Effects Of Optimation Of C/N On The Fermentation Process And The Quality Of Pu-erh Tea

The effect of different drying ways and temperature on the physico-chemical andaromatic characteristics of pile-fermented Pu-erh teas has been firstly sdudied, and the dryingtechonological process has been optimized. Based on the dynamic anaylisis ofpile-temperature, mold and yeast, polyphenol oxidase activity, contents of polyphenols, teapigments, aqueous extract, and some other indicators of Pu-erh teas pile-fermented onlaboratory-scale, the influence of different mixed compostion and their concentrations ofNitrogen(phenylalanine, alanine, leucine) and carbon(xylose, fructose, fectin) sources on thefile-fermentation process and the quality of pu-erh teas has been investigated. The free aminoacids and the aroma characteristics of the teas fermented with optimum mixed C/N had alsobeen analyzed.The teas at the end of pile-fermentation were dried by naturally air drying( 17~23℃)and in a drying oven at different temperatures(40°C, 60°C, 80°C, 100℃,120℃). The resultshowed that polyphenol and catechin content had slightly decreased, and the catechin contentof naturally drying group was higher than that of oven drying groups, the content of caffeineand the water extract respectively decreased and increased significantly whatever groups.Results also indicated that the drying temperature of 80°C was critical, oven drying higherthan 80℃, the conversion degree of polyphenol and catechin was higher, the content oftheabrownins and water extract decreased significantly. Results of GC-MS reviewed that thearoma components of tea dried by naturally air drying were more diversity. The oven dryinglead to the formation of baking aroma and scorch aroma, as well as some complexmacromolecular aroma components at drying temperature above 80℃. The oganoleptic andaromatic results indicated that oven drying at temperature below 60℃ was favour for theformation of critical aroma of Pu-erh teas, and the quality of Pu-erh teas dried by naturally airdrying was best.Effects of different combinations of amino acids and sugars optimized by earlierlaboratory group on the quality of pile-fermented teas have been studied. The results showedthat the addition of amino acids and sugars in the pile-fermentation could promote themicrobial growth and the pile temperature. Compared with the control group, the conversionrate of polyphenols was higher than that of the control. The content of theabrownins of teasfermented 18 days with added C/N was between 6.16%-8.04%, which was comparable to thehigh quality aged Pu-erh teas. While that of the control was only 4.98%, which indicatedinsufficient fermentation. According to the sensory analysis, two tea samples fermented withphenylalanine and fructose, phenylalanine and pectin had higher sensory scores.Based on the selected optimum C/N group(phenylalanine + fructose or pectin), effect ofconcentration gradient(0.4%, 0.6%, 0.8%) and C/N ratio(1:1, 1:2, 2:1) on the quality ofPu-erh teas was further studied. The results showed that the pile temperature, counts ofmicrobes, enzyme activity and other physio-chemical indicators were significantly affected bythe concentration gradient. When the concentration was up to 0.6% or 0.8%, the molds andyeasts grew more vigorous, the pile temperature was higher and maintained much long time,as well the peak activity of polyphenol oxidase was relatively high. However, too highconcentration as 0.8% led to decrease in quality as a result of the excessive oxidation, whichwas inflected by the lower water extract, and lower theabrownins content due to the violentoxidation which led to excessive fermentation.According to the analysis of the physical and chemical indicators and aroma componentsof 6 Pu-erh tea samples fermented with added optimum C/N composition, the results showedthat polyphenols and theabrownins had great impact on the sensory score of Pu-erh tea. Afterpile-fermentation of the raw sun-dried Pu-erh teas, the total contents of free amino acids andeach amino acid of the Pu-erh teas were greatly reduced. The main aroma components ofoptimized tea samples were mainly had smells of flower, fruit, wood.