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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 ultrasound-assisted process (UAP) was studied. A central composite rotate design (CCRD) was used to obtain the optimal conditions of ultrasound-assisted extraction (UAE), and the effects of operating conditions, such as the ratio of solvents to materials, ultrasonic power and extraction time, on the extraction yield of Acys were studied through response surface methodology (RSM). The optimized conditions of UAE were as follows: ratio of solvents to materials was 4:1 (ml/g), extraction time was 200s, and ultrasonic power was 400 W. Under these conditions 34.5 mg of Acys from 100g of fresh fruits (T(Acy), expressed as cyanidin-3-glucoside), approximately 78.13% of the total red pigments, could be obtained by UAE. The Acys compositions of extracts were identified by high-performance liquid chromatography-mass spectrometry (HPLC-MS), 12 kinds of Acys had been detected and eight 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, UAE is more efficient and rapid to extract Acys from red raspberry, due to the strong disruption of fruit tissue structure under ultrasonic acoustic cavitation, which had been observed with the scanning electron microscopy (SEM). However, the Acys compositions in extracts by both methods were similar, which were investigated using HPLC profile.

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Both microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE) have been widely applied in the extraction of a variety of biologically active compounds including carotenoids due to their lower pollution to environment, high extraction efficiency, lower cost, and shorter extraction time as compared to conventional extraction techniques. However, there are few reports on their effects on the stability of these compounds. In the present study, the stability of (all-E)-astaxanthin, one of the carotenoids, was examined under the action of both ultrasound and microwave. Results showed that microwave induced the isomerization of (all-E)-astaxanthin to its Z analogues, preferentially to (13Z)-astaxanthin as analyzed by HPLC coupled with diode array detection and LC-MS; and the percentage of the isomerization increased with increasing both treatment time and microwave power. In contrast to the microwave, the ultrasound degraded (all-E)-astaxanthin to unidentified colorless compound(s) as suggested by HPLC analysis and UV/vis measurements, and the degradation likewise increased as both treatment time and ultrasonic power increased. The results presented here emphasized that both MAE and UAE techniques should be carefully used in the extraction of unstable compounds such as (all-E)-astaxanthin.