Effects Of Orthogonal Ultrasonic Field And Multi-frequency Ultrasonic Field On Potato Freezing Efficiency And Quality

As a new type of rapid freezing technology,ultrasound-assisted freezing?UF?has attracted more and more researchers'attention in recent years,which has a good application prospect in the food industry.Based on the existing researches,this paper focuses on the effects of different ultrasonic directions and multi-frequency ultrasound on the freezing process of fruit and vegetable products.UF could further improve the freezing efficiency and quality of fruit and vegetable products,which plays a key role in the food freezing industry.In this paper,the distribution of sound field in ultrasound freezing chamber and the effect of different ultrasonic parameters on cavitation effect are investigated.The fresh potato is considered as the research object and the different ultrasound parameters of single-frequency ultrasound and the different directions of ultrasound wave are applied to the potato freezing process.In addition,the effects of dual-frequency and triple-frequency ultrasound on the freezing efficiency and quality of potato were studied and the freezing effects of single-frequency,dual-frequency and triple-frequency ultrasound treatment were compared.The freezing effects were evaluated from the macro perspective?drip loss,hardness?and microscopic perspective?total calcium content,L-ascorbic acid content,total phenolic content and microstructure?.The product's freezing efficiency and quality are simultaneously evaluated and the conclusions are the following:1.There is a significant difference in the distribution of ultrasonic sound intensity in the freezing chamber on the condition of different levels of test surface,ultrasonic direction,intensity and frequency.Therefore,it is necessary to place the material in a area,where the ultrasound intensity distribution is relatively uniform,to reduce the experimental error brought by the fluctuation of sound intensity.The suitable conditions are:The material placement area is near the middle of the freezing chamber.For single-frequency ultrasound,the material placement height is 10mm when using bottom ultrasound,and the material placement height is 80mm when the side and orthogonal ultrasound are used.For dual and triple-frequency ultrasound,the material placement height is 80mm.The results of the cavitation effect show that the cavitation effect increases as the amount of ultrasonic power and frequency increases when other conditions are same.2.When using UF treatment with different intensity ultrasound,the freezing rate of the sample increases with the increase of ultrasonic power.However,the physical and chemical indicators such as juice loss rate,hardness and total calcium content of the sample show a trend of rising first and then decreasing,which indicates that it is not only important to consider the freezing effect by freezing rate,but also to select the appropriate ultrasound parameters according to the quality of the frozen product.For single-frequency ultrasound,the optimal processing conditions are the frequency of 20 kHz and the intensity of 270 W,under which the sample has the highest freezing rate and good quality.3.For single-frequency ultrasound,UF treatment of the orthogonal direction increases the freezing efficiency by 38.2%and decreases the drip loss rate by 36.0%.The hardness value,the total calcium content,the L-ascorbic acid content and the total phenol content are increased by 31.7%,30.1%,20.7%and 25.0%respectively under the ultrasound intensity of 270W.Under this condition,the freezing efficiency was highest and the quality of the frozen product was best.For dual-frequency ultrasound,the UF treatment of the orthogonal direction also has the best freezing effect,while the UF treatment of the lateral direction can not improve the freezing effect significantly,which may be related to the 120-degree angle between the two ultrasound waves on the side.4.For dual-frequency ultrasound,the UF treatment with the frequency combination of20+28 kHz showed the highest freezing efficiency and the texture and nutrients of the sample were well preserved.For the triple-frequency ultrasound,the sample treated with B₂₀B₂₈S₄₀UF could improve the freezing rate by 48.1%and the drip loss rate decreased by 45.4%.The hardness value,total calcium content,L-ascorbic acid content and total phenol content were increased by 35.3%,42.5%,33.2%and 41.1%respectively.Therefore,B₂₀B₂₈S₄₀UF is the optimal treatment method during the triple-frequency ultrasound.5.Compared with the effects of single-frequency,dual-frequency and triple-frequency ultrasound during the potato UF freezing process,it can be found that the freezing rate gradually increases as the ultrasound frequencies increases,and the drip loss rate of the sample also gradually decreases.The texture and nutrients of sample are also better preserved after thawing.