Stability of proanthocyanidins from Picea koraiensis Nakai in solution

The aim of this study was to investigate the stability and degradation kinetics of proanthocyanidins from Picea koraiensis Nakai in solution at different pH values, temperatures and concentrations, and the residual rate was used as an index to measure the change of proanthocyanidins content. The results showed that the stability decreased with increasing temperature and pH value, the residual rate was the highest at the concentration of 4 mg/mL and the degradation reaction followed first-order kinetics with the activation energy Ea33 kJ/mol. Adding 1% sucrose and may contribute to delaying reaction rate and improving the stability of the proanthocyanidins only at low concentrations and low pH values. The Ea value in the test measured in the absence of additives was less than 42 kJ/mol, suggesting that the reaction rate under these conditions was high, and degradation reaction was mostly likely to happen. Under the conditions of 2 mg/mL concentration and pH 3.0, the activation energy Ea value could be increased by 19% if adding sucrose, and degradation reaction rate decreased, indicating that the additives significantly enhanced the stability of proanthocyanidins. Under the conditions of 2 mg/mL concentration, pH 3.0, and temperature 4 ℃, degradation rate was slow, and higher activation energy was required for the reaction and half-life period was longer, which was conducive to the storage stability of proanthocyanidins. Sugar could be added to improve the stability of proanthocyanidins under certain conditions, because the addition of sugar and other carbohydrates could enable proanthocyanidins and sucrose to form macromolecules which enhance the stability of proanthocyanidins.