Abstract: The effect of multi-frequency pulsed ultrasound (20 kHz, 20 + 28 kHz, and 20 + 28 + 40 kHz) on characteristics of a peach pulp-κ-carrageenan blend gel system containing erythritol as a cosolute was systematically studied. Rheological analysis showed that the blend gel system was a pseudoplastic fluid. With the increase in pulsed ultrasound frequency, the consistency coefficient increased and the flow index decreased. Dynamic rheological analysis showed that single-frequency and dual-frequency pulsed ultrasound could significantly enhance the elastic modulus (G’) and viscosity modulus (G”), while triple-frequency pulsed ultrasound had the opposite effect. The particle size was significantly reduced by the cavitation effect produced by multi-frequency pulsed ultrasound, the effect being most pronounced with triple-frequency pulsed ultrasound. Compared with the control group, D50, D[4,3], and D[3,2] of the samples treated by triple-frequency pulsed ultrasound were decreased by 12.32%, 9.80% and 7.57%, respectively. Additionally, multi-frequency pulsed ultrasound could increase the absolute value of the phase angle and conductivity, and reduce the impedance value. Compared with the control group, the absolute value of the phase angle and the conductivity were increased by 35.82% and 10.15% in the triple-frequency pulsed ultrasound group, respectively; and the impedance value was reduced by 38.52%. As the pulsed ultrasound frequency increased, the association between the blend system and water was enhanced, so that a bound water signal appeared. No new absorption peaks were found in the Fourier transform infrared spectra of ultrasound-treated samples, indicating that ultrasound treatment did not destroy the functional groups, but instead only strengthened hydrogen bonding. The micropores of the blend gel system were enlarged by both single-frequency and dual-frequency pulsed ultrasound treatments, while triple-frequency pulsed ultrasound treatment resulted in denser and more uniform pores. This study can provide a reference for improving the quality of blend gels of κ-carrageenan and developing gel-like peach pulp products.

Key words: multi-frequency pulsed ultrasound; frequency; blend gel system; peach pulp; carrageenan