Study On The Regular Of Flavor Quality Of Roasted Coffee Beans During Storage Based On Accelerated Induction

Coffee flavor is a key factor affecting the quality of coffee.The flavor includes two parts:aroma and taste In the early 20th century,the research on coffee flavor has became one of the important research contents in the coffee field.In recent years,consumers pay more attention to coffee flavor quality,the influence of various composition changes related to coffee flavor during coffee bean storage has became a hotspot.In this paper,the intrinsic influencing factors of the change of flavor quality of coffee roasted beans under different accelerated conditions(storage 40,50,60?)and storage time(0.5,10,15,20,25 days)were studied.Using ultra-high performance liquid chromatography(UPLC),headspace-solid phase microextraction-gas chromatography-mass spectrometry(HS-SPME-GC/MS),liquid chromatography-mass spectrometry(UPLC-Q-TOF)and electronic nose to analyze the changes of chemical composition,preliminary establishment correlationship between chemical components and flavor,in order to provide theoretical basis for improving the flavor quality in coffee storage process.The main results are as follows:1.Accelerate the oxidation degree,shelf life prediction and volatile matter changes of roasted coffee beans during storage.(1)During the accelerated storage period,the fats and oils of coffee oil are hydrolyzed to produce free fatty acids,and the acid value increased;the peroxide value is highest on the fifth day of storage,and then decreases,and at the same time,the TBARS value gradually increases from the fifth day.It is the largest in 20 days,indicating that the oil oxidation product-peroxide is formed most at the beginning of storage,and then decomposes to form secondary oxidation products;Oxidation index reflects the dynamic change of oil oxidation in coffee beans during storage.(2)Calculating the kinetic equation of accelerated storage of coffee through the acid value of coffee oil,the shelf life of coffee roasted beans under the experimental conditions was 60 days.The accelerated storage conditions at 40? were highly consistent with the room temperature storage,50,60? storage within 10 days can be used to characterize the oxidation changes of coffee oil during shelf life;15-25 days to characterize the subsequent changes of oxidation and rancidity of coffee oil.(3)The volatile substances of coffee were extracted by HS-SPME and analyzed by GC-MS.More than 100 kinds of compounds were identified,mainly aldehydes,alcohols,pyrazines,ketones,phenols,acids,pyrrole,furan 8 substances Among the benign flavors of coffee are:dimethylpyrazine and furanone with caramel flavor,coffee flavored furfural,bitter almond flavored benzaldehyde,creamy 3-methylbutanal,sweet scented phenylacetaldehyde and maltol,buta-scented 4-vinyl guaiacol,these substances all decrease with the prolongation of storage period,and the coffee aroma components are gradually lost;in addition,the oil oxidation product hexanal,alkenal and 2-butanone reached the maximum at the storage period of 5 days,the bad flavor increased,the acetic acid content increased on the 20th day,the pungent odor increased,and the coffee flavor quality deteriorated.(4)The electronic nose technology was used to effectively detect the change trend of the flavor of coffee during storage.Among them,sensors T30/1,T70/2,P30/2,PA/2,LY2/AA,LY2g/CT showed that coffee flavors peaked on the 10th day of storage;T70/2 sensor results showed aromatic substances in coffee at 15 days The peak value was reached;the six sensors of the electronic nose were all in the 40? accelerated storage model with the highest sensitivity.It is indicated that the electronic nasal sensory technology can completely distinguish the coffee samples of different storage periods by the sensor sensitivity to odor.2.Accelerate the change of the taste of roasted beans during storage(1)Eight chlorogenic acids and two alkaloids were simultaneously measured by UPLC.With the increase of storage days,the overall change trend of the content of 8 chlorogenic acids was gradually reduced.Under the accelerated storage conditions at 50 and 60?,the storage period on the 5th day due to the mutual transformation between the isomers,the content of chlorogenic acid and cryptochloric acid increased sharply and then decreased.The content of trigonelline decreased under storage period,while the content of caffeine did not change significantly during the whole storage period.The decomposition product of trigonelline and chlorogenic acids will become the key factors for the bitterness of coffee during the storage period.(2)Organic acids are the main substances affecting coffee flavors.UPLC analysis of seven organic acids found that malic acid and quinic acid varied greatly during storage.The content of malic acid decreased at 10th day,and there was no significant difference after 15-25th day because of increasing to the certainly value.The astringency of malic acid is not conducive to the flavor of coffee.That is,in the middle of shelf life,coffee has the lowest astringency.Quinic acid did not change significantly in the early stage of storage,and it increased rapidly to reach the peak at 15th day and then decomposed to the previous level.The bitterness of quinic acid is somewhat favored by some consumers,and its decomposition products partially enhance the flavor of coffee.(3)UPLC-Q-TOF was used to determine the chemical substances in the coffee samples.By comparing the literature and the corresponding standards,28 compounds were isolated in negative ion mode,and 20 compounds were isolated in positive ion mode.Several unknown substances are to be further isolated and purified to identify their structure.The results showed that different phenolic acid lactone isomers existed in the coffee samples,and their contents increased with the storage time,indicating that the formation of lactones is one of the causes of the increase in bitterness of coffee.