Optimization of microwave-assisted extraction of anthocyanins in red raspberries and identification of anthocyanin of extracts using high-performance liquid chromatography – mass spectrometry

Anthocyanins (Acys) are naturally occurring compounds that impart color to fruit, vegetables, and plants. The extraction of Acys from red raspberry (Rubus idaeus L. var. Heritage) by microwave-assisted process (MAP) was studied. A central composite rotate design (CCRD) was used to obtain the optimal conditions of microwave-assisted extraction (MAE), and the effects of operating conditions such as the ratio of solvents to materials, microwave power and extraction time on the extraction yield of Acys were studied through response surface methodology (RSM). The optimized conditions of MAE were ratio of solvents to materials 4:1 (ml/g), extraction time 12 min, and microwave power 366 W. Under these conditions 43.42 mg of Acys from 100 g of fresh fruits (T _Acy, expressed as cyanidin-3-glucoside), approximately 98.33% of the total red pigments, could be obtained by MAE. The Acys compositions of extracts were identified by high-performance liquid chromatography – mass spectrometry (HPLC-MS), 12 kinds of Acys had been detected and 8 kinds of Acys were characterized. Result indicated that cyanidin-3-sophoroside, cyanidin-3-(2 ^G -glucosylrutinoside), cyanidin-3-sambubioside, cyanidin-3-rutinoside, cyanidin-3-xylosylrutinoside, cyanidin-3-(2 ^G -glucosylrutinoside), and cyanidin-3-rutinoside were main components in extracts. In addition, in comparison with the conventional solvent extraction, MAE is more efficient and rapid to extract Acys from red raspberry, due to the strong disruption of fruit tissue structure under microwave irradiation, which had been observed with the scanning electron microscopepy (SEM). However, the Acys compositions in extracts by both the methods were similar, which were investigated using HPLC profile.