The Joint Use Of Microbubbles And Ultrasound In Freezing Liquid And Solid Model Foods

Ultrasound assisted freezing is one of the representatives of the thriving emerging freezing technology.In food industry,ultrasound assisted freezing mainly focus on the liquid foods(with dissolved gas)and solid vegetables and fruits(with respiration voids).The auther assumes that,the gas or voids can somewhat promote the freezing process assisted by ultrasound.To verify this assumption,this study took the object of sucrose solution and maltodextrin solution(as a representative of newtonian/non-newtonian fluid),sucrose solution with the concentration from 10%~40%(as a model of juice),gelatin with the concentration from 10%~30%(as a model of semi-solid foods)and mixed colloid(as a model of solid foods)and optimize their freezing process using micro-nano bubbles(MNBs)and ultrasound irradiation.The main research results are as follows:1)For newtonian fluid and non-newtonian fluid,joint use of MNBs and ultrasound can enhance the nucleation temperature(sucrose: 85.51%,maltodextrin: 75.00%),decrease the time of crystal growth period(sucrose: 23.87%,maltodextrin: 15.01%)and the total freezing time(sucrose: 17.82%,maltodextrin: 20.70%).2)For solution and semi-solid model,MNBs can enhance the initial freezing point and decrease the total freezing time,the larger the concentration,the more significant the effect(S1~S4,the initial freezing point increased 0.06 oC,0.11 oC,0.84 oC and 2.20 oC;G1~G5,total freezing time was shortened by 13.59%,17.86%,21.14%,19.00%,21.14%).3)For solid foods,using MNBs or ultrasound alone can hardly achieve better ice crystal size and roundness.Joint use of them can decrease the total freezing time by 20.31%,and the diameter of ice crystals is 79.54 ?m2,which is 61.78% better than control sample S.4)This study introduced the MNBs of about 300~500 nm,100~300 nm and 100 ?m to the object of liquid,semi-solid and solid food model,respectively.It is noticed that,these MNBs can act as cavitation nuclei and heterogeneous nucleation site to accelerate the nucleation period and can promote the heat and mass transfer by the high efficiency of dissolution.