmine tea industries to expand the market.This study focuses on the tea scenting technology by the essential oil extracted from jasmine in subcritial fluid conditions.The jasmine aroma releasing mechanism and the aroma absorption(desorption)dynamic principles were investigated.The integration of the multidisciplinary technologies(e.g.,the subcritical fluid extraction technology,the aroma absorption(desorption)technology,the controlling technology of tea processing conditions,the tea fragrant-adding technology,etc.)leads to the major progress in replacing the traditional tea-flower mixing scenting technology for jasmine tea.The featured study results are as follows:1.Dynamic detection and analysis on the basic scenting data for tea-flower mixtureDuring the scenting process,the temperatures of the ternary objects "piles,flowers,tea" rendered the tendency of "low-high-low-medium".The temperature of flowers(43.6 ?)was significantly(P<0.05)higher than leaves(42.02?)and piles(42.24?).The average temperature of piles rises at the rate of 0.63 ?/h.The average moisture content of fresh flowers(84.78%)was remarkably higher than tea leaves(5.25%).The temperature gradient and the moisture gradient enable the aroma absorption by the tea leaves.2.Collecting and absorbing technologies of jasmine fragrance based on the activated carbon with efficient absorbent capabilityThe common methods of gathering fragrance from jasmine flowers include grease absorption method,blowing air absorption method(activated carbon or resin),etc..Due to the extremely dense cellular structure and huge BET(specific surface area)in the activated carbon,plus its capability to absorb gaseous mixture with high humidity and aqueous solution,and its advantages of low cost and fast regeneration,this study applied activated carbon as the absorbent for jasmine flowers fragrance.Study of the absorption and desorption property based on different activated carbons(coconut sheet,shell and coal carbon)indicated that the absorption and desorption of coconut sheet JH-16×32 were 22.07%and 97.89%,respectively,which were significantly(P<0.05)higher than other activated carbons.The BET was up to 1224.79m2/g,which was higher than other activated carbons.Also,the coconut sheet has the micropore structures with lnm-7nm sizes,which was 3-4 times larger than the diameter of the aroma moleculars from jasmine flowers(less than 1nm).Therefore,the coconut sheet is suitable to absorb and isolate the essential oil from jasmine flowers.3.Development of devices for jasmine fragrance release and collection and its absorption test.This study developed a device for jasmine fragrance release and collection.The device consists of a control system for aroma releasing environment,a releasing cabin and an aroma absorption system.The dependency of aroma releasing property on the temperatures and relative humidity indicated that,the rate of water loss,openness,sensory quality and absorption rate of activated carbon were improved by the treatment T2(temperature of 30?,relative humidity of 85%),T3(30?,95%)and T5(35?,85%)than other treatments.The score of aroma quality was higher by the treatment T5(35?,85%),T4(35?,75%),T6(35?,95%).Overall,the best aroma releasing temperature and relative humidity of jasmine flower were 35? and 85%,respectively.Under the environment with suitable temperature,relative humidity and airflow,the flowers kept strong vigor and vitality,and the aroma releasing time was extended by 8 hours than the tradition treatment.Therefore,the aroma releasing efficiency was greatly improved.4.Processing optimization and aroma quality comparison of essential oil from jasmine flower through subcritial fluid extraction.Taking the temperature,solvent to material ratio and time as extraction factors,the study set up the response surface design of three factors and three levels via subcritical fluid extraction of headspace oil,the best extraction conditions were at temperature of 40.5?,solvent to material ratio of 3.4:1,time of 48.1 min.The modified processing parameters based on the practical production rendered the extraction rate up to 4.93%,which was 99.80%of the predicted value,and the total peak area was up to 79356374815,which was 98.26%of the predicted value.By comparing the headspace oil and the disposed flower(curlycue)essential oil from different extraction methods,the extraction rate of these two types of aroma extracts via subcritial fluid extraction were 0.12%and 0.28%,respectively,which were higher than the solvent extraction with 0.10%and 0.21%extraction rate.The quantity of aroma compounds was more than solvent extraction.The contents of alcohols and esters in headspace oil were higher via subcritial fluid extraction,and the contents of main fragrance given ingredients were higher(linalool,benzyl acetate,and methyl salicylate).Meanwhile,the content of alcohols and alkene in curlycue oil were higher via subcritical fluid extraction,and the contents of main fragrance given ingredient were higher which contained linalool,?-farnesene.Therefore,the aroma quality was better via subcritial fluid extraction than that via solvent extraction.Subcritial fluid extraction was a better extraction method for essential oil extraction from jasmine flowers.5.Selecting and optimization of jasmine aroma essential oil-tea scenting process.This study developed a hybrid-type scenting device,consisting of an incense system,a temperature and humidity control system and a suction system.Based on the comparison of chemical quality and sensory quality of different scenting methods,the levels of aqueous extract,tea polyphenol,amino acid,caffeine were significantly(P<0.01)higher in jasmine tea from the combined method than that from the spraying method,and the contents of main aroma compounds were higher(89.04%)than the spraying method(74.15%),including linalool,benzyl acetate,benzyl alcohol,?-famesene,hexenyl benzoate,indole,methyl anthranilate.In addition,the sensory quality from the combined method was superior to the spraying method.Therefore,the combined scenting method was determined as the advanced method for jasmine tea.After the optimization of the scenting process,the chemical quality and sensory quality was better with temperature of 35? and humidity of 85%.The total production cost of jasmine tea by the new scenting technology was 20.79%lower than that by the traditional scenting technology.The major sources for the cost reduction include the decrease of labor cost,fewer flowers required and the save on equipment operation cost.Therefore,the new scenting technology for jasmine tea features high quality and low production cost,hence is promising for extensive industrial applications.6.Effect of different scenting methods on the jasmine tea leave surface structure.The comparison of effects of different scenting methods on the jasmine tea leave surface structure indicated that the BET increased significantly(P<0.05)after tea given fragrance.The comparison of BET was in the order of:mixing method>vaporization method>spraying method,while the pore diameter was not significant different among these three methods.The average pore diameter was about 3.4nm.The pore structure majorly consists of mesoporous structures,with few micropore or macropore:the structure afforded main path for jasmine fragrance absorption.Images by scanning electron microscope demonstrated that the jasmine tea produced by mixing method and vaporization method were both covered with granular dust mixing internal substance,thus the absorption mechanisms of these two methods were similar.For the spraying method,its coverage substance has a different shape,which was regular granular materials,suggesting that the absorption mechanism was different from the two formers.According to the Fourier infrared spectrometer analysis,the active groups of jasmine tea were almost the same by vaporization method and mixing method,including O-H?N-H?C=O?C=C?C-N?O-H?C-H groups.However,the jasmine tea by spraying method was different.These results revealed the chemical and physical principles for the tea aroma absorption.