Ultrasonically aided enzymatical effects on the properties and structure of mung bean starch

• Ultrasound and enzyme were applied to the hydrolysis of mung bean starch.
• Ultrasound can promote the starch hydrolysis.
• Dual-frequency ultrasound has more evident effects on the starch.

In this research, the effects of the high power dual-frequency ultrasound of 25 kHz + 40 kHz with α-amylase on the properties and structure of mung bean starch (MBS) were investigated. Various ultrasounds with α-amylase (5U/1 g of MBS) treatments were used: the frequency was respectively 25 kHz, 40 kHz, and 25 kHz + 40 kHz, but ultrasonic intensity was the same for each ultrasonic treatment. Both single and dual-frequency ultrasounds could promote starch hydrolysis. Brabender instrument was used to examine the viscosity of MBS. The results indicated that the ultrasound with α-amylase treatment of MBS obviously decreased the peak viscosity. The results of laser granulometry measurements showed a decrease in granular size. The decrease in peak viscosity and particle size was associated with ultrasound frequency. The scanning electric microscope (SEM) revealed that a few pores and channels were found on the starch treated with α-amylase. Furthermore, some deeper holes and more broken parts were observed on the starch sonicated with 25 kHz, 40 kHz, and 25 kHz + 40 kHz, and dual-frequency ultrasound with α-amylase had greater effects on MBS, compared to single frequency ultrasound.Industrial relevanceModified starch has excellent performance, and is widely used in food, papermaking, textile, medicine and so on. Its production method mostly used in industries is chemical method, which often causes some problems such as chemical residues and environmental pollution. In recent years, physical modification method has been paid a lot of attentions. As one of novel physical methods, ultrasound has wide applications in modified starch production. In our work, different frequency ultrasounds and enzymes were applied to the hydrolysis of mung bean starch. Their effects on the properties and structure of the starch were investigated. The experimental results and conclusion provide a useful background to the application of this novel method in starch processing industries.