Optimization of ultrasonic-microwave assisted extraction of oligosaccharides from lotus (Nelumbo nucifera Gaertn.) seeds

The traditional technology replaced by ultrasonic or microwave assisted extraction has attracted considerable research interest. In order to maximize the yield of different degree polymerized oligosaccharides from lotus seeds, response surface methodology (RSM) was applied for optimization by ultrasound-microwave assisted extraction (UMAE) in this study. The results indicated that the optimal conditions for UMAE of lotus seed oligosaccharides were: extraction time 325.00 s, liquid-solid ratio 10.00 mL/g (L/S ratio), ultrasonic power 300.46 W, microwave power 250.00 W, and the yield of total oligosaccharides, trisaccharides, and tetrasaccharides was increased by 76.59%, 17.47%, and 27.21%, respectively. On the other hand, the extraction time was shortened by 12.18, 8.92, and 1.16 times, respectively, compared to the hot water extraction, ultrasonic-assisted extraction (UAE), and microwave-assisted extraction (MAE). These results confirmed that UMAE has a greater potential and efficiency for extraction of oligosaccharides than traditional hot water, ultrasonic or microwave assisted extraction alone.