Study On The Chemical Of Mellow And Thick Taste Of Pu-erh Ripe Tea

Pu-erh ripe tea is a special tea with a long history in Yunnan Province,China.The market demand for Pu-erh ripe tea is gradually increasing in recent years,and related research is receiving attention from home and abroad,owing to its pharmacological effects of hypoglycemic,lipid-lowering,anti-senescence,anti-anaphylaxis and anti-carcinogenic,etc.The mellow and thick taste is one of the typical taste characteristics of high-quality Pu-erh ripe tea.However,due to its overly specialized and abstract definition,there was still a lack of quantitative standard,and the key flavoring substances of the mellow and thick taste were rarely reported.In this study,we gradually separated Pu-erh ripe tea infusion with different mellow and thick taste,using microfiltration,ultrafiltration,ion exchange chromatography,and gel chromatography,and the key contributor for mellow and thick taste of Pu-erh ripe tea was revealed through the instrumental and sensory analyses on the different separated phases.The key contributor,soluble polysaccharide,was further isolated,purified,and identified,on which based a standard reference sample for the mellow and thick taste of Pu-erh ripe tea was constructed.These results would provide a theoretical basis for the quantitive evaluation of the mellow and thick taste,and have scientific guidance on the quality improvement of Pu-erh ripe tea.The main conclusions are as follows:(1)The contents of flavor components in different sources of Pu-erh ripe tea were determined by spectrophotometry and HPLC,including soluble sugars,tea polyphenols,free amino acids,soluble protein,caffeine,gallic acid,catechins and theabrownin.The results showed that soluble sugars,tea polyphenols,soluble proteins and theabrownin were the taste compounds highly correlated with the mellow and thick taste of Pu-erh ripe tea.(2)The taste characteristics and the contents of taste compounds of Pu-erh ripe tea infusion were investigated by combining microfiltration and ultrafiltration separation,sensory analysis and instrumental analysis.The results showed that the mellow and thick taste intensity was higher in the separated phases with molecular weight higher than 3 k Da;the contents of soluble sugars and theabrownin in different separated phases of Pu-erh ripe tea infusion were significantly different;the mellow and thick taste was significantly and positively correlated with the contents of soluble sugars and theabrownin;theabrownin and polysaccharide(crude polysaccharide and pectin)were the key contributors to the mellow and thick taste,but their individual compounds only provided sweetness,mellow taste or thickness,and the taste interactions among theabrownin,crude polysaccharide,and pectin,were essential to the mellow and thick taste of tea infusion.(3)The structural characteristics of the key contributors to the mellow and thick taste of Pu-erh ripe tea were analyzed,using a series of analytical techniques such as ion chromatography,SEC-MALLS-RI,FT-IR,Methylation binding GC-MS,NMR and SEM.The results showed that the polysaccharide PRTPS-S1 was a mixture of RG Ⅰ type pectin polysaccharide,mainly composed of Rhamnose,Arabinose,Galactose and Mannose,with a molar ratio of 2.01:1.50:1.85:1 and a heavy average molecular weight of 22.93 k Da,PRTPS-S1 contained several characteristic peaks of pectin,with the main chain was→2)-α-L-Rhap-(1→,→2,5)-α-L-Araf-(1→,→3,4)-α-D-Galp-(1→ and→6)-β-D-Manp-(1→,and the branched chains were α-L-Arap-(1→ and→2)-α-L-Rhap-(1→.(4)The key material basis of the mellow and thick taste of Pu-erh ripe tea was verified and the standard curve of the mellow and thick taste was constructed,based on the taste reconstitution experiment.The results showed that two representative components,i.e.,theabrownin and soluble polysaccharide,could be used to construct the mellow and thick taste of Pu-erh ripe tea infusion;the mellow and thick taste intensity of the reconstituted solution,with 1.5 g/L of theabrownin,30 mg/L of pectin and 150 mg/L of citric acid,was almost the same as the standard tea infusion.Based on that,the standard curve of mellow and thick taste was constructed,and the secondary sensory evaluation of11 tea samples was conducted according to the curve,the results obtained were consistent with the traditional sensory evaluation.