| Catechins are the main components of Tea Polyphenols in green tea infusion and make great contribution to the taste of it. This paper studied the taste characteristics of the 8 catechins existing in green tea infusion(EGCG, ECG, EGC, EC, GCG, CG, GC, C), including the taste thresholds and concentration-taste intensity curves of the 8 catechins, binary taste-taste interaction among 4 epicatechins, the effect of Ca2+ on the taste of 4 epicatechins, the effect of caffeine/ theanine/ monosodium glutamate/ sucrose on the taste of EGCG, and analyzed the chemical interactions between two taste components with 1H-NMR; finally, by establishing the relationship between the bitter as well as astringent taste and the chemical compounds in green tea, the contribution to the taste of green tea of the catechins was clarified. Results in details are as follows:(1) 8 catechins all tasted bitter and astringent, the bitter threshold of EGCG was 220 μmol/L and the astringent one was 160 μmol/L; the bitter threshold of ECG was 180 μmol/L and the astringent one was 135 μmol/L; the bitter threshold of EGC was 1630 μmol/L and the astringent one was 260 μmol/L; the bitter threshold of EC was 860 μmol/L and the astringent one was also 860 μmol/L as well; the bitter threshold of GCG was 330 μmol/L and the astringent one was 220 μmol/L; the bitter threshold of CG was 170 μmol/L and the astringent one was 115 μmol/L; the bitter threshold of GC was 1630 μmol/L and the astringent one was 330 μmol/L; the bitter threshold of C was 860 μmol/L and the astringent one was 690 μmol/L;(2) The concentration-taste intensity curves of the 8 catechins with concentrations in tea infusions could fit in cubic functions well and the R2-values of them were all above 0.996. Bitter score of EGCG =-0.258x3 + 1.3627x2 + 1.2414 x + 0.0692, astringent score of EGCG =-0.2445x3 + 1.026x2 + 2.2821 x + 0.025; bitter score of ECG =-0.7696x3 + 1.9319x2 + 2.9545 x + 0.0104, astringent score of ECG = 0.2145x3- 1.0431x2 + 4.8702 x + 0.0047; bitter score of EGC = 0.0022x3- 0.159x2 + 0.7938x- 0.0046, astringent score of EGC = 0.2067x3- 1.1405x2 + 2.5362 x + 0.0019; bitter score of EC = 0.0181x3- 0.119x2 + 0.9635x- 0.0123, astringent score of EC = 0.0612x3- 0.492x2 + 1.8105x- 0.0124; bitter score of GCG = 0.4597x3- 0.6968x2 + 2.5207x- 0.1063, astringent score of GCG = 0.7608x3- 1.974x2 + 4.2378x-0.1174; bitter score of CG =-0.3411x3 + 1.4757x2 + 1.9817x- 0.0009, astringent score of CG = 0.6306x3- 2.0033x2 + 4.372x- 0.0529; bitter score of GC = 0.1126x3- 0.6563x2 + 1.2374 x + 0.0095, astringent score of GC = 0.2126x3- 1.1816x2 + 2.22x- 0.0186; bitter score of C = 0.0593x3- 0.3471x2 + 1.1567x-0.0197, astringent score of C = 0.0233x3- 0.3185x2 + 1.4702 x + 0.01.(3) 4 epicatechins with concentrations in tea infusion barely had binary taste-taste interactions with each other and the taste intensity could be simply added; Ca2+, the water quality factor, could enhance the astringency of 4 epicatechins obviously but had little influence on their bitter taste. The effect of the main taste compounds in tea infusion on the taste of EGCG was as follows:(a) there was bitterness-hidden effect between EGCG and caffeine with concentrations in tea infusion, but caffeine could enhance the astringency of EGCG slightly;(b) theanine had little effect on the taste of EGCG;(c) monosodium glutamate at tea concentration could enhance the astringency of EGCG slightly while at concentration 10 times higher than that in tea infusion, it could suppress the bitterness and astringency of EGCG;(d) sucrose could enhance the bitterness of EGCG when its concentration was lower than 10 times in tea infusion, while at concentration 50 times higher than that in tea infusion it could suppress the bitterness obviously, meanwhile, sucrose had little effect on the astringency of EGCG only if at concentration more than 200 times higher than that in tea infusion the sucrose could suppress it slightly.(4) The 1H-NMR analysis showed that there were no binary chemical interactions among 4 epicatechins while Ca2+ could affect the taste of 4 epicatechins by changing the chemical structures of them; in the interrelationship between caffeine and EGCG, EGCG had greater influence on caffeine’s chemical structure than the effect of caffeine to EGCG; there was a slight chemical interaction between EGCG and theanine or monosodium glutamate while the interaction between EGCG and sucrose was little.(5) The relationship between the bitter-and-astringent taste of green tea and the chemical components in it showed that the intensity of the bitterness could be well quantfied only by the content of the catechins meaning that the bitter taste of green tea was mainly determined by catechins; but the astringency of green tea infusion was more complex while it must be quantfied by the content of catechins as well as the content of caffeine, gallic acid, flavonol glycosides and amino acids, to saying that the content of catechins could not completely determine the astringency of green tea infusion. |
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