Extraction of red cabbage anthocyanins by microwave and conventional methods

Red cabbage (Brassica oleracea L.) is a vegetable, which is unique in its anthocyanins and has a positive effect on health because of its high antioxidant capacity, which is used in the coloring of foods due to its color display at a very wide pH range. In the study, red cabbage anthocyanins were extracted by microwave assisted (MAE) and conventional methods. Total monomeric anthocyanin content (TMA), total phenolic material content (TPM) and total antioxidant capacities (TAKDPPH ve TAKCUPRAC) of red cabbage extracts were measured. Process conditions were optimized using the response surface method. The main types of anthocyanins found in red cabbage were determined by using DAD-LC-MS. In the conventional extraction method, three parameters were chosen as independent variables, which were extraction time (4 and 6 hours), extraction temperature (40 °C, 70 °C) and solvent type (water, ethanol/water (1/1, v/v)). According to the results, the highest values for TMA, TPM, TAKDPPH and TAKCUPRAC were given by the condition of ethanol/water (1/1, v/v) at 40 ° C and 4 hours of extraction. The results were 240,69 mg cyanidin / L, 1677,33 mg GAE / L, 66,34 mg DPPH / L, 16,77 mmolTE / L, respectively. The lowest values for TMA, TPM, TAC were given by the condition that the solvent was water at 40 ° C and 4 hours of extraction. The results were 125,91 mg cyanidin / L, 1018,52 mg GAE / L, 33,12 mg DPPH / L, 8.91 mmolTE / L. The Box-Behnken experimental design was used to determine the optimum conditions for MAE. The effects of independent variables chosen as extraction time (X1), solid/solvent ratio (X2) and microwave power (X3) on TMA, TPM, TAKDPPH ve TAKCUPRAC values (dependent variables) were investigated by a response surface methodology (RSM). When the solvent was the ethanol/water mixture, X1 and X2 affected the TMA values significantly (p≤0.05) and power values (X3) was found insignificant on TMA value. When the solvent type was water, X2 and X3 were significantly effective (p≤0.05) on the TMA amount in the extract while X1 was not effective. When the solvent was ethanol-water (1/1, v/v), optimum conditions were 9,85 minutes, 1/20 solid/ solvent ratio and 595,96 W microwave power. According to models detemined, optimum TMA amount was found to be 438 mg cyanidin / L, optimum TPM amount was 1143,43 mg GAE / L, optimum TACCUPRAC amount was 16,80 mmol TE / L and optimum TACDPPH amount was 134,823 mg DPPH / L. When the solvent was water, optimum conditions were 5 minutes, 1/20 solid/solvent ratio and 309,091 W microwave power. According to models detemined, optimum TMA amount was found to be 131,86 mg cyanidin / L, optimum TPM amount 1952,85 mg GAE / L, optimum TACCUPRAC amount 20,90 mmol TE / L, optimum TACDPPH amount 120,63 mg DPPH / L. It was observed that MAE gives similar results with conventional method in shorter time by using less solvent amount. Cyanidin-3-glucoside-5-glucoside, cyanidin-3-diglucoside-5-glucoside, cyanidin-3-glucoside-5-glucoside, cyanidin-3-(p-coumaroyl)-diglucoside-5-glucoside, cyanidin-3-(sinapoyl)-diglucoside-5-glucoside, cyanidin-3-(feruloyl) (feruloyl)-diglucoside-5-glucoside, cyanidin-3-(feruloyl) (sinapoyl)-diglucoside-5-glucoside, cyanidin-3-(sinapoyl)(sinapoyl)-diglucoside-5-glucoside are comman anthocyanins of red cabbage in ethanol-water and water extracts. Unlike water extracts, cyanidine-3-o-glucoside peak was found in ethanol-water extracts.