Analysis of Total Tannins

During natural or artificial removal of astringency, soluble tannin can change, probably by polymerization or conjugation, into an insoluble form, which is not 

Analyze by the Folin-Denis method (see Fig. 4) measurement of total tannins 

The hydrolysis of insoluble tannin with HCl solution can be used to measure the amount of total tannin (Manabe 1982). After insoluble tannins are hydrolyzed as shown in Fig. 6, total tannins can be measured by the Folin-Denis method. My group used this method in studying both PCNA and PVA fruit (Taira et al. 1990). 

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