Comparative analysis of the tannin and gallic acid contents of Chinese gallnut and the influencing factors.

The contents of tannin and gallic acid of 14 Chinese gallnut samples from different producing areas were determined by hide powder method and high performance liquid chromatography,respectively.The results showed that the tannin contents ranged from 61.59% to 68.30% and the mean content was 64.49%.Gallic acid content ranged from 70.35% to 77.61% and the mean content was 73.92%.The wall thickness of galls ranged from 1.55 to 2.01 mm,and density ranged from 0.16 to 0.33 g·mL-1.Correlation analysis indicated that the tannin contents had a positive significant correlation with the gallic acid contents,but the tannin and gallic acid contents had no significant correlations with the wall thickness and density,respectively.Meanwhile,both of the tannin and gallic acid content had a negative significant correlation with mean month temperatures of April to August and had no significant correlations with the relative humidity,precipitation,and sunshine duration respectively.It is suggested that temperature was an important factor affecting the quality of Chinese gallnut.The cluster analysis showed that 14 Chinese gallnut samples could be divided into 3 quality groups which stood for excellent,moderate and common categories.