Different-frequency ultrasonic effects on properties and structure of corn starch

BACKGROUND: Ultrasound is widely used to accelerate many reactions and unit operations, but few studies have reported its effects on starch properties and structure. RESULTS: Corn starch suspended in ethanol solution was treated by dual-frequency ultrasound (DFU) and single-frequency ultrasound (SFU). Results showed that the transparency of the starch treated under 20 + 25 kHz DFU improved by 26.94% and 31.70%, respectively, compared to 20kHz and 25kHz SFU. Hardness, brittleness, elasticity, adhesiveness, conglutination degree, chewiness and recoverability of starch was reduced after ultrasonic treatment, and with increasing ultrasonic frequency these properties decreased. Its enthalpy value also decreased with ultrasound. Compared with each SFU treatment, enthalpy value decreased by 1.41% and 0.82%, respectively, by DFU. The freeze-thaw stability of starch was also weakened by ultrasound, which was obviously changed by DFU. Under ultrasound, the crystal structure of starch was not damaged, characteristic diffraction peak intensity was significantly reduced and diffuse diffraction features increased, exhibiting a decline in crystal lattice ordering degree. In comparison to SFU, DFU caused a pronounced reduction in starch crystallinity. CONCLUSION: After ultrasonic treatment, the transparency of corn starch paste improved, but its hardness, brittleness, elasticity, adhesiveness, conglutination degree, chewiness and recoverability decreased, as well as starch crystallinity and enthalpy values. DFU was found to be more effective than SFU. (C) 2014 Society of Chemical Industry