Factors Acting On The Acoustic Field And The Effects Of Ultrasound On The Gel Properties Of Surimi

For the past few years, surimi is widely developed in china, gel strength is the major indicator to reflect the quality of surimi. In the production of surimi, exogenous additives and the optimization of technics are the main ways to strengthen the gel properties of surimi. However, exogenous additives may lead to some security issues, while improving the gel properties through the optimization of technics would meet the demand of consumers for the safety of foods. As one of technics, ultrasound is widely used in the process of meat processing, such as assisting salting of meat, the tenderization of meat, and it was reported that for ultrasound had some effects on myofibril protein, the gelation of surimi was the process of the degeneration and accumulation of myofibril protein. While the application of ultrasound used in surimi was rarely reported at home and abroad. Therefore, this paper started the effects of ultrasound assisted gelling on the gel properties of surimi, as well as the influence of several factors on the acoustic field and the mechanism of ultrasound acting on the surimi. Following are the major results:(1) The influence of frequency on the acoustic fieldThe ultrasound output devices with two frequencies and the one with one frequency were investigated, the acoustic field of devices at each frequency was measured. According to the results, we found that for the devices with two frequencies, the acoustic intensity of coordinate positions decreased as the frequency increased. The acoustic field of different devices not only depended on the frequency, but also on the working conditions, which has something to do with the resonant frequency of ultrasonic transducers. The acoustic field of each frequency also has connection with the distribution of ultrasonic transducers, the zones which next to the transducers had bigger acoustic intensity.(2)The influence of medium factors acting on the acoustic fieldThe influence of the level of media, the volume of media, the barrier effects of different materials were measured to evaluate the influence of medium factors acting on either the acoustic field or the acoustic intensity. The results indicated that there exits an optimal volume of media, neither too much nor too little volume would be good for the working of the devices. The acoustic intensity is greatest toward the bottom of the devices, while the further to the bottom, the lower acoustic intensity is, the barrier effect of materials is obvious, the barrier effect of PVC film was bigger than that of aluminum material, and the barrier effect depend not only on the nature of the materials itself, but also on the frequency of devices and the value of acoustic intensity.(3) The effects of ultrasound on the gel properties of surimiIn order to evaluate the effects of acoustic intensity, the treatment time, the treatment temperature on the gel properties of silver carp surimi, ultrasound was used to assist gelling of surimi, and determining the effects of ultrasound on the gel strength of silver carp surimi that had various water content, as well as the effects on the gel strength of different types of surimi. It was found that the ultrasound with bigger acoustic intensity had obvious effects on the gel properties of surimi, water- holding capacity and gel strength all increased. W hile when the treatment time is long, the gel strength decreased, samples treated for 20 mins had the biggest improvement. The samples treated by ultrasound at 40℃ had the biggest improvement, and the silver carp surimi had the best gel stength at this temperature, the higher water content was, the bigger improvement the ultrasound did, for the samp les whose water content was 81%, the maximum value of gel strength increased by 42% than the control samples, which indicated that ultrasound had better effects on the samples whose water content was high. Ultrasound had better effects on the low grade seawater trash fish, while the effects on the high grade besugo surimi was lower, which indicated that the effects of ultrasound on the gel strength have something to do with the grade of surimi.(4) The effects of ultrasound on other physical and chemical indexes of surimiThe influences of ultrasound on water- holding capacity and whiteness of the silver carp surimi was measured, Scanning Electron Microscopy and C ircular Dichroism were used to study the mechanism that ultrasound acting on the surimi. It is found that ultrasound with bigger acoustic intensity had positive effects on the water-holding capacity of surimi, and the trend is similar to that of gel strength. However, ultrasound almost had no influence on the whiteness of surimi, the surimi samples treated by ultrasound had better micro-structure with higher density, the secondary structure of surimi treated by ultrasound had several changes, the results showed that the content of α-helix increased.