Effects Of Orthogonal Single/dual Ultrasonic Field On Ice Cream Freezing Process And Quality

Ultrasound-assisted freezing is an emerging rapid freezing technology.Due to the cavitation effect,microstreaming effect,and mechanical effect produced by ultrasound,it helps promoting the nucleation of the freezing process,and controlling the size of ice crystals,thus improving the quality of frozen food.This study mainly explored the effect of orthogonal single-and dual-frequency ultrasound-assisted freezing on the quality of ice cream.Based on the construction of an ultrasound-assisted freezing equipment with a hexagonal freezing cavity,the following research were included:?1?The cavitation effect characteristics of orthogonal single and dual-frequency ultrasound in the freezing cavity were explored by foil damage method;?2?the spatial locations were formed into heatmaps through the R language heatmap program,which characterized the spatial sound intensity distribution under the single frequency ultrasound in the bottom,side and orthogonal directions,and the hierarchical clustering algorithm was used to obtain the relationship between 5 liquid levels of 4,8,12,16,20 cm and the ultrasound intensity of D1-D9 points at each liquid level;?3?Through Matlab platform programming,gridding and two-dimensional V4 interpolation method were used to fit the ultrasound intensity of the test surface,which help achieving the visualization of ultrasound intensity distribution under the orthogonal single and dual frequency ultrasound at8 cm liquid level.Then ice cream were used as raw material to study the changes of expansion rate,melting rate,fat stability,ice crystals and bubbles,color difference,texture under the optimal ultrasonic parameters of orthogonal single and dual frequency ultrasound.The following conclusions were obtained:1.When ultrasonic direction was taken as the single variable,the ultrasound cavitation effect in the orthogonal direction was greater than the single direction;when the ultrasonic frequency was taken as the single variable,the dual-frequency ultrasound cavitation effect was greater than the single frequency ultrasound,and the cavitation area of dual-frequency ultrasound was more uniform than that of single frequency.When the ultrasound power reached 450 W,the cavitation behavior became more obvious.2.Under the ultrasonic field in the bottom or side direction,the sound intensity decreased with the increasing distance from the ultrasonic probe,and the ultrasonic attenuation was greater when closed to the gas-liquid interface;Under the ultrasonic field in the orthogonal direction,the sound intensity value at 8 cm level was the highest,and it showed a decreasing trend at both ends with the liquid level of 8 cm as the center.At the same liquid level,the difference of sound intensity between D1-D9 at different positions was smaller than the difference of sound intensity between different liquid levels.Under the single-frequency ultrasound field at the bottom,the ultrasound field formed was approximately symmetrically distributed on both sides of the plane where the transducer was located,and the ultrasound intensity was highest at the point directly opposite the ultrasound transducer.In the orthogonal ultrasonic field,this rule was not obvious due to more emission frequency sites and the phenomenon of refraction and reflection in the cavity.3.For single-frequency ultrasound,under the optimal ultrasound parameters of ^{250 W}U_{40k Hz},the ultrasonic fields in three directions of side,bottom,and orthogonal directions were applied in sequence.Compared with IF,the phase change time and characteristic freezing time of ^{250 W}U_{40 k Hz} were reduced by 15.28%and 16.23%respectively,and the hardness and were decreased but there was no significance between ultrasound groups.Under this condition,the ice cream showed the lowest melting rate and less expansion rate loss,so the quality of the ice cream obtained by ultrasonic treatment in the orthogonal direction was the best.This might be due to the strong cavitation effect under the orthogonal ultrasonic field and the maximum freezing rate of the ice cream.The ice crystals of the ice cream were small and uniform,which improved the overall quality of the ice cream.4.For dual-frequency ultrasound,under the optimal ultrasound parameters of S₄₀B₂₀U^250W,applying five ultrasound methods with a ratio of side to bottom ultrasound power of 1:3,1:2,1:1,2:1 and 3:1.Under the conditions of ²S¹₄₀B₂₀U^{250 W},the phase transition time and characteristic freezing time were significantly reduced by 28.33%and 24.59%,the expansion rate was increased by 7.8%,the fat stability was reduced by 5.56%,the hardness and cohesiveness values were limited decreased,and?E had no Significant changes.In addition,the microscopic observation results showed that ²S¹₄₀B₂₀U^{250 W} treatment could help achieving more uniform bubbles in the system,increasing the freezing rate and forming finely and evenly distributed ice crystals.So ²S¹₄₀B₂₀U^{250 W} treatment was the best parameter to improve the quality of ice cream under dual frequency ultrasound.5.The effect of ultrasound on the expansion rate of ice cream depends on the ultrasound conditions.There is a critical point of ultrasound action.When the degree of ultrasound cavitation is greater than this critical point,the cavitation degassing action dominates and the expansion rate of ice cream will decrease.When the degree of cavitation is less than this critical point,some of these bubbles will be wrapped to increase the expansion rate,if sufficient cavitation bubbles are generated by ultrasound in the system.