Effect On Quality Characteristics Of Large Yellow Croaker (Larimichthys Crocea) By Multi-frequency Ultrasound-assisted Thawing And Freezing

Large yellow croaker（Larimichthys crocea）is a marine fish rich in protein,lipids,and other nutrients,which is widely loved by consumers.However,due to the easy protein degradation,lipid oxidative decomposition,and microbial contamination of large yellow croakers,the quality-holding of large yellow croakers has always been a problem.Frozen preservation is an effective method widely used to protect the quality of large yellow croakers,which can hinder the activities of microorganisms,reduce the biological activity of enzymes,and thus extend the shelf life of large yellow croakers.In recent years,ultrasound has been widely used in food storage and processing,such as freezing,thawing,microbial inactivation,and extraction.Ultrasound-assisted thawing and ultrasound-assisted freezing are gradually been widely used in the field of food preservation.Cavitation effect is the main physical mechanism of ultrasonic waves in a liquid medium.Multi-frequency ultrasound can generate more cavitation nuclei,which is conducive to enhancing the cavitation effect,microfluidic effect,and mechanical effect,and has the advantage of improving ultrasonic efficiency.Therefore,this paper intends to apply multi-frequency ultrasound to the process of thawing and freezing to study its impact on the quality of large yellow croakers in the process of thawing,freezing,and freezing storage,to promote the application of multi-frequency ultrasound in the food industry.Therefore,this paper studied the effect of ultrasound-assisted thawing on the quality of large yellow croaker at first,and then determined the best ultrasonic power based on studying the advantages of multi-frequency ultrasound-assisted thawing;Secondly,the effects of multi-frequency ultrasound-assisted freezing on the quality of large yellow croaker were studied.Finally,the effects of ultrasound-assisted freezing at different frequencies on the quality,myofibrillar protein structure and lipid changes of large yellow croaker during frozen storage were studied.The above research provides a theoretical and practical reference for the application of multi-frequency ultrasound in the thawing,freezing process,and frozen storage of large yellow croaker.The specific research contents and conclusions are as follows:1.The effect of ultrasound-assisted thawing with different frequencies on the quality of large yellow croaker was studied.The effects of ultrasound-assisted thawing（UAT）with different frequencies on the thawing rate and quality characteristics of large yellow croaker were evaluated.The results showed that the thawing time of the air thawing group（AT）was 3610 min,which was significantly longer than that of other thawing groups.The thawing time of the flowing water thawing group（FWT）,the single-frequency UAT group（SUAT）,the dual-frequency UAT group（DUAT）,and the triple-frequency UAT group（TUAT）were 101 min,53 min,39 min,and 36 min respectively,which showed that the multi-frequency UAT treatment（DUAT and TUAT）could significantly shorten the thawing time of large yellow croaker.At the same time,the samples treated with multi-frequency UAT（DUAT group and TUAT group）retained the original quality characteristics better than other thawed samples.The samples treated with multi-frequency UAT had higher water holding capacity,better texture characteristics,and lower TBARS value.From the low-field nuclear magnetic resonance spectrum detection and MRI images,it could be found that the fixed water content of the samples in the multi-frequency UAT group was closer to that of the fresh large yellow croaker.Multi-frequency UAT also played an important role in maintaining the flavor of the sample,retaining more amino acids with a fresh/sweet taste.The color of the large yellow croaker was not significantly affected by changing the ultrasonic frequency.Therefore,the above results showed that multi-frequency ultrasound-assisted thawing is an effective method to accelerate the thawing process of large yellow croaker and improve the quality characteristics of frozen large yellow croaker.2.The effect of different power multi-frequency ultrasound-assisted thawing on the quality of large yellow croaker was studied.The effects of multi-frequency ultrasound-assisted thawing（UAT）with different power on the quality characteristics and protein stability of large yellow croaker were studied.Multi-frequency UAT could significantly reduce the damage to the quality of large yellow croaker during thawing.Proper ultrasonic power（220 W）could effectively reduce