Effect of multi-mode dual-frequency ultrasound irradiation on the degradation of waxy corn starch in a gelatinized state

Ultrasound as “green chemistry and technology” can considerably modify the component, structure, and properties of starches derived from diverse plants. In the current study, the effect of ultrasound frequency modes on the degradation of gelatinized waxy corn starch (GWCS) was investigated. The frequency modes include single-frequency modes of 20, 40 kHz (SM-20 and SM-40), and dual-frequency of 20 and 40 kHz in sequential mode (SeDM) and simultaneous mode (SiDM). Results showed that ultrasound irradiation significantly decreased (p < 0.05) the Mw of GWCS under all the frequency modes compared to the native starch. Besides, reductions in Mw enhanced by dual-frequency ultrasound were higher than those enhanced by single-frequency ultrasound. For dual-frequency modes, the reductions in Mw of SiDM were higher than those of SeDM, indicating that the degradation of SiDM was the most serious. The significant decreases in the proportion of B3 chains, and increases in the proportion of A chains of GWCS irradiated by ultrasound indicated that the larger molecules were preferentially degraded. The results of 1H NMR spectroscopy showed that both α-1,4- and α-1,6-glycosidic bonds of starch were damaged by ultrasound irradiation, and the degree of branching (DB) of GWCS irradiated by SiDM was the lowest. In conclusion, the dual-frequency ultrasound can be used as an efficient and low-cost method to facilitate the degradation of amylopectin.