Screening And Application Of Lipase-producing Microorganisms During Pile-fermentation Of Qingzhuan Dark Tea

Qingzhuan dark tea is a kind of compressed tea produced in Hubei province.In the fermentation process of Qingzhuan dark tea,it is mainly the process of microbial action,and microorganisms can secrete extracellular enzymes such as lipase,pectinase and so on to transform the contained components in tea.In this experiment,the microbial community in the Qingzhuan dark tea pile was taken as the sources of strains,then the high lipase-producing strain was screened,and the enzyme production conditions were optimized,and the effect of high lipase-producing strain on the quality formation of Qingzhuan dark tea was explored.The results showed that 17 strains of bacteria and 19 strains of molds can produce lipase in the microbial community of the dark tea.And the enzyme activity of strain N8.11-20 was 7.82 U/ mL,and the strain was identified as Pseudomonas aeruginosa by cell morphology,physiological and biochemical data,16 S rDNA sequence,and gyrB function gene sequence data.The lipase-producing conditions and the fermentation medium of strain N8.11-20 were optimized.The results were as follows: the fermentation period was 72 h,the inoculation amount was 6%,the rotation speed was 200 r/min,the fermentation temperature was 34 ?,the liquid loading amount was 90 mL/150 mL,the initial pH value was 7.0,the nitrogen source was the yeast extract,the carbon source was sucrose,and the inorganic salt was magnesium sulfate.The results showed that the lipase activity of strain N8.11-20 increased with the extension of the fermentation time,and it was a rapid rise in early stage but a stable trend in the later stage.The mold MB47 J,MB30J,and Mq24 showed no enzymatic activity in the first 0 h-12 h,but there were a significant increase in the activity during the mid-stage,and a slight decrease in the latter.The strain N8.11-20 was used to ferment Laoqing tea.Using 20 g Laoqing tea per can,the fermented tea would possess better sensory qualities under 15 days of fermentation time,45 ? of fermentation temperature,10 mLof adding water volume,and 4.0 mLof inoculation quantity,Its aroma was mainly aged fragrant,the tea liquorcolor was orange and bright,the taste was mellow,and the leaf residue was bluish brown.There was significant correlation between fermentation factors and sensory evaluation scores.Through mixed strain fermentation,the aroma mainly was aged or flower fragrant,which wae equal to the standard of commercial tea.The effects of mixed strain fermentation on tea liquor was little,which mainly was orange and bright.Its effect on the taste was limited,which mainly was astringent,light and sour as a inappropriate taste.The low fermentation temperature and short fermentation time led to insufficient fermentation and insufficient transformation of phenolic substances in tea leaves.The volatile components of phenols,ketones and alcohols in the fermentation process of strain N8.11-20 were mainly nonanal,trans-,trans-2,4-heptadiene,trans-,trans-2,4-nondienal,benzaldehyde,trans-,trans-2,4-nondienal,octanal,n-heptanal,trans-2-octenal,green leaf aldehyde,2-ring citral,hexanal,1-methyloketone,geranyl acetone,1-methyroone,linalool,3-decyne-2-ol,n-heptanol,and 1-octene-3-ol.The effect of steaming on the volatile components of phenols,ketones and alcohols in tea leaves was different.In the fermentation process,the content of the volatile phenols and ketones obviously increased,and the content of the volatile alcohols was obviously reduced.