the thawing loss of large yellow croaker,help to avoid the increase of TBARS and TVB-N during the thawing process,weaken the degree of lipid oxidation,and make large yellow croaker retain better freshness.At the same time,the loss of total FAAs content in the UAT-220W group was also lower than that in other thawing groups.In addition,the UAT-220W group reduced the migration and loss of difficult-flowing and free water caused by freezing and thawing.UAT-220W showed slight protein structural damage,such as protein oxidation and degradation reaction.Therefore,it could be concluded that 220W multi-frequency ultrasound-assisted thawing can minimize the deterioration of the quality and protein stability of large yellow croaker caused by freezing and thawing.3.The effect of multi-frequency ultrasound-assisted immersion freezing on the freezing quality of large yellow croaker was studied.The effects of ultrasound-assisted freezing on the freezing speed,quality,and protein structure of large yellow croaker were evaluated.The results showed that the freezing time of the immersion freezing group（IF）was 241 min,the freezing time of the single-frequency UAF group（SUF）with different frequencies was as follows:220 min for the SUF-20 group,215 min for the SUF-28 group,208 min for the SUF-40 group,and the freezing time of dual-frequency UAF group（DUF）with different frequencies was as follows:202 min for the DUF-20/28 group,179 min for the DUF-28/40 group,192 min for the DUF-20/40 group,166 min for the triple frequency UAF group（TUF-20/28/40）.This showed that UAF significantly promotes the freezing process of large yellow croaker,and TUF has the fastest freezing speed.TUF maintained better quality characteristics than other frozen samples and produced less water migration.From MRI images,the content of difficult-flowing water in TUF is closer to FS.The sample treated with TUF had the color closest to FS.TUF also had lower TBARS and TVB-N values,which meant lower lipid oxidation and better freshness.In addition,from the infrared detection and fluorescence intensity analysis,it could also be found that TUF has a more stable protein secondary structure and tertiary structure.Therefore,the above results indicated that ultrasound-assisted freezing,especially multi-frequency ultrasound-freezing technology,is an effective method to promote the freezing process,improve the quality and stabilize the protein structure of large yellow croaker.4.The effect of multi-frequency ultrasound-assisted immersion freezing on the quality of large yellow croaker during frozen storage was studied.By investigating the effects of the different freezing methods,namely immersion freezing（IF）,40 k Hz single-frequency ultrasound-assisted freezing（SUF）,28/40 k Hz dual-frequency ultrasound-assisted freezing（DUF）,and 20/28/40 k Hz multi-frequency ultrasound-assisted freezing（TUF）,on the quality of large yellow croaker during freezing storage,we concluded that the large yellow croaker samples in the TUF group had a relatively low thawing loss,cooking loss and high water holding capacity.The samples of large yellow croaker from TUF group had good texture characteristics,which effectively improved the texture deterioration of large yellow croaker during frozen storage.With the extension of freezing storage time,compared with other freezing treatment groups,TUF treatment could better maintain the freshness of large yellow croaker,with lower TVB-N and K values.In conclusion,TUF could effectively slow down the quality deterioration of large yellow croaker during frozen storage.5.The effect of multi-frequency ultrasound-assisted immersion freezing on the protein structure and lipid of large yellow croaker during frozen storage was studied.By exploring the effects of the different freezing methods,namely immersion freezing（IF）,40 k Hz single-frequency ultrasound-assisted freezing（SUF）,28/40 k Hz dual-frequency ultrasound-assisted freezing（DUF）,and 20/28/40 k Hz multi-frequency ultrasound-assisted freezing（TUF）,on myofibrillar protein oxidative degradation and lipid oxidation of large yellow croaker during frozen storage,it could be concluded that the samples of large yellow croaker in TUF group had the lowest TBARS values,which could effectively inhibit lipid oxidation.TUF could slow down the rate of carbonyl formation,weaken the decline of Ca²⁺-ATPase activity and total sulfhydryl content,and protect the stability of the secondary structure and tertiary structure of large yellow croaker myofibrillar protein.In conclusion,TUF is an effective method to reduce the degree of protein and lipid oxidation of large yellow croaker during frozen storage.