Metabolomics Of Ejiao Processing And Different Skin Derived Gums Based On GC-IMS And UPLC-MS/MS Technology

Ejiao,(Colla Corii Asini,CCA),also known as donkey hide glue,is a solid glue made from the dried or fresh skin of equine donkey(Equus asinus L.)after boiling and concentration.As a traditional and precious traditional Chinese medicine in China,Ejiao has been used for more than2000 years.It has high application value and has played an important role in tonifying blood,bone repair,improving immunity,anti-inflammatory,anti-oxidation and so on.As Ejiao is boiled from donkey skin,it has a strong smell of animal and oil,and its flavor and sensory experience are poor.Therefore,although Ejiao has many benefits to human body,it is not accepted by most consumers.With people’s increasing attention to health,the demand for Ejiao is increasing,the price of Ejiao and raw materials is rising day by day,and the phenomenon of adulteration is serious.Based on the above problems,according to the method of metabolomics,the volatile and nonvolatile components in Ejiao samples at different processing stages were analyzed by Gas-ion mobility spectroscopy and Ultra-high performance liquid chromatography tandem secondary mass spectrometry,and the differential metabolites between Ejiao samples at different processing stages and different skin-derived gums were found by multivariate statistical analysis,to explore the difference and change law of flavor substances.This study is mainly divided into four parts:1.The first part is the analysis of volatile flavor substances in Ejiao at different processing stages based on gas-ion mobility spectrometry(GC-IMS).The samples are detected by GC-IMS and the different processing stages of Ejiao are distinguished by multivariate statistical analysis,The sample groups that can be well distinguished are further searched for volatile differential metabolites.Dry donkey skin is mainly composed of aldehydes and ketones,such as nonanal,octanal,benzaldehyde,2-methylbutyraldehyde,2-hexenal,cyclohexanone and octanone.After processing,these substances basically disappeared.The samples of wet donkey hide,after Huapi,after concentration and after foaming have certain similarities.After processing,some new components are produced,such as trimethylpyrazine,2,3-dimethylpyrazine,ethyl 2-methylpropionate,furfural propionate,etc.After excipients are also highly similar to the finished Ejiao products,which are mainly composed of esters.The addition of excipients finally promoted the formation of Ejiao flavor,and the addition of excipients played an important role in the processing process of Ejiao.The formation of volatile compounds during Ejiao processing can be attributed to Maillard reaction,the interaction between amino acids or proteins and oxidized lipids,the oxidation and degradation of lipids and the degradation of long-chain compounds during heating.2.The second part is the analysis of nonvolatile flavor substances of Ejiao in different processing stages based on Ultra-high performance liquid chromatography tandem secondary mass spectrometry(UPLC-MS/MS).This part mainly analyzes nonvolatile metabolites,uses UPLCMS/MS to detect samples,and uses multivariate statistical analysis to distinguish different processing stages,The original data is in Compound Discoverer 3.1 analyze and screen the nonvolatile differential metabolites in the software.In Ejiao at different processing stages,nonvolatile small molecular metabolites are mainly dipeptides,amino acids and their derivatives,including δ-Valproamide,proline,leucine,lysine,hydroxyproline,platelet activating factor,etc.Flavoring amino acids are an important factor in the unique flavor of Ejiao.At the same time,they may also be an important precursor substance affecting Maillard reaction in the processing of Ejiao.They play an important role in Ejiao,mainly bitter,sweet and delicious.The synergistic interaction of a variety of flavoring substances jointly determines the taste of Ejiao.In the process of Ejiao processing into high-temperature leather concentration,the dermis of donkey hide is gradually dissolved,the collagen is gradually degraded in this process,the polypeptide is decomposed into small molecular peptides and amino acids,and the changes of amino acids and peptides are obvious.The formation of nonvolatile flavor substances in Ejiao mainly comes from the degradation of collagen.The addition of excipients greatly improves the composition of nonvolatile flavor substances.3.The third part is the analysis of volatile flavor compounds in four kinds of skin-derived gum based on GC-IMS.There were differences in volatile components between donkey hide gum and the other three kinds of skin-derived gum.The content of aldehydes in donkey hide gum is much higher than that of the other three skin-derived gums,showing more oil flavor,burnt flavor and other slightly irritating odors.The content of octone,nonone and decanone in cow hide gum is much higher than that of other skin derived gums,showing oil flavor and natural woody flavor.The volatile flavor substances of horse hide gum and pig skin gum are very similar,The content of volatile components is similar and the difference is not significant.Other technologies may be needed to distinguish them.4.The fourth part is the analysis of nonvolatile flavor substances of four kinds of skin-derived gum based on UPLC-MS/MS.The content of nonvolatile differential metabolites in donkey hide gum is significantly higher than that of other skin-derived gums,mainly ketones,amines,alcohols and carboxylic acids.The difference between donkey skin and other skin-derived gums in collagen,amino acids and fatty acids may be the main reason for the difference,And the differences in processing technology between donkey hide gum and other skin-derived gum are also the reasons for the differences in nonvolatile flavor substances.In this study,the differences of Ejiao in different processing stages and different leather source gums were analyzed from two aspects of volatile and nonvolatile flavor substances.The comprehensive evaluation of Ejiao provided a basis for the flavor research,quality control and adulteration identification of Ejiao.At the same time,it provided a new idea for the flavor analysis of Ejiao.