Optimization of Depolymerization Process of Polymeric Proanthocyanidins from the Barks of Pinus kesiya var. langbianensis

Abstract

Objective(-)-epicatechin-(4β-8)-(-)-epigallocatechin 3-O-gallate (1) was found to be the main depolymerized product of polymeric proanthocyanidins (PPC) from the pine barks with tea polyphenols (TP), and showed higher DPPH and ABTS+ radical scavenging activities than both PPC and TP. In order to provide the basis for further development and utilization of depolymerized product of PPC, the objective of this study was to optimize the depolymerization process of PPC from the barks of Pinus kesiya var. langbianensis with TP, by using the content of 1 as an evaluation indicator. MethodThe content of compound 1 in reacted solution was analyzed by HPLC, and the effects of reaction temperature (50-90℃), reaction time (30-180 min), HCl concentration (0.1%-5%) and TP/PPC ratio (1:3-3:1, w/w) on the content of 1 were investigated by single factor experiments. The depolymerization process was optimized using response surface methodology, at a five-level, four-variable experiment central composite rotatable design. Using the content of 1 as response, and above four factors as variables, the twenty-eight experiments were conducted to analyze the response pattern and to establish model for reaction process. The responses obtained from the experimental design set were subjected to multiple nonlinear regression using Design-Expert V8.0.6 software to obtain the coefficients of the second-polynomial model, and its statistical significance was evaluated by variance analysis. ResultThe reaction temperature, HCl concentration and TP/PPC ratio strongly affects the content of 1 in the depolymerization reaction. The regression model was very significant (P < 0.000 1) with a good coefficient (R2=0.952 6), suggesting that the proposed experimental design was suitable to analysis and to predict the simulation of 1. The optimum depolymerization conditions were as follows:reaction temperature 70℃, reaction time 60 min, HCl concentration 1%, and TP/PPC ratio 3:2. Under the above-mentioned conditions, the experimental content of 1 was 718.57 nmol·mL-1, which was well matched with the predicted content (721.39 nmol·mL-1). ConclusionIt was feasible to use response surface method to optimize the depolymerization process of PPC from the barks of P. kesiya var. langbianensis with TP for the production of 1.