Comparison of Four Methods for Quantitation of Proanthocyanidin

Four methods for quantitation of proanthocyanidins (PC) including:sulfuric acid-vanillin method,ammonium molybdate method,N-butanol hydrochloric acid-HPLC method and thiolysis-HPLC method were evaluated in this paper. The results showed that linear correlation coefficients of the four methods were greater than 0.999,and the minimum detection limits were:2.21,5.47 μg/mL,7.3 ng and ≤ 2.0 ng,RSD were:2.52%,2.42%,1.85% and ≤ 0.70%,and the recoveries were:94.24%,96.20%,98.10% and ≥ 40.81%.The chromogenic reaction solution of the sulphuric acid vanillin method was not stable enough,and the other three methods were relatively stable within 10 h. A total of 21 samples of PC extract from commercially available grape seed,grape skin,peanut clothing and pine bark were analyzed by the methods. The results were 38.70%,18.80%,40.24% and 8.39%,respectively. The correlation coefficient between the results of sulfuric acid-vanillin method and HPLC method was the highest,0.5311,and the correlation coefficient between HPLC method and thiolysis-HPLC method was 0.4001,and the other correlation coefficients were less than 0.2.The average degree of polymerization of 21 samples of PC was analyzed by thiolysis-HPLC method between 1.21 and 5.04.Through analysis of variance,it could be seen that method,sample and the interaction between method and sample had a very significant effect on the proanthocyanidin content.