Effect of energy density and citric acid concentration on anthocyanins yield and solution temperature of grape peel in microwave-assisted extraction process

In order to verify the sensitivity of anthocyanins (Acys) yield of grape peel to the energy density (microwave power for a given unit of volume) and citric acid concentration in microwave-assisted extraction (MAE) process, the effect of energy density and citric acid concentration in MAE process were investigated. The results indicated that, Acys yield was more sensitive to energy density than to microwave power. The correlation between Acys yield and energy density follows well Gaussian function, suggested by higher R squares (R-2 > 0.9399). Exponential decay model can well describe the correlation between Acys yield and citric acid concentration, or between solution temperature rise and energy density. The solution temperature was a linear function of citric acid concentration and extraction time. Energy density was the most significant factor affecting the Acys yield, followed by citric acid concentration, ratio of liquid to solid and extraction time (p < 0.05). (C) 2011 Elsevier Ltd. All rights reserved.