Abstract
On the determination of tannin (catechins and catechin gallic ester) in tea leaves, the Löwenthal method gives a small value on account of the fact that free catechins are not sufficiently precipitated by the gelatin solution (Table 4).
So we have studied the nepherometric method to estimate the tannin content including free catechins in tea leaves (Fig.1. ).
When the catechin solution is mixed with HCl-formalin reagent and the nepherometric ratio (r) for the standard solution is determined, r is proportional to the concentration of catechins. (Figs. 2 and 3 and Tables 1 and 2.)
Its technique is as follows: the equal volume of the HCl-formalin reagent (35% HCl 100 cc., 30% formalin 200 cc., and water 50 cc.) is added to the clear extract of leaves. After 1 hour, this white turbid solution is compared to the standard catechin solution (50 mg of catechins in 100 cc. water with HCl-formalin reagent) and estimate the nepherometria ratio. From the standard curve (Fig: 4.) or the conversion table (Table 3.), we have been able to calculate the content of tannin in tea leaves (Table 4.).
