Chemical Underpinning of the Tea Bag Index: An Examination of the Decomposition of Tea Leaves

Table 1

Chemical shift regions for integration of CPMAS NMR spectra.

C functional group	Chemical shift (ppm)	Main classes of compounds included [10]; [11]	Fraction from sequential C extraction conducted by Keuskamp et al. [4]
Alkyl C	0–50	Side chains in amino acids, structures derived from cutins and suberins, aliphatic compounds, lipids, waxes	Nonpolar extractives (NPE), e.g., fats and waxes
O-Alkyl C	50–110	O-substituted C in alcohols and ethers including cellulose, hemicelluloses, and other polysaccharides, carbohydrates, lignin propyl side chains	Water solubles (WS), e.g., simple sugars
			Acid solubles (AS), e.g., cellulose
			Acid insoluble (AIS), e.g., lignin
Aromatic C	110–160	Condensed tannins, hydrolysable tannins, phenyl-propylene subunits of lignin	Acid insoluble (AIS), e.g., lignin
Carbonyl C	160–200	Peptides, carboxylic C in hydrolysable tannins and resins, secondary amide C in proteins