Isolation And Identification Of Eurotium Cristatum In Fuzhuan Brick Tea And The Application In Fermentation

Shanxi tea processing industry mostly used spring tea,and abandoned a lot of summer tea,resulting in serious waste of resources.In addition,Fuzhuan brick tea has a variety of health function and active effects such as lowering blood lipids,antioxidation,antibacterial activity,scavenging free radicals,and protecting cells from oxidative damage,which is inseparable from the beneficial components produced by the metabolism of golden flower bacteria.Therefore,this study used summer tea as raw materials to apply Eurotium cristatum isolated from Fuzhuan brick tea to liquid-fermentation,and the fermentation conditions were optimized.By real-time monitoring the relevant physical and chemical indicators and the main aroma components in the fermentation process,the liquid-fermentation of Eurotium cristatum and the liquid-fermentation of mixed strains were compard and evaluated.Then fermentation broth were prepared into instant brick tea power to provide guidance for the deep processing of tea products large-scale by spray drying.The main results are as follows:（1）In this experiment,33 strains were isolated from Fuzhuan brick tea in Hunan,which all were compared in the NCBI database by Blast.Among them,9 were identified as Eurotium cristatum,3 Penicillium oxalicum,6 Aspergillus amstelodami,4 Aspergillus cristatum,2 Aspergillus chevalieri,2 Aspergillus niger and other strains.In addition,the colony characteristics,microscopic morphology,electron microscope morphology,and growth curve of Eurotium cristatum were observed and studied.And the growth kinetics equation were obtained by polynomial fitting method:y=A+B₁×X¹+B₂×X²+B₃×X³+B₄×X⁴+B₅×X⁵+B₆×X⁶+B₇×X⁷,which fitting correlation coefficient was R²=0.9602,indicating that this model can better describe the growth peocess of Eurotium cristatum.（2）The optimization of the mixed strains liquid-fermentation were obtained through single factor optimization:the inoculum size 2%,the initial p H of the fermentation broth 6,and the proportion of mixed strains 1:2:1 and corresponding to Eurotium cristatum,Aspergillus niger and Penicillium oxalicum.By monitoring the process of mixed-strains fermentation and single bacteria fermentation,and the total tea polyphenols decreased to varying degrees,indicating that the polyphenols is the main carbon source for the metabolism of bacteria and multi-bacteria metabolism may promotes the conversion of monomer mutually;Through the analysis of several tea polyphenols monomers,the levels of caffeine（CAF）,catechins（C）,epigallocatechin gallate（EGCG）and epicatechin（EC）in the fermentation process of the single bacteria were reduced.The content of catechin gallate（ECG）and theaflavin（TH）increased.Meanwhile the contents of CAF,C,and EC in the mixed-strain fermentation process decreased,and the ECG content increased first and then decreased.It was speculated that the interaction between the strains could change the transformation pathway of the catechin.Under both fermentation methods,the total amino acid content showed an upward trend,which can greatly enrich the amino acid substances in the fermentation broth.（3）A total of 90 aroma substances were identified in the liquid-fermentation process of Eurotium cristatum and a total of 294 aroma substances in the mixed strain liquid-fermentation,which has more than 200 kinds of aroma substances than the former,this indicated that the mixed strain fermentation broth contained more aroma substances.At the end of the fermentation,the total amount of aroma substances in the mixed liquid fermentation broth was 80%,and which was 15%higher than that of the fermentation broth of Eurotium cristatum.And there are more kinds of aromas（alcohols,esters,ketones,hydrocarbons and heterocyclic compounds）in the mixed strain fermentation broth than in the fermentation broth of Eurotium cristatum（alcohols,acids,and heterocyclic compounds）.In terms of aroma substances,the mixed strain liquid-fermentation is superior to the liquid-fermentation of Eurotium cristatum.（4）The instant tea power was prepared by the spray drying with the fermentation broth.Among them,the highes yield of spray drying of No.2 samples was 11.829%,and the highest sensory score was 85.45,indicating that the instant tea power by mixed-strains fermentation broth was optimal.