Changes And Quality Control Of Main Active Components In The Processing Of Dandelion Black Tea

Dandelion is a kind of medicine and food,widely cultivated all year round,containing polyphenols,polysaccharides,flavonoids,organic acids,alkaloids,vitamins,minerals and other nutrients,with health care and medicinal value of bacterioinhibition,liver protection,gastric mucosa protection,tumor suppression,heat clearing and detoxification,swelling dispersing,diuretic drenching and galactagogue.At present,dandelion tea is mostly made by green tea processing technology,with single product form and poor flavor.In-depth study on the influence of processing process on active ingredients such as polyphenols and flavonoids of dandelion black tea and quality control technology can improve the shortcomings of bitter taste and cold nature of dandelion,and promote the development of high-quality dandelion black tea products.In this experiment,fresh dandelion leaves were used as raw materials to produce dandelion black tea by withering,rolling,fermentation,drying and flavoring.The effects of processing on the quality and antioxidant capacity of dandelion black tea,the effects of raw material tenderness and withering mode on the quality of dandelion black tea and the exogenous enzyme control technology of dandelion black tea quality were studied.The main results and conclusions were as follows:1.Influence of processing process on quality and antioxidant capacity of dandelion black teaDandelion black tea was made from fresh dandelion leaves by withering,rolling,fermentation and drying.The changes of main physicochemical,antioxidant components and in vitro antioxidant capacity during processing were studied.The results showed that during the processing of dandelion black tea,the content of free amino acids increased obviously,the content of total flavonoids decreased,and polyphenols decreased first and then increased.The antioxidant capacity decreased first and then increased,which was consistent with the trend of polyphenol content,indicating that polyphenols were the main factors affecting the antioxidant capacity of dandelion black tea.The contents of polyphenols and flavonoids were positively correlated with DPPH· scavenging ability and ·OH scavenging ability,and the contents of polyphenols were positively correlated with total reducing power.Rolling significantly reduces the content of polyphenols,flavonoids and antioxidant capacity,which is the key process affecting the antioxidant quality of dandelion black tea.Drying and flavoring can improve the content of polyphenols.2.Effects of tenderness and withering modes of different raw materials on the quality ofdandelion black teaUsing fresh dandelion leaves as raw materials,the effects of four different withering modes,namely,sunlight withering,indoor withering and mixed withering,on sensory,physical and chemical quality,polyphenols,flavonoids content and antioxidant capacity index(ORAC value)of dandelion black tea were studied.The results showed that the effects of different tenderness and withering modes of raw materials on the quality of dandelion black tea were quite different.With the increase of tenderness of raw materials,the L* value of dandelion black tea soup decreased rapidly,the a* value increased gradually,and the b* value was in a gentle state;the content of free amino acids increased first and then decreased,and the content of free amino acids in dandelion black tea made from fresh leaves of grade 2 was as high as 20.27%;the content of polyphenols in Dandelion black tea made from fresh leaves of grade 2 was the highest,which was 5.87 mg/g;the content of flavonoids decreased steadily;and the index of antioxidant ability decreased significantly.Among the three withering modes,the color L* value of dandelion black tea produced by mixed withering mode increased significantly,and the content of polyphenols increased significantly,which was 7.14 mg/g.Dandelion black tea produced by grade 2 dandelion fresh leaves and mixed withering method can significantly improve the color,taste quality and antioxidant capacity of the tea soup.3.Quality control technology and process optimization of dandelion black teaThe effects of three exogenous enzymes,including beta-glucosidase,pectinase and protease,on the color,free amino acids,polyphenols and flavonoids content of dandelion black tea soup was studied by mixed withering method with fresh leaves of dandelion as raw materials.The results showed that adding three exogenous enzymes,namely beta-glucosidase,pectinase and protease,could increase the content of polyphenols and flavonoids in dandelion black tea and improve the color of dandelion black tea soup;Among them,the effect of adding beta-glucosidase was the best,the polyphenol content was 3.44 mg/g,the flavone content was 10.90 mg/g,and the color b* value of tea soup was the highest.Dandelion black tea with high catechin content,bright red color and good taste can be obtained by adding0.75g/100 g of beta-glucosidase,rolling for 40 minutes and fermenting at 28? for 7 hours.The analysis of polyphenol components in different tea samples showed that the contents of protocatechuic acid,catechin,chlorogenic acid and quercetin in the dandelion black tea made by adding beta-glucosidase were significantly increased,and the content of catechin reached55.93 g/g.